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

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Presentation on theme: "Sources of Radiation in the Environment Ground Zero (New Mexico)"— Presentation transcript:

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

2 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. Working Framework ICRP Website:

3 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 Interaction with stable molecules production of radionuclides e.g. 14 N + 1 n 15 N 14 C + 1 p 14 N + 1 n 12 C + 3 H 3H2O3H2O global hydro-geological cycle 14 C 14 CO 2 global geochemical cycle National Radiological Protection Board (NRPB) estimate effective dose from cosmic radiation at about 300 Sv.y -1

4 Natural Sources: (b) Terrestrial radiation Earth originated from stellar material crust contains radioisotopes 40 K 3 -1 232 Th10-15 -1 234 U + 235 U + 238 U 3-4 -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 220 Rn and 222 Rn arise from natural decay of 238 U and 232 Th Gaseous radioisotopes percolate through soil and are trapped in modern buildings adsorption on dust particles lung tissue potential for short-range and irradiation NRPB estimates around 800 Sv.y -1 from this source

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

6 Medical Applications X-rays20 Sv per chest X-ray 99m Tcbone 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. 131 I

7 Nuclear testing since 1945 but predominantly 1954-8 and 1961-2 >1000 documented tests Atmospheric testing:tests in Australia, Pacific, etc high atmospheric dispersal of subsequent fallout globally Hiroshima bomb: 14 ktonne 8 x 10 24 Bq of activity including: 106 Ru, 137 Cs, 140 Ba, 144 Ce, 85 Kr, 89 Sr, 90 Sr, 99 Tc, and biologically significant 89,90 Sr, 131 I, 137 Cs Thermonuclear devices (hydrogen bombs) 3 H + fission products Activity from tests > 10 20 Bq: 2x10 -5 Gy (northern hemisphere) 2x10 -6 Gy (southern hemisphere) Atmospheric and (latterly) underground testing. Moratorium but testing still continues Activation of surrounding materials other nuclides, e.g. 14 C Natural background 1 x 10 15 Bq.y -1 From testing5 x 10 15 Bq.y -1

8 Transuranics 238 U + 1 n 239 U 239 Np + 239 Pu + Most significant: 239 Pu (t ½ = 24,360y) Estimated 239 Pu activity of 1.5x10 16 Bq: 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 1960s.

9 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 PWR with 100 tonnes of 3.5% enriched 235 U fuel contains 0.25 TBq of 235 Uand 1.1 TBq of 238 U unless an accident occurs, no fuel release expected gaseous products, 85 Kr (t ½ 10.8y) leakage to atmosphere activation products, 3 H fuel storage (cooling) water contamination (<350 Sv.y -1 ) Production of Fuel Reactor processes Fuel Reprocessing Separation of neutron absorbing fission products from unburnt fuel highly radioactive wastes

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