Ionizing radiation can cause biological damage through direct or indirect action on cells. The effects of radiation exposure depend on factors like total dose, dose rate, and part of body exposed. There are stochastic effects like cancer which occur randomly with no safe threshold, and deterministic effects like skin burns which have a threshold below which no effect occurs. Early effects appear within days of exposure while late effects can take years. Acute exposure involves a high dose over a short time compared to chronic low dose exposure. The principles of radiation protection are justification, optimization and dose limitation to reduce risk from radiation according to international standards.

1. Training Course on Radiation Protection for Radiation Workers
and RCO’s of BAEC, Medical Facilities & Industries - 2021
Biological Effects of Ionizing
Radiation
Siddha Moutoshi Shome
Principal Geologist
Health Physics and Radioactive Waste Management Unit,
Institute of Nuclear Science and Technology,
AERE, BAEC, Savar, Dhaka.
25/10/2021
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2. Contents
• Introduction
• Human Exposure Pathways
• Biological Effects
 Stochastic Effects
 Deterministic Effect
 Somatic Effect
 Genetic Effects
 Early and Late Effects
• Acute and Chronic Exposures
• Summary of Radiation Effects
• Principles of Radiation Protection
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3. Introduction
Radiation: is an energy in the form of electromagnetic waves or high-
speed particles, traveling in the air.
Radioactivity: spontaneous emission of radiation from the nucleus of
an unstable atom.
Ionizing Radiation: is radiation that has sufficient energy to remove
electrons from atom. Example- Alpha, beta, gamma etc.
Non-ionizing Radiation: refers to any type of electromagnetic
radiation that does not carry enough energy to ionize atoms or
molecules. Example - Radiowaves, Visible light etc.
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4. Cont’d..
 Ionizing radiations have many beneficial applications (Ex-X-
ray), but they also may have detrimental consequences for
human health and for environment.
 Radiation can cause biological damage on cells either direct or
indirect action.
 Direct action: Ex - direct interaction with DNA.
 Indirect action: Radiation can also produce free radicals by
ionizing water molecule of body. These radicals can further
interact with DNA, RNA or protein molecules and can cause
damage of tissues.
 To protect people and the environment it is essential to
understand how radiation-induced effects occur.
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5. α – rays
neutrons
Direct Action of Ionizing Radiation on DNA
(High LET Radiations)
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6. e-
X ray
 ray P+
O
H
H OH-
H+
H・
HO・
Indirect (free radical) Action of Ionizing Radiation
on DNA (Low LET Radiations)
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7. Human Exposure Pathways
There are two main categories of exposure
pathway:
 External exposure pathways (the source
of exposure remains outside the body)
 Internal exposure pathways (the source
of exposure is incorporated into the body).
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8. Biological Effects
Damage of cells:
 Cell death
 Abnormal cell division
 Permanent modification to cells
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9. Factors of Radiation Damage
The potential biological effects and damages caused by
radiation depend on the conditions of the radiation exposure.
 Total dose
A large dose given in a short amount of time: more
damaging than the same dose given over a longer period of
time
 Dose rate
 Part of the body exposed
 Uniformity of exposure
 Age of the victim
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10. Biological Effects of Radiation
Stochastic Effect Deterministic Effect
Somatic Effect Genetic Effect
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12. Stochastic Effects
• Stochastic means random. It occurs in a
statistical manner.
• No threshold dose. It can occur even at low
doses.
• The probability of effect increases with
increasing radiation dose.
• But the severity is not related to radiation dose.
• It can be further classified into somatic and
genetic (hereditary) effect.
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13. Stochastic Effects
• Examples- cancer and genetic effect
Dose equivalent/Sv
Probability
of
Effect
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14. Deterministic Effects
• Deterministic effects have a threshold dose.
• No effect observed below the threshold dose.
But once the threshold exceeded, the severity
of effect increases with increasing dose.
• Examples- cataract, reddening of skin, burns,
hair loss, blood changes, temporary or
permanent sterility, nausea, diarrhoea, etc. All
are somatic effects.
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15. Threshold
Severity
Dose
Deterministic Effects
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16. Cells Organs/tissues
Damages Type Symptoms/signs Mechanisms
DNA
Mutation
Germcell Heredityeffect
Stochastic
effect
Mutationof
singlecell
Somaticcell Cancer
Apoptosis
or
Necrosis
Germcell Infertility
Deterministic
effect
Celldeath
Somaticcell
Loss of function
(Skin injury,
ARS）
Stochastic and Deterministic Effects
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17. Thresholds
Tissue and effect Equivalent dose (Sv)
Testes
Temporary Sterility 0.15
Permanent Sterility > 3.5
Ovaries
Sterility > 2.5
Lens of the eye
Detectable Opacities > 0.5
Visual impairment (cataract) > 2.0
Source: ICRP 6017

18. Cont’d..
Whole body and Effect Dose (Sv)
Clinical blood changes 0.5 Sv
LD 50/60. 50% die in 60 days
Bone marrow depression ~ 3.0 Sv
Death in 48 hours
Central nervous system collapse ~100 Sv
Source: ICRP 60
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19. Classic Example of Stochastic and
Deterministic Effects
 Stochastic effects - smoking & lung cancer.
not everyone who smokes will develop
it, but the risk increases with the
number of cigarettes smoked.
 Deterministic effects - intake of alcohol.
a person must exceed a certain amount of
alcoholic intake before he/she begins to
show the signs of drinking.
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20. Somatic Effects
 Damage of ordinary cells
 Radiation effects that exposed individual
suffers during their lifetime and the effect is
only limited to the exposed person.
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22. Genetic Effects
 Damage of reproductive cells and appear only in the
offspring of the irradiated person.
 Genetic damage is permanent and cannot be repaired.
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23. Early and Late Effects
 Early Effects:
 Response that occurs within minutes or days after
exposure.
Example: Erythema, Radiation sickness (nausea,
vomiting, diarrhea).
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24. Early and Late Effects
 Late Effects:
 Response that occurs in months or years after
exposure.
 May occur in person who have been exposed
to acute exposure.
May also arise from chronic exposure.
Example: cancer, genetic effects, cataracts
and sterility.
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25. Latency Period
 The time that passes between being exposed
to radiation and detection of radiation-induced
effect (ex – cancer).
 Effects can be immediate or years later for
acute, high level exposures.
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26. Acute and Chronic Exposure
 Acute Exposure:
 A large amount of dose in a short period of time.
 Acute absorbed doses above about 1 Gy give rise to nausea
and vomiting, known as radiation sickness and it occurs a
few hours after exposure.
 Similarly, there is no well defined point above which death is
certain, but the chances of surviving an acute dose of about 8
Gy would be very low.
 Chronic Exposure:
 Small amount of doses over a long period of time.
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27. Acute Radiation Syndrome (ARS)
 A combination of clinical syndromes occurring in
stages during a period of minutes / hours to weeks
after exposure, as injury to various tissues and organs
is expressed.
 The acute radiation syndrome is subdivided into three
categories. In order of increasing severity, these are :
(1) Hemopoietic syndrome,
(2) Gastrointestinal syndrome, and
(3) Central nervous system syndrome
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28. Hemopoietic syndrome
 Signs appears after a whole body gamma dose of
2 Gy (200 rads)
 Symptoms start with anorexia, nausea, vomiting and
followed by bone marrow depression and infection.
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29. Gastrointestinal syndrome
 Signs appears following a total body dose of about
10 Gy (1000 rads) or greater.
 Early symptoms are severe nausea, vomiting,
diarrhea and followed by complete destruction of
bone marrow.
 Death within several weeks after exposure
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30. Central nervous system syndrome
 Signs appears after a total-body gamma dose in
excess of about 20 Gy (2000 rads)
 Damages the central nervous system as well as all
the other organ systems in the body;
 Unconsciousness occurs within few minutes.
 Death occurs in hours to several days.
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31. Summary of Radiation Effects
Erythema ARS Hereditary
Effects Cataract Cancer
Sterility
Early Effects Late Effects
Acute Exposure Chronic Exposure
RADIATION EXPOSURE
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32. Principles of Radiation Protection
Justification Optimization Dose limitation
Risk < Benefit
ALARA
(As
Low
As
Reasonably
Achievable)
Parameters Workers
(mSv/y)
Public
(mSv/y)
Effective Dose 20 1
Equivalent Dose
Lens of eye
Skin
Extremities
150
500
500
15
50
50
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33. Thank You
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