5.1
Inatroductica
Fouuoewixe A Necuzar detonation in the spring
of 1934, a large group of people were contam'nated with fission products. In addition to a
sublethal external gamma radiation exposure
and beta irradiation of the skin, delectable
amounts of radionuclides’ were deposited in
ternally. It has been assumed that in all situations resulting from a contaminating event, the
ratio of external to internal dose would be exceedingly high. However, 1. cetailed ‘study of
the internal contamination in’ the exposed
human population and in animals was made to
determine the kind and degree of internal
deposition. Three general problems were in-
vestigated: (1) The determination of the contribution of the internal contamination to the
acute radiation syndrome observed: (2) The
possibility of Jong term effecta, and (3) The
qualitative and quantitative nature of the internal contamination produced by exposure of
individuals to mixed fission products, There
Was no previous situation in which human be-
Ings were exposed to an environment contami-
nated with mixed fission products. Concurrent studiex were undertaken by the Japanese,
however, on radioactive materials to which a
small groupof Japanese tishermen, near Rongelap at the trme of the detonation, were exposed.
The report of the extensive investigations
undertaken on the ashes by the Japanese have
been published (4).
Evaluation of the internal contamination of
the human berngs was made by a study of the
radioelements excreted. As very little information is presently available concerning the
ratio of excreted radioelements to the amount
deposited in the body, it was necessary to base
the evaluation on data obtained from animals
which had been contamimated ino the same
event. Detailed studies of animal tissues and
animal excreta then provided data on which
estimates of the human body barden were bused,
§.2
General Nature of Interna!
Radiation
Toxicity
Tu. Natuae Ov the radiation hazard from internally deposited fimion products can best be
understood in terms of the biophysical behavior
of the radionuclides.
Fission product» entering the body throngh
inhalation of ingestion concentrate in various
tissues and act as sources of internal radiation.
The ability of 2 radionuclide to enter the blood
streamis determined byits solubility, chenneal
properties and physical state. The radioele-
ments formed in fision are predominantly ox-
ides which have a limited solubility in) body
fluids, On this basis, only a few of the radio
elements can become available to the body.
However, the amount which can produce injurions effects when depowted within the budty
is minute because of the close proximity of the
isotope to the tienes it irradiates, and because
the imtope continues to irradiate these tixeues
until it is removed by biological turnover or ts
rendered harmless by radioactive decay.
The
effects of radiation from internally depasted
emitters are the same as those from external
radiation.
The distinguishing feature of in-
ternal radiation, however, i its long continuing
nature.
Radioactive isotopes follow the <ame metabolic processes in the body as the naturally
OCCUCTIAY Inactive isotopes of the same element
and oof chemically
simolar elements.
Thus
strontium and barium. which are analogoas
chemically to calenum, are deposited in the calcifyving tissue of the bone. Sithoagh nearly two
hundred radioisotopes are produced in the tission process, only a few are potential chronic
internal radiation hazards. These fission prod.
ucts. which are listed in Table 3.1, constitute a
high percentaye of the fission sceld, and localize
chiefly in bene. The chone weker” have, im
“7