EFFECTS OF IOWISING RADpEATION
0
1.3
Snperfieist Doses of Radiation
From Beta and Soft Gamma
Rediaci
Teens Can Ke no doubt that the doses of radiation to the surface and the first few millimeters
of the buiy were substantially higher than the
mid-line dose of gamma radiation as a result of
physical considerations of gamma energy and
depth dose. In addition, the clinical observstions of the skin lesions (see Chap. TEI) force-
fully demonstrated that the dose to the akin
varied considerably between individuals and
over the surface of any given individual. As
will become evident in the following discussions
a
of surface dose, it is obvious that any numbers
presented are at best only estimates and represent an approximation of some minimal value.
In areas where lesions were severe the doses
must have been significantly higher than in nondamaged areas,
To arrive at some physical estimate of the
skin dowe, an attempt must be made to add up
the contributions of the high energy gamma.
the very soft gemma, and the higher energy beta
radiation from the large planar source in which
the individuals were of necessity existing.
However, ax alluded to above and emphasized
in Chapter ITT, the largest component of skin
irradiation resulted from the spotty local de-
posits of fallout material on exposed surfaces
of the body. The dose from deposited material
Is Impawsible to estimate: however, that from
the large planar source may be roughly esti-
tiated as follows:
The beta dose rate in air 3 feet above the
surface of an infinite plane contaminated with
mized 24 hour old fission products is estimated
to be about three times the total air gana dose.
The mid-line gamma dose is approximately 60
percent of the air dose remaining after excluding that portion of the dose below so KV.
This portion in turn is estimated to be 40 percent of the gamma dose measured in air by the
Instrument. Thus the dow at the surface of a
Phantom expowed to mised fission product
midiation from an external plane source night
ban wrervenrtent te bee R1AR) 1A moe mhweet Mf tomeme
the midline dow, if both are taken at 3 feet of
the ground. Such a depth dose measurement
has in fact been made experimentally at a previoun tent, using a phantom man exponed to beth
the initial and residual radiation (5). The
depth dones for each situation are shown in
Figure 1.5, with all data as percent of the 5 centimeter done. With the diverging initial radiation from the point of explosion, the exit dose
was seen to be 63 percent of the 3 cm. dose, bat
with the diffuse residual field of fission products
providing a semi-infinite planar source, # sur-
face dose some 8 times greater than the 4.cm. and
deeper dose from the harder gamma components
was obeerved. This is seen to be of the same
order of magnitude as that estimated above.
At heights above and below the 3 foot level this
surface dose would become lower and higher
respectively, but since it is due to soft radiation
of short range. it probably would not exceed 50
times the 3 foot air gamma dose or 8) times the
midline dose, even in contact with the ground.
An estimate of skin dose due to ground contam!nation for the Rongelap case would result, for
example, in a figure of about 2,000 rep at the
level of the dorsum of the foot, 600 rep at the hip
level and :4}0 rep at the head if continuous ew
posure with no shielding occurred. Unknown
variation in dose undoubtedly resulted from
shielding and movement. It thus seems probable that the external beta dose from local direct
skin contamination far outweighed that from
the ground in importance, since the latter was
not high enough to produce the observed lesions.
Clothing probably reduced the beta douse from
the ground by 10 to 20 percent.
1.4
Summary
Raptation Doses from ganima rays originating
externally were caleulated for the 267 individualx who were accidentally expaned to fallout
following the nuclear detonation at the Pacihe
Proving (rround in the Spring of 144. The
dee exfimations were inade using information
resulting from rasholagicnal safety surveys on