The Measurement
of Radioactivity
R 92
The Measurement of Radioactivity
R92
February 2001
February 2001
SCHOOL SCIENCE SERVICE
CONTENTS
Page
1.
What this guide covers
1
2.
Dataloggers
1
3.
Instruments specifically for radiation measurement
2
3.1
Scalers
2
3.2
Ratemeters
2
3.3
Combined instruments
2
3.4
Other instruments
2
4.
5.
6.
7.
Detectors of ionising radiation
3
4.1.
Spark counter
3
4.2
G-M tube
4
4.3
Solid-state detector
5
Summary of the instruments
6
5.1
Dataloggers
6
5.2
Instruments specifically for radiation measurement
7
Details of the instruments
8
6.1
Important features
8
6.2
Instruments for use with dataloggers
9
6.3
Combined instruments
10
6.4
Scalers
15
6.5
Ratemeters
18
Suppliers’ addresses
21
This guide replaces Scalers and Ratemeters R92 (August 1993)
Strictly confidential – Circulation to
Members and Associates only
© CLEAPSS 2001
School Science Service
Brunel University
Uxbridge UB8 3PH
Tel:
01895 251496
Fax:
01895 814372
E-mail:
science@cleapss.org.uk
Web site: www.cleapss.org.uk
R92
1.
The Measurement of Radioactivity
What this guide covers
In order to cover those parts of the National Curriculum Programmes of Study on radioactivity and ionising radiations, and the extension of this work to Advanced Level in
physics and chemistry, schools need to provide study topics involving the measurement
of levels of ionising radiations. A few schools have sadly chosen to do this only by means
of films or videos but the most popular method uses small, sealed radioactive sources
and suitable detection equipment, which is used for teacher demonstration up to GCSE
and by older students themselves.
In the past, the display part of this detection equipment has usually been a scaler or a
ratemeter (the difference is discussed below). Both functions may be included in a single
instrument which may have other functions as well, eg, acting as a timer or frequency
meter. This guide does not attempt to cover these other functions beyond a mention of
their existence.
However, increasingly schools are finding that there are advantages in recording and
displaying measurements using a datalogger with a suitable probe.
The results can be displayed on a computer screen in a form which is more visible and
comprehensible and which can be used to present data in a variety of formats, eg,
tables, graphs etc..
For schools already possessing a datalogger, the purchase of a suitable probe, usually
a G-M tube with an appropriate power supply, is likely to be less expensive than a
stand-alone instrument.
The recording of ionising radiation by this means provides a good opportunity to
develop pupils’ ICT skills in science as required by the National Curriculum.
All work with radioactive materials is controlled in the UK by legislation and regulations.
Guidance for schools is contained in Notes or Administrative Memoranda1 from the
DfEE, the Welsh Office, the Department of Education for Northern Ireland or the Scottish
Education Department as appropriate. The CLEAPSS guide L93, Managing Ionising Radiations and Radioactive Substances, incorporates this guidance.
The information in this guide has been derived from catalogues and enquiries made to
suppliers. We have not carried out practical tests to evaluate the accuracy of any claims.
2.
Dataloggers
A science department would be ill-advised to buy a datalogger just for measurements of
ionising radiations. Therefore, section 5.1 merely tabulates the dataloggers readily available, which a department is likely to have already purchased for other uses, together with
the probes appropriate for measurements of radioactivity and the means of display.
Section 5.2 gives details of stand-alone instruments.
The CLEAPSS guide to dataloggers is scheduled for revision. Any department seeking
advice should contact the CLEAPSS Helpline; details are inside the front cover.
1
Eg, the current advice for schools in England and Wales is in AM 1/92, The Use of Ionising Radiations in Education
Establishments in England and Wales, although it is made a little out of date by the Ionising Radiation Regulations 1999.
3.
Instruments specifically for radiation measurement
The radiation from low-level radioactive sources cannot be detected by any of the human
senses but, because it produces ions in the matter through which it passes, these ions can
be detected by a variety of methods and hence the presence of the radiation can be
inferred. Dataloggers, scalers or ratemeters all require a detector to be attached to their
inputs, the most common being the G-M tube. For details of how a G-M tube works, see
section 4.2.
3.1
Scalers
A scaler gives a total number of counts of impulses from the probe.
Some scalers still used in schools employ Dekatron tubes which indicate the count digit
from the position of a neon glow as it moves round ten cathodes. More recent devices use
digital displays, sometimes also with automatic timing. However, there is still a place in
education for devices that simply convert each detected event to a click or beep that can
be counted manually during a time determined by a stopwatch. When a sequence of
readings must be taken very rapidly, manual counting is impossible and using a scaler
can be difficult. However, computers are ideally suited to high-speed counting, another
reason why datalogging systems should be considered.
3.2
Ratemeters
The concept of a rate is one that needs frequent use to help students to master it. It is
therefore helpful to count some pulses and divide by the time of that count to obtain an
average rate. While ratemeters are designed to avoid the necessity for the calculation by
giving the reading in counts per second, usually they also have an audible output that
can be used to teach the idea and which is necessary for the lowest rates when the electronics do not work very well.
Most school ratemeters use a capacitor as the essential averaging component and a
different value of capacitance is required for different situations. When the pulse rate is
high, a small value will be effective and will allow the display to follow changes in the
rate quite quickly. When the pulse rate is low, a larger value is required giving a longer
‘time constant’ but the display will not then follow the changes so rapidly. Most instruments select the time constant automatically.
Further discussion of the applications of scalers and ratemeters and the reasons for
preferring one or the other are given in the CLEAPSS Laboratory Handbook, section 12.10.5.
3.3
Combined instruments
Many of the instruments on sale to schools have the functions of both scaler and ratemeter, often with timing and frequency measurement too. These combined instruments
often represent good value in that the extra features are added at minimal cost but with
considerable added complexity of operation and control.
3.4
Other instruments
Some ratemeters are calibrated to give the dose rate in sieverts per hour (Sv h-1) or
millisieverts per hour (mSv h-1). This calibration can hold only for radiation of a particular
2
type since the sensitivity of the detector used varies. Moreover, where such an instrument
is to be used seriously to check dose rates, the calibration needs to be repeated at regular
intervals and at least annually. Such an instrument might be used to explain the principles of dose control but it would be hard to justify the cost of repeated recalibration.
None included in this guide has this feature.
From time-to-time, schools ask whether there is an instrument to measure the activity of a
source or a way of using a school scaler or ratemeter to do it. This is difficult because
there are so many uncertainties, including:
a. the efficiency of the detector itself (the detected fraction of the radiation passing
through the detector);
b. the effect of the geometry of the source-detector combination (the fraction of the
radiation leaving the source material which passes through the detector);
c. the effects of self-absorption within the source (the fraction of the radiation which
leaves the source material).
Therefore, it is impracticable for schools to do more than estimate activities by making
guesses at the above factors. These and the decay of the radioactive material, significant if
it has a half-life of only a few years, may make the estimate differ from the value
engraved on the source.
4.
Detectors of ionising radiation
4.1
Spark counter
gauze
+ve
ions
Several
thousand volts
+-
-ve
wire
The simplest way to illustrate the production of ions by the passage of radiation from a
radioactive source is by means of a spark counter which is a stand-alone instrument
invaluable in teaching. In its basic form, this consists of a wire, in air, close to a wire
gauze and with a high voltage between the two.
The voltage is chosen to be just below that at which the air breaks down to pass a spark
so that, if some air molecules between the wire and the gauze are split into positive and
negative ions, these ions would be attracted in opposite directions, one towards the wire,
the other to the gauze. This constitutes an electric current and, if there are sufficient ion
pairs, it will be visible as a spark.
One alpha (a) particle, passing through the sensitive space, will produce sufficient ion
pairs1 to give a spark but the beta (b) and gamma (g) radiations will not. Alpha radiation
could therefore be measured by manually counting the number of sparks in a chosen
time. This has two problems: first, the device is very inefficient because only those a
1
It is not possible to predict what form these ions will take; an oxygen molecule could be split into a positive oxygen ion and a
negative one by the transfer of one or two electrons. Alternatively, there might be a free electron and a singly-charged oxygen
molecule.
3
particles which pass very close to the wire will be detected. This can be overcome by
using many wires as illustrated by a product formerly made by Philip Harris and
marketed as the ‘Alpha detector’.
+ve
fine wire
close to disc
output
-ve
brass
disc
This magnifies the second problem, that, if the sparks occur too rapidly, they cannot be
counted manually but that problem too is overcome in the Harris device by passing the
current resulting from the sparks through a resistor. When there are no sparks, the
voltage across the resistor is zero; when the current flows, a voltage appears across the
resistor for a short time. These voltage pulses can be passed to a scaler, which can cope
with many more pulses per second than a human counter.
Any school possessing a Harris Alpha Detector of this type could use it as an excellent
introduction to the detection of ionising radiation and the use of a scaler. Unfortunately,
it has not been manufactured for many years so it is not possible to purchase a new one.
A single-wire spark counter, available from Philip Harris, is a highly desirable item of
equipment.
4.2
G-M tube
The Geiger-Müller tube is really a development of the spark counter into a system having
so high a sensitivity that only one ion pair causes an easily-measured current to flow.
There are many variants of the design but that most commonly used in schools is the endwindow type.
The wire of the spark counter has become a needle down the centre of the tube and the
gauze a conducting cylinder around the needle. The thin mica window allows sufficiently
energetic particles to enter, while allowing the monatomic filling gas to be at a pressure of
about one-sixth of an atmosphere. When a potential difference of several hundred volts is
applied to make the needle positive, the radial electric field is strongest at its surface. This
will ionise the atoms of the filling gas in this region. The light, free electrons are rapidly
collected by the anode, leaving the positive ions lumbering across to the cathode.
4
Normally, the voltage is chosen so that the presence of these ions neutralises the electric
field near the needle, reducing it to such a value that little further ionisation occurs.
If an ion pair is produced anywhere in the tube by (for example) a b particle, the free
electron may be accelerated sufficiently to ionise another gas atom but, most likely, it will
be captured by one of the slow-moving positive ions already present. This re-formed
atom will lose energy as ultra-violet radiation (usually) which is sufficiently energetic to
ionise another atom. Since the UV can be emitted in any direction, the ionisation spreads
along the axis of the tube as well as towards the centre. In a very short time, many
electrons and ions are flowing across the tube, giving rise to a sudden increase in the
current flow which can be detected as a voltage pulse by means of an external series
resistor as before.
There are two possible problems with this device. If the applied voltage is too high, the
electrons of the initial ionisation are accelerated from such a distance that they can strike
another gas atom and ionise it before reaching the anode. This causes ‘avalanche breakdown’ (the first problem) and may be interpreted as a very high count rate by an inexperienced user. If this occurs, it can be stopped by switching off the supply and adjusting the
voltage to a lower value before switching on again.
The G-M tube is intended to produce one pulse for each b particle or g photon detected. If
the positive ions have sufficient energy when they eventually reach the cathode, they can
knock electrons out of it and start another pulse. To prevent this false pulsing, tubes
contain a little chlorine or bromine vapour. These diatomic molecules absorb energy from
the positive ions during impacts and dissociate into atoms. The energy is dissipated in
ways which do not produce more ions and the atoms recombine eventually so that a
‘halogen-quenched’ tube continues to work for many years. School G-M tubes are
universally of this type.
If the mica window is sufficiently thin, a particles can enter and will be detected.
g photons will normally pass right through a G-M tube, so that typically only 1% of them
is detected. It is sometimes suggested that this can be improved by passing the g rays
through the side wall of the end-window tube in the hope that they will eject electrons
from the wall into the gas and so be detected more efficiently. However, it is difficult to
demonstrate this effect. Nevertheless, the wall of the G-M tube can be successfully used to
filter out a particles and most b particles, allowing g radiation detection only.
The G-M tube remains the most appropriate detector for b particles since almost every b
particle entering the tube will produce at least one ion pair and be detected.
4.3
Solid-state detector
A solid-state detector (SSD) is just a large-area, semi-conductor diode. The base material
may be any semi-conductor, say silicon, doped with impurity to make it n-type. On this, a
thin layer of p-type silicon is deposited with a metal contact on top of that.
The n-type layer has free electrons and the p-type layer has ‘holes’ (places where electrons could be but are not) which can move like positive charges. These two move across
the boundary between the two layers to ‘neutralise’ each other until a sufficient potential
difference is set up by the movement to prevent further charged objects from passing
across. The layer without free electrons or holes is called the ‘depletion layer’; it can be
made smaller by applying an external voltage and a current then flows through it or it
5
can be made larger by reversing the applied voltage when the current falls to a very small
value. The latter is the arrangement used as an ionising radiation detector.
If an a particle enters the depletion layer, it produces many electron-hole pairs which
then flow to form a current pulse which is amplified and counted. Since a particles have a
very short range in solids, the depletion layer must be very close to the top surface so the
p-type layer and the contact layer must be very thin.
The device can also detect b and g radiation but here the depletion layer must be thick to
increase the chances of interaction before the radiation passes straight through. This is
achieved by increasing the reverse voltage from two or three volts up to nine or ten volts.
The solid-state detector is also sensitive to UV and must be suitably screened; pulses from
it require amplification before being fed to many scalers and ratemeters. These disadvantages have resulted in it seldom being used in schools and it does not appear in current
catalogues.
5.
Summary of the instruments
5.1
Dataloggers
Name of
datalogger
Easysense
LogIT
SensorMeter
Pasco Science
Workshop
Supplier(s)
Data Harvest Group
Griffin & George
Commotion
Philip Harris
Instruments Direct
Interface
Several available, all
able to take the
probe
Datameter, LIVE,
LogIT SL
DL+, CL200 etc
500 Interface
750 Interface
Radioactivity
probe
Geiger-Müller
Cat no 3265
Radioactivity probe
Griffin Cat no:
CRD-130-690N
Radioactive
Count Rate
SensorMeter1
A00681
Nuclear Sensor
SE-7997
Commotion
Cat no: 12224
Price of
probe
£210 (estimated
price – not available
until early 2001)
£198 from both
suppliers
Beta Gamma Nuclear
Sensor SN-7928
G-M Tube/Power Supply
SN-7927
£173 + System
SM Geiger Probe:
A00693: £156 or
G-M Tube
Adaptor A00709:
£472
SE-7997 £391
SN-7928 £197
SN-7927 £327
1
Can be used as a stand-alone instrument; see page 9.
2
Permits a standard G-M tube/holder combination to be connected to the SensorMeter.
6
5.2
Instruments specifically for radiation measurements
The instruments described in this section are difficult to classify since they often have
unique combinations of features. They are listed in each group with the most expensive
first. Table 12.7 in the Handbook shows that most investigations can be done with either a
scaler or a ratemeter and, in many cases, schools will choose one of each. Where funds
will not allow this, the Handbook table will guide the choice.
Stand-alone instruments for use with dataloggers
Harris Count rate
SensorMeter
Several instruments are provided with outputs for datalogging (see section 5.1).
However, the Harris SensorMeter is a datalogging sensor with audio-output and a
meter for instant display which makes a flexible and economical device.
Combined instruments
Pasco
Radiation Counter
Choice of functions including counts for a preset time, time for preset counts and
a wide range of count rates.
Harris (Unilab)
Digital Scaler-Timer
A very sophisticated instrument allowing a display of pulses counted, the count
rate, time intervals and frequency.
Harris S-Range
Digicounter
A very accurate timer, counter and frequency meter but without the direct display
of count rate.
Teltron
Scaling Ratemeter
This instrument is intended to connect easily to dataloggers.
Griffin Timer, Scaler and An easy-to-set instrument which counts pulses, measures time, frequency and
Frequency meter
count rate; fewer options on timing control.
Scalers
Harris
S-Range Scaler-timer
This unit has the essential counting and timing features without the extra
accuracy and facilities of the Harris S-Range Digicounter (see above).
Harris (Unilab)
Geigerteller
A robust, portable unit, suitable for environmental surveys where count rates are
low. It provides a large pulse for feeding to dataloggers, computers etc.
Harris (Unilab)
Modular Counter
Since the timing modules have been discontinued, this system has been reduced
to its basic counting function but, with six digits displayed, it represents good
value for a simple system.
Ratemeters
Pasco
Ratemeter
Portable, with a built-in analogue display; many ranges.
Teltron
Ratemeter
A sensor module suitable for computer use with a choice of plug-in displays,
showing either digits or bargraphs.
Griffin Ratemeter
Model 45
Another ratemeter giving a choice of display since any 2 V voltmeter can be used.
7
6.
Details of the instruments
6.1
Important features
The terms used in the sections below are explained in this section.
Form
A description of the instrument to indicate whether or not additional items are
required to make a useful measuring system.
Information display
Each event may be indicated audibly and the current count or count rate may be
shown on a digital readout or analogue (pointer) meter which may be integral or
separate.
Output sockets
Many systems with integral displays (as well as those without them) have output
sockets for additional meters, projection systems, computers, etc. There are
sometimes power outputs for accessories.
Maximum count rate
(scalers)
Few detectors can cope with count rates above 10 000 cps but the electronics
can usually work much faster.
Register capacity and
control (scalers)
The register, which holds the total number of counts, may be bigger than the
display. Counting may be automatic (for a preset time) or stopped and started
manually.
Ranges
Where a scaler has a display smaller than the register, the range may be
switched to display the part of most interest. On a ratemeter, range selection is
often essential to obtain a sensible reading.
Timer facilities
(combined instruments)
Features of these instruments for timing in dynamics etc are listed.
Timer control (combined Where timing is offered, it may be stopped and started by switches, or pulses
instruments)
when it is called ‘triggered’. The signals may come from light gates or mechanical
contacts.
Resetting (scalers)
Different instruments use different methods to allow personal preference.
Input sockets
The PET 100 series screw-type coaxial socket is traditional in education for
Geiger-Müller tubes. However, it has become so expensive that many manufacturers are changing to BNC connectors. Solid-state detectors, where available,
are often fitted with miniature BNC connectors and adaptor leads are often
needed to connect them up.
G-M tube power and its
control and monitoring
Where the Geiger-Müller tube to be used is always the same type, a fixed or
internally-preset supply is adequate unless the characteristic of the tube is to be
investigated. In this case, an external control and some means of monitoring the
voltage is required.
Input power source
Different instruments use the mains, a mains adaptor or a battery. Where an
adaptor is listed, it is usually only suitable for that manufacturer’s products.
Storage details
These are not likely to be a problem.
Detectors and other
accessories
Most instruments are sold without detectors and suitable ones are listed.
Price
The quoted price does not include a detector (unless integral) nor accessories
unless they are essential to the operation of the device.
All quoted prices are catalogue or list prices at the date of preparation. They can
be used as a guide to relative costs but users must check the current price, add
delivery charges where applicable and subtract any discounts available before
arriving at the price to be paid.
8
6.2
Instruments for use with dataloggers
Model
Count Rate
SensorMeter
Supplier
Philip Harris
Catalogue No
A00681
Form
Single unit, meter and sensor with separate special G-M probe
Information display
Liquid crystal display with 3.5 digits and analogue bar, audible click
Output sockets
5-pin DIN for DL+ or CL200
Ranges
0 to 50, 0 to 250 & 0 to 1000 cps
Time constants
3.3 s or 0.33 s switchable
Input sockets
BNC for G-M probe, miniature stereo jack for power
G-M tube power
Set for special probe
control and monitoring
Input power source
None, internally regulated
9 V MN1604 Manganese Alkaline battery, life 40 hours constant use
(or SensorMeter power adaptor)
Storage details
Dimensions
150 x 90 x 60 mm
Handle and Cable stowage
None
Detectors and other
accessories
G-M tube
A00693 Special System SM Geiger Probe for a b g detection:
G-M tube adaptor
A00709 Enables a standard G-M tube/holder combination to be
connected to the SensorMeter:
Others
–
Price
Count rate SensorMeter A00681; £178.20 excluding probe
G-M tube A00693; £160.70
G-M tube adaptor A00709; £48.40
9
6.3
Combined instruments
Model
Radiation Counter
Supplier
Instruments Direct
(Pasco)
Catalogue No
SN-7962A (IBM)
SN-7959
(Macintosh)
Form
Single unit with separate detectors
Information display
Six-digit light-emitting diode display with piezo alerter alarm
Output sockets
DB-9 male connector for RS-232 serial cable
Maximum count rate or frequency
1 Mcps
Register capacity and control
999 999 (manual control)
Ranges
Various counts min-1 and counts sec-1
Timer and counting facilities
Count for preset time, count for preset count
control
Knob and push buttons
Resetting
Single push button
Input sockets
BNC for G-M tube
G-M tube power
Variable in 25 V increments 0 to 1200 V
control and monitoring
Input power source
Push buttons and display
7.5 V dc
Storage details
Dimensions
310 x 210 x 120 mm
Handle and Cable stowage
–
Detectors and other
accessories
G-M tube holder and G-M tube
Student G-M Probe with sample holder, SN-8109A
Others
AC line/charger (included in price) or 4 C Nicad cells
Serial cable SN-7956
Price
Radiation Counter SN-7959/SN-7962A; £691.00
G-M probe and holder SN-8109A; £222.00
Serial cable SN-7956: £17.00
10
6.3
Combined instruments
Model
Digital Scaler-Timer
Supplier
Philip Harris (Unilab)
Catalogue No
C55932
Form
Single unit with separate detectors
Information display
Four-digit liquid crystal display, with switched speaker
Output sockets
Pulses at 4 mm pair, socket for projection readout, 12 V for lamps
Maximum count rate or frequency
1 Mcps (also measures frequency: 10 to 1 MHz)
Register capacity and control
9 999 999 (manual control)
Ranges
Normal, x 1 000
Timer facilities
99.99 ms to 9 999 s full scale
timer control
Switch selected: push buttons, light gates, etc
Resetting
Single push button
Input sockets
PET 100 for G-M tube, standard coax for SSD
G-M tube power
Variable 300 to 500 V
control and monitoring
Input power source
Pointer knob with scale on the case
240 V mains via detachable lead
Storage details
Dimensions
347 x 170 x 175 mm
Mass
3.3 kg
Handle and Cable stowage
Integral with cleats on the back
Detectors and other
accessories
G-M tube holder
A49736 (or use the Unilab equivalent C50995)
G-M tube
ZP1481, Catalogue number A49724:
Solid-state detector
No longer in catalogue
Others
Light gates, microphone
Price
Digital Scaler-Timer C55932; £522.21
G-M tube holder A49736; £96.90 (C50995: £54.69)
G-M tube A49724; £135.51
11
6.3
Combined instruments
Model
S-Range Digicounter
Supplier
Philip Harris
Catalogue No
A87189
Form
Single unit with separate detectors and optional external speaker
Information display
Six-digit, light-emitting diode display (automatic decimal point)
Output sockets
Pairs of 4 mm sockets for loudspeaker and power at 2 V and 6 V for
light gates
Maximum count rate or frequency
Detector limited but at least 3 MHz on frequency
Register capacity and control
999 999 manual or automatic timing
Ranges
999 999 counts
Timer facilities
99.9999 ms, 999.999 ms, 9999.99 ms, 999.99 s, 99999.9 s ±
0.005% ± 1 count, period for low frequency
timer control
Manual, light gate, switch and triggered
Resetting
Single push button
Input sockets
PET 100 series coax for G-M tube, miniature BNC for SSD
G-M tube power
Variable, 300 to 500 V
control and monitoring
Input power source
Pointer knob with scale on case
240 V mains via detachable lead
Storage details
Dimensions
380 x 165 x 140 mm
Handle and Cable stowage
Integral with cleats on the back
Detectors and other
accessories
G-M tube holder
A49736 (or use the Unilab equivalent C50995)
G-M tube
ZP1481, Catalogue number A49724
Solid-state detector
No longer in catalogue
Others
Light gate A41920 (2 V power from timer)
Price
S-Range Digicounter A87189; £455.26
G-M tube holder A49736; £96.90 (C50995; £54.69)
G-M tube A49724; £131.51
Light gate A41920; £54.37
12
6.3
Combined instruments
Model
Scaling Ratemeter
Supplier
Teltron
Catalogue No
TEL2806
Form
Modular design with choice of display and separate G-M tube
Information display
Controlled speaker. Extras: either four channel 31/2 digit meter with
alarm limits (Alarmed meter TEL2021) or a unit showing a dual
bargraph (Peak display meter TEL2022)
Output sockets
4 mm sockets: count or rate, at 0 to 200 mV and 0 to 1 V
Maximum count rate or frequency
20 000 cps
Register capacity and control
Not stated (automatic timing)
Ranges
20 000, 2 000 cps, Counts in 3, 15, 30 or 60 s
Timer facilities
None
timer control
Resetting
Automatic after 10 s delay
Input sockets
BNC with EHT for G-M tube, miniature jack for input to µA
measurement
G-M tube power
Variable, 250 to 500 V
control and monitoring
Input power source
Miniature preset monitored via channel 3 on meter
Mains via adaptor or battery kit via 6-pin latched connector
Storage details
Dimensions
170 x 105 x 45 mm plus additional height for display
Handle and Cable stowage
None
Detectors and other
accessories
G-M tube holder
Holder and clip, TEL2547
G-M tube
LND712, Catalogue number TEL2546
Others
Alarmed meter TEL2021, Peak display meter TEL2022,
Powerplug TEL2016, Battery kit TEL2018
Price
Ratemeter TEL2806; £194.95 plus either of the items in (i) below::
(i) Alarmed meter TEL2021; £131.00 or Peak display meter
TEL2022; £92.60, plus either of the items in (ii) below:
(ii) Powerplug TEL2016; £29.50 or Battery kit TEL2018; £23.90
G-M Holder and clip TEL2547 + G-M tube TEL2546; £93.10
13
6.3
Combined instruments
Model
Timer, Scaler and
Frequency Meter
Supplier
Griffin & George
Catalogue No
XKS-351-010W
Form
Single unit with separate detectors
Information display
Four 7-segment light-emitting diodes, loud speaker with rate setting
Output sockets
4 mm sockets
Maximum count rate or frequency
999 900 cps or 999.9 kHz ± 0.1%
Register capacity and control
9999 (manual control)
Ranges
0 to 9 999, 10 to 99 99 and 100 to 999 9 automatically selected
Timer facilities
0 to 9.999 s, 0 to 99.99 s, 0 to 999.9 s
timer control
Start/stop on 1 input or 2 inputs, time between pulses
Resetting
Biased switch gives reset, run, hold
Input sockets
PET 100 series coax for G-M tube, min BNC for Solid-state detector
G-M tube power
Variable, 300 to 500 V
control and monitoring
Input power source
External knob with pointer and scale on case
240 V mains via detachable cable
Storage details
Dimensions
225 x 220 x 110 mm
Handle and Cable stowage
Detachable cable
Detectors and other
accessories
G-M tube holder & lead
XKS-510-O
G-M tube
ZP1481, Catalogue number XKS-800-030R
Solid-state detector
Not in Griffin Catalogue
Others
Photo timing gate XBG-441-N
Price
Timer, Scaler and Frequency Meter XKS-351-010W; £253.00
G-M tube holder & lead XKS-510-O; £152.00
G-M tube XKS-800-030R; £126.00
Photo timing gate XBG-441-N; £40.30
14
6.4
Scalers
Model
Supplier
Philip Harris
Catalogue No
A81334
Form
Single unit with separate detectors and optional external speaker
Information display
Six-digit, light-emitting diode display (leading zeros blanked)
Output sockets
Pairs of 4 mm sockets for speaker and power at 2 V and 6 V for
light gates
Maximum count rate or frequency
Unspecified
Register capacity and control
999 999 (manual control)
Ranges
999 999 counts
Timer facilities
0 to 999.999 s ± 0.5% max
timer control
Manual, light gate, switch and triggered
Resetting
Single push button
Input sockets
PET 100 series coax for G-M tube, miniature BNC for SSD
G-M tube power
Variable, 300 to 500 V
control and monitoring
Input power source
Pointer knob with scale on case
240 V mains via detachable lead
Storage details
Dimensions
380 x 165 x 140 mm
Handle and Cable stowage
Integral with cleats on back
Detectors and other
accessories
(or use the Unilab equivalent C50995)
G-M tube holder
A49736 (or use the Unilab equivalent C50995)
G-M tube
ZP1481, Catalogue number A49724
Solid-state detector
No longer in catalogue
Others
Light gate A41920 (2 V power from timer)
Price
S-Range Scaler-Timer A81334; £323.42
G-M tube holder A49736; £96.90 (C50995: £54.69)
G-M tube A49724; £135.51
Light gate A41920; £54.37
15
6.4
Scalers
Model
Geigerteller
Supplier
Philip Harris (Unilab)
Catalogue No
C51008
Form
Self-contained; no readout or meter fitted
Information display
Controlled audio signal via loudspeaker or earpiece
Output sockets
4 mm pulse (9 V) to scaler, sub-miniature jack to earpiece
Maximum count rate or frequency
Limited by user unless scaler connected
Register capacity and control
None
Ranges
One
Timer facilities
None
timer control
Resetting
Not required
Input sockets
Not required - G-M tube built in
G-M tube power
Pre-set for the internal tube
control and monitoring
Input power source
None
9 V battery PP3 or 6F22 (Current drain < 5 mA)
Storage details
Dimensions
170 x 95 x 75 mm
Mass
0.55 kg
Handle and Cable stowage
None. Not needed
Detectors and other
accessories
G-M tube holder
–
G-M tube
–
Price
£273.98
16
6.4
Scalers
Model
Modular Counter unit
and accessories
Supplier
Philip Harris (Unilab)
Catalogue No
C55531 & C55529
Form
Separate modules: G-M Tube EHT unit and Counter unit
Information display
Six-digit liquid crystal display on Counter Module, switched speaker
on EHT module
Output sockets
Pulse output at 4 mm socket from EHT Module
Maximum count rate or frequency
Limited by G-M tube (1 MHz on frequency)
Register capacity and control
999 999 (manual control)
Ranges
One
Timer facilities
None
timer control
Resetting
Single push button
Input sockets
PET 100 for G-M tube
G-M tube power
Fixed internally at 420 V
control and monitoring
Input power source
None
6 to 12 V dc, PP3 (6F22) battery recommended (external)
Storage details
Dimensions
Each module: 90 x 90 x 35 mm
Handle and Cable stowage
–
Detectors and other
accessories
G-M tube holder
C50995
G-M tube
ZP1481, Catalogue number A49724
Price
G-M Tube EHT unit C55531; £78.37, plus
Counter unit C55529; £81.92
G-M tube holder C50995; £54.69
G-M tube A49724; £135.51
17
6.5
Ratemeters
Model
Ratemeter
Supplier
Instruments Direct
(Pasco)
Catalogue No
SN-7955A
Form
Single unit with separate detectors
Information display
Analogue, pointer meter, large scale
Output socket
DB-9 male connector for RS-232 to take a serial cable for
connection to IBM-compatible computer
Ranges
600, 1.5k, 6k, 15k, 60k, 150k counts min-1, 10, 25, 100, 250, 1k, 2.5k
counts sec-1
Time constants
–
Input sockets
BNC for G-M tube
G-M tube power
0 to 1200 V
control and monitoring
Input power source
Continuously variable by 10-turn potentiometer
7.5 V dc at 500 mA
Storage details
Dimensions
310 x 210 x 120 mm
Handle and Cable stowage
Metal handle on one side
Detectors and other
accessories
G-M tube holder and G-M tube
Student G-M Probe with sample holder SN-8109A
Others
AC line/charger (included in price) or 4 C Nicad cells
Serial cable SN-7956
Price
Ratemeter SN-7955A; £498.00
G-M tube holder and G-M tube SN-8109A; £222.00
Serial cable SN-7956; £17.00
18
6.5
Ratemeters
Model
Ratemeter
Supplier
Teltron
Catalogue No
TEL2807
Form
Modular design with choice of display, and separate G-M tube
Information display
Controlled speaker. Extras: either four channel 31/2 digit meter with
alarm limits (Alarmed meter TEL2021) or a unit showing a dual
bargraph (Peak display meter TEL2022)
Output sockets
4 mm sockets for count rate, 0 to 200 mV or 0 to 1 V
Ranges
20 000, 2 000 cps
Time constants
1 s at 2 000 cps and 0.75 s at 20 000
Input sockets
BNC with EHT for G-M tube, sub-miniature jack for input to µA
measurement
G-M tube power
Variable, 250 to 500 V
control and monitoring
Input power source
Miniature knob monitored via 4 mm sockets to display meter or as 0
to 1 V output (channel 3)
Mains via adaptor or battery kit via 6-pin latched connector
Storage details
Dimensions
170 x 105 x 45 mm plus additional height for display
Mass
300 g
Handle and Cable stowage
None
Accessories
G-M tube holder
Holder and clip, TEL2547
G-M tube
LND712, Catalogue number TEL2546
Others
Alarmed meter TEL2021, Peak display meter TEL2022,
Powerplug TEL2016, Battery kit TEL2018
Price
Ratemeter TEL2807; £140.00 plus either of the items in (i) below::
(i) Alarmed meter TEL2021; £131.00 or Peak display meter
TEL2022; £92.60, plus either of the items in (ii) below:
(ii) Powerplug TEL2016; £29.50 or Battery kit TEL2018; £23.90
G-M Holder and clip TEL2547 + G-M tube TEL2546; £93.10
19
6.5
Ratemeters
Model
Ratemeter, model 45
Supplier
Griffin & George
Catalogue No
XKS-703-Q
Form
Single unit requiring G-M tube and separate high impedance
voltmeter
Information display
Speaker and analogue or digital meter as chosen
Output sockets
One pair of 4 mm sockets, red & black, for 2 V voltmeter
Ranges
0 to 1999 cps
Time constants
Not controllable, no information given
Input sockets
G-M tube socket
G-M tube power
Variable, 300 to 500 V
control and monitoring
Input power source
External knob with pointer and scale on case
Mains, detachable lead
Storage details
Dimensions
150 x 100 x 60 mm + G-M tube + meter
Mass
644 g
Handle and Cable stowage
None
Case
ABS plastic
Detectors and other
accessories
G-M tube holder
Built in
G-M tube
ZP1481, Catalogue number XKS-800-030R
Solid-state detector
Not suitable
Others
2 V voltmeter, digital or high impedance analogue
Price
Ratemeter, model 45 XKS-703-Q; £120 plus
G-M tube XKS-800-030R; £126
2 V digital voltmeter EHB-250-010-010M; £39.95
20
7.
Suppliers’ addresses
Commotion
Unit 11, Tannery Road
Tonbridge TN9 1RF
Tel:
01732 773399
Fax:
01732 773390
E-mail:
Tim@commotiongroup.co.uk
Web site: Data Harvest Group Ltd
Woburn Lodge
Unit 1, Eden Court
Leighton Buzzard LU7 8FY
Tel:
01525 373666
Fax:
01525 851638
E-mail:
sales@data-harvest.co.uk
Web site: www.data-harvest.co.uk
Griffin & George
Bishop Meadow Road
Loughborough LE11 0RG
Tel:
01509 233344
Fax:
01509 231893
E-mail:
griffin@fisher.co.uk
Web site: www.griffinandgeorge.co.uk
Philip Harris Education
Novara House, Excelsior Road
Ashby Park
Ashby de la Zouch LE65 1NG
Tel:
0870 6000 193
Fax:
0803 7310 003
E-mail:
sales@philipharris.co.uk
Web site: www.philipharris.co.uk/education
Instruments Direct (for Pasco)
Unit 14, Worton Court
Worton Road
Isleworth TW7 6ER
Tel:
020 8560 5678
Fax:
020 8232 8669
E-mail:
sales@InstrumentsDirect.co.uk
Web site: www.InstrumentsDirect.co.uk
Teltron Ltd
Unit 14, 98 Victoria Road
London NW10 6NB
Tel:
020 8453 1224
Fax:
020 8963 0310
E-mail:
Web site: 21