Environmental Engineering Reference
In-Depth Information
Table
.
Typical yearly radiation doses
Source
Radiation dose (mR/year)
Natural radiation
Natural in body
Medical (average)
Nuclear plant (
GW electric)
.
Coal plant (
GW electric)
.
Included in the natural total for a
kg person.
Source: National Council on Radiation Protection Report
(
)
The unit of radiation is called the roentgen
(desig-
nated R and named after Wilhelm Conrad Roentgen,
the discoverer of X-rays). It is used to measure the total
radiation dose received. It is a relatively big unit compared
with natural or medical radiation, and people usually talk
of milli-roentgens (mR), which are one-thousandth of a
roentgen.
Table
gives typical radiation doses from
various sources. Natural and unavoidable radiation does
vary from place to place, and the table gives the average
dose received by a person at sea level in the United States
from all the natural sources mentioned above.
The largest component of natural radioactivity is radon
gas, which comes from the radioactive decay of the uran-
ium and thorium that has always been part of the planet
for the
.
billion years of its existence. It varies in inten-
sity depending on location. The cosmic-ray portion
comes from particles that have been racing through space
.
A more modern unit is called the sievert (S). One S is equal to
R.
You will also see milli-sieverts and milli-R.
mR is equal to
mS.
