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TABLE I
CoMPARISON OF PRINCIPAL DosE RATES From Natural BACKGROUND AND
Worip-WIDE FaLLouT Dose RATES IN MREM/YEAR?
World-wide fallout from nuclear
weaponstests up to 1961
Natural
fraction of
back- dose rate
ground July 1959)
UK only
,
External radiation to whole body:
Cosmic rays
From radioactive substances
annual
dose rate
1954-2000
total dose
dohned
until after
AD
2000 AD
30
50
_
4.2
_
0.65
_
3%
15-20
1.2
—_
—
0.2
1.5
—
0.16-0.26
0.24-0.42
_
90%
Nil
Internal sources:
To whole body (rangefor different tissues):
Potassium 40
Carbon 14
Caesium 137
To new bone:
Uranium & thorium series
Strontium 90
To bone marrow (blood forming
organs):
Uranium & thorium series
Strontium 90
—
13
8.1
—
1.6
—
—_
5
—
—_
2.7
—_
0.81
—_
9%
120-130
6-14
1.3
—
9%
Total dose (range for different
tissues)
Notes: Column 1: world average from UN Report (2), p. 21.
Column 2: based on Loutit e ai. (4).
Columns 3 & 4: world average based on UN Report (2), p. 27.
Fallout from nuclear weapons is, however, not the only source of environmental contamination; releases from nuclear reactors may also occur.
In the normal operation of such establishments, iodine 131 is likely to be
the most significant component released into the atmosphere. Dilute radioactive effluent containing both fission products and induced radioactive subStances is usually discharged, but at controlled levels which make it an insignificant source of exposure to the population. Accidents at nuclear re-
actors may give rise to considerably higher levels of local contamination.
Both past experience and theoretical studies indicate that internal and not
external radiation will be the main risk to the population; iodine 131 is