Done by: Fatma Al-Gafri
Sr. Medical Physicist
Sultanate of Oman
o Radiation Detection Devices
o Personal Dosimeters
o What is TLDs
o How does it work
o Types of TLDs
o Advantage & Disadvantage
o Alpha (α) and Beta (β) particles.
– Do not travel very far.
o Gamma (γ) and X-ray.
– Travel further than Alpha or Beta.
o Radiation that has enough energy to break chemical bonds is referred
to as “ionizing radiation”.
o Ionizing radiation is potentially damaging to cells/ tissue.
Radiation Detection Devices
o Instruments that can identify the presence of
• In the environment
• On the surface of people (external contamination)
• Inside people (internal contamination)
• Received by people as exposure
o There are many types of radiation detection
• No single device can detect all kinds of radiation.
• No one device is useful in all situations.
Partial contamination Whole body contamination
Digestive system Respiratory system
Types of exposure:
Whole body exposure: Person receives penetrating
radiation, ( no portion of the body is shielded).
Partial body exposure: Shielding of sufficient thickness
blocks a significant portion of the person from receiving
A measure of the amount of ionizations produced in air by photon
What can radiation devices
detect and measure?
o Specific types of radiation:
(e.g., alpha, beta, gamma, neutron).
o Specific levels (ranges) of radiation energy (kV).
o "Counts" per unit time (minute or second)
o Accumulated dose (units of gray or rad)
o Current dose rate (units of gray or rad per unit time)
• What is a personal dosimeter?
– A small radiation monitoring device worn
by persons entering environments that
may contain radiation .
• Who should wear a personal
– Workers in ( emergency / non emergency)
environments that may contain radiation .
– Workers in industrial environments where
radiation is used .
Personal monitoring – Why??
• To ensure dose limits are not exceeded
20 mSv /y for whole body.
• To check that doses are ALARA
• Provides documentation in case of
ionization incident / emergency.
Types of personal monitor
Chest badge for whole body monitoring:
has two discs of lithium fluoride.
Approximately 20mg of lithium fluoride
Where are personal
dosimeters usually worn?
o Flat badges are usually worn
on the torso, at the chest level,
but can be worn on the
o Ring shaped badges can be
worn on the finger.
Thermoluminsecence Dose meter
o The primary form of personal radiation monitoring
o Thermo luminescence is the emission of light by
o TLD measures ionizing radiation exposure by
measuring the amount of visible light emitted from
a crystal in the detector when the crystal is heated.
o The most commonly used TL phosphors are:
o lithium fluoride
o calcium fluoride
o lithium borate
o calcium sulphate.
o They are usually manufactured in the form of chips:
o (3.2 mm square by 0.9 mm thick)
o small rods
o Lithium fluoride exhibits suitable characteristics and
is commonly used in dosimetry .
Why LiF ????
o LiF atomic number 8.1.
o Which is near to the atomic
number of soft tissue (7.4),
than silver (z=47).
o Can store energy during
exposure to ionizing radiation
and subsequently release it as
light when heated.
Used for X-ray + gamma ray and beta radiation.
Measured does to the
o whole body 𝑯 𝒑(10)
o skin 𝑯 𝒑(0.07)
Body TLD comprises :
o TLD Card
o 2 pellets( LiF:Mg,Cu,P).
– Thicker elements: strongly penetrating
– Thinner elements: weakly penetrating
– Covered( front + back) with thin retaining
layer (PTFE) Polytetrafluoroethylene.
o Cards: bar coded
o Wrapper ( Aluminized polyester) :
protect dosimeter from contamination
( chemical+ dirt).
o Holder :
– Thicker filter (PTFE) : cover thick
element 𝐻 𝑝(10)
– Circular open window: covered thin
element 𝐻 𝑝(0.07)
– Rectangular open window: viewing
the wearer information text.
o Printed wearer information
– Serial #
– Worker #
– Change date
• The TLD gives a measurement of dose
absorbed in the TLD in (mGy) with an
accuracy of about 10%.
• However what we need to know is not the
absorbed dose in the badge, but the deep
equivalent dose 𝐻 𝑝(10) in (mSv) in tissue.
How does it work
• TLDs work by storing the energy they receive
from the ionizing radiation
• until they are heated to a high temperature
(around 250°C). ( reader)
• on heating, the absorbed energy is released in
the from of visible light.
• A plot of light intensity emitted against
temperature is know as a glow curve.
How it worksOperate by
E released in the
form of Photon
by heating 250 C
• Heat up the TLD using
nitrogen gas (250 C).
• Detect the resulting light
• Calculate the radiation
• Restores the TLD to the
Thermoluminescence glow peak that
results from heating an irradiated TL
o Incident radiation elevates electrons to trap states.
o when exposed to heat electrons return to ground state
(Releasing light ).
o Light can be measured and used to determine amount of
radiation (Equivalent Dose) .
o Doses usually monitored every month
o Expired TLD’s sent to UK for evaluation
o Records of doses received sent back to Oman
o Should be no greater than 0.5 mSv (Per month).
o Maximum annual dose limit = 20 mSv (WB)
• The detection limit of Dosimeter under laboratory conduction is less
than 10 microSv
• The detector absorb radiation energy in the same way and to the same
extent as human tissue as does the holder material.
• The dosimeter is capable of retaining the stored dose information for
extended periods before assessment with no measurable change in
response over at least 6 month.
• TL glow curves of all dosemeter reading are kept for at least 5 years.
• The dosimeters are designed to measure
doses from x ray , beta and gamma
radiations to the skin of the extremities in
terms of the radiation quantity 𝐻 𝑝 0.07 .
• worn on the fingers or taped to the ankles to
measure the external equivalent dose to the
extremities i.e. hands, forearms, feet and
• Extremity TLDs are designed to measure beta
radiation at a depth equivalent to that of the
sensitive basal layer of the skin (about 0.3
• Small discs of LiF which are sealed in plastic
• The holder shields the TLD from the lower
energy betas (70 keV and less) which can not
penetrate to the basal layer.
When to Wear Extremity TLDs
whenever you handle unshielded beta sources.
when working with the whole body shielded except for the
when handling small non-shielded gamma sources.
for decontamination jobs when beta contamination is
for Iodine source operations.
• The minimum detectable dose for
TLD ring dosimeters :
– [ 30 millirem for x-rays and gamma
– [40 millirem for energetic beta
• Both the body and ring badges do
not detect radiation from beta
emitters with energies less than
• To avoid contaminating your ring
badge when using open sources,
wear your ring under the glove.
Advantage (WB TLD)
o Lithium Fluoride is almost tissue equivalent.
o No darkroom processing / chemicals required to obtain result.
o Small size
o High sensitivity.
– 15% ( low doses)
– 3% (high doses)
o They can be used to measure dose over a long period (months or
even a year) .
o Excellent resistance to environment (i.e. temperature, humidity)
o Can distinguish between types of radiation by using different
Disadvantage ( WB TLD)
• Re-usable: stored signal is cleared .
• The process of reading out eliminates the dose
effect, so it can only be done once.
• Not permanent record.
• Dust on the detector will glow when heated and
will be recorded by the phototube as a false
• The TLDs are sensitive to exposure by ultraviolet
light and therefore must be sealed in a light-tight
The dosimeter is designed to measure doses from
neutrons to the whole body and to the skin in terms
of the radiation quantities Hp(10) and Hp(0.07)
• These are used in rare situations where,
although radon levels are elevated, no cost-
effective remediation measures are available.
• This is usually in underground workplaces.
Guidelines for Use
o Never share your badges or wear another
o Do not intentionally expose badges to radiation.
o No matter how curious you are, do not wear
your badges when you receive a medical x-ray or
other medical radiation treatment. Your badges
are intended to document occupational dose,
not medical dose.
o Store your badges in a safe place, at work rather than
o Be sure to store badges away from sources of radiation.
o If you store your badges clipped to your lab coat, make
sure that your lab coat (or any other lab coat near it) is
o Store your badges away from sources of heat (some
badges such as TLDs show some sensitivity to
environmental factors like heat). For example, badges
left in cars over hot summer weekends may give false