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
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
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
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
Nuclear testing

• since 1945 but predominantly 1954-8 and 1961-2
• gt1000 documented tests

Atmospheric and (latterly) underground testing.
Moratorium but testing still continues
8
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 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