irradiated by internal sources;
that 1s, by radionuclides
incorporated in body tissues.
These radionuclides gain
entrance
inhalation or
inte the boly
threugi
taminated feod or water.
through
con-
Once inside they behave like their
non-radioactive counterparts.
Radioactive iodine,
for exainple,
accumulates in the thyroid gland in the same fashion as
stable iodine,
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and radioactive strontium or calcium accumulate
in the bone similar to their naturally occurring non-radio-
active counterparts.
The radioactive iodine will thus deliver
a dosage to the thyroid gland that is many times larger than
that to the other organs or to the whole body, and the
radioactive strontium and calcium will mainly irradiate the
bone.
Because of the uneven distribution of radionuclides
in the body organs, radiation exposure standards have been
developed not just for the whole body, but also for individual
organs.
In this report we will be referrjng to the maximum
permissible whole body and lung doses.
Largely as a matter of convenience,
radiation standards have been developed.
secondary or derived
These secondary
standards, which limit radionuclide concentrations or organ
burdens, are often more easily employed than the primary dose
standards.
We shall examine two secondary standards in this
le