External exposure. At the me of detonation the
almost instantaneous gamma rays released wil! be
of concern out to about a mile for a nominal bamb
(7) and out to a few miles for high-yield weapons.
However, significant amounts of radioactive fallout
may occur at more than 300 miles downwind from
high-yield weapons. This material emits gamma
rays similar to the instantaneous ones but with les
quantum energy.
About 25 roentgens of gamma radiation, deliv-
ered in a short time (about a day or jews) over the
whole body, are required to produce minor and
burns caused by the beta radiation frem the
material being in contact with their skin
ti f
Radiations
continental tests. All were within 20 miles of
zero. Cattle from the 1945 exposure have
under observation at Oak Ridge. There have been
no observable changes in the animals, except skin
damage and low of hair in spots that regrew but
was gray in color. Their offspring have been normal
in all respects.
These experiences have showa the need for larger
warning areas when high-yield weapons are to be
detonated. These are now established during operational periods; and withthe continuing improve-
transitory changes in the blood; about 100 roentgens are required for some persons to show radia-
tion sickness; about 450 roentgens may be lethal wo
half of the exposed persons (3). (A roentgen is 8
unit for measuring the um of radiation, or dese,
that has been received. For example, a normal
x-ray will deliver about 1/10 roentgen or more to
the chest; abou: 10 roenqgens are received im a
lfetame from cosmic rave and from naturally e-
Cusving radioactivity im the asr, waeer and snl, ¢).
The highest radiation exposure to any individual mm the Unierd Seners outside the Nevada
Ten See bas been about 7 rocmegens (about 12
gracng wear the Nevada Test Ser during the spring
of 1953 The esumated radiation dose w thei thvtoads was thout 30D rrentgens 9. Owing wo the
- +° -waespread dtnbunon of fallout fram the
Pacwic tests in the spring of 1954, racoactive sodime
was fond im the thyrosds of cattle and sheep im
vanous parts of the Usted Seases 10). The high-
Fallout caasevial alen ext beta rave that travel
at most afew mreen m as and are of principal concern when heghly acuve fallout matenal remame
est total radzatom doer tw the thvroid from ths
wres was estamated to be about 40 reenteem. The
1952 aad maw’ horses in 1983 capenienced
beings resudung from mtake of fallout materia) has
been measured. The highest radiacon exposure
measured was in mdividuals near the Nevada Test
Site m the spring of 1955, but there is some un-
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