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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