Sources of Radiation in the Environment

Ground Zero (New Mexico)

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: http://www.icrp.org/

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. 14N + 1n 15N 14C + 1p

14N + 1n 12C + 3H

3H2O

global hydro-geological cycle

14C 14CO2

global geochemical cycle

National Radiological Protection Board (NRPB) estimate effective dose fromcosmic radiation at about 300 Sv.y-1

Natural Sources:(b) Terrestrial radiation

Earth originated from stellar material crust contains radioisotopes

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 Daughters220Rn and 222Rn arise from natural decay of 238U and 232Th

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

Natural Sources:(d) Radioactivity in Food and Water

mainly 226Ra (and daughters 222Rn and 218Po) and 40K.

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

[tobacco leaves can absorb Ra decay products cigarettes activity 6-7 mSv.y-1 from this source]

uptake of 40K 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

Medical Applications

• X-rays 20 Sv per chest X-ray• 99mTc bone and brain scans

Need to balance potential benefits from potential hazardse.g. anti-cancer treatments can involve high dose rates of X and radiation in addition to internally administered radio-nuclides, e.g. 131I

Nuclear testing• since 1945 but predominantly 1954-8 and 1961-2• >1000 documented tests

Atmospheric testing: tests in Australia, Pacific, etchigh atmospheric dispersal of subsequent fallout globally

Hiroshima bomb: 14 ktonne 8 x 1024 Bq of activityincluding: 106Ru, 137Cs, 140Ba, 144Ce, 85Kr, 89Sr, 90Sr, 99Tc, andbiologically significant 89,90Sr, 131I, 137Cs

Thermonuclear devices (hydrogen bombs) 3H + fission productsActivity from tests > 1020Bq: 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. 14CNatural background 1 x 1015 Bq.y-1

From testing 5 x 1015 Bq.y-1

Transuranics

238U + 1n 239U 239Np +

239Pu +

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.

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 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)

Production of Fuel

Reactor processes

Fuel ReprocessingSeparation of neutron absorbing fission products from unburnt fuel highly radioactive wastes