RADIATION hazards n protection

Objectives of radiation protection
• The International commission of Radiation protection (ICRP)
Stated that “the overall objectives of radiation protection is to
provide an appropriate standard of protection for man
without unduly limiting the beneficial practices giving rise to
radiation exposure”.
• NCRP (1993)- “The goal of radiation protection is to prevent
the occurrence of serious radiation induced conditions in
exposed persons & to reduce stochastic effects in exposed
persons to a degree that is acceptable in relation to the
benefits to the individual & society from activities that
generate such exposure”.

RADIATION UNITS
• ROENTGEN– unit of
radiation exposure that
will liberate a charge of
2.58x10-4coulombs/kg
of air.
• Independent of the
area or field size

Absorbed dose
• Deposition of energy in pt by radiation exposure
• Independent of composition of irradiated
material and energy of beam
• RAD: unit of absorbed dose
• GRAY: SI unit of absorbed dose
• Gray defined as the quantity of radiation that
results in an energy deposition of 1 joule per
kilogram.
• 1 GRAY = 100 RAD
• 1RAD = 1 cGY

Dose equivalent
• It is a measure of biological effectiveness of radiation
• REM: unit of absorbed dose equivalent
• SIEVERT : SI unit
• 1 sievert = 100 rems
• Dose equivalent=Absorbed dose x QF.
• REM = RADS X QUALITY FACTOR

Quality factor
• It is the parameter used to describe the quality of beam.
• Gives the amount of energy deposited per unit length travel.
Expressed in KEV per micron.
Type of radiation Q factor
X rays 1
Gamma rays 1
Beta particle 1
Electrons 1
Thermal neutrons 5
Other neutrons 20
Protons 20

EFFECTIVE DOSE EQUIVALENT
• Purpose – to relate exposure to risk
• It is calculated by multiplying the dose equivalent
received by each individual organ or tissue (DT) by an
appropriate tissue weighting factor (WT) and
summing for all the tissues involved.

Absorbed dose
Multiplied by a factor to reflect harm by a specific radiation
Equivalent dose
Multiplied by a factor to reflect sensitivity of a specific tissue
Effective dose, commonly called “dose”
8

Is there
RADIATION
in this room?

Radiation - We live with
Natural Radiation: Cosmic rays, radiation within our
body, in food we eat, water we drink, house we live
in, lawn, building material etc.
Human Body: K-40, Ra-226, Ra-228
e.g. a man with 70 kg wt. 140 gm of K
140 x 0.012%
0.0168 gm of K-40
0.1 Ci of K-40

Radiation - We live with
Gy/yr
New Delhi 700
Bangalore 825
Bombay 424
Kerala 4000
(in narrow coastal strip)

Radiation - We eat with
Food Radioactive levels (Bq/kg)
Daily intake
(g/d)
Ra-226 Th-228 Pb-210 K-40
Rice 150 0.126 0.267 0.133 62.4
Wheat 270 0.296 0.270 0.133 142.2
Pulses 60 0.233 0.093 0.115 397.0
Other
Vegetables
70 0.126 0.167 -- 135.2
Leafy
Vegetables
15 0.267 0.326 -- 89.1
Milk 90 -- -- -- 38.1
Composite
Diet
1370 0.067 0.089 0.063 65.0
Dose equivalent=0.315 mSv/yr
Total dose from Natural sources = 1.0 to 3.0
mSv/yr

SOURCES OF RADIATION
• Natural radiation:
1. External: Cosmic and gamma radiation
2. Internal: radionuclides with in the body
ingested or inhaled
• Medical procedures:
1. Diagnostic
2. Therapeutic
• Nuclear weapons/industry/accidents

Electromagnetic Waves
Low HighENERGY
Radio
waves
Microwaves
Radar
Infrared
Visible
light
Ultra-violet
X-ray
Gamma-ray
Non-ionizing radiation
Ionizing radiation

Primary Types of Ionizing Radiation
• Alpha particles
• Beta particles
• Gamma rays (or
photons)
• X-Rays (or photons)
• Neutrons
Ionizing Radiation
alpha particle
beta particle
Radioactive Atom
X-ray
gamma ray

Direct Ionization Caused By:
• Protons
• Alpha Particles
• Beta Particles
• Positron Particles

Indirect Ionization Caused By:
• Neutrons
• Gamma Rays
• X-Rays

Stages in the
Biological Damage Process
Damage can be broken down
to three distinct time frames:
Physical
Chemical
Biological

Physical Stage - IONIZATION
• Radiation deposits energy
• Excess energy removes an electron from an
atom (ionized)
• Very quick! ~10-12 s

Biological Damage
Chemical Stage
• Ionized water can produce what are called
“free radicals”
• Radicals can be very reactive chemically
• The problem occurs when it reacts with
DNA
• Ionization of DNA directly can also result
in unwanted chemical reactions
• Still very quick! ~10-7 s

Biological Damage
Biological Stage
• Biological change reveals itself when a cell tries to
replicate
• During replication, the cell reads the DNA
• Several things can happen to irradiated cells:
1. Cell Necrosis, Apoptosis
2. DNA damage could lead too:
- death during next division
- prevention of division
- mutation (transformed)
3. No effect(damage repaired by proof reading)

H2O
H2O
+
e-
H
+
H2O2
OH
o
HO2
OH
-
Ho
H2
WATER
Radiation Induced Decomposition of
Water Within a Cell
Incoming
Radiation
Production of free radicals within the cell can result in indirect effects
Most abundant molecule within humans: Water

• Deterministic
(Threshold/non-stochastic)
• Existence of a dose threshold
value (below this dose, the effect
is not observable)
• Severity of the effect increases
with dose
• A large number of cells are
involved
• More prominent in rapidly dividing
cells
Radiation injury from an industrial source
Deterministic effects

Stochastic Effects
• Stochastic(Non-Threshold)
– No threshold
– “All or non law”
–Probability of the effect increases with dose
– Generally occurs with a single cell
– e.g. Cancer, genetic effects

RADIATION EFFECTS
DETERMINISTIC EFFECT
• Mechanism is cell killing
• Has a threshold dose
• Deterministic in nature
• Severity increases with dose
• Occurs only at high doses
• Can be completely avoided
• Causal relationship between
radiation exposure and the effect
• Sure to occur at an adequate
dose
STOCHASTIC EFFECT
Mechanism is cell modification
Has no threshold
Probabilistic in nature
Probability increases with dose
Occurs at even at low doses
Cannot be completely avoided
Causal relationship cannot be
established at low doses
Occurs only among a small
percentage of those exposed

RADIATION EFFECTS
DETERMINISTIC EFFECT
• Radiation Sickness
• Radiation syndromes
– Haematopoietic syndrome
– GI syndrome
– CNS syndrome
• Damage to individual organs
• Death
• Late damage
STOCHASTIC EFFECT
• Chromosomal damage
• Cancer Induction (Several
years after exposure to
radiation)
• Genetic Effects
(Hereditary in future
generations only)
• Somatic Mutations

10-6
10-12
10-9
10-15
10-3
1 second
1 hour
1 day
1 year
100 years
1 ms
100
109
106
103
Energy deposition
Excitation/ionization
Initial particle tracks
Radical formation
PHYSICAL INTERACTIONS
PHYSICO-CHEMICAL INTERACTIONS
BIOLOGICAL RESPONSE
MEDICAL EFFECTS
Diffusion, chemical reactions
Initial DNA damage
DNA breaks / base damage
Repair processes
Damage fixation
Cell killing
Promotion/completion
Teratogenesis
Cancer
Hereditary defects
Proliferation of "damaged" cells
Mutations/transformations/aberrations
TIME(sec)
Timing of
events
leading to
radiation
effects.

CHAIN OF EVENTS FOLLOWING EXPOSURE TO IONIZING
RADIATION
CELL DEATH
DETERMINISTIC EFFECTS
CELLULAR TRANSFORMATION
MAY BE SOME REPAIR
STOCHASTIC EFFECTS
CELLULAR LEVEL
SUBCELLULAR DAMAGE
(MEMBRANES, NUCLEI, CHROMOSOMES)
molecular changes
(DNA,RNA, ENZYMES)
free radicals
(chemical changes)
ionisation
exposure

Radiosensitivity [RS]
• RS = Probability of a cell,
tissue or organ of suffering an
effect per unit of dose.

RS laws (Law of Bergonie & Tribondeau)
Radiosensitivity of living tissues varies with
maturation & metabolism;
1. Stem cells are radiosensitive. More mature cells
are more resistant
2. Younger tissues are more radiosensitive
3. Tissues with high metabolic activity are highly
radiosensitive
4. High proliferation and growth rate, high
radiosensitivty

Radiosensitivity
Muscle
Bones
Nervous
system
Skin
Mesoderm
organs (liver,
heart, lungs…)
Bone Marrow
Spleen
Thymus
Lymphatic
nodes
Gonads
Eye lens
Lymphocytes
(exception to the RS laws)
Low RSMedium RSHigh RS

PRINCIPLES
OF
RADIATION
PROTECTION

PRINCIPLES OF RADIATION PROTECTION
1. Justification of practices
2. Optimization of protection by
keeping exposure as low as
reasonably achievable
3. Dose limitation

Justification of procedure
versus the net benefit
i.e. no practice involving exposures to radiation
should be adopted unless it provides sufficient
benefit to offset the detrimental effects of
radiation.

Optimization of protection
Protection should be optimized in relation to
the magnitude of doses,
number of people exposed
for all social and economic strata of patients.

• Optimization of protection can be achieved by
optimizing the procedure to administer a radiation
dose which is
as low as reasonably achievable,
so as to derive maximum diagnostic information with
minimum discomfort to the patient

All doses should be kept
• As
• Low
• As
• Reasonably
• Achievable

X-ray tube
Primary beam
Scattered radiation
Patient

Radiation emitted by the X Ray tube
• Primary radiation: photons before interacting;
• Scattered radiation: after at least one interaction;
• Leakage radiation: not absorbed by the X Ray tube
housing shielding
• Transmitted radiation: emerging after passage
through matter

X-ray Tube Position
• Position the X-ray tube
under the patient not above
the patient.
• The largest amount of
scatter radiation is
produced where the x-ray
beam enters the patient.
• By positioning the x-ray
tube below the patient, you
decrease the amount of
scatter radiation that
reaches your upper body.
X-ray Tube
Image Intensifier

• TUBE CURRENT
• TUBE POTENTIAL
• HIGH OR LOW Z TARGET MATERIAL
• FILTRATION
• TYPE OF WAVEFORM
FACTORS AFFECTING X Ray BEAM

Tube current
• Determines the quantity of the photons which
also contribute to the patient dose.
• Increased exposure time also contributes to
an increased patient dose.

X Ray spectrum: tube current
Change of QUANTITY
NO change of quality
Effective kV not changed

X Ray spectrum: tube potential
Change in QUANTITY
&
Change in QUALITY
- spectrum shifts to higher
Energy
- characteristic lines appear

• use of high KV technique and low mAs (using the
shortest exposure time)
• The high KV beam has higher energy photons,
which undergo a lesser degree of beam attenuation
and greater penetration of the beam through the
patient.
• Therefore the tissue deposition of photons is
reduced, which reduces the radiation dose to the
patient

A. At high KVp, majority of the photons are of high energy;
therefore minimum number of photons are deposited in the patient
(dark area).
B. At low KVp, a large number of photons are of low energy;
therefore larger number are deposited in the patient (dark area).

X Ray spectrum: Target Z
Higher Z
Lower Z
X Ray Energy (keV)
Number of X
Rays per unit
Energy

Tube filtration
• Inherent filtration (always present)
– reduced entrance (skin) dose to the patient (cut off the
low energy X Rays which do not contribute to the
image)
• Additional filtration (removable filter)
– further reduction of patient skin and superficial tissue
dose without loss of image quality
• Total filtration (inherent + added)
• Total filtration must be > 2.5 mm Al for a > 110 kV
generator

Filtration
Change in QUANTITY
&
Change in QUALITY
spectrum shifts to higher energy
1- Spectrum out of anode
2- After window tube housing
(INHERENT filtration)
3- After ADDITIONAL filtration

Collimation
Collimate tightly to the
area of interest.
Reduces the patient’s
total entrance skin
exposure.
Improves image
contrast.
Scatter radiation to
the operator will also
decrease.

• Antiscatter grids
Antiscatter grids reduce scattered radiation reaching
the film thus improving the quality of the resulting
the radiograph and reducing chances of repeat
exposures.
Source of -rays
LeadScattered X Rays
Useful X Rays
Film and cassette
Patient

Patient Protection
• Correct filtration
– 0.5 mm Al equivalent (inherent)
– Added filtration is good
– Minimum total filtration (inherent + added) must
be 2.5 mm Al equivalent
– Accurate collimation
• Minimum repeats

• Good technique to avoid re-takes:
– use of correct film for the view intended
– use of appropriate film holder
– correct film placement within film holder
– correct placement (angulation) of film holder
– correct tube angulation
– correct exposure time

AMOUNT & TYPE OF RADIATION EXPOSURE
– TIME
– DISTANCE
– SHIELDING

Time
• The exposure time is related to radiation exposure
and exposure rate (exposure per unit time) as
follows :
• Exposure time = Exposure
Exposure rate
Or
Exposure = Exposure rate x Time
The algebraic expressions simply imply that if the
exposure time is kept short, then the resulting dose
to the individual is small

TIME
- Take foot off fluoro pedal if physician is not viewing the TV monitor
- Use last image hold (freeze frame)
- Five-minute timer
- Use pulsed fluoro instead of continuous fluoro
- Low-Dose mode: 40% dose of Normal fluoro
- Pulsed Low-Dose provides further reduction with respect to Normal Dose
continuous mode:

• Distance
• The second radiation protection action relates to
the distance between the source of radiation and
the exposed individual.
• The exposure to the individual decreases inversely
as the square of the distance. This is known as the
inverse square law, which is stated mathematically
as :
1
I ~ ———
d2

Inverse-square law states that the
intensity (quantity) of X-ray is inversely
proportional to the square of the
distance from the source of radiation
69

Equipment to Control Distance
• In case of X-ray equipment operating up to
125 kVp, the control panel can be located in
the X-ray room.
AERB recommends that the distance between
control panel and X-ray unit/chest stand
should not be less than 3 m for general
purpose fixed x-ray equipment.

• In mobile radiography,
where there is no fixed protective control booth, the
technologist should remain at least 2 m from the
patient, the x-ray tube, and the primary beam
during the exposure.

Shielding
• Shielding implies that
certain materials
(concrete, lead) will
attenuate radiation
(reduce its intensity)
when they are placed
between the source of
radiation and the
exposed individual.

• Lead is used as a radiation shielding material as it has
a high atomic number (i.e. 82)
• Atomic number of an element is the number of
protons in the nucleus (which is equal to the number of electrons
around the nucleus)
• For the photoelectric process, the mass absorption
coefficient increases with the cube of the atomic
number (z3)

• It is known that
• 0.25 mm lead thickness attenuates 66% of the
beam at 75kVp
• and 1mm attenuates 99% of the beam at same kVp.
• It is recommended that for general purpose
radiography the minimum thickness of lead
equivalent in the protective apparel should be
0.5mm.

- Lead aprons: cut exposure by factor of 20
distant scatter: 0.25 mm Pb eq
direct involvement:0.5 mm Pb
Alpha




Beta
Gamma and X-rays
Neutron
Paper Plastic Lead Concrete


n

 g

Four aspects of shielding in diagnostic radiology
1. X-ray tube shielding
2. Room shielding
(a) X-ray equipment room shielding
(b) Patient waiting room shielding.
3. Personnel shielding
4. Patient shielding (of organs not under
investigation)

1) X-ray tube shielding (Source Shielding)
• The x-ray tube housing is lined with thin sheets of
lead because x-rays produced in the tube are
scattered in all directions.
• This shielding is intended to protect both patients
and personnel from leakage radiation.
• Leakage radiation is that created at the X-ray tube
anode but not emitted through the x-ray tube
portal.
• Rather, leakage radiation is transmitted through
tube housing.

• According to AERB recommendations
manufacturers of x-ray devices are required to
shield the tube housing so as to limit the leakage
radiation exposure rate to
0.1 R/ hr at a distance of 1 meter
from the tube anode.

2) Room shielding (Structural Shielding)
The lead lined walls of Radiology department are
referred to as protective barriers because they are
designed to protect individuals located outside the
X-ray rooms from unwanted radiation.

• There are two types of protective barriers.
(a) Primary Barrier:
is one which is directly struck by the primary or the
useful beam.
(b) Secondary Barrier:
is one which is exposed to secondary radiation
either by leakage from X-ray tube or by scattered
radiation from the patient.

The shielding of X-ray room is influenced by the nature
of occupancy of the adjoining area. In this respect two
types of areas have been identified.
Control Area:
• Is defined as the area routinely
occupied by radiation workers
who are exposed to an
occupational dose.
• For control area, the shielding
should be such that it reduces
exposure in that area to
<26mSv/kg/week
Uncontrolled areas:
• Are those areas which are
not occupied by
occupational workers.
• For these areas, the
shielding should reduce the
exposure rate to
<2.6mSv/kg/week

• AERB has laid down GUIDELINES for shielding of
X-ray examination room and patient’s waiting room
which are as follows.
• The room housing an X-ray unit is not less than
18m2 for general purpose radiography and
conventional fluoroscopy equipment.

• Unshielded openings in an X-ray room for
ventilation or natural light, are located above a
height of 2 m.
• Rooms housing fluoroscopy equipment are so
designed that adequate darkness can be achieved
conveniently, when desired, in the room.

Rooms housing diagnostic X-ray units and related
equipment are located as far away as feasible from
• areas of high occupancy and general traffic,
• maternity and paediatric wards
• and other departments of the hospital that are not
directly related to radiation and its use.

• Shielding of the Xray control room :
• The control room of an X-ray equipment is a
secondary protective barrier which has two
important aspects:
• (a) The walls and viewing window of the control
booth, which should have lead equivalents of
1.5mm.
(b) The location of control booth, which should not
be located where the primary beam falls directly,
and the radiation should be scattered twice before
entering the booth

Operator `
Lead barrier
Using a lead barrier allows less than
2 M distance
X- ray
Patient
Danger

• Patient waiting area
• Patient waiting areas are provided outside the X-ray
room.
• A suitable warning signal such as red light and a
warning placard is provided at a conspicuous place
outside the X-ray room and kept ‘ON’ when the unit
is in use to warn persons not connected with the
particular examination from entering the room

• 3) Personnel shielding
• Shielding of occupational workers can be achieved
by following methods:
• Personnel should remain in the radiation
environment only when necessary (step behind the
control booth, or leave the room when practical)

• Lead aprons are shielding apparel recommended
for use by radiation workers. These are classified as
a secondary barrier to the effects of ionizing
radiation.

• These aprons protect an individual only from
secondary (scattered) radiation, not the
primary beam .
• The thickness of lead in the protective apparel
determines the protection it provides.

Care of the lead apparel:
• It is imperative that lead aprons are not abused,
such as by
– dropping them on the floor,
– piling them in a heap
– improperly draping them over the back of a chair.
• Because all of these actions can cause internal
fracturing of the lead, they may compromise the
apron’s protective ability.

• When not in use,
– all protective apparel should be hung on properly
designed racks.
• Protective apparel also should be radiographed for
defects such as internal cracks and tears at least
once a year

• Other protective apparel include eye glasses
with side shields, thyroid shields and hand
gloves.
• The minimum protective lead equivalents in
hand gloves and thyroid shields should be
0.5mm.

• 4)Patient shielding
• Most radiology departments shield the worker and
the attendant, paying little attention to the
radiation protection of the patient.
• It has been recommended that the thyroid, breast
and gonads be shielded, to protect these organs
especially in children and young adults

Rooms
Notification of hazard presence
Signs, Posting, Warning signs
Only authorized users may
have access to x-ray devices
Energized equipment must be
attended at all times
Lock lab door when
equipment not attended

Posting, Warning sign
Door sign
Warning sign

Exposure to X-ray radiation is reduced if:
TIME exposed to source is decreased
DISTANCE from source is increased
SHIELDING from source is increased
To sum up……

• It has been estimated that although CT accounts for
less than 50% of all x-ray examinations it
contributes upto 40% of the collective dose from
diagnostic radiology .
• CT Scanners have scattered radiation levels that
may prove hazardous.
• The dose unit used in CT is the
computed tomography dose index “CTDI”.

• This measurement is defined in relation to the
radiation field delivered at a specific point (x, y) by
the CT Scanner.
• CTDI is usually expressed in terms of absorbed dose
to air and is called CTDI air.
• Absorbed dose to tissue (Dtissue) is related to
absorbed dose to air (Dair) by a mathematical
coefficient which has a value of about 1.06

RADIATION PROTECTION
IN CT SUITE

It was concluded that
• adequate shielding should be provided for the floor
and roof areas of a CT suite depending on which
floor the CT is located.
• It was proposed an additional thickness of 2.5mm
of lead or 162mm of concrete to shield the front
and rear reference points, so as to reduce the dose
to 1 mGy/year

• The highly collimated X-ray beam in CT results in
markedly non uniform distribution of absorbed
dose perpendicular to the tomographic plane
during the CT exposure.
• Therefore the size of the CT room housing the
gantry of the CT unit as recommended by AERB
should not be less than 25m2

• The greatest risk to the fetus of chromosomal
abnormalities and subsequent mental retardation is
between 8 and 15 weeks of pregnancy and
examinations involving radiation to the fetus should
be avoided during this period.
• For examinations which may involve rather heavy
doses of radiation such as Barium enemas, pelvic or
abdominal CT, the examination should be carried
out during the first 10 days of the menstrual cycle
to avoid irradiating any possible pregnancy

Radiation detection
and measurement

• The instruments used to detect radiation are
referred to as
radiation detection devices.
• Instruments used to measure radiation are called
radiation dosimeters

Devices monitor and record
ionizing radiation doses
(occupational exposure)
Must distinguish from
background radiation
DOSIMETRY

• Personnel Dosimetry
Personnel dosimetry refers to the monitoring of
individuals who are exposed to radiation during the
course of their work.
Personnel dosimetry policies need to be in place for
all occupationally exposed individuals.
The data from the dosimeter are reliable only when
the dosimeters are properly worn, receive proper
care, and are returned on time.

The radiation measurement is a time-integrated
dose, i.e., the dose summed over a period of time,
usually about 3 months.
The dose is subsequently stated as an estimate of
the effective dose equivalent to the whole body in
mSv for the reporting period.
Dosimeters used for personnel monitoring have
dose measurement limit of 0.1 - 0.2 mSv

Proper care includes
• not irradiating the dosimeter except during
occupational exposure
• and ensuring proper environmental conditions
Monitoring is accomplished through the use of
personnel dosimeters such as
• the pocket dosimeter,
• the film badge
• the thermoluminescent dosimeter

Pocket Dosimeter
• Outwardly resembles a
fountain pen .
It consists of
• a thimble ionization
chamber with an eyepiece
and a transparent scale,
• a hollow charging rod
• a fixed and a movable fiber.
• electrometer----separate
-----built-in (self
reading type)

The ability of radiation to produce ionization in air is
the basis for radiation detection by the ionization
chamber.
It consists of an electrode positioned in the middle
of a cylinder that contains gas.
When x-rays enter the chamber, they ionize the gas
to form negative ions (electrons) and positive ions
(positrons).

The electrons are collected by the positively charged
rod, while the positive ions are attracted to the
negatively charged wall of the cylinder.
The resulting small current from the chamber is
subsequently amplified and measured.
The strength of the current is proportional to the
radiation intensity.

• Is sensitive for exposures upto 0.2 R
• Disadvantages------
– Easily damaged
– Unreliable in inexperienced hands
– Does not provide a permanent record

Film badge Monitoring
detects beta, gamma, X Ray

Film Badge Monitoring
• These badges use small x-ray films sandwiched
between several filters to help detect radiation.
• The photographic effect, which refers to the
ability of radiation to blacken photographic films,
is the basis of detectors that use film.

Wearing the badge
-wear the badge on the collar region, because the collar region
including head, neck, and lens of the eyes are unprotected.
Wearing period-
• Each member of staff wears film badge for a period of 4
weeks.
• At the end of period the film inside is changed.
• The exposed film is sent to BARC.
• Useful for detecting radiation at or above 0.1 msv (10 mrem)

Advantages
– inexpensive,
– easy to use,
– permanent record of exposure,
– wide range of sensitivity ( 0.2 – 2000 msv),
– identifies type and energy of exposure,

disadvantages
• they are not sensitive enough to capture very low
levels of radiation( < 0.15 msv),
• Their susceptibility to fogging caused by high
temperatures , humidity and light means that they
cannot and should not be worn for longer than a 4-
week period at a stretch,
• Enormous task to chemically process a large
number of small films and subsequently compare
each to some standard test film.

Thermo luminescent dosimetry (TLD)
Monitoring
• The limitations of the film badge are overcome by
the thermo luminescent dosimeter (TLD).
• Thermo luminescence is the property of certain
materials to emit light when they are stimulated
by heat.
• Materials such as lithium fluoride (LiF), lithium
borate (Li2B4O7), calcium fluoride (CaF2), and
calcium sulfate (CaSO4) have been used to make
TLDs

• When an LiF crystal is exposed to radiation, a few
electrons become trapped in higher energy levels.
For these electrons to return to their normal energy
levels, the LiF crystal must be heated.
As the electrons return to their stable state, light is
emitted because of the energy difference between
two orbital levels.
The amount of light emitted is measured (by a
photomultiplier tube) and it is proportional to the
radiation dose.

• The measurement of radiation from a TLD is a two-
step procedure.
• In step 1, the TLD is exposed to the radiation.
• In step 2, the LiF crystal is placed in a TLD analyzer,
where it is exposed to heat.

• As the crystal is exposed to increasing
temperatures, light is emitted.
• When the intensity of light is plotted as a function
of the temperature, a glow curve results.
• The glow curve can be used to find out how much
radiation energy is received by the crystal because
the highest peak and the area under the curve are
proportional to the energy of the radiation.

Advantages
• The TLD can measure exposures to individuals as low as 5 mR can
withstand a certain degree of heat, humidity, and pressure
• Their crystals are reusable
• Is very compact ( suitable even for finger dosimetry)
• And instantaneous readings are possible if the department has a TLD
analyzer.
• Response to radiation is proportional upto 400 R
Disadvantages
• Very expensive
• No permanent record ( other than glow curves)
• Cannot distinguish radioactive contamination.
The greatest disadvantage of a TLD is its cost

Storing TLD Badges
• Badge must not be left in an area
where it could receive a radiation
exposure when not worn by the
individual (e.g. On a lab coat or
left near a radiation source)
• Store badges in a dark area with
low radiation background (in low
light away from fluorescent or uv
lights, heat and sunlight)
• Lost or damaged badges should
be reported immediately to the
radiation safety officer and a
replacement badge will be issued

• There are various Regulatory Bodies at the
international and National level, which lay down
norms for radiation protection.
• These are
• the International Commission for Radiation
Protection ( ICRP),
• the National Commission for Radiation Protection
(NCRP ) in America,
• and the Atomic Energy Regulatory Board (AERB) in
India.

We live with
1-3 mSv
Can kill
4000 mSv
Radiation
Where to stop, where is the safe point?

RADIATION hazards n protection

RADIATION hazards n protection

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RADIATION hazards n protection