International Atomic Energy Agency
ASSESSMENT OF OCCUPATIONAL
EXPOSURE DUE TO EXTERNAL
RADIATION SOURCES AND INTAKES
OF RADIONUCLIDES
Personal Dosimeters
Personal Dosimeters - Unit objectives
The objective of this unit is to provide an overview of
personal dosimeters used for occupational radiation
protection. It is intended to provide a review of the
radiation detection mechanisms that are employed,
methods for readout, advantages and limitations of
dosimetry systems, and the radiation types for which
these systems are appropriate. It also provides a
comparison of traditional passive systems and newer
electronic dosimeters.
At the completion of this unit, the student will be able
to understand how dosimetry systems function, and
make informed judgements on dosimetry system
selection.
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Personal Dosimeters - Module outline


Introduction
Passive, integrating dosimeters
 Photon Dosimetry






Photographic Film
Thermoluminescence
Photoluminescence
Optically Stimulated Luminescence
Beta and Low Energy Photon Dosimetry
Neutron Dosimetry




Nuclear Track Emulsions
Solid State Nuclear Track Detectors
TLD Albedo
Bubble Detectors
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Personal Dosimeters - Module outline

Electronic Dosimeters

Introduction

Pocket Dosimeters


Charged fiber (electroscope) pocket
dosimeters

Ion chambers
Commercial Electronic Dosimeters

Geiger Mueller

Silicon Diode

Direct Ion Storage
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Introduction
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A basic objective of personal dosimetry

Provide a reliable measurement of the operational
quantities,



independent of type, energy and direction of
incidence of the radiation, and
with a prescribed overall accuracy.
No dosimetry system can meet these requirements
without additional information from workplace
monitoring and information about the type of work
involved.
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Workplace characteristics dictate
dosimetry needs

Different dosimeters may be required for low
energy x-rays and gamma fields.

Different dosimeter types may be needed for
photons and neutrons.

Complication exists at nuclear power stations,
high energy accelerators, fuel reprocessing
plants, etc., where there is a mixed radiation
hazard.

Beta dosimetry is difficult, particularly in mixed
fields.
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Exposure geometry is also important

Workers at different glove boxes (+, +n) are
dealing with sources for exploration or radiography
will primarily have A-P exposure.

Workers at X-ray diagnostic machines are in a
scattered, low photon energy, mostly isotropic
radiation field.

Operators of radiation sources may be exposed
largely from the back: P-A exposure.

Places where collimated beams are in operation can
be characterized by a rotational geometry.
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Personal dosimeters can be considered to fall
into five classes.

Photon dosimeters only for Hp(10).

Beta-photon dosimeters giving information on
Hp(0.07) and Hp(10).

Discriminating photon dosimeters that, in addition
to Hp(10), provide some indication of radiation type
and effective energy, and detection of high energy
electrons.

Extremity dosimeters for beta-photon radiation
only giving information on Hp(0.07), and

Neutron dosimeters giving information on Hp(10).
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Passive, Integrating Dosimeters
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Detection mechanisms for personal dosimeters
Passive, integrating dosimeters

Photographic film

Thermoluminescence

Photoluminescence

Optically stimulated luminescence

Solid state nuclear track detection
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A wide range of passive dosimeter designs has
been developed
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Photographic Film Dosimetry
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Photographic film

Film emulsion is made of AgBr crystals
suspended in a gelatinous medium.

A thin emulsion layer is coated on a plastic base.

Ionizing radiation interacts with emulsion grains to
produce a latent image.

In development, silver ions in the latent image
produce permanent blackening.

Blackening is measured with a densitometer.
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Photographic film

Degree of blackening is a function of film type,
developing process, temperature, and radiation
type and energy.

Film has been used to determine personnel
exposure to photons, betas and thermal neutrons.

For personnel monitoring, films are commonly
placed inside suitable holders, or "film badges”.

Compensation for energy dependence of the film
dosimeter is achieved either by the use of one or
more filters having different atomic numbers.
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Illustration of exposed film showing filter
density pattern
A
B
Film
Package
C
D
E
C
B
A
D
E
O
A - Plastic filter
B to E - Metallic filters
O - Open window
Film dosimeter with film packet and filters.
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Photographic film

One filter is adequate for photons > 0.1 MeV.

Multiple filters (e.g. Cu, plastic and open window)
are used for lower energy photons.

Blackening produced by gamma rays from neutron
capture in a cadmium filter is often used to detect
thermal neutrons.

Type and dose of incident radiation can be
estimated from the ratio of responses behind
different filters.
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Film density patterns following exposure to
radiation fields of different qualities
FOG
*
FILM INVERTED
50 kV X-rays
0.25 mGy
100 kV X-rays
0.25 mGy
75 kV X-rays
1.50 mGy
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Film has a strong photon energy dependence
1.5
Relative sensitivity
Normal - 0°
1.0
35°
80°
0.5
45°
Kodak RM
0.71 mm Sn
+ 0.31 mm Pb
0
10
20
50
100
200
500
1000
2000
Photon energy - keV
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Photographic film

Optical density does not vary linearly with dose.

At higher doses, a reversal of optical density solarization - takes place.
Dose

Linear combination of the responses behind
suitable filters can be used to determine the dose.
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Typical photographic film calibration curve
6
Net optical density
5
4
0.6 Sv/s
11. Sv/s
0.3 mSv/s
3
2
0.013 Sv/s
1
0
10-1
1
10
102
103
104
105
106
Hp(10) - mSv
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Films with different sensitivities extend the
measurable dose range of the film badge
7
6
Net density
5
4
A
3
B
2
1
0
0.1
1
10
102
103
104
Hp(10) - mSv
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Photographic film

New calibrations are necessary for each new film
batch, or the developing process changes.

Operational films are often calibrated by using
identical standard films irradiated to known doses
and processing them simultaneously with the
operational dosimeters.

Perform calibrations at doses that cover the full
range for which the dosimeter is used.

Film badges are used for issue periods up to one
month.
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For longer periods, fading is a problem
1.0
30% relative humidity
Relative optical density
0.8
0.6
60%
0.4
Kodak RM
80%
0.2
0
0
2
4
6
8
10
Storage time - weeks
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Photographic film

Film can be used in discriminating dosimeters to
give qualitative information in addition to dose.

Film dosimetry can be economical depending upon
the degree of automation adopted.

Film disadvantages include fading and energy
dependence, requiring a complex and expensive
holder.

Film dosimeters can be designed for HP(10) and
HP(0.07), and beta radiation with (Emax) > 0.5 MeV.
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Commercial film supply information
Dosimetry suppliers
ICN Dosimetry Service
http://www.dosimetry.com/dx/external/default.html
Radiation Detection Company
http://www.radetco.com/film.htm
Landauer, Inc
http://www.landauerinc.com/products.htm
General product source listing
Double Film Badge
Wrist Film Badge
Health Physics Society Buyer’s Guide
http://hps.org/aboutthesociety/affiliates/services.html
Exposed Film
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Thermoluminescence
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Thermoluminescent dosimeters - TLD

The thermoluminescence mechanism is complex,
and each TL phosphor is unique.

After exposure the latent measure of the absorbed
dose is the number of electrons which remain
trapped in the various trapping levels.

TLD readout consists of heating, light detection
and data recording.
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Thermoluminescent dosimeters - TLD
TLD heating can be done in a number of ways

Electrical heating with a hot finger

Hot nitrogen gas

Radio frequency heating

Infrared light
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Thermoluminescent dosimeters - TLD

Luminescent brightness vs. temperature at a
constant heating rate is called the "glow curve”.

A photomultiplier or other light-sensitive device
measures the TL glow emission during readout.

Entire glow curve or the peak brightness is
recorded.

Area under the curve or glow peak brightness is
used as a measure of dose.
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Illustration of TLD readout
High
voltage
supply
D.C.
amplifier
PM
tube
Recorder
Suitable filter
Phosphor material
Heater power
supply
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Modeling the TL effect
TLD
Gamma rays,
X-rays, etc.
The number of
photons emitted is
proportional to the
energy of the ionizing
radiation
Heat
PMT
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Simplified thermoluminescent process
Electron
Conduction band
Thermal
release
E
T
L
Ionization
T
T
L
L
Light
Hole
Valence band
a) Irradiation
b) Storage
c) Heating
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Time-temperature profile (TTP)
Anneal temp.
Temperature °C
Max. temp.
Max. temp.
ramp rate
Preheat
temp.
Ambient
Preheat Acquisition
Anneal
Ambient
Time
Time-temperature profile and glow curve for LiF:Mg,Ti freshly exposed to 1 Gy
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Relative thermoluminscent intensity
Sample glow curves
100
80
CaSO4
CaF2
LiF
60
40
20
0
0
100
200
300
400
Temperature - Degrees C
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Glow curves for various TL phosphors
LiF:Mg,Ti
195 °C
Lithium fluoride
CaF2:Mn
260 °C
Calcium fluoride manganese
LiF:Mg,Cu,P
220 °C
Lithium fluoride
Al2O3:C
185 °C
Aluminum oxide
CaF2:Dy
180 °C
Calcium fluoride dysprosium
CaSO4:Dy
220 °C
Calcium sulfate dysprosium
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TLD is attractive for radiation protection
dosimetry

Some TL materials are nearly tissue-equivalent.

TL offers high sensitivity, accuracy, low detection
limit and linearity over a wide dose range.

Many TL materials are commercially available as
small solid detectors adaptable for automatic
processing.

Particularly suited to beta skin and extremity
dosimetry.
International Atomic Energy Agency
General characteristics of commercially
available TLDs
TLD type
LiF:Ti,Mg
LiF:Na,Mg
LiF:Mg,Cu,P
Li2B4O7:Mn
Li2B4O7:Cu
MgB4O7:Dy
BeO
CaSO4:Dy
CaSO4:Tm
CaF2:Mn
CaF2 (natural)
CaF2:Dy
Al2O3
Effective
atomic
number
Zeff
8.3
8.3
8.3
7.3
7.3
8.4
7.1
14.5
14.5
16.3
16.3
16.3
10.2
Main peak
(°C)
200
200
210
220
205
190
190
220
220
260
260
215
360
Emission
maximum
(nm)
400
400
400
605
368
490
200-400
480-570
452
500
380
480-570
699
Relative
sensitivity
1
1
25
0.20
2
10
0.20
30
30
5
23
15
4
Fading
(at 25 °C)
5%/year
5%/year
5%/year
4%/month
10%/2 months
4%/month
8%/2 months
1%/2 months
1-2%/2 months
16%/2 weeks
very slight
8%/ months
5%/2 weeks
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Calculated relative response
Photon energy dependence of various TLDs
101
1
10-1
101
102
103
104
Photon energy - keV
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Thermoluminescent fading

Unintentional release of trapped electrons before
readout is called fading.

Fading may be due to thermally or optically
stimulated release of the electrons.
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Fading of various phosphors
110
LiF
CaF2:Dy
90
CaSO4:Dy
Relative dosimeter reading - %
110
90
70
50
25 °C, 97% RH
25 °C, 50% RH
20
50 °C, 31% RH
100
40
60
CaSO4:Dy
LiF
80
60
50
50 °C
40
0
60
60
CaSO4:Dy
LiF
40
0
40
20
80
20
20
0
100
20
0
Li2B4O7:Mn
60
CaF2:Dy
Li2B4O7:Mn
40
CaF2:Dy CaSO4:Dy
70
Li2B4O7:Mn
0
LiF
CaF2:Dy
Li2B4O7:Mn
0
20
40
60
Storage time - days
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TL signal ratios under different filters
Theoretical chip ratios
10.
PTFE/Sn(0.33 mm)
PTE/Cu
Ratio
5.
PTFE/Sn(1.3 mm)
PTFE/Sn(0.635 mm)
2.
1.
0.5
10
100
1000
Photon energy - keV
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X-ray and  response of a 4-element dosimeter
using LiF
3.5
Relative response
3.0
Deep dose photon energy response
2.5
1000 mg/cm2
Copper filter
Open window
300 mg/cm2
2.0
1.5
1.0
0.5
0
10
100
1000
Photon energy - keV
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Thermoluminescent dosimeters - TLD

Dosimeters have excellent long term stability.

Dose evaluation is rapid, and dosimeters are
reusable.

TLD currently used for personnel beta dose
monitoring have energy threshold problems
because the detector is too thick, or non-tissue
equivalent.

Multi-element method is complex and can be
inaccurate.
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Thermoluminescent dosimeters - TLD

Neutron response of TL materials depends on
detector composition, TLD encapsulation and
neutron energy.

Some TL phosphors have high thermal neutron
sensitivity, but low fast neutron response.

Techniques to increase TL fast neutron response
include use of a moderator to thermalize the
neutrons.
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Short time exposure dating with LiF
Time post exposure - Hours
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Long time exposure dating with LiF TLD
Time post exposure - Days
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Harshaw 7776/8814 badge
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Panasonic badge
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Harshaw 6600 automated TLD reader
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ENDOS automated TLD reader
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Commercial TLD supply information
Dosimetry suppliers
ThermoRMP
www.thermormp.co.uk/
Landauer, Inc
www.landauerinc.com/products.htm
ICN Dosimetry Service
www.dosimetry.com/dx/external/default.html
Panasonic
www.panasonic.com/industrial/other/other_components_radiation_measurement_home.htm
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Photoluminescence
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Photoluminescent Dosimeters - PLD

Photoluminescence is based on formation of
induced luminescent centers in silver doped
phosphate glass.

When exposed to UV light, fluorescent light of a
larger wave length is emitted with intensity
linearly related to absorbed dose up to 30 Sv.

Unlike TL centers are not destroyed by normal
read-out and are extremely stable.

Fading at room temperature is negligible.
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Photoluminescent dosimeters - PLD

Dose information can be obtained at any time
during long-term dose accumulation.

Commercial phosphate glass has good
reproducibility and constant sensitivity.

Individual calibration of dosimeters is not needed.

Pulsed UV laser read-out reduces the pre-dose of
unirradiated glasses to a value of about 10 µSv.

Because of the high Z value of the glass materials,
energy compensation filters are required.
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Sensitivity relative to 60Co
Energy dependence of a typical PL glass
Photon energy - keV
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Relative RPL intensity - %
Example of an PL dosimeter design
Photon energy - keV
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Photoluminescence dosimeters - PLD

Newer generation flat glass dosimeters have an
energy dependence ±15% for photons >15 kev.

Automated phosphate glass dosimetry systems are
a possible alternative to TLD or film based systems.

PLDs have been used in accident dosimeters.

In criticality accidents, fast and thermal neutrons
can be measured using the 31P(n,p)32Si and
31P(n,)32P reactions and counting the emitted betas.
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Photoluminescence dosimeters - PLD


PLD advantages include permanent and long-term
integration of dose information, good accuracy,
negligible fading and remeasurability.
A PLD disadvantage is need for energy
compensation filters, excluding measurement of
low energy photons.
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Commercial PLD supply information
Dosimetry supplier
Chiyoda Technol
http://www.c-technol.co.jp
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Optically Stimulated Luminescence
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Optically stimulated luminescence - OSL

Pulsed OSL dosimetry - A narrow spectrum of light
repetitively illuminates an aluminum oxide film.

Optical energy releases a small fraction of the
trapped charge carriers created during exposure.

Released charge carriers combine with luminescent
centers to emit light detected with a PMT tube.

Each luminescence accumulation period ranges
from 25 msec to 100 msec.
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Optically stimulated luminescence - OSL

With 10 accumulation periods per dose
measurement, the analysis time is approximately
250 msec.

The wavelength of the stimulation beam is 532 nm.

A series of optical filters between the OSL film and
photomultiplier tube reject the green stimulation
light and pass the blue luminescence which has a
peak wavelength of 420 nm.
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Commercial dosimeter based on OSL
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Optically stimulated luminescence - OSL

In the commercial version, aluminum oxide powder
is obtained by grinding solid crystals and sifting
the powder into the desired size range.

The powder is mixed with a polyester binder and
coated onto a roll of clear polystyrene film.

The coating is 18 mm wide by 0.15 mm thick and
each roll is generally 150 meters long.

The film roll is cut to produce film chips with an
aluminum oxide coating area of 18 mm x 17 mm.
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Optically stimulated luminescence - OSL

Each film chip contains approximately 80 mg of
aluminum oxide powder.

Dosimetry is performed by stimulating three
circular areas 4 mm in diameter; each containing
3.3 mg of aluminum oxide powder.

Absorbers placed on both sides of the OSL film
alter the dose response of the film so that the
personal dose quantities can be assessed.
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Optically stimulated luminescence - OSL

A fourth area, 6 mm x 6 mm, serves to image
determine static and dynamic exposure conditions.

A special absorber containing an array of
perforations projects a distinctive image on the
film.

A research grade, image intensified CCD camera
captures the luminescent image.

Computer programs interpret the image data and
can display the image in various configurations.
International Atomic Energy Agency
Relative response for several photon energiesa
ISOb X Ray
Quality
Average Energy
(keV)
Response Relative
to 137Cs
M30
20
1.95
M50
29
2.30
M60
34
2.22
M100
50
1.96
M150
71
1.48
H150
117
0.96
137Cs
662
1.00
a From data of Landauer, Inc.
b INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, X and Gamma Reference Radiations for Calibrating
Dosemeters and Doserate Meters and for Determining Their Response as a Function of Photon Energy, ISO 4037/Part
1: Radiation Characteristics and Production Methods, ISO, Geneva (1996).
International Atomic Energy Agency
Commercial OSL supply information
Dosimetry suppliers
Landauer, Inc
www.landauer.com/poducts.htm
International Atomic Energy Agency
Beta and Low Energy Photon
Dosimetry
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Beta and low energy photon dosimetry

Beta sources external to the body do not cause
significant irradiation of deeper-lying tissue in the
body.

Can contribute significant exposure of the eye lens.

Particularly important in causing irradiation of the
hands, and especially of the finger-tips.
International Atomic Energy Agency
Beta and low energy photon dosimetry

If photon or beta irradiation is fairly uniform, a
single dosimeter worn on an appropriate part of the
body is sufficient, however,

Beta irradiation of the body is usually non-uniform.

For non-uniform irradiation, additional dosimeters
on other parts of the body may be necessary.

Frequently, it is necessary to wear an additional
suitable dosimeter on the hands or fingers.
International Atomic Energy Agency
Beta and low energy photon dosimetry
Commercial dosimetry services offer finger
rings in addition to conventional badges.
International Atomic Energy Agency
Beta and low energy photon dosimetry

Dosimeter may need to measure skin dose from a
mixture of beta rays and photons.

Dosimeters based on a high Z detector materials
are not appropriate because of photon energy
dependence.

Better to use tissue equivalent dosimeter material.

Most photon dosimeter types can be used.
International Atomic Energy Agency
Ideal dosimeter for beta/gamma skin dose

Tissue equivalent detector approximately 5 mg•cm-2
thick in close contact with a tissue equivalent filter
of the same thickness and kept in a tissue
equivalent holder.

Would provide a good estimate of tissue dose at
7 mg•cm-2 depth, independent energy, angle of
incidence, or source configuration and geometry.

Dosimeter should be easy to handle and suited to
manual as well as automatic processing.
International Atomic Energy Agency
Beta and low energy photon dosimetry

Several practical solid state detectors with good
dosimetric characteristics have been developed.

Thin layers of TL materials on a nonthermoluminescent graphite base

Mixed MgB4O7:Dy TLDs

BeO TSEE detectors

Threshold detection levels as low as 100 µSv (or
about 20 µSv for BeO TSEE detector).

Small ion chambers adapted to electron
measurements by use of a thin entrance window.
International Atomic Energy Agency
Neutron Dosimetry
International Atomic Energy Agency
Neutron dosimetry presents unique challenges

Neutron interactions produce more densely ionizing
charged particles than photons.
Photons
Electrons
Neutrons
Recoil protons
Alpha particles
Heavy charged
particles


Neutron energies span 9 orders of magnitude vs. 3
for photons.
wR  5.
International Atomic Energy Agency
wR is very important for neutron dosimetry
30
ICRP Recommendation
25
ICRP Approximation
20
WR
15
10
5
0
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
Neutron energy - MeV
1
10
International Atomic Energy Agency
102
Dosimeter energy response is very important
103
E
H*(10)
Hslab(10)
102
10
1
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
10
102
103
Neutron energy - MeV
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Nuclear Track Emulsions
International Atomic Energy Agency
Neutron dosimetry - Nuclear track emulsions

Fast neutrons interact with the hydrogen in the
emulsion and film, producing recoil protons.

Protons pass through the emulsion to create latent
images or tracks which leads to film darkening
after processing.

Below 10 eV, neutrons interact with nitrogen nuclei
of the gelatin and produce recoil protons.

Tracks are counted with high magnification
microscopes.
International Atomic Energy Agency
Neutron dosimetry - Nuclear track emulsions

NTA energy threshold is about 0.7 MeV.

Saturates at relatively low doses (about 50 mSv).

Accuracy depends on operator skill.

Thermal neutron sensitivity is undesirable,
dosimeter should be kept under a filter of neutron
absorbing material such as 6LiF or 10B carbide.
International Atomic Energy Agency
Recoil proton tracks from 14 MeV neutrons
International Atomic Energy Agency
NTA detects only fast neutrons
Relative response
103
102
NTA response
101
Slab phantom conversion coefficients
1
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
10
Neutron energy - MeV
International Atomic Energy Agency
102
Neutron dosimetry - Nuclear track emulsions

High fading is a disadvantage of emulsion.

Fading is severe when used without protection in
high temperatures and humidity (~ 75% per week).

Fading can be controlled if the films are
desiccated and sealed in a moisture-proof pouch
prior to use.

Photon sensitivity is also a serious disadvantage.

Other methods are replacing film.
International Atomic Energy Agency
Solid State Nuclear Track
Detectors
International Atomic Energy Agency
Solid state track detectors (SSNTD)

Heavy charged particles such as fission
fragments, alpha particles or neutron induced
recoils produce damage along their path in
dielectric materials.

Tracks are etched chemically and become visible
under a microscope.

Electrochemical etching (ECE) enlarges the track
diameter to make large area counting possible.
International Atomic Energy Agency
Solid state track detectors (SSNTD)
Three SSNTD techniques have been used for
neutron dosimetry :

Fission track detectors

Recoil track detectors

Track detectors based on (n,p) reactions
International Atomic Energy Agency
Fission track detectors

Detector has 2 components;

Fissionable material (radiator or converter)

The fission fragment detector

All SSNTD materials can be used to detect high
LET fission fragments.

Efficiency is typically between 85 and 92%.
International Atomic Energy Agency
Fission track detectors


Fission reactions have neutron energy thresholds;

0.6 MeV for
237Np

1.3 MeV for
232Th

1.5 MeV for
238U
or very high cross sections for thermal neutrons
(e.g. 235U or 239Pu).
International Atomic Energy Agency
Fission track detectors

Neutron energy can be determined using
different radiators.

Thermal neutron shields (e.g. Cd or 10B) can be
used to separate thermal neutrons from those at
higher energies.

Use of fissionable radiators leads to increased
radiation risk.

Use of fissionable materials in dosimeters is
restricted or forbidden in certain countries.
International Atomic Energy Agency
Recoil track detectors

Neutron interactions in the track detector or
radiator may produce recoil charged particles such
as protons, carbon, oxygen and nitrogen.

Recoils produce latent tracks which also can be
visualized by etching.

A combination of chemical etching and
electrochemical etching (ECE) or a two-step ECE
technique can be used to detect recoil tracks.
International Atomic Energy Agency
Recoil track detectors

Track density can be counted with a microfiche
reader or an automatic particle counter.

Response depends on the detector and energy.

Etching techniques are optimized for each
combination of radiator, absorber and detector
material.

Energy response curves must be experimentally
established and are only valid for conditions used.
International Atomic Energy Agency
Recoil track detectors

Most common detector materials are
polycarbonate, cellulose nitrate and CR39.

Polycarbonate is simple, inexpensive and very
stable, with an energy threshold is between 2 and 5
MeV.

CR39 has a low threshold (~100 keV) and high
sensitivity.

A number of services use CR39.
International Atomic Energy Agency
Electrochemical etch tracks
Plastic surface
Side
view
~50 m
Early tree formation
Etched track
Top view for
counting
International Atomic Energy Agency
CR39 is a fast neutron detector
Relative response
103
102
CR39 (ECE*)
10
Slab phantom conversion
coefficients
* Electrochemically etched
1
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
10
Neutron energy - MeV
International Atomic Energy Agency
102
(n,) Track Detectors

Uses neutron induced alpha particles in an
external particle radiator or “converter”:
6Li (n,) 3H or 10B (n,) 7Li

Cross sections are high for thermal neutrons and
decrease as 1/v with increasing energy.

Efficiency depends on the type of material and
etching conditions.

Limit of detection for intermediate neutrons is as
low as a few mSv, and 1 mSv for fast neutrons.
International Atomic Energy Agency
TLD Albedo Dosimeters
International Atomic Energy Agency
TLD albedo dosimeters

Detection of low energy neutrons reflected from the
body with thermal detector.

TLD with 6LiF (TLD 600) and 7LiF (TLD 700) with
various shields.

Neutron dose is determined by difference between
6LiF and 7LiF detector readings.

Relative response can vary by a factor of 50.

Energy response can be improved slightly by the
dosimeter encapsulation.
International Atomic Energy Agency
Albedo response is poor for fast neutrons
103
Relative response
Bare 6Li
Hankins albedo
102
101
1
10-8
Slab phantom
conversion cofficients
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
10
102
Neutron energy - MeV
International Atomic Energy Agency
TLD albedo dosimeters

For albedo dosimeters, neutron fields can be put in
4 categories:





Reactors, linear accelerators and accelerators
for medical therapy
Nuclear fuel fabrication areas
Radioactive neutron sources
High energy accelerators with little or no
shielding
Within a neutron field class, relative neutron
response does not vary by more than a factor of 2.
International Atomic Energy Agency
TLD albedo dosimeters

Very large energy dependence is a disadvantage.

Energy dependence can be improved with a second
detector for fast neutrons.

Albedo dosimeters detect neutrons of all energies
coupled and have simple, automatic TLD read out.

Extensive field calibrations of each dosimeter type
is necessary.
International Atomic Energy Agency
TLD albedo dosimeters

Calibration curves for working areas can reduce of
albedo response within  30%.

Depending on neutron field the lowest detectable
dose using TLD albedos varies from 50 to 200 µSv.

Albedo dosimeters can be combined with track
detectors for separate measurement of fast
neutrons.

Albedo detector serves as the basic neutron
detector for screening purposes.
International Atomic Energy Agency
Bubble Detectors
International Atomic Energy Agency
Bubble Damage Polymer Detector

Superheated droplets are
suspended in a firm elastic
polymer.

Neutrons trigger droplets
giving rise to formation sites.

Number of bubbles is a measure
of the neutron dose.

Completely passive device which can be stored
until required for use.
International Atomic Energy Agency
Bubble damage polymer detector

Does not require electronic readout.

Automatic reader can be used for a large number of
detectors.

Extremely sensitive to neutrons (in µSv range).

Completely insensitive to gamma rays.

Can be made with neutron energy thresholds from
<20 keV to several MeV.
International Atomic Energy Agency
Bubble damage polymer detector

Set of detectors can be used for crude
spectrometry.

One type of a bubble detector has flat energy
response for dose equivalent from about 200 keV to
>15 MeV.

Significant temperature dependence.

Limited dose range, so several dosimeters with
different sensitivities must be worn.

Finally, bubble detectors can be expensive.
International Atomic Energy Agency
Superheated Drop and Bubble detectors use
different detection mechanisms
Bubble Technology
BD-100R Bubble Dosimeter
TM
APFEL
Liquid Matrix
Superheated Drop Detector
Cap
Glass or Plastic
Tube
Elastic Polymer
Event
Acoustical
Transducer
Event
Acoustical
Transducer
(Gel)
Trapped Bubbles
~1 mm diam.
Superheated
Liquid Drops
~0.025 mm diam.
Anti-Coincidence
Circuitry
Counting and
Display Circuitry
Noise Acoustical
Transducer
International Atomic Energy Agency
Bubble detectors can have a wide energy range
International Atomic Energy Agency
Electronic Dosimeters
International Atomic Energy Agency
Passive dosimeters have limitations

Lack of direct dose display.

No alarm or indication of high dose rate or
dose.

Limited sensitivity.

Limited accuracy in some cases.

Need for significant laboratory investment.
International Atomic Energy Agency
Why are electronic dosimeters needed?

Instant or direct readout where the potential for
high exposures exists.

Alarm at given levels of dose and dose rate.

Indication of Hp(10) and Hp(0.07).

Better characteristics for neutron dosimetry.

Data transfer to and from computer networks.
International Atomic Energy Agency
Commercial electronic dosimeters also
have limitations

Potential dosimeter cost.

Passive dosimeters are used extensively.

Market is not growing vastly for photon and beta
dosimeters.

Market is very small for neutron dosimeters.
International Atomic Energy Agency
Detection mechanisms for electronic
(active) dosimeters

Charged fiber (electroscope) pocket dosimeters.

Ion chambers.

Silicon diodes.

Geiger-Müller counters.

Direct ion storage.

Charged particle radiators for neutrons.
International Atomic Energy Agency
Pocket Dosimeters
International Atomic Energy Agency
Pocket dosimeters

Based on ionization of gases in a small chamber.

Suitable for monitoring different types of radiation.

Direct-reading devices with and without built-in
charger: pocket electrometers.

Indirect-reading devices: Condenser type pocket
ion chambers require a readout device.
International Atomic Energy Agency
Direct reading pocket dosimeter
International Atomic Energy Agency
Pocket dosimeters

Useful when immediate indication of the worker's
radiation exposure is required.

Commonly used as supplementary dosimeters.

Should have appropriate wall materials and
thicknesses for adequate response to electron,
photon or neutrons.

Single dosimeters will have a limited dose range.
International Atomic Energy Agency
Pocket dosimeters

Care should be taken against erroneous readings
due to electrical leakage.

Such dosimeters are called alarm and warning
devices.

A high degree of accuracy is not important, but
reliability is.

Proper functioning may be crucial to the safety of
personnel.
International Atomic Energy Agency
Commercial Electronic
Dosimeters
International Atomic Energy Agency
Electronic dosimeters

Over 20 types of electronic dosimeters are
commercially available.

Several GM devices for photons >30 keV.

Electronic dosimeters for Hp(10) have been
developed based on a single silicon diode.

Commercial dosimetry system based on 3 silicon
diode detectors, suitable for the simultaneous
measurement of HP(10) and HP(0.07) for photons
and betas.
International Atomic Energy Agency
Commercial electronic dosimeters

Large variation in specifications and quality.

Some photon dosimeters are well advanced.

Few photon/beta dosimeters are available.

Neutron dosimeters are new.

Careful evaluation needed.
International Atomic Energy Agency
Commercial electronic dosimeters
A credit card size routine individual dosimeter
has been developed,

silicon diode detector

measures dose and dose rate

adjustable alarm

stores daily integrated dose for 12 months.
International Atomic Energy Agency
Selected commercial electronic
dosimeters
International Atomic Energy Agency
Selected dosimeters - Eurisys
Very small and lightweight dosimeter for photon
radiation with EEPROM memory for detailed dose
history. One of the first advanced systems, today in
various applications.
International Atomic Energy Agency
Selected dosimeters - Fuji Electric
Small and lightweight dosimeter with versions for
photon or photon, beta and neutron radiation. “Trend
dose collection” (i.e. dose data stored every minute).
In use in Japanese nuclear power plants.
International Atomic Energy Agency
Selected dosimeters - MGP
Small, rugged and lightweight dosimeter for photon,
or photon and beta radiation. Different versions of
this system are in numerous applications, including
military.
International Atomic Energy Agency
Selected dosimeters - RADOS
Systems with silicon detectors for photon
radiation. Small, rugged and lightweight dosimeter
with various applications, including civil defense.
International Atomic Energy Agency
Selected dosimeters - RADOS
Passive electronic system
with Direct Ion Storage (DIS).
Small and rugged devices for
measurement of Hp(10) and
Hp(0.07) for photon and beta
radiation of wide energy range.
Especially rugged version for
military application and
special version for neutron
radiation.
International Atomic Energy Agency
Selected dosimeters - Siemens
Sophisticated dosimeter with standard version for
measuring Hp(10) and Hp(0.07) for photon and beta
radiation. Special version for neutron radiation.
Photon and beta version approved for legal
dosimetry in UK.
International Atomic Energy Agency
Electronic dosimeter energy responses
International Atomic Energy Agency
Electronic dosimeters encounter several
problems

Lack of security of data storage.

No adequate mechanical and climatic resistance.

Mass and size of dosimeter.

Battery type and life span.
International Atomic Energy Agency
Electronic dosimeters encounter several
problems

Poor low energy photon energy dependence.

Poor beta radiation response.

Sensitivity to electromagnetic fields.

Saturation at high dose rates.
International Atomic Energy Agency
Basic features of Direct Ion Storage (DIS)
systems

Nondestructive readout

Tissue equivalent detector

Passive operation

Small dimensions

Low production cost

Suitable for data networks

Options for various applications
International Atomic Energy Agency
Analog EEPRom memory cell
Control gate
Silicon oxide
Oxide
Electron
tunneling
paths
Floating gate
Source
Drain
Si
International Atomic Energy Agency
Cross section of DIS
Fill gas
Oxide
Opening
Floating gate
Electron
tunneling
path
Source
Drain
Si
Modified Transistor with ion chamber
International Atomic Energy Agency
DIS photon detector
Electrons
Gas
Photons
Graphite
or teflon
International Atomic Energy Agency
DIS-2 Detector Element
International Atomic Energy Agency
DIS-2 system
International Atomic Energy Agency
Personal alarm neutron dosimeters
P.A.N.D.s are based on several techniques:

Counter for measuring recoil protons.

3He

Tissue equivalent proportional counter with a
microprocessor.

Silicon surface-barrier detector to detect recoil
ions from polyethylene and 10B radiators.
detector in a small CH3 moderator with
thermal neutron shield.
International Atomic Energy Agency
Commercial neutron dosimeters

Aloka PDM-313 (Si diode)

Fuji Electric NRY-22001 (Si diode)

Overhoff Technology Corporation Neutron
/Gamma electronic Dosemeter (Si diode)

Rados DIS-N (passive), (Ion chamber)

Siemens EPD-N (Si diode)
International Atomic Energy Agency
Example of a silicon diode based neutron
dosimeter
International Atomic Energy Agency
Prototype TEPC dosimeter
International Atomic Energy Agency
Bubble detector dosimeter
Event
acoustical
transducer
Anti-coincidence
circuitry
Event
acoustical
transducer
Counting and
display circuitry
Noise acoustical
transducer
An active dosimeter, based on bubble detection,
has been produced commercially. It is based on
acoustical detection of bubble formation and
includes noise rejection anticoincidence circuitry.
International Atomic Energy Agency
Energy dependence of prototype
electronic neutron dosimeters
Relative response
10
SDD
MC-TEPC
ME-TEPC-24
ME-TEPC-144
ME-TEPC-PD
DIS
SWD
1
01
10-8
10-2
10-1
1
10
102
Neutron energy - Mev
International Atomic Energy Agency
DIS neutron detector
thermal
neutrons
 particles
fast
neutrons
protons
photons
electrons
A-150 tissue
equivalent
plastic with
BN
International Atomic Energy Agency
RADOS DIS-N dosimeter
International Atomic Energy Agency
Conclusions and outlook

Several electronic dosimeter types are
commercially available.

Small number of types fulfill demanding
requirements.

Some electronic dosimetry systems are legally
approved for photon and beta radiation.

New products are available and development is
ongoing on neutron dosimetry.

Quality and application of electronic dosimetry are
expected to increase significantly.
International Atomic Energy Agency
References
BARTHE, J., et al., New devices for individual neutron dosimetry, Radiat. Prot. Dosim. 54 (1994) 365-368.
BORDY, J.M., BARTHE, J., BOUTRUCHE, B., SEGUR, P., A new proportional counter for individual neutron dosimetry,
Radiat. Prot. Dosim. 54 (1994) 369-372.
BURGKHARDT, B., ROBER, H.G., PIESCH, E., Phosphate glass energy compensation filters for the measurement of
operational dose quantities, Radiat. Prot. Dosim. 6 (1983) 287-289.
CHRISTENSEN, P., Review of personnel monitoring technique for the measurement of absorbed dose from external beta
and low energy photon radiation, Radiat. Prot. Dosim. 14 (1986) 127-135.
GRIFFITH, R.V. and TOMMASINO, L., “Etch track detectors”, Radiation Dosimetry: The Dosimetry of Ionizing Radiation,
Vol. III (KASE, K.R., BJARNGARD, B.E., ATTIX, F.H., Eds), Academic Press, New York (1990) Ch. 4.
HARRISON, K.G., TOMMASINO, L., Damage track detectors for neutron dosimetry: II. Characteristics of different detection
systems, Radiat. Prot. Dosim. 10 1-4 (1985).
HARVEY, J.R., BATES, J.R., MACKFARLINE, B., “An assessment of a commercial individual dosemeter suitable for low
penetrating radiation”, paper presented at Symp. on Personnel Radiation Dosimetry, Knoxville, 1984.
HÖFERT, M., PIESCH, E., Neutron dosimetry with nuclear emulsions, Radiat. Prot. Dosim. 10 1-4 (1985).
ING, H., The status of the bubble damage polymer detector, Nucl. Tracks Radiat. Meas. 12 (1986) 49-54.
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No. 252, IAEA, Vienna (1985).
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Reports Series No. 109, IAEA, Vienna (1970).
International Atomic Energy Agency
References
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, X and Gamma Reference Radiations for Calibrating
Dosemeters and Doserate Meters and for Determining Their Response as a Function of Photon Energy, ISO 4037/Part 1:
Radiation Characteristics and Production Methods, ISO, Geneva (1996).
LACOSTE, F., LUCAS, M., Le système Dosicard, Radioprotection 28 1 (1993) 77-81.
MARSHALL, T.O., POOK, E.A., BARTLETT, D.T., HALLAM, J., “An approved personal dosimetry service based on an
electronic dosemeter”, paper presented at International Radiation Protection Association Conf. Montreal, 17-22 May 1992.
PIESCH, E., BURGKHARDT, B., “Albedo neutron dosimetry”, Neutron Dosimetry in Radiation Protection (ING, H., PIESCH,
I., Eds), Nuclear Technology Publishing, Ashford (1985) 175-188.
PIESCH, E., BURGKHARDT, B., “LiF albedo dosimeters for personnel monitoring in a fast neutron radiation field”, Neutron
Monitoring for Radiation Protection Purposes, (Proc. Symp. Vienna, 1972), Vol. 2, IAEA, Vienna, (1973) 31-35.
PROKI‚ M.S., Beta dosimetry with newly developed graphite mixed TL detectors, Phys. Med. Biol. 30 4 (1985) 323-329.
Wernli, C., Neutron Dosimetry with Ion Based DIS System, Proc. 10th International Congress of the International Radiation
Protection Association, Hiroshima, Japan, Paper T-13-4 (2000).
International Atomic Energy Agency