Personal Dosimetry Techniques (TLD)

1. E-8. Personal Dosimetry Techniques (TLD)
Hideaki OMURA
Nuclear Technology and Education Center,
JAERI
C O N T E N T S
Introduction
1. Principle of measurement
2. Outline of TLD(UD-5120PGL)system
2.1 Composition
2.2 Measured data and correction
3. Outline of operating procedure
4. Cautions for use
4.1 Handling of the reader
4.2 Handling of TLD element
5. Outline of Experiment
6. Apparatus
7. Procedures
Preparation for measurement
8. Primary Handling of the TLD Reader
8.1 TLD Reader and Quality Assurance
8.2 Practice to make measurement by the TLD reader and preparation of
TLD elements
8.3 Irradiation of TLD elements
8.4 Measurement of exposure dose
8.5 Using ICRU type phantom and irradiation of TLD elements
8.6 Comparison of experimental results between the measurement
without and with phantom
9. Determination of Personal Dose equivalent

2. 1
Introduction
The determination of occupational dose is composed of two components,
one is external exposure, the other is internal exposure from radionuclides
entering into the body. The effective dose equivalent from external
exposure used to compare with the legal dose limit is generally obtained
from a device worn outside of the worker's body.
Thus, the reading from such device must relate to the effective dose
equivalent. Since 1985 the ICRU had put out a report (ICRU Report 39)
designated to "the operational quantities". The set of quantities are used
for calibration of external radiation measuring devices to the estimation of
Effective Dose Equivalent, HE. The Personal Dose Equivalent, Hp(10), is
one of the quantities which is used for calibrating personal dosimeters.
The Personal Dose Equivalent, Hp(d), is the dose equivalent in soft
tissue below a specified point on the body at an appropriate depth, d. For
weakly penetrating radiation, a depth of 0.07 mm for the skin and 3 mm for
the eye are employed. The personal dose equivalent for those depths is
then denoted by Hp(0.07) and Hp(3), respectively. For strongly penetrating
radiation, the depth of 10 mm, Hp(l0), is employed. Hp(d) can be measured
with a detector which is worn at the surface of the body and covered with an
appropriate thickness of tissue-equivalent material. The calibration of the
dosimeter is generally performed under simplified conditions on an
appropriate phantom.
1. Principle of measurement
Thermoluminescent dosimeters (TLD) utilizes the effect in some
materials which can store the energy of ionizing radiation in excited state
electrons in the abnormality of lattices. When a Thermoluminescent
element is heated, its radioactive energy accumulated inside is emitted in
the form of light. By detecting this light, the dose can be measured. The
amount of light is proportional to the energy deposited. TLD is widely used
for personal dosimeters as well as for area monitoring. Example of TLD
materials are compounds of LiF, Li2B4O7, BeO, CaF2 and CaSO4, doped with
various activators. LiF, Li2B4O7 and BeO are nearly tissue-equivalent for
photons while CaF2 and CaSO4, although far from tissue-equivalent, have
the advantage of being 20 to 30 times more sensitive.

3. 2
2. Outline of TLD (UD-5120PGL) system
2.1 Composition
The TLD system is composed of UD-5120PGL, TLD element, finger
holder, and annealing oven.
(1) The UD-5120PGL is a thermoluminescent dosimeter reader
comprising a microcomputer.
(2) The TLD element is available in CaSO4 type, BeO type, etc. and is
presented in glass capsule seal shape and film shape.
(3) The finger holder is offered in various types to be suited to versatile
applications, purposes and element shapes.
(4) The annealing oven is an electric heating oven for removing the
residual dose when re-using the element.
2.2 Measured data and correction
The data displayed in the display unit and the data printed out by the
built-in printer after measuring the TLD element by this reader are
direct reading values.
In this reader, the direct reading value is stored, and is arithmetically
operated in terms of output correction factor (correction factor applied to
all measuring elements), element sensitivity correction factor for each
TLD element, and background value (BG), and the processed data is
printed out again or transmitted to an external system.

4. 3
Thermoluminescent Dosimeters System UD-5120PGL General specification
Items Contents
Dose display range 0.1μSv to 999Sv (0.01 mR to 99.9 kR)
Measuring range
UD-200S (CaSO4:Tm) X and γ-rays
1μSv to 200mSv ( 0.1 mR to 20 R)
Display
8 digits, 4 range automatic changeover
with range-over display
Measuring time Standard 10 seconds
Heater temperature Approx. 430 degree Celsius fixed
Photomultiplier Voltage Approx. 560V fixed
Calibration
Automatic sensitivity correction by built-i n
calibration light source (CAL) measurement
Dark Current Compensation
Dark current of photomultiplier is
automatically compensated (manual
compensation is possible by selection).
Memory of correction value
Output correction factor (energy, fading
correction) 1 point. Element sensitivity
correction factor of each TLD element 999
data
Measured data memory Measured data before correction 99 data
ID number 001 to 999, 3 digits
Printer 17 digits discharge built-in printer
External output
Transmission output: RS-232C
Glow output: 5-volt full scale
Operating temperature,
Humidity
0 to 40 degree Celsius,
10 to 80%RH
Power source 100 V± 10%, 50/60 Hz, 350 W
Dimensions
493 mm (wide) x 366 mm (deep) x 273 mm
(high)
Weight A pprox. 24 k g

5. 4
Fig. 2 Glow curve for CaSO4:Tm Element

6. 5

7. 6
3. Outline of operating procedure
Preparation for measurement of TLD elements by this reader and normal
measuring operation are outlined as below.
Preparation for measurement normal measuring operation
Turn on power Draw out slider
Confirm and set the date Press RESET key
Raise temperature Insert TLD element
Ready to measure Push in slider
Select TLD element type Press READ key
Calibration light source
Measurement processing
(CAL measurement)
End of measurement
Display of
Measured value
Display and set ID
number
Output to printer
and external unit

8. 7
4. Cautions for use
The operating temperature of this reader is 0 to 40 0C. Preferably, use at
the ambient temperature of 15 to 25 0C .
4.1 Handling of the reader
(1) Make sure to supply the specified power source as defined on the name
plate.
(2) Avoid damp, dusty or vibrating places.
(3) When moving or transporting the reader, be careful not to give a shock.
(4) Since a high voltage power source is built in, do not touch the internal
parts while the power is on.
(5) Various variable resistors for adjustment provided in the case, have
been correctly adjusted before shipping. Do not touch them.
(6) After turning off the power, cool for more than 30 minutes before
putting the vinyl cover on it.
(7) If the reader is shut down for a long period or when used in a damp
place, water drops may be collected on the convergence glass surface of
the slider. Wipe off with a dry gauze, and push in the slider and press
the READ key (this process is called empty running). By repeating this
empty running, dry the convergence glass sufficiently before use.
(8) If any abnormality occurs, an error code is shown on the display unit,
and the error message is printed out.
For details, see the error code list elsewhere in the manual.
4.2 Handling of TLD element
(1) Do not touch the TLD element by hand.
(2) Deposit of flammable dust or fat from fingertip may burn when heating,
which may result in an error.
(3) If the element (contained in glass capsule) is contaminated, clean the
glass tube with ethyl alcohol (reagent first grade or special grade) and a
gauze, and dry it at ordinary temperature.
(4) Do not expose the element directly to sunlight.
(5) Anneal the element in the annealing oven after measurement or
before use.

9. 8
5. Outline of Experiment
1) Practice on the method of primary handling of the TLD reader.
2) Basic treatment of the TLD element.
3) Reading of background dose by the TLD reader.
4) Annealing of the TLD element.
5) Attachment of TLD elements to the phantom.
6) Irradiation of the radiation to TLD elements.
7) Reading of exposure dose by the TLD reader.
8) Estimate the Calibration Factor (K).
6. Apparatus
1) Radiation sources: Cs-137.
2) TLD elements UD-200S and TLD reader Panasonic UD-5120PGL.
3) Annealing oven.
4) Ionization chamber type survey meter.
5) ICRU Type Phantom.
6) (Tape measure.)
7) (Stop Watch.)
7. Procedures
Preparation for measurement
1) Turn on the power of the TLD reader.
2) Prepare the TLD elements.
3) Put the Annealing oven in operation.
4) Prepare an ionization type survey meter.
5) Set the ICRU type phantom at the place of irradiation.
6) Place correctly the Cs-137 source.
7) (Prepare a tape measure.)
8) (Prepare a stop watch.)
9) Prepare to use alcohol and gauze.

10. 9
8. Primary Handling of the TLD Reader
8.1 TLD Reader and Quality Assurance
1) Calibration by the Internal Light Source
① Draw out the slider and rotate 90 degrees clockwise. CAL will be
displayed.
② By pushing the READ key, calibration measurement will be
automatically started for 10 times. Reader calibration factor
RDR.C. F. is displayed and printed out. If the value has not
changed from the previous reading, that indicates the stability of
the reader.
③ Rotate the slider 90 degrees anti-clockwise and insert the slider.
2) Handling of TLD elements
In advance of an actual irradiation, a quality assurance is
recommended using TLD elements irradiated to a certain dose by
standard radiation field. However, for the practice, the following steps
① to ③ are carried out by any of the TLD elements.
① Draw out the slider, take off one side of TLD elements by its plastic
cap and set it at the appointed position on slider, then insert it.
② Push READ key, a blast of hot air will blow to the TLD element for
10 second then the result will be displayed and printed out.
③ Record the results in data sheet.
④ Compare the results with the standard irradiation values by
drawing a calibration curve.
8.2 Practice to make measurement by the TLD reader and preparation
of TLD elements
1) Insert a TLD element (not irradiated) in TLD reader and then read
background radiation dose of each element and record it.
2) Make measurement twice for each TLD element, and confirm an
indication of the second measurement is 0 mSv.
3) Repeat measurements over 10 elements.
4) Anneal all TLD elements, for the sake of correctness , by using the
Annealing oven.
5) If the TLD elements was dirty, then clean them by using a piece of
gauze soaked with alcohol.

11. 10
8.3 Irradiation of TLD elements
1) Place the Cs-137 source at the position to irradiate.
2) Using ionization chamber survey meter to measure the radiation dose
rate, decide place and time to irradiate considering the radiation dose
t o be obtained.
3) Irradiate TLD elements.
8.4 Measurement of exposure dose
1) Read TLD elements by the reader and take record of the measured
values.
2) Confirm and record the result of exposure in the unit of mSv for
instance of measurement for each TLD element.
3) Calculate an apparent calibration factor (k) as a ratio of the measured
value of TLD divided by that value of the ionization chamber survey
meter.
4)Anneal the TLD element by Annealing oven.
8.5 Using ICRU type Phantom and irradiate the TLD elements
1) Irradiate the indicated number of TLD elements at the same distance
from the source.
2) Read the TLD elements by the reader and record the measured
values .
3) Confirm and record the result of measurement for each TLD element.
4) Calculate the calibration factor (k) as a ratio of the measured value by
the TLD to that value by the ionization chamber survey meter.
8.6 Compare the experimental results between the measurements
without and with phantom
9. Determination of Personal Dose Equivalent, by TLD.
1) Record the results in data sheet.
2) Fill the work sheet and compare the results.