Download - Radiation protection
Radiation Protection(radiation units)
Presenter Dr. SANDIP BARIK Moderator Dr. N K PAINULYMr NAVIN SINGH
Radiation protection
Radiation protection is the protection of the people from harmful effects of ionized radiation which include both particle radiation and high energy electromagnetic radiation.
Sources of Radiation Exposures◦Occupational◦Non-occupational
Naturally occurring sources Radon Sources in the human body Sources in earth’s crust (terrestrial) Cosmic radiation
Manmade sources Medical radiation Building materials Atmospheric testing of
nuclear weapons. Industrial sources
The Biological Effects Of RadiationPrompt personal effects
Delayed personal effects
Racial effects
PROMPT PERSONAL EFFECTS On receiving very large doses
Occurs within few hours or days
Symptoms associated are erythema,vomiting.diarrhoea
A single dose of 500 rad could result in death
DELAYED PERSONAL EFFECTS Chronic low dose irradiation over a considerable period of
time or few exposures giving a high dose
Clinical Features
Scaling ,warty growth on hands Skin cancer Thyroid cancer Cataract formation Bone marrow compromise leading to fatal anaemia and
leukaemia Premature ageing Growth and development of fetus and young children
RACIAL EFFECTS Effect is produced in the long run and may be far
more important than any purely personal injury
Occurs mainly due to changes produced by radiation in hereditary materials
The harmful effects of radiation are classified into stochastic effects and non stochastic effects
Health risk Estimated Loss of Life Expectancy
Smoking 20 cigarettes a day 6 years
Overweight by 15% 2 years
Alcohol consumption (U.S. Average) 1 years
Agricultural accidents 320 days
Construction accidents 227 days
Auto accidents 207 days
Home accidents 74 days
Occupational Radiation dose (1 rem/yr), from age 18 – 65 (47 rem total)
51 days
All natural hazards (hurricane, earthquake, flood)
7 days
Medical radiation 6 days
Stochastic effect Non stochastic effect
Is one in which the probability of occurrence increases with increasing absorbed dose.
The severity in affected indivisuals dose not depend on magnitude of absorbed dose
Have no threshold levels of radiation dose,all or none phenomenon.
Is one in which severity increases with increase in absorbed dose in affected indivisuals
Have definite threshold levels of radiation dose
PERMISSIBLE DOSES
Regulating Bodies
One of the first bodies involved in regulating radiation hazards is the ICRP (international commission on radiation protection)
In U.S the regulatory board is the NCRP(National council on radiation protection and measurements)
In India the board is the AERB(Atomic energy regulatory board)
Constituted in Nov 15,1983. Headquarters in Mumbai.
Permissible doses cont…
ICRP has recommended a series of maximum permissible dose(MPD) for different body tissues.
The quoted values are maximum and every effort should be made to keep the doses to absolute minimum.
The dose for general public are set at1/10 th of maximum possible dose for corresponding tissues
ICRU has also recommended maximum values for amounts of different radioisotopes which can be deposited in the body without constituting radiation hazards
M.P.D. FOR SOME IMP. RADIOISOTPOES
RADIOACTIVE ISOTOPE M.P.D. IN µCi
TRITRIUM 1000
CARBON- 14 300
P -32 6
Fe -59 20
Iodine-131 0.7
Ra-226 0.1
Californium-252 0.01
Radiation units
The quantity used are:
Activity
Exposure
Absorbed dose
Equivalent dose1) a
;
Activity
Amount of radioactivity material expressed as the nuclear transformation rate
Conventional unit: curie
SI unit:Bequerel
1 curie=3.7* 1010 Bq
Exposure
Amount of ionization per mass of air due to x and gamma rays
The ICRU defines exposure (x) as quotient of dQ by dm where dQ is the absolute value of total charge of ions of one sign produced in air when all the electrons liberated by photons in air of mass dm are completely stopped in air..
X=dQ/dm
Conventional units: Roentgen®
SI unit:c/kg
1R=2.58*10-4 c/kg
ROENTGEN
Roentgen was defined as 1R=1 electrostatic unit(esu)/cm3 air at standard temp and pressure(STP)
Current definition is 1R=2.58 *10-4 C/kg air is equivalent to original if charge is expressed in Coulombs(1 esu=3.333*10-10 C) and the volume of air is changed to mass
Absorbed dose
Amount of kinetic energy imparted by radiation per unit mass.
Conventional unit: radiation absorbed dose(rad)
SI unit :Gray(Gy)
100 rad=1 Gy
Dose Equivalent
Biologic effects of radiation depend not only on dose but also on the type of radiation.
The dosimetric quantity relevant to radiation protection is dose equivalent.
A measure of radiation specific biological damage in man.
H=D*Q(D is absorbed dose)(Q is quality factor for radiation )
Dose equivalent
RADIATION Q.F.
X-rays & gamma rays 1.0
Electron (incld. β-rays) of energy >30kv
1.0
Thermal ( slow) neutron 5
Fast neutrons 20
Conventional unit :Roentgen equivalent in man(rem)SI unit is Sivert1rem=10 Sivert
Effective dose equivalent
Whole body exposures are rarely uniform.
Tissues vary in sensitivity to radiation induced effects
Effective dose is a measure of radiation and organ system specific damage in man
The effective dose equivalent H E=Sum of WT*HT
Wt=weighing factor of tissue t
Ht= mean dose equivalent received by the tissue t
Effective dose equivalent limits NRCP recommendation on exposure limits of radiation
workers are based on following criteria.
a) At low radiation levels the nonstochastic effects are esentially avoided.
b) The predicted risk factor for stochastic effects should not be greater than the average risk of accidental death among workers in safe industries.
c) Safe industries are defined as those having an associated annual fatality accident rate of 1 or less per 10,000 workers.
d) The ALARA principle should be followed for which the risks are kept as low as reasonable achievable.
ALARA concept
◦ ALARA stands for As Low As Reasonably Achievable.
◦ Because some risk, however small, exists from any radiation dose, all doses should be kept ALARA.
◦ Includes reducing both internal and external radiation dose.
◦ ALARA is the responsibility of all employees.
Dose limits for pregnant women
The total dose equivalent limited to fetus is 5 mSv(0.5 rem)
Exposure not exceeding 0.5mSv(0.05 rem) in any 1 mths
If the dose equivalent to the embryo/fetus is determined to have already exceeded 500 mrem when a worker notifies her employer of her pregnancy, the worker shall not be assigned to tasks where additional occupational radiation exposure is likely during the remainder of the pregnancy.
Conclusion The dosimetric quantity relevant to radiation protection
is the dose equivalent.
Harmful effects of ionizing radiation are classified as stochastic and non stochastic.
Effective dose equivalent limits for occupational and general population has been recommended by the regulatory board of that country
The values quoted for radiation workers are such that the hazards that the doses represent to health is small compared with ordinary hazards of life
A radiation worker is far more likely to be involved in a motor car accident an to suffer from ill effects of radiation,even if receiving the MPD.
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