2. - The maximum allowable dose is limited to 20 mSv
per year for people working with radiation. This
limit is 1 mSv for the normal population.
- The effects of irradiation on an organism may
change according to the dose, type of contamination,
and the features of the radiation source.
- It is crucial to perform measurements on the
radiation generators used for diagnostic or
therapeutic purposes.
- The measurement of radiation is called dosimetry,
and the equipment used for dosimetric procedures is
r n I l/"»rl n rlnc rw n ^etector
3. - Dosimetry is the monitoring of individuals to accurately
determine their radiation dose equivalent.
- When radiation interacts with the human body, there
are no perceptible sensations and usually no immediate
effects.
- We could therefore receive an amount of radiation that
could injure our tissues severely without realizing it at the
time.
- To protect ourselves and others, we must use
and^elyupon instruments to quantify and qualify
niliiliMNmeamiiminl
4. Radiation Controlled area: An area where entry, activities,
and exit are controlled to help ensure radiation protection
and prevent the spread of contamination.
Radiation Restricted Area:- it includes all "Radiation Areas,"
"High Radiation Areas," rooms or areas in which there is
radioactive materials in such quantities that "Caution:
Radioactive Material" signs are required , and certain other
areas which may be so defined by the "Health Physicist."
DANGE
R
Radiation controlled
area
Access
restricted
RADIATION
RESTRICTED
A.A AREA A.A
4k 4k
5. METHODS OF MEASURING ABSORDED DOSE:-
A> Calorimetry:- Basic Method Of Determining absorbed
dose.
- It Is Based On Principle That The Energy Absorbed In A
Medium From Radiation Appears Ultimately
As Heat Energy, thus Resulting In Increase In Temp of
Absorbing Medium.
- To measure such change in temp ,thermistor is used
(it’s a semiconductor which show change in electrical
resistance with small change in temp).
- Most of these apparatus are difficult to construct ,and
considered impractical for clinical dosimetry.
6. B> Chemical dosimetry:- Energy absorbed from ionizing
radiation may produce chemical changes,& if this change
can be determined , it can be used as a measure of
absorbed dose.
- Ferrous sulphate or fricke’s dosimeter is considered
to be most developed system for precision measurement
if absorbed dose.
- Dosimeter consist of 1mmol/l of fes04 ,1 mmol/l of
nacl & 0.4 mol/l h2so4
- When solution is irradiated fe2+ —^ fe3 +
determined by ieter
solution.
7. C> Solid state methods:-
I l
Integrating type dosimeter Electrical
conductivity
(a) thermoluminescent dosimeter crystals
(a) Semiconductor
(b) radiophotoluminescent junction detector glass
(c) films
^Of this most widely used for measurement of
abson se are TLD , diodes and films
8. THERMOLUMINESCENE DOSIMTETRY
- Thermoluminescence:- when a crystal is
irradiated ,very minute fraction of absorbed energy is
stored in crystal .some of this energy can be
recovered later as visible light if material is heated.
- Two categories
- Fluorescence - emission of light during or immediately
after irradiation( time < 10 power -8 sec)
- Not a useful reaction for TLD use.
- Phosphorescence - emission of light after the irradiation
period. Delay can be seconds to months.
e phosphorescence to detect radiation.
9. Theory of thermoluminescent dosimetry:- In crystal
lattice .electronic energy level by mutual interaction
between atoms give rise to energy bands.
- Impurities in crystals create energy traps , providing
metastable states for the electrons.
- When the material is irradiated , some of e- in
valence band(ground state)receive sufficient energy to be
raised
to the conduction band.
- The vacancy thus created is called positive hole.
The e- and the hole moves independently ,until they
fall fall into a trap(metastable state).
11. - Emission of light during these transition is called
fluorescence.
- If e- in the trap requires energy to get out of the trap
and fall to the valence band, emission of light is called
phosphorescence(delayed fluorescence).this process can
be speeded up with moderate amount of heating ,the
phenomenon is called as thermoluminescence.
Conduction
Band
Electron Trap TL Photon
Valence
Band
a) Irradiation b) Heating
FIG. 8.11. A simplified energy -level diagram to illustrate thermoluminescence process
12. Glow Curves
- Plot of thermoluminescence against temp is called glow
curve.
- As the temp of TL material exposed to radiation is
increased the probability of releasing e- increases.
- Area under this curve is directly proportional to the
amount of radiation that was absorbed in the chip.
-The individual glow peaks are numbered and correspond
to different trap depths.
190*C
13. - The light emitted (TL) first increases, reaches a
maximum
value and falls again to zero.
- Most phospor contain a number of traps at various
energy levels in the forbidden band.
14. - TLD must be calibrated before it can be used for
measuring an unknown dose, because response of tld is
affected by their previous radiation and thermal history.
- The material must be annealed to remove residual
effect.
- Standard preirradiation annealing procedure for liF is 1
hour of heating at 400c and then 24hour at 80c
- Slow heating removes peak 1 and 2 of glow curve,
making it more stable.
- Tld is available in many forms and sizes, hence can be
used for measuring dose in build up region ,around
brachytherapy sources, and for personnel dose
monitoring
15. ANNEALING
- Annealing is used to determine trap of interest
- Low temperature traps fades away with time at room
temperature.
- Basically just want high temperature traps to remain.
- 400 d celsius for 1 hour reset trap structure and
eliminates any electron in residual trap.
80 d celsius for 24 hour eliminates the trap
;esult in peak 2 to stabilize glow curve.
16. TLD READER CONSTRUCTION
- Irradiated material is placed in heater cup or planchet
- Emitted light is measured by photomultiplier tube
converts light into electrical energy. current is then
amplified and measure by recorder
17. - TL dosimeters most commonly used in medical
applications are LiF:Mg,Ti, LiF:Mg,Cu,P because of their
tissue equivalence.
- Other TLDs, used because of their high sensitivity, are
CaSO4:Dy, Al2O3:C and CaF2:Mn.
- TLDs are available in various forms (e.g., powder,
chips, rods, ribbon, etc.).
- Their range of measurement spans anywhere from <1
mrem up to as much as 100000 rem.
18. PROPERTIES OF TL MATERIAL
- It should have a single glow curve no interfering glow
curve
- High TL sensitivity i.e. more light output per unit of
dose
- Emissive spectra in visible, preferably in the range
400500 nm
- Negligible thermal fading (loss of TL signal due to
ambient conditions like temperature etc.)
- Glow peak preferably around 200 degree celsius
- Should be tissue equivalent
- Should be cheap, easy to manufacture and simple
annealing procedure
- Linearity between dose and light output over wide range
19. - In India CaS04:Dy(l :3) embedded Teflon TLD
disk are used for personnel monitc
Characteristics of CaSQ4:Dv
- Effective Atomic No- 1 5.
- Main Peak -200 degree Celsius
- Emission Maximum480-570 nm
- Fading- less than 5 % per month(at 25 degree
Celsius)
- Self fading - 0.01 mSv/month
- Linearity in Response :linear upto 30 Gy
- Colour of emitted light :yellowish -white
20. TLD BADGE
CROCODILE CLIP
METALLIC FILTER
SEALED
POLYTHENE POUCH
TRANSPAREN
T PLASTIC
> PERSONNEL NUMBER
NAME
RADIATION TYPE
PERIOD OF USE
21. Regions of TLD Cassette
Front: Cu (1.0mm thick) 3.5 cm x 1.5 cm
Dosimeter +AI (1-0 mm thick) disc of dia 15.6 mm. Discl(DI)
Back: Cu (1.0mm thick) disc of dia 15.6mm +Al (1.0
mm thick) disc of dia 15.6 mm.
Dosimeter : Front Perspex 180mg.cnrr2
Disc2(D2) Back! Same as front
Dosimeter : Openl 12mg.cnr2 (identification paper + Disc3(D3)
polythene seal)
on the card
22. -A TLD badge based on CaSO4: Dy Teflon discs has been designed
and is in regular Personnel Monitoring use since 1975.
- The TLD badge has shown satisfactory performance for
monitoring beta and gamma doses of radiation workers.
- At present about 40,000 radiation workers are covered with TLD
monitoring service in our nuclear industry, medical and industrial
institutions as well as research institutions.
- The complete Personnel Monitoring TLD badge consists of a TLD
card and a plastic cassette for holding the TLD card. The badge is
affixed to the clothing of a person with the help of a crocodile clip
attached to
the badge.
23. -Adults, minors, and declared pregnant women who are likely to
exceed of 10% of the below values from external sources of
radiation must be monitored.
Also, monitors must be worn by anyone who enters a high
radiation area.
TABLE 1 - SUMMARY OF IDNS DOSE LIMITS
ANNUAL OCCUPATIONAL LIMITS ADULTS MINORS
Total Effective Dose Equivalent (TEDE) - cr -
Total Organ Dose Equivalent (TODE)
5.000 mrem - or -
5(LOGO mrem
500 mrem - or -
5,000 mrem
Lena of Eye (LDE) 15r000 mrem 1.500 mrem
Skin cf the Whole Body (SDEAVB) 50.000 mrem 5.000 mrem
Extremities (SDE.ME) 50.000 mrem 5.000 mrem
OTHER APPLICABLE LIMITS
Dose to Embryo Fetus (Declared pregnancies) - 500 mreni
Members of the Public - 100 mrem year
Unrestricted areas - 2 mrem in any one hour
24. APPLICATION OF TLD
- Measurement of output from Co-60 units and accelerators used in medicine and
industry.
- Area survey of medical (diagnostic and therapeutic) and industrial radiographic
installations.
- Measurement of stray and leakage radiation around X-ray tubes and source
containers.
- Monitoring of high levels of contamination from beta sources.
- Estimation of activities of various radionuclides used in brachytherapy and
nuclear medicine.
- To measure dose rates in rectum and bladder of patient undergoing treatment
with Cobalt on Cesium implants for carcinoma of uterine cervix.
- Personnel Monitoring.
25. rv/"
O-
O
O-
Teflon
Discs
^
jj>
1d2
ifsO--
Personnel
No. —♦-405C003
-
Name —>M. R. Sane
Rad.Type--*► X - Rays
Dec.
1997-
Sealed
polythene
pouch
Card with
wrapper
Period of
use
Ni -plated aluminium card
(bare)
Card to be loaded in cassette
and to be returned to PMS after
use
Metallc filter 11100
mg/cm-*0
Plastic (transparent)
(180 mg / cm2)
Open window
-2
(Paper 12mg /cmz)
Fig. 1. Assembly of TLD badge
Front view,of TLD badge
26. POSITIONING OF THE BADGE
- One badge should be worn at chest level.
- Should be worn below the lead apron if used.
- If selectively high doses are expected to hands
and head- additional wrist and head badges may be
used.
• Load the card properly in the TLD cassette, name and
personnel NO. should be in the front, visible from
outside
• Use TLD card of the valid service period.
• Handle the TLD badge with care
ation free place when not in use
DO’s
INSTRUCTION FOR USERS OF
TLD BADGES
iation incident to your RSO
27. INSTRUCTIONS FOR USERS OF TLD BADGES
Don’t
- Don’t share your TLD badge with someone else,
your badge is your own.
- Once loaded don’t open the badge till the end of
the service period.
- Don’t pierce or open the sealed polythene pouch
of the TLD card
- Don’t use a damaged or broken cassette of which
filters have come out ask for replacement.
- Don’t leave the badge in radiation area, in washing
machines or near the vicinity of hot plates or ' naces.
28. ADVANTAGES (AS COMPARED TO FILM DOSIMETER
BADGES) INCLUDES:
- Able to measure a greater range of doses.
- Small in size - point dose measurements
possible.
- Available in various forms.
- Some are reasonably tissue equivalent .
- Not expensive.
29. TLD DISADVANTAGES
- Lack of uniformity - batch calibration needed
- Storage instability
- Fading
- Light sensitivity
- Spurious TL (cracking, contamination)
- No permanent record
30. GEIGER -MULLER COUNTER
- A Geiger-Muller counter, also called a Geiger
counter, is a type of particle detector that measures
ionizing radiation.
- It detects the emission of nuclear radiation alpha
particles, beta particles, and gamma rays by the
ionization produced in a low-pressure gas in a
Geiger-Muller tube.
- In wide and prominent use as a hand-held radiation
survey instrument, it is perhaps one of the world's
best-known radiation instruments.
31. - A GM counter consists of a tube filled with "Q-gas” (98%
helium and 1.3% butane)
- As in an ion chamber, the detector records every interaction
instead of measuring the average current that occurs after
several reactions. In other words, one ionizing event will
produce a pulse or a count in the GM tube.
- GM counter does not differentiate between types of
radiation or their energies. For this reason, most GM counters
are calibrated to give counts per minute (CPM).
i
4
*
- GM counters are usually used to simply
detect the presence of radioactive
material.
- GM counters are used to detect low-
energy X and gamma rays.
32. G.M. COUNTER Ml 1.42 Simple
illustration ol a (icipet
MOIIef counter
APPLICATION OF GM COUNTER:-
PARTICLE DETECTION - GAMMA RAY
AND XRAY DETECTION
- NEUTRON DETECTION
Geiger tube filled with BF3 for
detection of thermal neutrons
GAMMAMEASUREMENT - PERSONNEL PROTECTION AREA
GAMMA ALARMH^ND PROCESS CONTROL.
33. CaS04:Dy and LiF:Mq, Cu. P thermoluminescent dosimeters for
environmental monitoring in ambient areas of a nuclear power
plant.
Zeng XS1, Zeng JX, Tan GX, Mai WJ.
Author information Abstract
This paper describes CaSO4:Dy and LiF:Mg, Cu, P which were used
for ambient environmental monitoring before the nuclear power
plant operation in Guangdong Daya Bay, China, in 1991. Since
LiF:Mg, Cu, P was first used as an environmental dosimeter in this
laboratory, the intercomparison of both thermoluminescent
dosimeters, including laboratory irradiation and environmental
exposure in Beijing reference spots, was conducted in cooperation
with National Institute of Metrology and Laboratory of Industrial
Hygiene, measured values of both thermoluminescent dosimeters
were in agreement with the error being less than +or- 2% for the
laboratory irradiation. The results of measurement by both
thermoluminescent dosimeters were quite in agreement with
environmental reference exposure rates measured by a pressurized
ionization chamber. The largest error of CaSO4:Dy environmental
monitoring results in Daya Bay also showed that the differences of
measurement results between two thermoluminescent dosimeters
were not significant. The experiment results indicated that
Cu, P was a good environmental dosimeter.
PMID: 8 PubMed - indexed for MEDLINE]
