Radiation Protection(radiationunits) Presenter Dr. SANDIP BARIK Moderator Dr. N K PAINULY Mr 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 OfRadiation Prompt 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 ExpectancySmoking 20 cigarettes a day 6 yearsOverweight by 15% 2 yearsAlcohol consumption (U.S. Average) 1 yearsAgricultural accidents 320 daysConstruction accidents 227 daysAuto accidents 207 daysHome accidents 74 daysOccupational Radiation dose (1 rem/yr), from 51 daysage 18 – 65 (47 rem total)All natural hazards (hurricane, earthquake, 7 daysflood)Medical radiation 6 days
Stochastic effect Non stochastic effect Is one in which the probability Is one in which severity of occurrence increases with increases with increase in increasing absorbed dose. absorbed dose in affected indivisuals The severity in affected indivisuals dose not depend Have definite threshold levels on magnitude of absorbed of radiation dose dose Have no threshold levels of radiation dose,all or none phenomenon.
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. RADIOISOTPOESRADIOACTIVE ISOTOPE M.P.D. IN µCiTRITRIUM 1000CARBON- 14 300P -32 6Fe -59 20Iodine-131 0.7Ra-226 0.1Californium-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 Conventional unit :Roentgen equivalent in man(rem) SI unit is Sivert 1rem=10 SivertRADIATION Q.F.X-rays & gamma rays 1.0Electron (incld. β-rays) of energy 1.0>30kvThermal ( slow) neutron 5Fast neutrons 20
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.