tld

1. PRESENTER- DR. VIJAY P RATURI
MODERATOR-MR.TEERTHRAJ VERMA
J.R 2, king george medical university,
lucknow

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
called a dosimeter or a detector .

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 rely upon instruments to quantify and qualify
radiation measurements.

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."

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
are 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+
,fe3+ conc is determined by
spectrophotometry of dosimeter solution.

7. C> Solid state methods:-
Integrating type dosimeter
(a) thermoluminescent
crystals
(b)radiophotoluminescent
glass
(c)films
Electrical
conductivity
dosimeter
(a) Semiconductor
junction detector
- Of this most widely used for measurement of
absorbed dose are TLD , diodes and films

8. - 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.
- TLDs use phosphorescence to detect radiation.
THERMOLUMINESCENE DOSIMTETRY

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).

10. (forbidden band)
BAND THEORY OF SOLIDS
BOHR’S ATOM
LEVELS

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.

12. - 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.

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
that result 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. - 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 400-
500 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 CaSO4:Dy(1:3) embedded Teflon TLD
disk are used for personnel monitoring.
Characteristics of CaSO4:Dy
- Effective Atomic No- 15.
- 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
PERSONNEL NUMBER
NAME
RADIATION TYPE
PERIOD OF USE
TRANSPARENT
PLASTIC
SEALED POLYTHENE
POUCH
METALLIC FILTER
CROCODILE CLIP

21. Dosimeter
Disc1(Dl)
Regions of TLD Cassette
Front: Cu (1.0mm thick) 3.5 cm x 1.5 cm
+Al (1.0 mm thick) disc of dia 15.6 mm.
Back: Cu (1.0mm thick) disc of dia 15.6mm
+Al (1.0 mm thick) disc of dia 15.6 mm.
Dosimeter
Disc2(D2)
: Front: Perspex 180mg.cm-2
Back: Same as front
Dosimeter
Disc3(D3)
: Open: 12mg.cm-2 (identification paper +
polythene seal)

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.

24. - 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.
APPLICATION OF TLD

26. - 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.
INSTRUCTION FOR USERS
OF TLD BADGESDO’s
• 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
• Store the badge in radiation free place when not in use
by you.
• Report any unusual radiation incident to your RSO

27. 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
furnaces.

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.
- Reusable.

29. - Lack of uniformity – batch calibration needed
- Storage instability
- Fading
- Light sensitivity
- Spurious TL (cracking, contamination)
- No permanent record
TLD DISADVANTAGES

30. - A Geiger–Müller 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–Müller 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.
GEIGER –MULLER COUNTER

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).
G-M counters being used as gamma
survey monitors, seeking radioactive
satellite debris
- 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
APPLICATION OF GM COUNTER:-
- PARTICLE DETECTION
- GAMMA RAY AND XRAY DETECTION
- NEUTRON DETECTION
- GAMMA MEASUREMENT – PERSONNEL PROTECTION( AREA
GAMMA ALARM) AND PROCESS CONTROL.
Geiger tube filled with BF3 for
detection of thermal neutrons

33. CaSO4:Dy and LiF:Mg, 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
LiF:Mg, Cu, P was a good environmental dosimeter.
PMID: 8609029 [PubMed - indexed for MEDLINE]

34. THANK YOU.