1. Thermo Luminescence
Dosimeter (TLD) Badges for
Radiation Monitoring
Dr. Saurabh Raut
Medical Physicist –Radiological Safety Officer
Department of Radiation Oncology
MAMC-Lok Nayak Hospital, New Delhi
2. • As per Radiation Protection Rules – 2004, all occupational
radiation workers need to be monitored to safe guard them
from the deleterious somatic and genetic effects of ionizing
radiations.
• This radiation monitoring is done with TLD Badges. A badge
consists of 3 TLD discs.
• 2 types of TLD badges are available one to measure whole body
dose and the other to measure the dose in the wrist.
• The TLD cards are read by TLD reader which is controlled by PC
and a software. The software displays the dose received by the
TLD Badge in a given period.
3. • The radiation received by the person is monitored with these
TLD badges.
• These TLD badges are to be sent for radiation monitoring once
in 3 months and the user gets the replacement TLD badges
• the personnel doses should not exceed 100 mSv in a 5 year
block (current year and previous 4 years). And in any one year
maximum allowable dose is 30 mSv.
• If the radiation worker uses lead apron then the TLD Badge to
be worn inside the lead apron.
• These TLD badges are not transferable, one should not use
other person’s badge.
• UNITS OF EQUIVALENT DOSE
• Sievert is the unit of Radiation Equivalent Dose
• 1 Sievert (Sv) = 1 joule/Kg = 100 Rem
• 1 milliSievert (mSv)= 1/1000 Sv = 100 mRe
4. 1. The measurement of radiation is called dosimetry,
and the equipment used is called a dosimeter
2. When radiation interacts with the human body, there
are no perceptible sensations and usually no
immediate effects
3. We could therefore receive an amount of radiation
that could injure our tissues severely without
realizing it at the time
4. To protect ourselves and others, we must use and
rely upon instruments to quantify and qualify
radiation measurements
5. METHODS OF MEASURING ABSORDED DOSE
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. 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 of 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+ concentration is determined by
spectrophotometry of dosimeter solution.
7. Solid state methods
1. Semiconductor junction detector
2. Thermo luminescent crystals
3. Optically stimulated luminescence detectors
4. 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:-
1. In crystal lattice ,electronic energy level by mutual
interaction between atoms give rise to energy
bands.
2. Impurities in crystals create energy traps ,
providing metastable states for the electrons
3. When the material is irradiated , some of e- in
valence band(ground state)receive sufficient
energy to be raised to the conduction band
4. The vacancy thus created is called positive hole
5. The e- and the hole moves independently ,until
they fall fall into a trap(metastable state).
11. Traps due to impurities
•In perfect semiconductors, there exist a band gap
(forbidden band) between valence band (bottom) and
conduction band (top).
•When impurities are introduced, there exist allowed
energy states somewhere in the band gap.
•The states that are close to the band edges (either
conduction band or valence band), then we call them
shallow traps.
•If the states are close to the middle of band gap, then we
call them deep traps.
12. - 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.
13. - 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.
14. -The light emitted (Thermoluminiscence)
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.
15. - 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.
- 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.
16. 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.
17. 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
18. -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.
19. - 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
20. oring.
-In India CaSO4:Dy(1:3) embedded Teflon TLD
disk are used for personnel monit
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
21. GENERAL FEATURES OF TLD
BADGES
SEALED POLYTHENE
POUCH
TRANSPARENT
PLASTIC
PERSONNEL NUMBER
NAME
RADIATION TYPE
PERIOD OF USE
METALLIC FILTER
CROCODILE CLIP
22. GENERAL FEATURES OF TLD
BADGES
A TLD badge consists of a TLD card and a TLS cassette.
TLD card
1. A TLD card consists of three CaSO4: Dy-Teflon TLD discs (13.3mm dia x
0.8 mm thick)
2. These discs are mechanically clipped over three symmetrical circular
holes each of diameter 12 mm, on a nickel plated aluminum plate
(52.5mmx29.9mmx1mm)
3. An asymmetric V cut provided at one end of the card ensures a fixed
orientation of card in the TLD cassette. A thin paper wrapper provides
personal data & the period of use.
4. To protect the TLD discs from dust and mishandling, the card along is
sealed in a thin plastic (polythene) pouch.
5. Pouch also protects the card from radioactive contamination while
working with open sources.
23. GENERAL FEATURES OF TLD
BADGES
TLD Cassette
1.TLD cassette (card holder) is made of high impact plastic.
2.TLD card when inserted in the proper position in the cassette will
have the first disc (D1) sandwiched between a pair of filter
combination of 1 mm Al & 0.9 mm Cu.
3.The second disc (D2) is sandwiched between a pair of 1.5 mm
thick plastic filters
4.The third disc (D3) is positioned under a circular open window.
5.A crocodile clip or strap attachment affixes the badge to the
user’s clothing or to the wrist.
26. INSTRUCTION FOR
USERS
OF TLD BADGES
Do’s
1. Load the card properly in the TLD cassette, name and
personnel NO. should be in the front, visible from
outside
2. Use TLD card of the valid service period.
3. Handle the TLD badge with care
4. Store the badge in radiation free place when not in use
by you.
5. Report any unusual radiation incident to your RSO
27. 1. One TLD badge should be worn compulsorily at the chest level.
2. The dose recorded by the TLD badge worn at the chest level represents
the whole body dose equivalent
3. If a lead rubber apron is used, (e.g. in diagnostic X- ray departments) TLD
badge should be worn under the lead apron at the chest level
4. if the doses to the hands and forearms are expected to be significantly
higher than at the chest level, additional wrist badges may be procured
and used.
5. Radiologists doing the special investigations such as cardiac
catheterization, angiography’s may use wrist badge
Where to Wear TLD badge?
28. Don’ts
1. Don’t share your TLD badge with someone else; your badge
is your own
2. Once loaded, don’t open the badge till the end of the
service period.
3. Don’t pierce or open the sealed polythene pouch of the
TLD card
4. Don’t use a damaged or broken cassette/of which filters
have come out. Ask for replacement.
5. Don’t leave the badge in a radiation area, in washing
machines or in the vicinity of hot plates, ovens or furnaces.
6. Don’t wait till the end of the service period; if you suspect a
high radiation exposure report it immediately to your
supervisor who will arrange to send the TLD card for urgent
processing
29. 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.
30. What if overexposure occurs?
1. Dose equivalent recorded by the chest badge exceeding 10 mSv
(1000 mRem) is treated as overexposure and the same is reported
promptly to the institution and the individual concerned.
2. The institution should arrange to investigate the causes of
overexposure and report the findings to Ultratech lab that will be
communicated to the appropriate authorities for overexposure at
BARC.
3. The persons receiving more than 100 mSv will be subjected to
hematological examination including differential blood counts and
chromosome aberration test at Bhabha Atomic Research Centre,
Mumbai
4. After receiving the investigation reports from the institution the
overexposure cases are reviewed by BARC and advice on necessary
follow-up will be intimated to the concerned institution.
