Guide to
“The Risø TL/OSL Reader”
DTU Nutech, Denmark
August 2015
Precautions!
• Do not remove the signal cable before removing the HV cable from
the PMT! Removing the signal cable while HV is connected may
damage the amplifier inside the PMT. When the lid is open the HV
is switched off automatically.
• Do not heat samples on aluminum discs higher than 500 ◦ C! If the
aluminum disc is heated above 500 ◦ C it will be in risk of melting,
and the heating element may be damaged. In the Sequence Editor
a maximum temperature can be set to prevent higher temperatures.
• Do not block the rear vacuum outlet when not using the quartz
window! If the quartz window is not used e.g. for single grain, the
vacuum outlet must not be connected or blocked in order to be able
to let out the excessive air in the chamber when closing the lid.
• Maximum sample height is 2 mm! If the sample is too high the
carousel may be jammed.
• Make sure the heater element is down, before closing the lid! If
the heater element is up, remove the carousel, and then close the
lid. Connect with control program, and send lx command to the
heater in the services tab. On later versions of Controller there is
an audible alarm when the lid is closing while the heater lift is up.
• Acid fumes will seriously damage the reader! Severe corrosion and
failure in instrumentation will occur from contaminated laboratory
atmospheres or measurement of inadequately washed samples. It is
very important to avoid any possibility of acid-fume contamination
of the reader:
1. Make sure that the atmosphere in the room containing the
reader is not connected to the air circulation in a chemistry
preparation room (e.g. through an air-conditioning circuit or
a door).
2. Make sure that all acid-treated samples are thoroughly washed
before loading into the reader. If in doubt, check the pH is >6.
Contents
List of Figures
iv
1 Overview
2 The Risø TL/OSL Reader
2.1 Sample carousel . . . . . . . . . .
2.2 Light detection system . . . . . .
2.2.1 Photomultiplier tube . . .
2.2.2 Detection filters . . . . . .
2.3 Luminescence stimulation system
2.3.1 Heating system . . . . . .
2.3.2 Optical stimulation system
2.3.3 Calibration LED . . . . .
2.4 Irradiation sources . . . . . . . .
2.4.1 Beta irradiation . . . . . .
2.4.2 External dose rates . . . .
2.4.3 Alpha irradiation . . . . .
2.4.4 X-ray irradiation . . . . .
1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
3 Installation of the Risø TL/OSL reader
3.1 Components . . . . . . . . . . . . . . . .
3.2 Installing the hardware . . . . . . . . . .
3.2.1 Unpacking . . . . . . . . . . . . .
3.2.2 Nitrogen connections . . . . . . .
3.2.3 Attaching the flow meter . . . . .
3.2.4 Mounting the PMT . . . . . . . .
3.2.5 Connecting to the Controller . . .
3.2.6 Connecting the N2 /air supply to
(not yet loaded) . . . . . . . . . .
3.3 Installing the Risø software package . . .
3.4 Testing . . . . . . . . . . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
the beta irradiator
. . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
5
5
6
6
7
10
10
11
16
18
19
21
21
22
.
.
.
.
.
.
.
23
23
25
25
26
29
29
31
. 33
. 33
. 36
CONTENTS
3.5
iii
3.4.1 Resetting the sample carrousel
3.4.2 Checking the lift . . . . . . .
3.4.3 Checking the Blue LEDs . . .
3.4.4 Adjusting the N2 flow rate . .
3.4.5 Checking the beta irradiator .
3.4.6 Checking the alpha irradiator
3.4.7 Measure PMT counts . . . . .
Loading the beta source . . . . . . .
4 Changing detection filters
4.1 Mounting detection filters
4.2 Removing the PMT . . . .
4.3 Replacing the filter basket
4.4 Disabling the blue LEDs .
4.5 Reconnecting the PMT . .
4.6 Check for light leaks . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
37
37
38
38
38
38
38
39
.
.
.
.
.
.
49
49
49
51
51
51
51
5 Optimising the Signal-to-Noise ratio
53
6 Dead time correction
58
7 Frequently answered questions
7.1 Power requirements . . . . . .
7.2 User PC requirements . . . .
7.3 Laboratory recommendations
7.4 Changing filters . . . . . . . .
7.5 Nitrogen requirements . . . .
7.6 Vacuum . . . . . . . . . . . .
7.7 Operation . . . . . . . . . . .
7.8 Maintenance and comments .
References
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
60
60
60
61
62
63
63
64
64
66
List of Figures
1.1
1.2
1.3
Schematic drawing of the Risø TL/OSL reader . . . . . . . . .
Schematic overview of the Risø system . . . . . . . . . . . . .
Picture of the Controller . . . . . . . . . . . . . . . . . . . . .
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
Discs, cups and sample carrousel . . . . . . . . . . . .
Quantum efficiency of 9235QB PMT . . . . . . . . . .
Emission spectra of sedimentary quartz and K feldspars
Detection filters . . . . . . . . . . . . . . . . . . . . . .
Detection filters and emissions . . . . . . . . . . . . . .
Picture of the heating element . . . . . . . . . . . . . .
Precision of the heater element . . . . . . . . . . . . .
Stimulation modes . . . . . . . . . . . . . . . . . . . .
Schematic diagram of the stimulation unit . . . . . . .
Picture of the OSL stimulation head . . . . . . . . . .
Blue LED emission spectrum and filter transmissions .
Calibration LED . . . . . . . . . . . . . . . . . . . . .
TL flange . . . . . . . . . . . . . . . . . . . . . . . . .
Pictures of the irradiators . . . . . . . . . . . . . . . .
Cross section of the beta irradiator . . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
6
7
8
9
9
10
11
12
13
14
15
17
18
19
20
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
Components . . . . . . . . . . . . . . . . . . . . . .
Unpacking the shipment . . . . . . . . . . . . . . .
N2 tubing . . . . . . . . . . . . . . . . . . . . . . .
Two separate compressed input sources . . . . . . .
Reduction Valve . . . . . . . . . . . . . . . . . . . .
PMT mounting . . . . . . . . . . . . . . . . . . . .
Connecting to the Controller . . . . . . . . . . . . .
Example of the Risø PM-Tube Testsheet . . . . . .
Connecting the N2/air supply to the beta irradiator
Software installation USB 1 . . . . . . . . . . . . .
Software installation USB 2 . . . . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
24
26
27
28
30
31
32
33
34
35
36
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2
3
4
LIST OF FIGURES
v
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
3.20
3.21
3.22
3.23
Testing the system using CONTROL
Removing the air tube . . . . . . . .
Removing Pb shielding . . . . . . . .
Removing the irradiator . . . . . . .
Preparing for loading/unloading . . .
Items in the irradiator . . . . . . . .
Removing the circlip . . . . . . . . .
Removing items in the irradiator . .
Inserting the source I . . . . . . . . .
Inserting the source II . . . . . . . .
Reinsert spacers . . . . . . . . . . . .
Mounting the circlip . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
37
40
41
41
42
43
43
44
45
46
47
48
4.1
Mounting detection filters . . . . . . . . . . . . . . . . . . . . 50
5.1
5.2
5.3
Adjusting the HV of the PMT . . . . . . . . . . . . . . . . . . 54
Using CONTROL to determine optimal S/N . . . . . . . . . . 55
S/N ratio of the PMT . . . . . . . . . . . . . . . . . . . . . . 57
6.1
6.2
Dead time correction 1 . . . . . . . . . . . . . . . . . . . . . . 59
Dead time correction 2 . . . . . . . . . . . . . . . . . . . . . . 59
7.1
Disabling the LEDs . . . . . . . . . . . . . . . . . . . . . . . . 61
1
Overview
Essential components of the Risø TL/OSL reader (model TL/OSL-DA-20)
are:
1) light detection system
2) luminescence stimulation system (thermal and optical )
3) irradiation source
The light detection system comprises of a photomultiplier tube (PMT) in
combination with suitable detection filters (see section 2.2). The luminescence stimulation system comprises of a heating element and an optical stimulation unit. Theses two facilities can be used separately or in combination
(see section 2.3). In situ irradiation is achieved using either a beta source,
an alpha source or an X-ray generator (see section 2.4).
The Risø TL/OSL measurement system enables measurement of both thermoluminescence and optically stimulated luminescence. The system allows
up to 48 samples to be individually heated to any temperature between room
temperature and 700 ◦ C, to be individually irradiated (using alpha, beta or
X-ray radiation) and to be optically stimulated by various light sources in
situ. The measurements are carried out in a vacuum chamber. The emitted
luminescence is measured by a light detection system comprised of a photomultiplier tube and suitable detection filters. A schematic drawing of the
system is shown in Figure 1.1.
The Risø TL/OSL reader consists of two separate units:
a) The Reader (hardware; a) picture title page)
b) The Controller (Control of hardware, PMT preamplifier etc.; b) picture
title page)
2
Figure 1.1: Schematic drawing of the Risø TL/OSL reader
The system is run using one of two programmes - the SEQUENCE EDITOR (used to write elaborate measurements sequences) and the CONTROL
Program (used to carry out simple tests on the equipment) - installed on a
standard PC. It is very important that the user PC is using a “.” (full stop) as
decimal separator and not a “,” (comma). In Windows XP this is setup in the
Control Panel/Regional and Language Options/Regional options. In Vista
it is set up in the Control Panel/Regional and Language Options/Formats.
Most continental language options (e.g. German and French) will use the “,”
as a separator whereas all English language options (and many others) will
use a “.”. If the decimal separator is not a “.” then an error massage will
appear (Error 112).
All direct hardware control of the reader has been incorporated into the
Controller (see Figure 1.2). The Controller is a 586 processor based PC with
a 32 MB flash disk and 32 MB of RAM. The Controller connects to the host
computer (user PC) via an RS-232 serial cable or a USB connection (USB for
Controller version D or later). The Controller is responsible for maintaining
proper timing, sample positioning, data acquisition, error checking, etc. The
Controller is also equipped with a two-line text display, which shows the current system status and the command which is currently being executed. This
display also reports failure messages such as thermal failure and the receipt
of invalid commands.
3
A picture of the Controller is shown in Figure 1.3. The use of the indicators and the buttons on the front panel of the Controller is described
below.
LID The reader lid is opened and closed using the two buttons located in
the lower left corner. The status of the reader lid is indicated by the
three red lights positioned directly above these two buttons (e.g. when
the reader lid is “DOWN” the red light above the “DOWN” button is
on. This light must be on before a measurement sequence can begin)
TURNTABLE When “RUN” is on the sample carousel is rotating. When
the“POS”light blinks the system has detected a sample position. When
“POS.1” is on the system has located sample position 1 (see section 2.1
for further details)
LIFT The three red lights indicate the status of the lift. A sample is not in
measurement position before the “UP” light is on
MODE The three red lights indicate whether the heating element is heating,
an irradiation is being performed and if an OSL command is being
executed
PM The red light “COUNTS” blinks every time a count has been registered
by the light detection system. The red light “CAL” indicates when the
calibration LED is on (see section 2.3.3)
ATMOSPHERE The red light “VAC. PUMP” indicates when the vacuum
pump is being activated. Please note that a vacuum pump is not part
of a standard Risø TL/OSL system. The “N2 ” light is on when the
system is requested to flush the measurement chamber with Nitrogen
Figure 1.2: Schematic overview of the Risø system
4
Figure 1.3: Picture of the Controller
Display The two-line text display showing the current status of the system
is positioned in the middle of the front panel of the Controller. The
light level of this display can be adjusted by gently pressing the “ADJ”
button located directly below the display
VACUUM A vacuum gauge is located on the right side of the Controller. If
an external vacuum pump is attached to the reader, the measurement
chamber can be evacuated to a preset level. This level is selected by
pressing the “PRESET” button simultaneously with a thin screwdriver
inserted into the “ADJ” hole (located to the right of the “PRESET”
button). For alpha irradiations we recommend a pressure of 0.4 mbar
H.V. At the very right the HV dial for the PMT is located. This dial is
labelled: “H.V. 500 V - 1500 V”
The software used to control the Controller is based on a Windows program for creating, editing and executing measurement sequences. The central
feature of the Controller software is a specially designed command language
interpreter. The command language consists of approximately 40 commands
which allow full control of system hardware and data acquisition methods.
The Sequence Editor translates commands (e.g. “OSL”) into low level commands which the Controller can understand, checks that the commands have
actually happened, and collects data. The software also allows the user to
easily create their own high level commands. Furthermore, the command
language allows users to write their own control programs (using e.g. Labview) and thus construct alternative measurement options to those included
in the user application software.
2
The Risø TL/OSL Reader
Samples are either mounted on 9.7 mm diameter stainless steel discs using
silicone oil as an adhesive or poured (as loose grains) into sample cups (see
Figure 2.1). Samples are loaded onto an exchangeable sample carousel that
can accommodate up to 48 samples. The sample carousel is placed in the
sample chamber which can be programmed to be evacuated or have a nitrogen atmosphere maintained by a nitrogen flow.
The sample is lifted through slots in the sample carousel into the measurement position by a lift, which also functions as heating element. In the
measurement position the sample can be stimulated thermally and/or optically. Thermal stimulation is obtained by linearly increasing the temperature
of the heating element and optical stimulation is provided by different light
sources focused onto the sample position. The emitted luminescence is measured by the light detection system.
2.1
Sample carousel
The sample carousel rests on a motor driven turntable, which enables rotation of the sample carousel. Rotation is computer controlled and position
holes drilled though the carousel in close proximity to the sample positions
enable the system to keep track of the position of the carousel using optoelectronics. An infrared light emitting diode (LED) is positioned underneath
the turntable, which is switched on during rotation. The measurement is initiated by moving a given sample to the measurement position located directly
underneath the light detection system. The sample carrousel rotates at two
different speeds (two-speed turntable) to reduce processing time. If a sample
is moved to the next position then the turntable turns at the normal speed.
2.2 Light detection system
6
Figure 2.1: Sample discs and cups (planchettes) are shown on the left. On the right a
sample carrousel (also known as a “turntable”) is shown.
If, however, the turntable must advance several positions, it is accelerated
to a high speed for most of the move and decelerated to slow speed before
stopping.
2.2
Light detection system
The essential components of the light detection system are 1) a photomultiplier tube (PMT) and 2) suitable detection filters. The detection filters serve
both to shield the PMT from scattered stimulation light and to define the
spectral detection window.
2.2.1
Photomultiplier tube
The emitted luminescence is detected by a photomultiplier tube (PMT). The
light sensitive component in the PMT is the cathode. This is coated with a
photo-emissive substance; CsSb and other bialkali compounds are commonly
used for this material. Typically, ten photons in the visible range striking the
cathode are converted into one to three electrons. Electrons emitted from
the photocathode are accelerated towards a series of dynodes maintained
at a positive voltage relative to the photocathode. Electrons with sufficient
velocity striking the dynode will eject several secondary electrons from the
surface.
The standard PMT in the Risø TL/OSL reader is a bialkali EMI 9235QB
PMT, which has maximum detection efficiency between 200 and 400 nm,
making it suitable for detection of luminescence from both quartz and feldspar
(see emission spectra in Figure 2.3).
2.2 Light detection system
7
Figure 2.2: The quantum efficiency of the photomultiplier tube EMI 9235QB PMT (Bialkali) as a function of photon wavelength and energy
Figure 2.2 displays the quantum efficiency (i.e. sensitivity) as a function
of incident photon wavelength for EMI 9235QB. The PMT is operated in
“photon counting” mode, where each pulse of charge arising at the anode is
counted. Many samples are only weakly luminescent making optimisation of
light collection important. Thus, it is critical that the PMT extends as large a
solid angle as possible. As the stimulation sources have to be placed between
the sample and the PMT the sample-to-PMT cathode distance in the Risø
TL/OSL reader is ∼ 55 mm, giving a detection solid angle of approximately
0.4 steradians.
2.2.2
Detection filters
The intensity of the stimulation light is ∼ 1018 orders of magnitude larger
than the emitted luminescence. In order to be able to measure the emitted
luminescence, detection filters must be used to prevent scattered stimulation
light from reaching the PMT, and the spectral stimulation and detection
windows must be well separated. Quartz has a strong emission centred on
365 nm (near UV) and many types of feldspars have a strong emission centred
on 410 nm (violet). In Figure 2.3 emission spectra from several samples of
sedimentary quartz and K feldspars are shown.
The Risø TL/OSL reader comes with the following three detection filters:
2.2 Light detection system
8
Figure 2.3: Emission spectra of sedimentary quartz and K feldspars (from Huntley et al.,
1991). a) Emission spectra of several sedimentary quartz samples from South Australia
obtained for stimulation using the 647 nm line from a Krypton laser. b) Emission spectra
of several sedimentary K feldspars using IR diode stimulation.
1. Hoya U-340 (7.5 mm thick, ø = 45 mm)
2. Schott BG 39 (2 mm thick, ø = 45 mm)
3. Corning 7-59 (4 mm thick, ø = 45 mm) or BG31 (3 mm thick, ø = 45
mm)
The individual filter characteristics are shown in Figure 2.4. Quartz OSL is
often detected using the Hoya U-3402 filter, whereas feldspar OSL often is
detected using the so-called blue filter pack comprising of Schott BG-39 in
combination with Corning 7-59 or BG3. The transmission curves for these
two combinations are shown in Figure 2.5. Also shown are the emission
spectra for quartz and feldspar.
1 From
May 2010 the Corning 7-59 (CN7-59) filter has been replaced by BG3
though the main transmission of the U-340 filter is slightly off-set compared to
the main emission of quartz its high transmission makes it favorable compared to e.g. U-360
2 Even
2.2 Light detection system
9
Figure 2.4: Transmission characteristics of the three detection filters (U-340, BG 39 and
CN7-59 or BG3) supplied with the Risø TL/OSL Reader.
Figure 2.5: Transmission characteristics of Hoya U-340 and the blue filter pack using either
CN7-59 or BG3 in combination with BG39. Also shown are emission spectra from quartz
and feldspar.
2.3 Luminescence stimulation system
10
Figure 2.6: a) Picture of the heating element in the measurement position, b) Same as a)
but with the sample carrousel in place. The small position holes on the sample carrousel
enabling the system to keep track of the position can also be seen.
2.3
Luminescence stimulation system
The Risø TL/OSL reader has two luminescence stimulation systems: 1) a
heating system that can be used for TL measurements and 2) a light stimulation system that can be used for OSL measurements. The two stimulation
can be used in combination, e.g. OSL at elevated temperature is possible.
2.3.1
Heating system
The heating element and lift mechanism is located directly underneath the
photomultiplier tube. The heating element (see Figure 2.6) has two functions: 1) it heats the sample and 2) it lifts the sample into the measurement
position. The heater strip is made of low-mass Kanthal (a high resistance
alloy) which is shaped with a depression to provide good heat transmission to
the sample and to lift it securely and reproducibly into the measurement position. Heating is accomplished by feeding a controlled current through the
heating element. Feedback control of the temperature employs a CromelAlumel thermocouple (0.5 mm) mounted underneath the heater strip. The
thermocouple is fixed to the heater element using a gold rivet. Heating is
provided by a continuous non-switching fixed frequency sine wave generator.
The heating system is able to heat samples to 700 ◦ C at constant heating rates
from 0.1 to 10 K/s. To minimise thermal lag between sample and heater strip
heating rates above 5 K/s are usually not employed. The heating strip can
be cooled by a nitrogen flow, which also protects the heating system from
oxidation at high temperatures.
2.3 Luminescence stimulation system
11
Figure 2.7: a) Actual temperature as a function of Set temperature, b) Systematic deviation between Actual and Set temperature as a function of Set temperature.
Software corrects for systematic deviations (primarily related to electronic
non-linearity) between set temperature and actual temperature of the heating
element. The calibration for each heating system is unique. After calibration
the systematic deviations are all within 0.25 ◦ C of the Set temperature (see
Figure 2.7).
2.3.2
Optical stimulation system
In OSL, the probability of eviction depends on the rate at which photons
arrive at the trap and the sensitivity of that particular trap to photoeviction. The sensitivity of the trap depends strongly on the wavelength of the
stimulating light, generally the shorter the wavelength the greater the chance
of eviction. However the wavelength of the stimulation light is not the only
factor to take into consideration. The wavelength of the emitted luminescence must also be considered. The intensity of the emitted luminescence is
many orders of magnitude smaller than the intensity of the stimulation light,
so in order to effectively prevent stimulation light from reaching the PMT,
the wavelengths of the stimulation light and the luminescence must be well
separated or appropriate filters used.
Conventionally, the samples are stimulated at constant light intensity
(continuous wave CW-mode), which produces an exponentially decaying signal as the electron traps are being depleted. However, the decay curves for
most samples contain more than one component (i.e. traps with different optical cross-sections), and require several exponential functions to adequately
describe the data. In linearly modulated OSL (LM-OSL) the stimulation
2.3 Luminescence stimulation system
12
Figure 2.8: Illustration of three different stimulation modes: CW-OSL, LM-OSL and
POSL. Also shown are experimental results obtained using the three stimulation modes
on sedimentary quartz.
light intensity is varied linearly (usually from zero to a predefined value).
Electrons in traps most sensitive to light will be evicted at low intensities,
whereas the less light sensitive traps will empty at higher intensities. Thus,
by ramping the light intensity a stimulation curve is obtained in which different peaks represent different sensitivities to light (Bulur, 1996). In pulsed
OSL (POSL, McKeever et al., 1996) the stimulation light is pulsed and the
OSL is only measured in between the pulses (see Figure 2.8). Pulsing provides insight into the luminescence recombination process, reduces the need
for filtering and provides an instrumental way of separating the luminescence
emitted from different phosphors.
2.3 Luminescence stimulation system
13
Figure 2.9: Schematic diagram of the combined blue and IR LED OSL unit. The unit
contains 28 blue LEDs (in 4 clusters) emitting at 470 nm delivering ∼80 mW/cm2 at the
sample and 21 IR LEDs (in three clusters) emitting at 870 nm delivering ∼145 mW/cm2
at the sample.
In the standard Risø TL/OSL reader (Bøtter-Jensen et al., 2000) a choice
of two stimulation sources exists: 1) infrared (IR) light emitting diodes
(LEDs) and 2) blue LEDs (see Figure 2.9). LEDs are inexpensive, compact, have short response times and the illumination power density can be
controlled electronically. The latter offers the possibility of stimulation at
different intensities and varying the stimulation intensity as a function of
stimulation time. The array of LEDs is equipped with an optical feedback
servo-system to ensure the stability of the stimulation power. Stimulation in
CW-mode and LM-mode is possible in all Risø readers. Stimulation in pulsed
mode requires additional hardware and is only offered as an additional option.
The LEDs are arranged in clusters, which are mounted concentrically in
a ring-shaped holder located between the heater element and the photomultiplier tube. The holder is machined so that all individual diodes are focused
at the sample. Each cluster contains seven LEDs and the ring-shaped holder
can contain up to seven clusters (i.e. a total of 49 LEDs). The distance between the diodes and the sample is approximately 20 mm. A picture of the
2.3 Luminescence stimulation system
14
Figure 2.10: Picture of the OSL stimulation unit and the U-340 detection filter. The filter
basket is inserted directly into the OSL stimulation unit (see Figure 3.6).
OSL stimulation unit is shown in Figure 2.10.
Infrared LEDs
Infrared (IR) stimulation in the region 800–900 nm can stimulate luminescence from most feldspars (Hütt et al., 1988, but not from quartz at room
temperature). This has the important advantage that a wider range of wavelengths for the detection window becomes available. The IR LEDs used
(Vishay TSFF 5210) emit at 870 nm (FWHM 40 nm), which is at the IR resonance wavelength found in most feldspars (Bøtter-Jensen et al., 2003). The
IR LEDs are arranged in 3 clusters each containing seven individual LEDs.
The maximum power from the 21 IR LEDs is approximately 145 mW/cm2
at the sample position (Bøtter-Jensen et al., 2003).
The LED emission spectrum is shown in Figure 2.11. When stimulating with
the IR diodes both detection filter combinations can be employed (Hoya U340 or the blue filter pack).
2.3 Luminescence stimulation system
15
Figure 2.11: The emission spectrum of IR and blue LEDs. Also shown are the transmission
curves for the GG-420 green long pass filter (cut-off filter in front of the blue LEDs) and
the Hoya U-340 filter and blue filter pack (detection filters in front of the PMT)
Blue LEDs
The Risø reader is equipped with blue LEDs (NICHIA type NSPB-500AS)
with a peak emission at 470 nm (FWHM = 20 nm). They have an emission angle of 15 degrees and a power output of ∼ 4.8 cd at 20 mA. The blue
LEDs are usually arranged in 4 clusters each containing seven individual
LEDs. The total power from 28 LEDs is 80 mW/cm2 at the sample position (Bøtter-Jensen et al., 2003). The advantage of using the stimulation
spectrum from the blue LEDs is that the OSL decay will be rapid because
of the short wavelength, but the disadvantage is that the spectrum has a
significant tail into the detection window (centred on 340 nm). To reduce
the intensity of this tail, and thereby minimise the amount of directly scattered blue light reaching the light detection system, a green long pass filter
(GG-420) is incorporated in front of each blue LED cluster. The filter effectively attenuates the high energy photons from the blue LEDs at the cost of
approximately 5% attenuation of the peak centred on 470 nm. Figure 2.11
displays the measured LED emission spectrum compared with the published
transmission curve for the GG-420 filter and the U-340 detection filter.
2.3 Luminescence stimulation system
16
When stimulating with the blue LEDs only the U-340 detection filter can be
used. SWITCHING ON THE BLUE LED’S WITH THE BLUE FILTER
PACK IN PLACE WILL SERIOUSLY DAMAGE THE PMT.
Cross-talk
On a 48-sample carousel the distance between the centres of adjacent sample
positions is 17 mm. The consequence of this close spacing is that optical
stimulation of one sample may affect adjacent samples. This phenomenon
is referred to as optical cross-talk (or cross-bleaching). In the following the
optical cross-talk is expressed as a percentage of the equivalent stimulation
time on the adjacent sample. Bray et al. (2002) measured the optical crosstalk using an array of blue LEDs delivering 18 mW/cm2 to the sample and
estimated it to be 0.014%. Bøtter-Jensen et al. (2000) measured the optical
cross-talk on a similar instrument to be 0.006% using an array of blue LEDs
delivering 28 mW/cm2 to the sample. Although this cross-talk can be significant in highly sensitive samples, the effects can usually be disregarded if
care is taken with the measurement sequence design.
2.3.3
Calibration LED
A weak reference light source (known as the blue “calibration LED”) is incorporated in the reader and is used for routine check of the detection system. A
single blue (470 nm) LED is mounted into a temperature stabilised (± 0.5 ◦ C)
aluminium housing to provide a stable light output. A thin fibre guides the
emitted LED light to the top of the heater unit where it points through a
hole in the bottom part of either the TL flange or the OSL stimulation unit3 .
The reference light (barely visible to the naked eye) thus passes through the
interface quartz glass and the detection filter pack before reaching the cathode of the photomultiplier tube. The reference LED source serves two major
purposes:
1. checking that the correct detection filter is placed in front of the PM
tube before starting a sequence
2. long term stability control of the detection system where blue transmission filters are used (e.g. in TL mode)
When using blue light stimulation a U-340 detection filter is normally used.
The U-340 does not pass blue light. If the U-340 filter is not inserted and
the powerful blue stimulation light by accident is switched on, this will cause
3 This
hole must always be oriented towards the middle of the measurement chamber.
2.3 Luminescence stimulation system
17
Figure 2.12: A weak blue LED is positioned on the main reader circuit board (in the
metal cube). A light guide (black cable) transmits the light from this LED to the top of
the heater unit. The purpose of this weak blue LED is to provide a check on the filter
combination in place and to provide a check on the sensitivity of the light detection system
when blue detection filters are used.
severe damage of the PM tube because of heavy illumination. Before beginning any measurement sequence the SEQUENCE EDITOR automatically
checks that an appropriate detection filter is in place before the sequence
can actually start. First the normal PM dark counts are measured with the
reference LED switched off and immediately after a measurement is made
with the reference LED switched on. If the second measurement increases
more than 10% over the first measurement and the sequence contains blue
light stimulation (using the blue LED command) the sequence is not allowed
to begin automatically and a warning will appear on screen. However, this
safety precaution will only be effective when the bottom flange (e.g. the TL
flange or the OSL stimulation unit) is oriented correctly. It is possible to
mount it with an off-set of 180 ◦ C which would prevent the reference light
from reaching the PM tube regardless of the detection filter in place. Thus,
it is recommended that whenever a blue light transmitting detection filter
combination is used then the blue LEDs are manually disabled. This can be
done using the switch at the back of the Controller (see Figure 7.1 page 61).
In TL mode it is common to use blue detection filters. Here the blue reference LED source can be used for long term testing of the day-to-day stability
of the PM tube or whether the detection filters or the interface quartz filter
2.4 Irradiation sources
18
Figure 2.13: Picture of the TL flange. A hole has been drilled in the bottom of both the
TL and OSL flanges. This hole allows the passage of a weak blue light flux (from the blue
calibration LED). The flange must be positioned in such a way that it is pointing towards
the middle of the measurement chamber. a) Seen from above b) seen from below
have been contaminated (e.g. from silicone or moisture evaporated from the
samples during heating).
2.4
Irradiation sources
In the Risø TL/OSL reader samples can be irradiated in situ using three
different types of radiation.
1. Beta radiation (90 Sr/90 Y)
2. Alpha radiation (241 Am)
3. X-ray radiation (50 kV/1 mA filament tube)
Irradiations are software controlled allowing single irradiations (minimum
irradiation time of 1 s). Figure 2.14 show pictures of the various irradiators.
2.4 Irradiation sources
19
Figure 2.14: Picture of the various irradiators: beta irradiator, alpha irradiator and filament X-ray generator. All three irradiators can be fitted on the same reader.
2.4.1
Beta irradiation
A detachable beta irradiator is located above the sample carousel and a
schematic drawing of the irradiator unit is shown in Figure 2.15. The irradiator is made of brass (outer diameter 10 cm) and is surrounded by 20 mm of
lead on the sides, and 40 mm on the top. Furthermore, an aluminum safety
helmet (outer diameter 222 mm) covers the entire irradiator and lead shielding. This irradiator accommodates a 90 Sr/90 Y beta source, which emits beta
particles with a maximum energy of 2.27 MeV. The half life is 30 years. The
source strength is usually about 1.48 GBq, which gives a dose rate in quartz
at the sample position of approximately 0.1 Gy/s.
The source is mounted into a rotating, stainless steel wheel, which is
pneumatically activated; it takes the source 0.11 s to rotate from the closed
position to the open position (Markey et al., 1997). This off-set time is
constant for all irradiations and is negligible for long radiations. In brief
irradiations it can be compensated for by subtracting it from the programmed
irradiation time.
The source-to-sample distance should be as small as possible to provide
the highest possible dose rate at the sample, however any spatial variations
in dose rate across the source will be accentuated at small source-to-sample
distances, so a compromise is required. The distance between the source and
the sample is 7 mm.
The source is placed inside the irradiator, directly followed by a 20 mm
thick aluminum spacer, a 20 mm thick lead spacer, a spring washer, and
finally a 25 mm thick aluminum spacer (see Figure 3.17). When the source
2.4 Irradiation sources
20
Figure 2.15: Schematic diagram of the cross section of the beta irradiator. The 90 Sr/90 Y
source is placed in a rotating stainless steel wheel, which is pneumatically activated. The
source is shown in the on (irradiating) position. When the source is off the wheel is
rotated 180 ◦ , so that the source points directly at the carbon absorber.
is “off” (default position) it is pointing upwards directly at a 10 mm Carbon
absorber. When the source is “on” (activated position) it is pointing downwards towards the measurement chamber. A 0.125 mm beryllium window
is located between the irradiator and the measurement chamber to act as
vacuum interface for the measurement chamber.
On a 48 sample carousel the distance between the centres of adjacent
sample positions is 17 mm. The consequence of this close spacing is that
irradiation of one sample will lead to a dose being absorbed in the adjacent
samples. This phenomenon is referred to as irradiation cross-talk. Thomsen
et al. (2006) measured the irradiation cross-talk to be 0.250% ± 0.003% for
adjacent samples and 0.014% ± 0.002% for second nearest samples.
2.4 Irradiation sources
2.4.2
21
External dose rates
External dose rate originates entirely from bremsstrahlung due to interaction
with beta particles in surrounding materials. All dose rates reported below
were measured using an Automess Scintomate 6134A, which is a calibrated
plastic scintillation detector, specifically intended for measuring dose rates
from photons down to 40 keV. The measurements were carried out in a room
with a background dose rate of ∼ 0.15 µSv/hr.
• When the source is not activated the dose rate at a distance of 1 m
from the front surface of the Risø reader is < 0.4 µSv/hr. When the
source is activated the dose rate is < 0.5 µSv/hr.
• The dose rate directly on the surface of the irradiator is < 5 µSv/hr
both when the source is activated and not activated.
• The maximum dose rate directly on the side of the reader (the side
closest to the irradiator) increases from 5 µSv/h to < 100 µSv/h when
the source is open. It is not possible to be situated close to this side
of the reader (the 100 µSv/h drops to 17 µSv/h even 10 cm away from
the surface), but nevertheless this dose rate can readily be reduced
to << 1 µSv/h by placing one cm of lead shielding right under the
irradiator along this side of the reader. However, we do not regard it
as necessary to shield either the front or the other sides of the reader.
We also recommend that the reader is positioned in such a way that
the space underneath it is inaccessible (the dose rate underneath a
wooden table with a thickness of 25 mm is < 3 µSv/h when the source
is inactivated and < 40 µSv/h when the source is activated).
The lid is both electronically and mechanically inter-locked so it cannot
be opened while the source is energized. If the lid is forced open software and
hardware interlocks will de-energize the irradiator and returning the source
to its default safe position. An external indicator positioned next to the
irradiator glows red when the source is activated and green when the source
is de-energized.
2.4.3
Alpha irradiation
The alpha irradiator normally accommodates a 10.7 MBq (290 mCi) 241 Am
foil source, which is a mixed alpha/gamma emitter. The dominating alpha
energy is 5.49 MeV (85.1%) and the dominating gamma energy is 59 keV.
The source is mounted behind a pneumatically controlled shutter. The alpha
irradiator option is integrated with the system lid and a sealed shaft allows
2.4 Irradiation sources
22
operation of the irradiator under vacuum. The dose rate in quartz at the
sample position is approximately 45 mGy/s.
2.4.4
X-ray irradiation
The X-ray irradiator is a filament type X-ray: Varian VF-50J X-ray tube
(50 kV, 1 mA, 50 W) with tungsten target and a 4-50 kV DC Spellman
high voltage power supply (Andersen et al., 2003). The tube is mounted on
a 35 mm long brass collimator (internal diameter 10 mm) with a 50 µm Al
end window at the exit. A 7 mm thick mechanical shutter made of stainless
steel is positioned within the length of the collimator to prevent the sample
from being irradiated until the X-ray output has stabilized. At the end of an
irradiation the shutter is closed before the X-ray is switched off. It takes the
shutter 62 ms to open and 145 ms to close. Thus, the actual irradiation time
is about 80 ms longer than the programmed time. The distance from the
face of the X-ray tube to the sample is 35.5 mm, and the average dose rate
at 50 kV and 1 mA (maximum power) to quartz grains mounted on stainless
steel discs is approximately 2 Gy/s.
Spooner and Allsop (2000) examined the spatial variation of dose-rate
from a 90 Sr/90 Y beta source and found that the dose rate could vary by
15% across a 10 mm sample area for a source/sample distance of 15 mm.
Others have reported higher spatial dose rate variations for their sources
(Ballarini et al., 2006). The spatial variation of dose-rate for the filament
X-ray is less than 1%. For the filament X-ray the irradiation cross-talk is
0.0012% ± 0.0001% for the adjacent samples and less than 10−4 % for second
nearest samples.
There is an excellent linearity between tube current (as set by the user)
and dose rate. It has a dynamic dose rate range between 10 mGy/s and
2 Gy/s at 50 kV and 2-30 mGy/s at 10 kV) when mounted on a standard
OSL/TL reader. The short-term stability is better than about 0.2% (Andersen et al., 2003). The X-ray irradiator incorporates an enhanced security
control and fail-safe system to meet the individual “regulations for operation”
as issued by the different local governments of different countries
3
Installation of the Risø
TL/OSL reader
This section details how to install the Risø TL/OSL reader.
3.1
Components
Below is a list of the components supplied with a standard Risø TL/OSL
system (see also Figure 3.1).
1. The Reader (40 cm × 55 cm × 55 cm)
2. The Controller (50 cm × 55 cm × 20 cm)
3. PM tube
4. Nitrogen tubing
5. Nitrogen fittings
6. Flow meter
7. Tools for loading the source
8. Manuals (e.g. Analyst, Sequence Editor)
9. Risø software (CD). Includes programmes required for running the system, analysis software, electronic versions of all manuals, short movies
showing how to load the beta source, how to connect the Nitrogen
supply etc.
10. Two sample carrousels
3.1 Components
Figure 3.1: Various components supplied with a standard Risø TL/OSL system.
24
3.2 Installing the hardware
25
• A 48 position sample carrousel for cups (planchettes)
• A 48 position sample carrousel for discs
11. 100 stainless steel cups (to be used with the sample carrousel labelled
“CUPS”)
12. 100 stainless steel discs (to be used with the sample carrousel labelled
“DISCS”)
13. Filter basket with 7.5 mm Hoya U-340 filter (already placed in the OSL
stimulation unit when the system is received by the end-user)
14. Filters: Corning 7-59 (4 mm) or BG3 (3 mm) and Schott BG-39 (2
mm)
15. Extra filter basket
16. Flange for TL measurements including a special filter basket to be
used with the TL flange. If no OSL measurements are to be made
it is advantageous to remove the OSL stimulation unit and replace it
with this TL flange because of the improved detection geometry (the
PMT is situated closer to the sample when the OSL stimulation unit
is replaced by the TL flange)
17. OSL test cable. This test cable can be used to monitor the current
through the OSL stimulation unit (see Figure 7.1)
18. Circlip pliers. These pliers are only used when the beta source has to
be loaded/unloaded (see section 3.5)
3.2
3.2.1
Installing the hardware
Unpacking
The Risø TL/OSL reader is shipped in a durable wooden box (59 cm×66 cm×
80 cm). Please, keep this box in case you need to move the reader to a different
location or have it sent back to Risø for repair.
The beta irradiator is surrounded by lead shielding which again is surrounded
by an aluminium safety helmet (outer diameter 222 mm). The lead shielding
weighs about 20 kg, so before lifting the reader out of the box it is advisable
to remove this shielding. The aluminium helmet is held in place by two
screws.
The reader it self weighs 80-90 kg so it is advisable that two persons lift the
3.2 Installing the hardware
26
Figure 3.2: Unpacking the shipment.
reader out of the wooden box using the white ropes (see Figure 3.2). Rest the
reader on the corner of the wooden box while obtaining a better grip on the
reader. Then place the reader on a flat, stable surface at least 90 cm long.
The system is run using a standard PC (usually supplied by the customer). If
this PC is also placed on the work bench, we recommend that an additional
bench space of 90 cm is available, bringing the total recommended bench
space to 180 cm.
If the Risø system is equipped with a beta source then it is recommended
that the Controller is placed on the left side of the reader (see Picture on
the front of this manual) to prevent this desk space from being used as work
space. When the source is irradiating the external dose rate can be 100 µSv/h
directly on the reader surface.
It is further recommended that the reader is positioned in such a way that
the space underneath the reader is inaccessible (the dose rate underneath a
wooden table with a thickness of 25 mm is < 3 µSv/h when the source is
inactivated and < 40 µSv/h when the source is activated).
3.2.2
Nitrogen connections
Pressurized nitrogen is required when samples are heated above 200 ◦ C and
to activate the pneumatically-controlled beta and alpha irradiators. A high
quality pressure regulator must be provided that can maintain a stable output
pressure of 2.5 bar (0.25 MPa). 1/4” NPT threads will fit the nitrogen tube
3.2 Installing the hardware
27
Figure 3.3: Attaching the N2 flow meter. The arrows indicate the Nitrogen flow.
connectors provided by Risø.
If a single source of pressurized nitrogen is used to both flood the measurement chamber and to activate the source(s) then the main N2 supply is
connected directly to the N2 input coupling as shown in Figure 3.3.
The consumption of nitrogen for activating the pneumatically-controlled
beta and alpha irradiators is very small, but if a compressed air installation already exists in your laboratory you may chose to chose to feed the
source control from a separate compressed air source. The following section
describes how to do this.
Two separate compressed input sources
The numbers in the following list correspond to the picture numbers given in
Figure 3.4. All required fittings can be found in the N2 -fittings bag provided
by Risø.
1. Dismount the backplate using a 2 mm Allen key. The backplate is
3.2 Installing the hardware
Figure 3.4: Installing two separate compressed input sources.
28
3.2 Installing the hardware
29
being held in place by 5 screws.
2. Remove the cap.
3. Dismount the two tube couplings on the top and the blanking plug on
the side.
4. Mount two blanking plugs on the top and a tube coupling on the side
of the manifold using a 7 mm key.
Remount the backplate.
5. Connect the compressed air to the N2 input (the third tube coupling
from the left).
Connect the tube from the N2 main supply to the just mounted tube
coupling (the fourth tube coupling from the left).
Mount the enclosed label over the old label.
3.2.3
Attaching the flow meter
The flow meter and its position on the reader is shown in Figure 3.3. Attach
the N2 tubes as shown. The arrows indicate the Nitrogen flow. Also shown
is advantageous places to position cable straps. Using cable straps in this
way reduces the risk of getting the Nitrogen tubes caught between the lid
and the reader while opening and closing the lid.
The 2.5 bar N2 input pressure is reduced to 0.8 bar to reduce the risk
of discs being blown off the heater element when the measurement chamber
is flooded with N2 . However, if a different flow pressure is required it can
be adjusted manually using the reduction valve located on the pressured air
manifold (see Figure 3.5). The inlet pressure can be read off the manometer
located next to the reduction valve. To gain access to this reduction valve
either remove the backplate as shown in Figure 3.4 or simply remove the
cover.
3.2.4
Mounting the PMT
The PMT is mounted directly on top of the OSL stimulation unit (see Figure
3.6c). The PMT is a very sensitive device that ought to be handled with great
care. Please avoid exposing the photocathode to direct light (even when
the PMT is not powered). Remember to insert the detection filter before
mounting the PMT. Ensure that the o-ring below the filter basket is in place
before inserting the filter basket (see Figure 2.10). Ensure that the o-ring
located underneath the PMT is in place. This is important to prevent light
3.2 Installing the hardware
30
Figure 3.5: Position of the reduction valve controlling the N2 inlet pressure seen from the
back of the reader (top) and from the side (bottom).
3.2 Installing the hardware
31
Figure 3.6: Mounting the PMT on the reader. a) Top of the OSL stimulation head. The
arrows indicate where the PMT is to be mounted (three screws). b) Bottom of PMT. Do
not expose the PMT cathode to direct light. Ensure that the o-ring indicated is in place
before mounting the PMT. c) Mounting of the PMT
leakage into the reader. Screw the PMT on the reader alternating between
the different bolts. Do not screw the bolts too tight.
3.2.5
Connecting to the Controller
DO NOT POWER THE CONTROLLER AT THIS STAGE!!!
Connecting the PMT
Connect the HV (yellow) and SIGNAL (black) cables from the PMT to the
Controller. Always connect the SIGNAL cable before the HV cable! Put the
cables below the N2 tubes so they can NOT get stuck under the lid when
it closes. The cables should be able to move freely. Connect the cables as
shown in Figure 3.7a
3.2 Installing the hardware
32
Figure 3.7: Connecting the Controller. a) Back of the Controller. b) Enlargement of the
back of the Controller showing the RS 232 com 1 port that should be connected to the
user PC. c) Front of the Controller. The position of the HV dial is indicated by the arrow.
The HV must be set to zero prior to switching on the power.
Connecting the rest
Figure 3.7a shows the back of the Controller. All connections are clearly
indicated. Figure 3.7b is an enlargement of Figure 3.7a showing the RS 232
com 1 port that should be connected to the user PC. Please note that not all
slots need to be connected (e.g. ETHERNET, VGA, RS 422/RS 455, KEYBOARD and USB are not normally used).
Only when all connections have been made, the power to the Controller
and the Reader may be switched on. Prior to switching on the power, the
HV setting on the front of the Controller (see Figure 3.7c) must be set to zero.
After switching on the power the HV should be slowly increased to the
setting specified on the Risø PM-Tube Testsheet (red arrow, see an example
of a test sheet in Figure 3.8). The HV supply ranges between 500 and 1500
V. The dial ranges between 0 and 10. An increase of “1 ” corresponds to an
increase in HV of 100 V. To set the HV to 1000 V the dial must be set to
3.3 Installing the Risø software package
33
Figure 3.8: Example of the Risø PM-Tube Testsheet. The red arrow indicates the HV
setting of the PMT (1200 V in this case).
“5.00”. To set the HV to 1200 V the dial must be set to “7.00”.
3.2.6
Connecting the N2 /air supply to the beta irradiator (not yet loaded)
Before connecting the beta irradiator to the N2 /air supply a coupling must
be fitted to the top of the pneumatic actuator which protrudes from the top
of the beta irradiator. The coupling is found in the bag with N2 fittings. Note
that a plastic washer must be fitted between the coupling and the actuator.
The black plastic tube (already connected to the reader on the left hand side
of the tower) should be connected to the coupling fitted to the top of the
pneumatic actuator. See Figure 3.9.
3.3
Installing the Risø software package
To install the Risø software package on the user PC insert the CD in the appropriate drive (installation will begin automatically). If the installation does
not start automatically, it can be started manually by running the setup.exe
program located on the CD root directory. Follow the instructions provided
3.3 Installing the Risø software package
34
Figure 3.9: Connecting the N2 /air supply to the beta irradiator.
by the installation program. You can choose between three different installation modes: 1) Typical, 2) Customised, and 3) Full. The features installed
in “Typical” and “Full” installation modes are shown in Table 3.1. In “Customised”mode you may select which features to install. Select the installation
ode and follow the instructions during the installation.
You may run the installation CD at a later stage if you wish to add or
remove features from your installation. The Controller Software Update program that can be installed using the Update Installer program is removed by
Add or remove programs in the Windows Control Panel.
The Risø Controller Version D (or later) supports USB connection as an
alternative to RS232 connection to the controlling PC. If your controlling PC
uses Windows XP then you are prompted to install two drivers the first time
you connect the PC and the Risø Controller. In the first screen select “No,
not at this time” and in the second select “Install the software automatically”
(see Figure 3.10a and b). In the dialog box informing you that the driver
has not passed the Windows Logo testing select “Continue anyway”. If your
controlling PC uses Windows 7 the installation is done automatically.
The Risø Controller is now connected to a COM port. The COM port
number, which you will need for setting up the Sequence Editor and the
Control Program, you will find in: Control Panel → System → Hardware →
Device manager as shown in Figure 3.11. If the COM port number is > 8
then you need to change it to a number ≤ 8. This is done by choosing the
“Advanced...” in the USB Serial Port Properties window and specifying a
new number (which does not conflict with other ports on your computer) for
3.3 Installing the Risø software package
Feature
35
Typical Full Description
Sequence Editor
X
X
Control
X
X
Viewer
X
X
Analyst
X
X
Manual
X
X
PTanalyse
X
Extras
X
Update Installer
X
Used to define and run the sequence of actions
you want the instrument to do
Used to check the functionality of the system
It is mainly used for service and maintenance
Used to inspect the data acquired using
the Sequence Editor
Used to inspect and analyse the data acquired
using the Sequence Editor
The manuals for the Reader and the available
options
Used to inspect and analyse data acquired using
the Photon Timer option
Extra material including pictures, videos,
examples etc.
Used to install a tool for updating the Controller
software. The Update installer installs a shortcut
to the Controller Software Update program in the
Risoe program folder
Table 3.1: Features installed in “Typical” and “Full” installation modes.
Figure 3.10: Software installation using USB connection
the COM port (see Figure 3.11).
3.4 Testing
36
Figure 3.11: Selecting the appropriate COM port
3.4
Testing
It is now time to test if the reader has been installed correctly. The lid of
the reader is opened by pressing the “UP” button located on the front panel
of the Controller (in the bottom left corner, see Figure 3.7c). The reader
lid opens sideways to the left (see Picture on the title page). Insert one of
the sample carrousels. After placing the sample carrousel rotate it a little
to ensure that it has been positioned correctly. Close the reader lid by continuously pressing “DOWN”. Continue pressing “DOWN” until the lid stops
moving. For security reasons the lid will stop moving as soon as the “DOWN”
button is released.
Open the CONTROL program, choose “connect to Minisys” and select the
tab: “Services” (see Figure 3.12). When closing CONTROL it is important to
remember to choose “Disconnect from Minisys” (only available when CONTROL is connected to the Controller) on the tab “Connection”.
In the following sections the basic reader performance is tested using the
CONTROL program.
3.4 Testing
37
Figure 3.12: Testing the system using CONTROL.
3.4.1
Resetting the sample carrousel
Open CONTROL, choose “connect to Minisys” and select the tab: “Services”
(see Figure 3.12). Reset the sample carrousel1 by clicking the “Reset the
Turntable” button located in the horizontal panel entitled: “Turntable” (second button from the left. Resting the cursor on the individual buttons will
show an explaining text string). The system keeps track of the individual
positions by the use of a weak infrared light emitting diode (LED) positioned
underneath the turntable and a light sensor located directly above the LED.
This IR diode switches on during rotation of the sample carrousel. At each
sample position a small hole (Ø = 1 mm) is drilled on the outer perimeter
of the sample carrousel. Every time IR light is detected by the light sensor
the system knows that it is at a new position. When the sample carrousel is
rotating the display on the Controller will read: “Resetting Turntable” and
the appropriate red lights will light up in the TURNTABLE column (top left
corner on the Controller).
3.4.2
Checking the lift
Only carry out these instructions if the sample carrousel has been reset (see
above) and is on position. It is impossible to lift the lift if the sample carrousel
1 Resetting
the sample carrousel/turntable means that position 1 on the sample carrousel will be positioned on the measurement position directly underneath the PMT
3.4 Testing
38
is not on position.
Raise the lift by clicking the “Lift up” button (arrow up, vertical columns
on the left of the screen). Monitor the lights on the front of the Controller.
The “LIFT RUN” light is on during movement and the “LIFT UP” light is
on when movement stops. Lower the lift by clicking the “Lift down” button
(arrow down, vertical columns on the left of the screen). Monitor the lights
on the front of the Controller. The “LIFT RUN” light is on during movement
and the “LIFT DOWN” light is on when movement stops.
3.4.3
Checking the Blue LEDs
To check that the blue LEDs can be switched on, press the “Blue LEDs”
button and open the lid. The light from the blue LEDs should be clearly
visible by eye. Close the lid again and switch off the Blue LEDs.
3.4.4
Adjusting the N2 flow rate
To adjust the N2 flow rate, switch on the N2 flow (“N2 valve”) and adjust
the flow on the flow meter (see Figure 3.3) to 1 l/min using the black knob.
Switch off the N2 flow.
3.4.5
Checking the beta irradiator
To check if the beta irradiator is operational click the“beta irradiator”button.
A clicking sound should be clearly audible (the sound of the pneumatically
activated rotating stainless steel wheel).
3.4.6
Checking the alpha irradiator
To check if the alpha irradiator is operational click the “alpha irradiator”
button. A clicking sound should be clearly audible (the sound of the pneumatically activated shutter).
3.4.7
Measure PMT counts
This section is used to measure the counts detected by the PMT. On the left
the time interval being integrated can be changed (default 1 s). Measurement is started by clicking “Start”. Whenever the PMT has been taken off
the reader (e.g. because of filter changing) the user ought to check if any light
leaks have been introduced into the system. This can be done by measuring
the PMT counts with and without the white room lights switched on. If
3.5 Loading the beta source
39
the counts increase when the room lights are switched on it means that a
light leak has been introduced into the system - probably because an o-ring
has been forgotten or the PMT is not mounted properly. It is normal that
the dark count will be slightly elevated immediately after mounting the PMT.
Close CONTROL by choosing “Disconnect from Minisys” (only available
when CONTROL is connected to the Controller) on the tab “Connection”.
3.5
Loading the beta source
This section describes the procedure of loading/unloading the 90 Sr/90 Y source
in the Risø beta irradiator. Please read the instructions carefully and watch
the video showing how to load the source (C:\Risoe\Movies\Cable connection.mpg) before attempting to unload/load the source.
Before beginning the procedure of unloading/loading the beta source,
make sure that
a) an empty desk space of 60 × 60 cm is available to handle the irradiator
during unloading/loading
b) the following tools are kept within reach:
• Two hexagonal keys (Allen keys), 4 mm and 5 mm
• The circlip pliers (delivered with the Risø reader)
• The source handling rod (delivered with the source)
• 10 mm perspex/plexiglass plate and a vice to hold it. This plate
is to be used as protection when the source is exposed
You should now be ready to begin the procedure of loading/unloading the
beta source. The source will be exposed in item 8 and 9.
1. Remove the plastic air tube (Figure 3.13). If the irradiator module is
fitted with an aluminium helmet (new models) remove it. Then remove
the lid of the lead shielding
3.5 Loading the beta source
40
Figure 3.13: Removing the air tube.
2. Remove the lead shielding cylinder by removing the socket screw using
a 4 mm hexagonal key (Allen key, see Figure 3.14)
3. Remove the irradiator from the reader by unscrewing the two screws
on the top using a 5 mm hexagonal key.(Figure 3.15)
3.5 Loading the beta source
41
Figure 3.14: Removing Pb shielding.
Figure 3.15: Removing the irradiator.
4. Place the lid of the lead shielding UPSIDE DOWN on the circular lead
shielding as shown in Figure 3.16a. Lift up the irradiator from the
reader (Figure 3.16b). Place the irradiator upside down using the hole
in the lid (Figure 3.16a)
3.5 Loading the beta source
42
Figure 3.16: Preparing for loading/unloading.
5. The items shown in Figure 3.17 are located within the irradiator and
must be removed and handled individually using the special tools delivered with the beta source. The source will only be present if the
irradiator is to be unloaded
6. Remove the circlip using the circlip pliers delivered with the equipment
(Figure 3.18)
3.5 Loading the beta source
43
Figure 3.17: Items in the irradiator.
Figure 3.18: Removing the circlip.
7. Remove the long Al spacer using the special handling rod with thread
(included in the beta source packing) and then the Pb spacer with
spring washer and finally the short Al spacer (Figure 3.19)
3.5 Loading the beta source
44
Figure 3.19: Removing items in the irradiator.
8. Place a 10 mm thick perspex/plexiglass plate (or another beta-thick
transparent absorber e.g. 3 mm of window glass) in front of the irradiator (this transparent sheet will absorb all beta rays during loading).
Place the lead container with the source behind the perspex and take
off the container lid. Remove the plastic lid from the inner container
as quickly as possible. Lift out the foam plastic packing using a pair
of tweezers. Then use the handling rod to lift up the source from the
container (turn rod clockwise to fix it in the tread hole of the source).
The source must always be pointed away from the operator. The operator must wear safety glasses and must at all times look through the
perspex plate during the loading operation (Figure 3.20)
3.5 Loading the beta source
45
Figure 3.20: Inserting the source I.
9. Place the source in the irradiator and gently unscrew the handling rod
from the source (Figure 3.21)
3.5 Loading the beta source
46
Figure 3.21: Inserting the source II.
10. The perspex plate can now be removed for ease of access. Use the
handling rod to place the short Al spacer, then the Pb spacer with
spring washer and finally the long Al spacer on top of the source (Figure
3.22)
3.5 Loading the beta source
47
Figure 3.22: Reinsert spacers.
11. Mount the circlip using the circlip pliers (Figure 3.23a). Hold the circlip in your left hand and use the pliers to squeeze the circlip closed
with your right hand. Keep holding the circlip with the left hand and
the pliers and insert on the top of the irradiator. Ensure that the points
of the pliers and the pliers line up with the cut step (Figure 3.23b) in
the long Al spacer (already fitted in the irradiator). Use the points of
the pliers to press down around the circlip to ensure that it is fitting
properly in the groove of the irradiator body. (Hold the black plastic
wheel (Figure 3.23a) firmly to prevent the irradiator from rotating accidentally). Ensure that the circlip is fixed securely in locked position.
12. Put the irradiator back onto the reader and bolt firmly in place
13. Place the Pb shielding around the irradiator, making sure that the slot
3.5 Loading the beta source
48
Figure 3.23: Mounting the circlip.
in the Pb cylinder fits over the metal shaft of the black plastic wheel.
Insert the screw and secure. Ensure that the wheel and shaft are able
to freely rotate without touching the lead shielding
14. Place the lead lid on the top and check that it is located correctly. If
the source module is fitted with an aluminium helmet then replace this
15. Re-connect the plastic air tube
4
Changing detection filters
The U-340 detection filter is mounted in a filter basket and placed in the
OSL stimulation unit when the system is shipped from Risø. The following
section describes how the detection filters are replaced. The procedure can
be divided into six steps:
1. Mount the detection filter in the extra filter basket
2. Remove the PMT
3. Replace the previously inserted filter basket with the new one
4. Disable the Blue LEDs
5. Mount the PMT
6. Check for light leaks
4.1
Mounting detection filters
Figure 4.1 shows how the detection filters should be mounted in the filter
basket. Use the nut to secure the filters in the filter basket. The detection
filters are made of glass so care should be taken when tightening the nut tightening the nut too much may result in cracks in the filters. Remember
to inset o-rings at each interface.
4.2
Removing the PMT
Never expose the photocathode of the PMT directly to white light. Always
use subdued light when removing/mounting the PMT. There are two ways
in which one can disconnect the PMT:
4.2 Removing the PMT
50
Figure 4.1: Mount the detection filters in the filter baskets as shown in the picture. The
top row shows the blue filter pack and the bottom row shows the UV filter pack (U-340).
Always remember to insert an o-ring first and then a o-ring between each filter. Secure
the detection filters by tightening the nut. The nut should be sufficiently tight to prevent
the filters from moving. Be careful not to crush the (glass) detection filters.
1. SAFE PROCEDURE: disconnect the power from the Controller and
the reader!
2. ADVANCED PROCEDURE: First the HV cable (yellow) must be removed from the PMT and subsequently the signal cable (black) must
be removed. Changing the order may damage your light detection system. When the HV is removed from the PMT the red light indicator on
the Controller flashing every time a count is recorded (PM COUNTS)
will either stop shining or be continuously on.
After successful disconnection, the PMT can be removed by removing the
three screws holding it in place (see Figure 3.6c). Put the PMT in a safe
place and make sure the photocathode is not damaged.
4.3 Replacing the filter basket
4.3
51
Replacing the filter basket
Remove the the previously inserted filter basket from the OSL stimulation
unit. Please ensure that the o-ring between the filter basket and the OSL
stimulation unit is in place before inserting the new filter basket. If this
o-ring is missing a light leak has been introduced into the system.
4.4
Disabling the blue LEDs
If the blue filter pack is positioned in the OSL stimulation unit the blue LEDs
should be disabled manually to reduce the risk of shining blue stimulation
light directly into the PMT and thereby damaging it. The blue LEDs are
disabled using the switch on the back of the Controller (see Figure 7.1). The
blue LEDs should be enable once the U-340 detection filter is reinserted into
the stimulation unit.
4.5
Reconnecting the PMT
Before remounting the PMT ensure that the o-ring located in the bottom
of the PMT is in place (see Figure 3.6b). The PMT is remounted using
the three screws. Do not tighten them excessively since it may damage the
threads in the OSL stimulation unit.
Reconnect the PMT by fist connecting the SIGNAL cable (black) and then
the HV cable (Yellow). If the cables are connected in the reverse order the
PMT preamps may be damaged. If the SAFE PROCEDURE was adapted
then remember to reconnect the power to the Controller and the Reader.
4.6
Check for light leaks
After reconnection of the PMT it is advisable to ensure that no light leaks
have been introduced into the system. This can be done by using the test
program CONTROL.
1. Open CONTROL and press “connect to Minisys”
2. Choose the tab “Services”
3. Switch off the white room light (if it is not already off)
4. Click “Start” in the “Measure PMT counts” panel (see Figure 3.12) and
note down the “Counts:”.
4.6 Check for light leaks
52
5. Switch on the white room light and note down the “Counts:”. If the
number of detected counts is higher when the room light is on compared
to when it is off, a light leak has been introduced. This light leak must
be eliminated before it is advisable to use the reader.
6. Click “Stop” to stop measuring the PMT counts
7. Click “disconnect from Minisys” on the “Connection” tab in CONTROL
5
Optimising the Signal-to-Noise
ratio
The sensitivity of the PMT can be adjusted by changing the HV setting of
the PMT. The HV of the PMT is adjusted on the dial located to the right
on the front panel of the Controller (see Figure 5.1). Each PMT has its own
characteristics and Risø provides a “PM-Tube Testsheet” (see Figure 3.8) for
each individual PMT, in which the recommended HV setting for the PMT
is indicated. However, this setting may not be optimal with respect to the
signal-to-noise (S/N) ratio. The following section describes a procedure for
optimising the S/N ratio by adjusting the HV setting. Optimising the S/N
ratio is particularly important when working with weak signals comparable
to the PMT dark count.
In order to optimise the S/N ratio properly the PMT must have been
mounted and connected for at least one week to ensure that is has reached
a stable condition. During the optimisation process we make use of the light
from the blue LEDs. To reduce the amount of light reaching the PMT it is
very important to use the neutral density filter (Schott NG9 - OD 7.5) which
is provided with the reader. If this filter is not in place the PMT may be
damaged.
1. Disconnect the power to the Controller and the Reader.
2. In subdued light remove the three screws on the bottom flange of the
PMT (see Figure 3.6).
3. Replace the existing filter basket with that containing the 5 mm Schott
NG9 neutral density filter (originally delivered mounted in a separate
filter basket). Please ensure that the o-ring between the filter basket
54
Figure 5.1: Picture showing the dial controlling the HV setting of the PMT.
and the OSL stimulation unit is in place before inserting the new basket.
If this o-ring is missing an undesired light leak to the PMT will result.
4. Remount the PMT using the three screws.
5. Reconnect the power to the Controller and the Reader.
6. Place an empty sample carrousel in the reader.
7. Start the CONTROL program and press “Connect to Minisys”
8. Choose the “Services” tab.
9. Adjust the HV setting of the PMT to 700 V (“2.00” on the dial, see
Figure 5.2)1 .
10. On the “Services” page, set the blue stimulation power to 2 % by typing
the command “IR SET 2” and press “Send” (see Figure 5.2).
11. Switch on the blue LEDs by selecting “Blue LEDs”.
12. Press “Start” and write down the “Counts”.
1 The
HV supply ranges between 500 and 1500 V. The dial ranges between “0” and “10”.
An increase of “1” corresponds to an increase in HV of 100 V.
55
Figure 5.2: Use the test program CONTROL to optimise the S/N ratio. Adjust the blue
LED stimulation power to 2% by sending the command “IR SET 2”(purple oval). Change
the “Integration time (s)” in the “Measure PMT Counts” panel from “1” to “10”(red oval)
when measuring the background. Click “Start” in the “Measure PMT Counts” panel (blue
oval). Switch on the blue LEDs by pressing “Blue LEDs” in the vertical panel (green oval).
13. Increase the HV setting by 50 V to 750 V (2.50 on the HV dial) and
write down the “Counts”.
14. Repeat this process each time by increasing the HV by 50 V (increments
of 0.5 on the HV dial) until a HV setting of 1100 V (6.00 on the HV
dial) or until there is a very rapid increase in count rate (e.g. by a factor
of 10 per adjustment).
15. Press “Stop” to stop the “Counts” reading. Switch off the blue LEDs.
16. Plot the readings on a log scale as a function of HV (see Figure 5.3).
56
17. Change the “Integration time (s)” in the “Measure PMT Counts” panel
from “1” to “10”2 (see Figure 5.2). You will now measure the dark count
(N) as a function of HV.
18. Turn the HV back to 700 V (2.00 on the HV dial) and repeat the
measurements in steps of 50 V as before but with the blue LEDs turned
off.
19. Calculate the S/N ratio at each HV setting to determine the optimal
HV setting. The optimal setting is where the S/N ratio is large and
the signal (S) is within the “plateau” region. In the example shown in
5.3, the setting lies between 800 and 900 V.
20. Select the “Connection” tab and disconnect. Close the CONTROL
program.
21. Adjust the HV setting of the PMT to this chosen setting.
You may use the Excel template“PMT-XXXXX.xltx”in the Extra\Instructions
folder on your hard drive or on your installation disc to plot Signal, Background and S/N ratio as shown in Figure 5.3.
2 The
longer this time is selected to be the more accurate the count will be, but the
optimisation process will also take longer.
57
Figure 5.3: The data obtained from the blue LEDs (S) are shown as a function of HV
setting (blue data). Also shown is the PMT dark count (N, red data) as well as the S/N
ratio calculated from S and N. The optimal HV setting for this particular tube is in the
interval 800 to 900 V.
6
Dead time correction
When the PMT detects a photon it gives rise to a current pulse which has a
duration of approximately 20 to 30 ns. In this time interval the PMT is not
able to detect additional photons. As a result of this “dead time” the PMT
counting system becomes significantly non-linear at high count rates. For
an uncorrected system we would not recommend accepting data with count
rates > 5 Mcps. However, it is possible to correct for this dead time loss
by enabling the “Dead time correction” in “System options” in the Sequence
Editor program. This enables the system to be used up to a count rate of
about 40 Mcps.
The actual dead time relevant to a particular system should be measured
using the CONTROL program as described below.
1. Insert the neutral density filter (5 mm Schott NG9-OD 7.5) as a detection filter (see section 4 or 5).
2. Place a sample carrousel in the Reader with an empty disc/cup in
position 1.
3. Open the CONTROL program, connect to Minisys, and press “Start”
in the “Dead time correction” window.
The blue stimulation LEDs are then automatically switched on and the
count rate as a function of LED power is measured. When the power reaches
100 % or the count rate exceeds 15 Mcps the program stops and the dead
time is calculated.
The dead time can be saved and stored, so it can be used automatically
by the Sequence Editor. This is done by pressing “Save to System Setup”
in the bottom right corner of the “Dead time correction” window. The dead
time correction value can also be entered manually in the “Systems Options”
in the Sequence Editor.
59
Figure 6.1: Light detected by the PMT in the dead time correction routine. The power of
the blue LEDs is ramped from 0 to 100 % or until the count rate exceeds 15 Mcps. The
neutral density filter NG9 is used as detection filter.
Figure 6.2: The red curve shows the dead time corrected count rate. The resulting dead
time is given in the bottom right corner.
7
Frequently answered questions
In this section you will find a list of questions that we frequently answer.
7.1
Power requirements
1. Do I need to switch off the power to the reader? It is OK to leave the
equipment ON all the time. Only turn it off if you will not be using it
for a few weeks.
2. What is the power consumption of the reader? The peak power consumption is about 120 W. If power failure is known to occur the use of
a battery driven 500 W UPS (uninterruptible power supply) is recommended, to ensure a reliable supply of power.
7.2
User PC requirements
3. What is the recommended PC configuration? We recommend a Pentium 4 (or better) with Windows XP or Vista installed. The PC must
have a 9-pin RS-232 serial connector to be able to connect to the Controller.
4. Is there a regional setting that I must choose? It is very important that
the user PC is using a “.” (full stop) as decimal separator and not a “,”
(comma). In Windows XP this is setup in the Control Panel/Regional
and Language Options/Regional options. In Vista it is setup in the
Control Panel/Regional and Language Options/Formats. Most continental language options (e.g. German and French) will use the “,” as a
7.3 Laboratory recommendations
61
Figure 7.1: Back of the Controller showing how to disable the LEDs. Every time the blue
filter combination (BG 39/CN 7-59 or BG3) is used the blue LEDs should be disabled to
prevent shining blue light directly onto the photocathode and thereby damaging the PMT.
Also shown is the position where the OSL test cable can be inserted. This is only done
if the user wish to determine if the current through the LEDs (the power output) is as it
was specified by delivery at the time of delivery (see attached specification sheet). This is
normally only done if Risø has advised you to do so.
separator whereas all English language options (and many others) will
use a “.”. If the decimal separator is not a “.” then an error message
will appear (Error 112).
7.3
Laboratory recommendations
5. What is the recommended laboratory lighting? In OSL laboratories it is
recommended to use subdued red/orange light during sample handling.
Standard dark room lights (e.g. those used in photographic laboratories) are preferable (e.g. “Kaiser 4220 spectral 590 darkroom safelight”).
If fluorescent tubes are used in the laboratory or the immediate area
(e.g. corridors) it is strongly recommended that electronic starters are
fitted. Glow switches emit electromagnetic noise that can be picked
up by the PMT preamplifier and thus result in unwanted noise in the
7.4 Changing filters
62
measurements.
The Risø TL/OSL reader is light tight enabling the use of normal white
light during measurement. It is recommended that the light switch for
white light is placed high on the wall to avoid the risk of switching on
white light while samples are being prepared.
6. What is the recommended laboratory climate? The PMT is sensitive
to temperature and humidity. The laboratory temperature should not
exceed 30 ◦ C and the humidity should be below 80%.
7. Is it a good idea to combine the OSL laboratory with the chemistry laboratory? No! In fact air flow between the chemical sample preparation
room and the reader room should be avoided. Over time acid fumes
will damage the electronic components inside the reader.
7.4
Changing filters
8. How do I change filters? : To change filters the PMT must be removed
from the OSL stimulation unit.
• The signal cable (black) must always be connected when connecting or disconnecting the HV cable (yellow), i.e.:
a) Disconnect: HV cable first
b) Reconnect: signal cable first
If in doubt then switch off the power to the entire system
• Make sure the thick o-ring below the filter basket and the thinner
o-ring in the bottom flange of the photomultiplier tube are in place
• No white light when the photomultiplier tube is removed from the
OSL stimulation unit
9. Which stimulation light sources can I use with which filter combination?
ONLY use IR stimulation with the BG 39/CN 7-59 or BG3 (blue) filter
combination. NEVER use blue LEDs since this could severely damage
the photomultiplier tube. You can switch off the blue LEDs with the
switch at the back of the Control Box (see Figure 7.1):
a) Using U-340 filter: IR and blue switch can be on
b) Using blue filter pack: blue switch must be off
7.5 Nitrogen requirements
7.5
63
Nitrogen requirements
10. Why do I need Nitrogen? Pressurized nitrogen is required when samples
are heated above 200 ◦ C and to activate the pneumatically-controlled
beta and alpha irradiators. A high quality pressure regulator must be
provided that can maintain a stable output pressure of 2.5 bar (0.25
MPa). 1/4” NPT threads will fit the nitrogen tube connectors provided
by Risø.
For the control of the irradiator(s) we suggest the use of a separate
compressed air source. This can either be piped compressed air (if
such an installation already exists in your laboratory) or a separate
bottle of nitrogen (or air) equipped with a pressure regulator (output:
2.5 bar). The extra nitrogen bottle is recommended as this is a “clean”
source and is convenient as the nitrogen consumption for the control
of the irradiators is extremely low (a normal 40 l bottle should last for
more than one year).
11. What is the required pressure on the N2 bottle? Gas pressure on the
output dial on the N2 bottle should be below 2.5 bar (0.25 MPa)
12. What is the recommended Nitrogen flow rate? Typical N2 flow rate is
about 1 liter/min. The flow rate is adjusted on the flow meter located
on the reader (to the right). The Nitrogen must be switched on in order
to adjust the flow rate. Only use N2 when you heat above 200 ◦ C.
7.6
Vacuum
13. Is the system vacuum tight? Yes, it is.
14. How do I evacuate the measurement chamber? A vacuum pump must
be connected to the reader (at the back). The vacuum pump must
have a KF NW 25 connection and a maximum power consumption of
500 W (e.g. the Leybold Trivac D8B, 220V, RED. NW25-16KF from
Granzow A/S (www.granzow.dk)). It is also desirable to fit an oil mist
filter to avoid air pollution in the laboratory.
15. When do I need vacuum? If the Risø TL/OSL reader is equipped with
an alpha source the measurement chamber should be evacuated before
alpha irradiation is undertaken. Evacuating the chamber to about 0.1
bar is usually sufficient.
7.7 Operation
7.7
64
Operation
16. How do I open the reader? The reader is opened and closed using
the two buttons located in the left corner on the front panel of the
Controller. Pressing “UP” will make the reader lid open up to the left
(see picture on the title page). Pressing “DOWN” will make the reader
lid close. Do not release the button until the reader lid stops moving.
If the button is released before the lid is fully closed the lid movement
will stop automatically for security reasons.
17. Any advice with respect to placing the discs/cups on the sample carrousel? Please ensure that you place the discs on the DISCS sample
carrousel and the cups on the CUPS sample carrousel. Before placing
the discs/cups wipe the bottoms clean of grains to optimise the thermal
contact between sample and heating element.
18. Any advice with respect to placing the sample carrousel in the reader?
When you insert the sample carrousel in the measurement chamber
(especially in the dark) always rotate it a little afterwards to make sure
that the lift/heater is in its down position before lowering the lid.
19. When I close the lid the is a loud noise from the Controller. Why?
Controllers delivered after 1.1.2015 will have an audible alarm that will
sound, if the heater lift is up when you try to close the lid. This is to
make you aware of the potential risk of damaging the heater element if
the sample carousel is in the reader while closing the lid. To close the
lid when the heater lift is up, remove the sample carousel first. To reset
the heater lift, use the control program or switch off the Controller, and
then on again.
7.8
Maintenance and comments
20. How do I clean the reader? We recommend that you clean the heater
plate every time you change sample carrousels by wiping any grains off
using tissue paper or a soft brush. Once per month we recommend that
a) The position holes (Ø = 1 mm) in the sample carrousel (see Figure
2.6b) are cleaned with a paper clip. If grains accidentally gets
stuck in the position holes the system will be unable to keep track
of the sample position.
7.8 Maintenance and comments
65
b) The space where the lift mechanism is located is cleaned with a
small vacuum cleaner
c) The quartz window (located between the measurement chamber and
the OSL stimulation unit) is cleaned with tissue paper dipped in
alcohol. This interface may become dirty as a direct result of using
silicon oil to mount sample grains onto the sample discs.
d) The outer rim of the bottom of the lid is cleaned using a little alcohol
(Do NOT clean the rubber seal below the lid on the reader body).
e) The sample carrousels are washed with water and soap to prevent
contamination with sample material.
References
Andersen, C. E., Bøtter-Jensen, L., and Murray, A. S. (2003). A mini X − ray
generator as an alternative to a 90 Sr/ 90 Y beta source in luminescence dating. Radiation Measurements, 37:557–561.
Ballarini, M., Wintle, A. G., and Wallinga, J. (2006). Spatial variation of
dose rate from beta sources as measured using single grains. Ancient TL,
24 No.1:1–8.
Bray, H. E., Bailey, R. M., and Stokes, S. (2002). Quantification of crossirradiation and cross-illumination using a Risø TL/OSL DA-15 reader. Radiation Measurements, 35:275–280.
Bøtter-Jensen, L., Andersen, C. E., Duller, G. A. T., and Murray, A. S.
(2003). Developments in radiation, stimulation and observation facilities
in luminescence measurements. Radiation Measurements, 37:535–541.
Bøtter-Jensen, L., Bulur, E., Duller, G. A. T., and Murray, A. S. (2000).
Advances in luminescence instrument systems. Radiation Measurements,
32:523–528.
Bulur, E. (1996). An alternative technique for optically stimulated luminescence (OSL) experiment. Radiation Measurements, 26:701–709.
Hütt, G., Jaek, I., and Tchonka, J. (1988). Optical dating: K − feldspars
optical response stimulation spectra. Quaternary Science Reviews, 7:381–
385.
Huntley, D. J., Godfrey-Smith, D. I., and Haskell, E. H. (1991). Lightinduced emission spectra from some quartz and feldspars. Nuclear Tracks
and Radiation Measurements, 18:127–131.
Markey, B. G., Bøtter-Jensen, L., and Duller, G. A. T. (1997). A new flexible system for measuring thermally and optically stimulated luminescence.
Radiation Measurements, 27:83–89.
REFERENCES
67
McKeever, S. W. S., Markey, B. G., and Akselrod, M. S. (1996). Pulsed
optically stimulated luminescence dosimetry using α−Al2 O3 :C. Radiation
Protection Dosimetry, 65:267–272.
Spooner, N. A. and Allsop, A. (2000). The spatial variation of dose rate
from 90 Sr/ 90 Y beta sources for use in luminescence dating. Radiation
Measurements, 32:49–56.
Thomsen, K. J., Bøtter-Jensen, L., Denby, P. M., and Murray, A. S. (2006).
Luminescence response to irradiation using mini X − ray generators. Nuclear Instruments and Methods in Physics Research Section B, 252:267–
275.