STRONTIUM-90 IN MILE
k as an
tioned.
acumuThis
fallout,
In the initial blast there are about 170
one is krypton-90, the radioactive precursor
occurs by the successive elimination of beta
decays further by eliminating 8 particles
after a
- radiofallout,
reloped
d little
yeneral
retical
’ Rand
on the
ference
mixed
sult of
irector.
—8
gelr??
krypton
——_—_—_—_—_—
33 see.
ger?
rd
—B
strontium
28 yr.
5, each
oo
yttrium
—p
65 hr.
oZr
zirconium
Sr-90, and Sr-89, all decay to Y-90 and, finally, to Zr-90 which is stable. Sr-91
indocu-
TABLE 1
Pn
| bomb
which
of the
m (n)
apy°°
gare
strontium
has a half-life of 10 hr. and Sr-89 has a half-life of 53 days. These two are of
little concern in studies on long-term fallout because of their short half-life, and
their deeay product, Y-90, is not absorbed readily by the digestive tract.
Other principal isotopes of biological interest produced in the fission reaction
are summarized in Table 1, and their occurrence as a function of time after the
initial blast 1s given (19m). The radioactive isotopes of iodine can be concentrated readily by the thyroid, but are of little importance in long-term fallout,
since their half-lives are very short. The half-life of I1*! is eight days. The rare
diation
States,
n man.
of the
})-page
assified
‘orages.
r-90 in
—_
2.7 min.
The time indicated below each arrow is the half-life of that element and repre-
tes and
ne was
phases
i. terms
—B
a7Rb”
rubidium
sents the time for one-half of a given quantity of the element to decay. The
long half-life of 28 yr. for Sr-90 is one of the properties that make it a problem
in long-term fallout. Y-90, the daughter of Sr-90, eliminates a 8 particle prior
to forming stable Zr-90. Its half-life is only 65 hr.; thus, the radioactive effects
of Sr-90 are actually due to the combined disintegrations of Sr-90 and Y-90 to
stable Zr-90 (1, 19K).
There are four natural isotopes of strontium, Sr-84, Sr-86, Sr-87, and Sr-88,
all of which are nonradioactive (190). In the fission reaction six isotopes of
strontium are produced, all of which are radioactive. Three of these have extremely short half-lives and are of no practical concern. The other three, Sr-91,
nimals,
ire apt
fission fragments produced, of which
to Sr-90. The decay of Kr-90 to Sr-90
(8) particles. The Sr-90 formed then
until stable zirconitum-90 is formed.
Principal biological isotopes from slow neutron fission of 1 kg. of U-235 (19m)
Time after fission
Isotope
&% Total activity
1 day
T-133
Sr-91
Ce-143
1-135
I-131
Ba-140
Ce-141
T-131
Sr-89
Ce-144, Pr-144
Ce-144, Pr-144
Sr-89
Sr-90, Y-90
Sr-90, Y-90
Cs-137, Ba-137
7.3
6.7
6.7
5.7
0.9
12.0
9.7
5.6
5.0
2.6
52.8
2.7
3.7
48.0
45.0
20 days
lyr.
20 yr.
[3]