Section
2: Background radiation
Radiation is
Everywhere...
It
is traditional to preface a
discussion of workplace radiation safety with a brief discussion about
the
radiation in our natural background. Retired professor of Zoology, past
chairperson of the Atomic Energy Commission and Governor of Washington
State from
1977-81, Dixy Lee Ray, Ph.D., opens a 1992 essay entitled
“Radiation Around Us”
with this statement, “For
all those who do not like
radioactivity, the Earth is
no place to live.” She goes on to say, “Our bodies
receive the impact of about
15,000 radioactive particles per second – that’s
500 billion per year and 40
trillion in a lifetime.”
However,
the probability that one of those particles will cause cancer or
genetic damage
is one in 50 quadrillion (1/50,000,000,000,000). This gives an
approximate risk
from natural background of 1 in 1,250. Remember, the risk of getting
cancer
from all causes in the United States
is about 1 in 5.
Where
does the natural background radiation come from?
 Of
the average total radiation received by each American every year (360 mrem),
82% comes from Natural Sources. Of these, the largest contribution (55%
or 200 mrem) comes from radon gas, a natural decay product
of
uranium and thorium in the soil. Another 8% (27mrem) come from above,
from cosmic
sources & solar flares, and 8% (28 mrem) come from
the natural radioactive isotopes of uranium, thorium and potassium in
the Earth
below us (terrestrial radiation). Because
our environment is naturally radioactive, our own
bodies are
a source of radiation (11%, or 40 mrem), primarily
because of a long-lived natural radioactive isotope of potassium, K-40
and cosmogenically generated
carbon-14. (We know about C-14 because of
it’s
usefulness in determining the age of organic fossils through carbon
dating.)
Remember these percentages are averages and can vary with location
(altitude,
soil composition), housing construction (radon) and health habits
(smoking).
For
example:
Radiation
levels can
be 2 or 3 times higher in Denver, CO
than they are in Dallas, TX.
The difference (57 to 111 mR) represents a higher dose than what the
NRC
or OSHA
allows the general public to receive from a licensed facility (100
mR/y.)
Click on map to visit the U. S. Geological Survey
 Calculate
your average radiation dose
Man-Made Sources
Part
of our exposure in the U.S.
(18%) comes from man-made sources. Again, these are average numbers,
which can
vary with individual circumstances. The average person
gets 11%
(40 mrem) from
medical X-rays
and 4% (14 mrem) from
diagnostic or therapeutic
nuclear medicine. Consumer products we can
purchase at flea markets (red Fiestaware with uranium glazing) or
even
off the shelf at department stores (lantern
mantles, smoke
detectors) contribute
3%
(11 mrem) to the average exposure. The last 1% (3 mrem) comes from
all
other
sources, including occupational exposures (0.3%), fallout (0.3%)
nuclear energy
(0.1%).
Here's a fact
sheet from the Health Physics Society on
Here's a fact
sheet from the Health Physics Society on
from Energy &
Motion Songs by Tom Glazer & Dottie Evans
These numbers
are not meant
to
alarm or placate you, but to point out that radiation is a fact of
life. The exposure
we receive depends a lot on our lifestyles. The health effects from
radiation
are the same, whether the source is natural or "man-made".
from
the Health Physics Society
|
UW
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