5.3
PHOTODOSIMETRY AND RECORDS SECTION
This section consisted of one officer, six photodosimetry technicians, and five clerks. The
Section operated two facilities, one at the Rad-Safe Center on Parry and one in a Signal Corps
laboratory trailer on the hangar deck of the USS Bairoko. Two shifts of technicians and clerks
functioned throughout the 24-hr day aboard the Bairoko while one shift handled the program at
Parry.
:
§.3.1
Film Packet
The presently accepted film badge for test operations resulted from the recommendations
of a conference of interested individuals at the AEC Division of Biology and Medicine on 18
;
,
The conference recognized that the film dosimeter to be devised must be a compromise between known factors of film response and poorly known factors of energy spectrum andbiological
response. The exact spectrum of energy to which personnel are exposed when in a field of bomb
debris is unknown; in fact, the spectrum probably varies considerably with time and place.
There is good evidence that the spectrum contains a large amount of degraded gamma energy
in the region below about 0.1 Mev. The biological effects of radiation in this energy region are
difficult to assess. The amount of beta-ray energy associated with these fall-out fields and its
biological effect are likewise difficult to assess.
It was agreed that the blood-forming organs would be considered as the critical tissue.
Degraded gamma energies of less than 0.05 Mev might be neglected, Beta radiation would be
ignored in ordinary fall-out fields, except where there is direct contact with contamination.
Ordinary shoes and clothing may be considered as adequate protection against beta rays from
contaminated ground.
As a result of this meeting and further discussions with the National Bureau of Standards,
the AEC Division of Biology and Medicine recommended adoption of the procedures used for
personnel dosimetry at the proving grounds.
The accepted film badge consists of:
1. Film pack: For convenience and reliability two films, Du Pont 502 ana 606, were recommended. Du Pont 502 has a reasonably accurate range up to about 3.0 r, with a measurable
range up to about 10 r. Du Pont 606 has a range between approximately 10 to 300 r. This particular combination of films has the disadvantage of being unable to evaluate accurately exposures in the region of 10 r, although both films may be used to assist the evaluation.
2. Metal shield: Not only does the spectrum to be measured have a peak in the region of
about 0.1 Mev but also the film responseis high in this region, 2 combination which can lead to
sizable errors in the photodosimetry of personnel exposed to fall-out radiation. To suppress
the high response of the film to radiation in the region of about 0.1 Mev, a metal shield is ordinarily used. The Radiation Physics Laboratory of the National Bureau of Standards collected
data that indicated 0.72 mm of lead would give the approximate sensitivity response desired.
Until more complete information on the fall-out spectrum is available, the observed dose may
be considered reasonably accurate (see Appendix A).
Except for minor changes, procedures of photodosimetry were followed according to the
operating procedures outlined in Appendix B.
5.3.2
Dosimeters
Considerable difficulty was encountered in the use of pocket dosimeters during the Bikini
phase. Three types were used, namely, the Victoreen, 0 to 5 r; the Cambridge, 0 to 1 r; and
the Keleket, 0 to 200 mr. These instruments were issued to monitors during missions only.
Becauseof their sensitivity to low-energy radiation, the dosimeters consistently gave
readings higher than the measured integrated dose from film badges. In general, these readings were higher by approximately a factor of 2. This phenomena had also been encountered
during Operation Ivy. Although the true exposure could be approximated by dividing the dosimeter reading by two, other characteristics proved this practice to be unsatisfactory.
43
cc|
August 1952.