antual cadioactive material. Of more importance {gs the indication that in fallou. ireas,
an perhaps under other conditions ae well, one may be dealing with individual yeint
sources ruther than 'niform a.eas of contarnination. This experiment concluded that
the total raciation hazard to the sensitive layec of the akin was jess than six Uimee the
gamma hazard at heights of 14 inch to 6 feet zbove a desert surrace contatinated with
.
fallout fission fragmenio and neutron-induced activity.
Another undertakirg of considerabie importance wis carried out during Operation
Greenhouse and extended during Operation Buster-Jangle (References 4 ani 5). Meas~
urements of Loth gamma energies urd so-called beta-gamma ratios were made on fisaion
fragments collected on plaques that had been flown through nuclear clcuds or placed in
.
fallout areas. During Buster-Jangle, the beta-gammaratio }.: faliout areas was found
to be a maximum of 14 for a surface shot ind 24 for an undergrouid shot. During Greenhouse this ratio was found to be 156 at times of 72 to 168 Fours ‘o.lowing detonation. It
ig apparent that a wide variation exists in ihe results of experimental n.casuremen:ts of
the ratio of beta to gummu ionization intensities from fisalon frag.nents, depend! g on
the history of the radiation source and the experimental crrangemeut.
One muy not infer from these results that the beta-gammaratios obtained from math-
ematical considerations are tot correct. Instead, [t should be empnasized thet the experimental ratios depart from theory because the experimental conditions differ from
those asaumedin the calculations. The distribution of the contamination appears to be
the mosi-critica!l variable.
:
In any study of the contact radiation hazard on aireraft, the distribution of the con-
tamination must be determined.
Certainly, the contamination consists of discrete
particies of matter. ‘ine flux of {lesion products, aa aren ry an aircraft fly.ag throvgh
a nuciear cioud, could be such as to result in #: rface contamination ranging from widely
spaced particles to a condition ap). oximating a uniform radiation flrid. Insight into just
how much separation the pai ticles :nay have and still be treated as a uniformly distributed
source may be had by considering thut the thinnest layer of inert skin is about 0.1 mm
thick. This inert layer will always intervene (except In the case of open wounds) between
the particles and the papillary, or sensitive, layer of the skin. Consequently, uniform
particles separation not excceding 0.1 nim will appear to the living tissues os essentially
uniform contamination.
The problem of determining the ratio of effective surface radia-
tion to gamma field radiation becomes grvatly simplified {f uniform contamination extats
on the surface.
On the other hand, departure from uniform contamination might result in intense
radiation at a discrete particle that registers as a low Jose rate on a atandard survey
meter, such as the T1B. This apparent lack of intensity resulta from the fact that an
ion-chamber survey meter suitable for 1. 2ld use must, of necessity, have a rather large
fonization chamber. As a result of this large size, the Intense ionization in a small
volume of the chember near a highly active particle appesra to be moderate when averaged
throughout a volume of several hundred cubie centimeters.
Nevertheless, if une tuuches this highly active particle, the scusitive tilssuca nearest
the particle reccive the full impact of the iniense radiation, and a burn hazard exists.
Other important considerations in evaluating a skin -radfation hazard ars the effect of
scattering, filtration of beta and low-energy gamma radiction by !nsirument walls, and
the penetrating charac‘eristics of the radiation. To make an absolute measurementof
the dose rate near a surface contaminated with fission fragments and to trarslate this to
a personnel hazard is difficult. However, a few practical approaches developed in previous studies (References 3 and 6) permit one to make empirical measurements that are
directly applicable to tne determination of dose.
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