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Sources of Radiation in the Environment

Explore different natural and man-made sources of radiation in the environment and understand the guidelines for limiting effective dose equivalents. Learn about cosmic radiation, radon, radioactivity in food, medical applications, nuclear testing, and nuclear reactor operations.

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Sources of Radiation in the Environment

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  1. Sources of Radiation in the Environment Ground Zero (New Mexico)

  2. Working Framework ICRP Guidelines: ‘the effective dose equivalent from all sources, excluding background radiation and medical procedures, to representative members of a critical group, should not exceed 1 mSv in any one year; effective dose equivalents of up to 5 mSv are permissible in some years provided that the total does not exceed 70 mSv over a lifetime’. ICRP Website: http://www.icrp.org/

  3. Interaction with stable molecules production of radionuclides e.g. 14N + 1n 15N 14C + 1p 14N + 1n 12C + 3H 3H2O global hydro-geological cycle 14C 14CO2 global geochemical cycle Natural Sources: (a) Cosmic radiation (high energy protons and  particles from the sun and other stars) • Direct interaction - dose received depends on altitude and latitude National Radiological Protection Board (NRPB) estimate effective dose from cosmic radiation at about 300 Sv.y-1

  4. Earth originated from stellar material crust contains radioisotopes Gaseous radioisotopes percolate through soil and are trapped in modern buildings adsorption on dust particles lung tissue potential for short-range  and  irradiation Natural Sources: (b) Terrestrial  radiation 40K 3 mg.kg-1 232Th 10-15 mg.kg-1 234U + 235U + 238U 3-4 mg.kg-1 NRBP estimates annual effective  dose equivalents from these sources and their daughters to be around 400 Sv.y-1 . Local variations due to locations and building materials. (c) Radon and its Daughters 220Rn and 222Rn arise from natural decay of 238U and 232Th NRPB estimates around 800 Sv.y-1 from this source

  5. uptake of 40K  activity in plants and animals (0.2% body tissue) (NRPB 170 Sv.y-1 from this source) [tobacco leaves can absorb Ra decay products cigarettes  activity 6-7 mSv.y-1 from this source] Natural Sources: (d) Radioactivity in Food and Water mainly 226Ra (and daughters 222Rn and 218Po) and 40K. NRPB estimate total effective dose to individuals at  200 Sv.y-1 Examples: fish - Ra absorbed in partial replacement of Ca (Pacific salmon) plants - both 210Po and 210Pb enter food from soil and by wet and dry deposition from the atmosphere

  6. Medical Applications • X-rays 20 Sv per chest X-ray • 99mTc bone and brain scans Need to balance potential benefits from potential hazards e.g. anti-cancer treatments can involve high dose rates of X and  radiation in addition to internally administered radio-nuclides, e.g. 131I

  7. Thermonuclear devices (hydrogen bombs) 3H + fission products Activity from tests > 1020Bq: 2x10-5 Gy (northern hemisphere) 2x10-6 Gy (southern hemisphere) Hiroshima bomb: 14 ktonne 8 x 1024 Bq of activity including: 106Ru, 137Cs, 140Ba, 144Ce, 85Kr, 89Sr, 90Sr, 99Tc, and biologically significant 89,90Sr, 131I, 137Cs Atmospheric testing: tests in Australia, Pacific, etc high atmospheric dispersal of subsequent fallout globally Activation of surrounding materials other nuclides, e.g. 14C Natural background 1 x 1015 Bq.y-1 From testing 5 x 1015 Bq.y-1 Nuclear testing • since 1945 but predominantly 1954-8 and 1961-2 • >1000 documented tests Atmospheric and (latterly) underground testing. Moratorium but testing still continues

  8. 238U + 1n 239U 239Np +  239Pu +  Transuranics Most significant: 239Pu (t½ =24,360y) Estimated 239Pu activity of 1.5x1016Bq: NRPB estimate average effective dose today in the UK from weapons testing to be around 10 Sv.y-1. This was around 8 times higher in the 1960’s.

  9. Production of Fuel Reactor processes • PWR with 100 tonnes of 3.5% enriched 235U fuel contains • 0.25 TBq of 235Uand 1.1 TBq of 238U • unless an accident occurs, no fuel release expected • gaseous products, 85Kr (t½ 10.8y) leakage to atmosphere • activation products, 3H • fuel storage (cooling) water contamination (<350 Sv.y-1) Fuel Reprocessing Separation of neutron absorbing fission products from unburnt fuel highly radioactive wastes Nuclear Reactor Operations • mining (exposure to miners and contamination of water courses) • purification, enrichment and fabrication of fuel elements NRPB estimates equivalent doses of 100 Sv.y-1 to populations close to reactors

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