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the earth or on towers and the like induce radicactivity in a variety
of mterials.
‘his results for the most part in radionucleides of
relatively short half-life suchas Fe-59 half-life 47 days, mnganese
54 half-life 310 days, S1-131 half-life 2.6 hours, and C1-38 half-life
37 minutes, sodium-24 half-life 14.8 hours.
Measurable amounts of
' 2n-65 halflife 250 days, and CO-60 half-life 5.3 years have also been
detected in fallout mterial.
In early fallout from a surface explosion radioisotopes of short
half-lives are quite abundant and may represent a very important part
of the total activity.
In fact the external radiation dose from the
short-lived gamma ray emitting isotopes in near-~in fallout my constitute
the principal hasard to unshielded persons aa was the case with the
Marshall Islanders onthe ATOLL of Rongelap at the time of the March 1,
1954 detonation (31).
From the standpoint of possible damage from radio-
isotopes which may be ingested or inhaled soon after fallout the dose to
the thyroid gland, to the gastro-intertinal tract and to other regions of
the body from I-131 with a half-life of eight days, and M-140, Strontium89
and Strontium-91 with half-lives of 12.8 days fifty-five days and ten hours
respectively my overshadow in significance the effects of the longer-lived
fission products.
These fission products have been identified in fallout
and in biological mterial, plants, animals, and animal and human urine
collected a few days toa few weeks, and in the case of Sr-39 several
months, after the passage of a cloud of nuclear debris over an area (16, 33,
11, 32).
These isotopes are important in tropospheric latitudinal fallout