Training Course on Radiation Protection for Radiation Workers and RCOs of BAEC, Medical Facilities & Industries 24 - 28 October 2021 Training Institute Atomic Energy Research Establishment, Savar, Dhaka

1. Institute of Nuclear Science and Technology
Atomic Energy Research Establishment, Savar, Dhaka
E-mail: dpaulbaec@yahoo.com
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FUNDAMENTALS OF RADIATION
PROTECTION – EXTERNAL & INTERNAL
Dr. Debasish Paul
Chief Scientific Officer & Director
Training Course on Radiation Protection for Radiation Workers
and RCOs of BAEC, Medical Facilities & Industries
24 - 28 October 2021
Training Institute
Atomic Energy Research Establishment, Savar, Dhaka

2. Objective
 To encourage and enable the
radiation worker to limit his/her
exposure to potentially harmful
radiation.
 To limit unnecessary exposure of
patients and the general public
which results from poor working
habits.
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3. Introduction
Two types of radiation hazard involved in working with
radioactive materials:
external radiation hazard
internal contamination hazard
 Sealed source involves only the external radiation
hazard unless the source is damaged/leaked.
 Unsealed source involves both external and
internal hazard.
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4.  Sealed source – radioactive material that is sealed or
contained in such a way that none can escape under normal
working conditions.
 Calibration sources
 Sources in a solid form
 Radioactive waste drums
 Unsealed source – radioactive material which is not sealed
or contained and may lose some of its contents under
normal working conditions.
 An open vial or beaker containing
radioactive liquid or powder
 An open vial containing a volatile material
Sealed and Unsealed Sources

5. External Radiation Hazards
For example:
 X-ray sets when turned on
 Nuclear reactor
 Particle
accelerator/cyclotron
 Radiopharmaceutical in a
transport package
Hazards caused by radiation sources outside the body.

6. Internal Radiation Hazards
Radioactive material can get into the body
via:
 Inhalation
 Ingestion
 Through a wound
 Absorption through the skin
Hazards caused by radiation sources inside the body.
If radioactive contamination enters the body then it is an
internal radiation hazard.

7. Principles of Radiation Protection
 Justification of the practice: No practice
involving exposure to radiation should be adopted
unless it produces a benefit than the harm it causes
or could cause.
Benefit > Risk
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8. Principles of Radiation Protection (contd..)
 Optimization of protection: Radiation doses and
risks should be kept as low as reasonably achievable
economic and social factors being taken into
account.
The ALARA Principle
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A
L
A
R
A
As
Low
As
Reasonably
Achievable*
*economic and social factors taken into account

9. 9
Occupational Exposure
In any period of 5 years, an
average effective dose of
20 mSv per year
10 Sv per hour [50wks/yr,
40hrs/wk]
and in any 12 month period,
less than 50 mSv
In any period of 5 years, an
average effective dose of
1 mSv per year
0.5 Sv per hour
and in any 12 month
period, less than 5 mSv
Public Exposure
Principles of Radiation Protection (contd..)
Radiation Dose Limits
 Limitation of individual risk: Exposure of
individuals should not exceed specified dose
limits.

10. 10
NUCLEAR SAFETY AND RADIATION CONTROL RULES
SRO. NO. 205-LAW/97
BANGLADESH ATOMIC ENERGY REGULATORY ACT
ACT NO. 19 Of 2012

11. External Hazards
The four ways to reduce the external hazards from
radioactive sources are :
 minimize the activity used
 minimize the handling time
 keep as much distance as reasonably
practicable between people and the source
 if necessary provide adequate shielding
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12. 12
Basic ways for controlling external
radiation hazards.
D  T D  1/r2 D = D0 e-µt

13. Protection by Time
Dose  Time
Dose = Dose-rate x Time
The total dose is a product of the exposure time
and dose rate.
Example-1: In a particular radiation area, dose rate was
measured 10Sv/h. If a worker has to spend that place for
half an hour, how much dose he/she will be received?
Dose = 10 Sv/h x 0.5h = 5 Sv

14. Protection by Distance
Dose-rate  1/(distance)2
dose-rate
distance
Inverse square law : radiation dose rate (D) at a distance (r)
from a point source is inversely proportional to the square
of the distance. i.e.
D1r1
2 = D2r2
2
where D1 is the
dose rate at distance
r1 from the source,
and D2 is the dose
rate at distance r2
from the source.
The inverse square law applies only to a point source.

15. Protection by Distance (contd..)
If you double your
distance you quarter
your dose
1
2
3
4
5
6
7
8
1 1/4 1/16 1/64
1/9 1/25 1/36 1/49
Distance
(m)
Dose Reduction
1000
250
111
62
40
28
20
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Dose
Rate
(μSv/h)

16. Example-1: The dose rate at distance 2 meter
from a particular gamma-ray source is 400
Sv/h. At what distance will it give a dose rate of
25 Sv/h?
D1r1
2 = D2r2
2
400 x 22 = 25 x r2
2
r2
2 = 64, r2 = 8 meter
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17. Protection by Shielding
The thickness of shielding required depends on the type of
radiation, the energy of the radiation and the shielding material.
Shielding is necessary if a combination of low activity,
short handling time and reasonable distance cannot
decrease doses to an acceptable level.
Lead and Concrete
shielding is commonly
used for X and gamma
radiation.

18. Protection by Shielding (Contd...)
incident
radiation
transmitted
radiation
Thickness t
Do Sv/h Dt Sv/h
The dose rate due to X or gamma radiation emerging from a
shield can be written as: Dt = Doe-µt
where Do is the dose rate without shielding, Dt is the dose rate after passing through
a shield of thickness t and µ is the linear absorption coefficient of the material of the
shield. (µ is the ability of the shield material to attenuate photons of particular energy.)

19. Half-Value Layer (HVL)
incident
radiation
transmitted
radiation
HVL
Do Sv/h Dt = Do/2 Sv/h
A half-value layer (HVL) or half-value thickness (HVT), is
defined as the thickness of a material required to reduce the
intensity of a photon beam to half its initial value.
A half-value layer is determined as follows: Dt = Doe-t
or, Dt/Do = e-t or, ½ = e-t
½ or, ln½ = -t½
or, -0.693 = -t½ or, t½ = 0.693/ i.e. HVL = 0.693/

20. Table: Approximate half value thickness of lead for
different gamma ray sources
Gamma source Half thickness lead
(cm)
Gamma energy
(MeV)
Cobalt-60 1.6 1.17, 1.33
Caesium-137 0.9 0.66
Iridium-192 0.25 0.30 – 0.61
Thulium-170 0.1 0.052 – 0.084
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Half-value thickness depends on the energy of the gamma rays and is
greater for high-energy gamma-rays. The half thickness is also
different for different materials.

21. Tenth-Value Layer (TVL)
incident
radiation
transmitted
radiation
TVL
D Sv/h D/10 Sv/h
Tenth-Value Layer (TVL) or Tenth-Value Thickness (TVT) is the
thickness of a material required to reduce the intensity of a
photon beam to one tenth of its initial intensity. TVL = 2.303/

22. Relationships for Calculating Dose
DoseTotal = Dose Rate X Exposure Time ….. (1)
Exposure Time = DoseTotal / (Dose Rate) …… (2)
Dose Rate = DoseTotal / (Exposure Time) ….(3)
Dose Rate = AT/d2 …….. (4), where
A is the activity in Ci
 is the gamma factor ( R/h at 1 meter for 1 curie)
T is the transmission factor for any attenuators
(if shielding needs to be considered),
otherwise T = 1 .
d is the distance from the sources in meters.
Dose rate from a gamma source,D=ME/(6r2) µSv/h …….(5)
where M in MBq, E in MeV and r in meter 22

23. Specific Gamma Factors (  )
It is usually the gamma dose rate measured at one
meter from a source of a standard activity. It can be
stated as :
The Absorbed Dose Rate in (Gy/h) per GBq
measured at 1 meter.
The Equivalent Dose Rate in (Sv/h) per GBq
measured at 1 meter.
The Equivalent Dose Rate in (Rem/h) per
Curie measured at 1 yard.
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24. Value of the Gamma Factor
The value of the gamma factor depends on the
energy of the radiation emitted
Isotope Dose-rate @ 1 m from 1 GBq
Iridium-192 120  Sv/h
Cobalt-60 370.3  Sv/h
Caesium-137 90  Sv/h
Dose - rate  source activity

25.  Example-2: Calculate the dose rate at 5 m distance
in air from a 500 kCi Co-60 irradiator when the rod are
raised to the operating position. For this exercise,
assume a point source.
For Co-60  = 370.3 Sv/h/GBq at 1 m
Converting Ci to Bq : 500 kCi = 500000x3.7x1010 Bq
= 18500000 GBq
Dose rate at 5 m distance = A x  x 1/d2
= 18500000 x 370.3 x 1/ 52
= 2.74 x 108 Sv/h at 5 m.
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26. Internal Radiation Protection
When radioactive material is not contained inside some
form of sealed container it constitute a potential internal
radiation hazard.
Internal radiation exposure occurs when radioactive
materials enters the body by (Routes of Entry) :
(1) direct inhalation of airborne contamination;
(2) ingestion, that is entry through the mouth;
(3) entry through the skin, or through a contaminated
wound;
(4) direct irradiation of the skin.
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27. CANBERRA FASTSCAN WHOLE
BODY COUNTER (MODEL 2250)
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Internal Radiation Protection [contd…..]
Protection may be ensured by minimizing and controlling
contamination, using proper protecting clothing.
 For low levels of surface contamination ordinary laboratory
coat, overshoes and gloves may be sufficient.
 For airborne contamination
it is necessary to have fully
enclosed dry suit and filter
mask or mask fitted with air
supply.
Internal radioactivity measurements
are conducted using a whole
body counter.

28. Internal Radiation Protection [contd…..]
PERSONAL PROTECTIVE EQUIPMENT (PPE)
Lab coats, overshoes, disposable gloves, respiratory
protection

29. 1. Installed Equipment
2. Portable Survey Meters
Dose rate alarm, hand/foot monitor,
stack monitor etc.
Dose rate meter, contamination
monitor, air sampler etc.
Hand-Foot Monitor Survey Meters
Measuring Radiation
Radiation Protection Equipment
Ionising radiation cannot be detected by any of our senses.
Therefore we have instruments designed to detect and measure radiation.

30. Measuring Radiation
Radiation Protection Equipment [contd…]
3. Personal Dosimeter 4. Laboratory Equipment
TLD/Film badge, digital
personal monitor, personal air
sampler etc.
HPGe detector, Whole body counter,
Scintillation counter, Thyroid
counter etc.
TLD
Digital
Personal
Monitor
HPGe
Detector
Whole
Body
Counter

31. Measuring Personal Doses
TLD
(Thermo-Luminescent Dosimeter)
 Measures radiation dose to your body.
 Is read at the end of a 3 month period.
EPD
(Electronic Personal Dosimeter)
• Measures radiation dose and dose rate.
• Your dose can be read from the screen as
you wear it.

32. Wearing Your TLD
 Only wear the badge that has been assigned to
you.
 Always leave your badge on the badge rack in
your building when leaving site.
 Wear it on the chest with the foil circle facing
outwards.
 Your TLD will be collected on a quarterly basis.

33. Area Demarcation
 Routine control of personal dose is based on a system of area
classification. A typical system of classification considers four
types of area:
 Uncontrolled Area – in which the dose rate does not exceed
1 µSv/h. Personnel can work for 40 h/week and 50 weeks/year
without exceeding 2 mSv/year.
i.e. Dose rate ≤1 µSv/h
 Supervised Area – in which the dose rate does not generally
exceed 3 µSv/h and hence, in which personnel will not exceed
three-tenths of the dose limit.
i.e. Dose rate >1 µSv/h and ≤ 3 µSv/h
 Controlled Area – in which dose rate exceeds 3 µSv/h.
i.e. Dose rate >3 µSv/h and ≤ 10 µSv/h
 Restricted Area – in which the dose rate exceeds 10 µSv/h.
i.e. Dose rate >10 µSv/h
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34. THANK YOU
Things to remember
Your safety and the safety of your
fellow workers depends on the
care you take.