blood stream is determined by its solubility, chemical properties, and physical state. The
radioelements formed in fission are predominantly oxides which have a limited solubility in
body fluids. On this basis only a few of the radioelements can become available to the body.
However, the amount that can produce injurious effects when deposited within the body is
minute because of the close proximity of the isotope to the tissues it irradiates and because
the isotope continues to irradiate these tissues until it is removed by biological turnover or
is rendered harmless by radioactive decay. The effects of radiation from internally deposited
emitters are the same as those from external radiation. The distinguishing feature of internal
radiation, however, is its long continuing nature.
TABLE 1.1-—Biologically Hazardous Internally Deposited Fission Products
Fission*
Fraction reaching
critical organt, {¢
Half life
Radioelement
Type * of
radiation
abundance
(%)
Radiological*
(days)
Biologicalt, t
(days)
By
ingestion
By
inhalation
sr®?
yi
zr
Ru!
)
B
BY
By
4.6
5.9
6.4
3.7
53
57
65
42
3.9 x 103
>500
>100
20
0.25
2.8 x 1074
0.35
0.04
0.22
0.14
y!31
Balto
La!40
Cel!
B,y
B, y
By
By
2.8
6.0
6.0
5.7
180
~ 200
35
>100
0.2
0.07
1.2 x 1073
0.25
0.15
0.20
0.1
Ru!
pri43
Cel4
B
B
Byy
0.5
5.4
5.3
;
365
8
12.8
1.7
28
13.8
275
20
50
500
0.04
1.3 x 1073
2x 1074
0.063
0.10
*From G. T. Seaborg and I. Perlman, Rev. Mod. Phys., 20: 585 (1948).
{From J. G. Hamilton, Rev. Mod. Phys., 20: 718 (1948).
tFrom National Bureau of Standards Handbook 52, U. S. Government Printing Office, Washington 25, D. C., 1953.
Radioactive isotopes follow the same metabolic processes in the body as the naturally
occurring inactive isotopes of the same element and of chemically similar elements. Thus
strontium and barium, which are analogous chemically to calcium, are deposited in the cal-
cifying tissue of the bone. Although nearly 200 radioisotopes are produced in the fission
process, only a few are potential chronic internal radiation hazards. These fission products,
listed in Table 1.1, constitute a high percentage of the fission yield and localize chiefly in
bone. The “bone seekers” have, in general, long radiological and biological half lives and
produce high-energy beta particles. Thus they cause greater damage to bone andto the radiosensitive bone marrow than to other tissues. The damageto the blood-forming tissue results
in a reduction of blood cells and thus affects the entire body.
Information on the biological effects of internally deposited isotopes is derived from the
limited studies of accidental radioisotopic poisoning in humans or from animal experimen-
tation. The best documented data on the effects of small amounts of internally deposited emitters in human beings are obtained from studies of radium poisoning. As a result of radium
deposition, terminal anemia, bone necrosis, and osteogenic sarcoma appeared after a number
of years. The residual activity in the body associated with these effects was 1 to 2 ug of
radium. Radium is a particularly hazardous element when deposited internally becauseof its
very long radiological half life.
Very few data are available on the long-term biological effects in human beings of the
shorter lived isotopes such as Sr®, 1'5!, p32, and Na”. The metabolism, excretion, and bio12