Sources of Radiation in the Environment

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