radiochemical data taken at the time of the fallout, estimates of duration of
fallout, exposure time, etc.
(Sondhaus et al.).
Spectrographic data of the
fallout showed gamma energy peaks at roughly 100, 700 and 1500 kev.
The
varied energy distributions, the greater depth dose due to the near 47 geometry
of exposure make the fallout. dosimetry significantly different from that of
radiation therapy or experimental radiobiology.
Table 1 shows the calculated
gamma doses (dose in air) for the different island groups.
12.5.2
Skin Dose.
Skin exposure was large ly from beta radiation.
The dose
to the first few millimeters of the body surface were considerably greater than
the midline gamma dose.
Measurement of beta doses from the skin from Fallout
was an exceedingly difficult problem due to the complicated spectrum of different
energy beta emitters present,
the non-uniform distribution on the skin, and the
fact that practical dose meters were not available to adequately discriminate
between beta radiation and contaminating gamma radiation.
The penetration of beta particles into the skin depended on the beta energies
of the component isotopes.
Each isotope has its own characteristic spectrum
of beta energies. Figure 4 shows roughly the tissue depth necessary to produce
50% attenuation of the beta particles from several isotopes.
In animal studies
the dose required to produce recognizable skin lesions by a particular beta
emitter has been demonstrated to be dependent on the energy of the beta particles.
(Henshaw et al., Davis and Alpen, Snider and Raper, Lushbaugh and Hale, Moritz
and Henriques).
For example it was found that it takes 20,000 to 30,000 rep
35s (avg. energy 0.05 mev) to produce a reaction while it takes only 1,000 to
2,000 rep of 905 5 or 90y (ave. energy
5061302
0.3-0.7
mev) to produce the same reaction