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 Film Badges

Two types of film badges were used at CROSSROADS. One type, called a personnel or mission badge, had a range from 0 to 2 R. Badges were issued to some of the men about to enter possibly radioactive areas and most badges were worn for 2 or 3 days, and a few worn for as long as 9 days have been noted. Each badge contained a piece of Kodak Type X double-coat film in a dental film packet holder. Strips of lead were crossed over the film at right angles, leaving the film's corners without lead covering. Each badge was sealed in a tropical weather-proof envelope to protect it against the hot, humid Bikini climate (Reference C.0.5, p. 2-2).

The badges were designed to measure both beta and gamma exposure, but the beta readings obtained and recorded are now considered questionable (Reference C.13.2). There are several reasons for this. One is that the response of the double-coated film dosimeter emulsions depends on the energy of the beta particles they are exposed to. Unless additional thin metal foils are used over the films to filter or sort the beta radiation into known energy groups, or unless the energy distribution of the beta radiation is otherwise known, very large errors in interpreting the film darkening can result. There also appear to have been some incorrect assumptions made concerning whether gamma as well as beta would darken the unfiltered areas (Reference C.13.2). Despite the doubtfulness of the validity of the beta readings, the values as originally assigned have been accepted and used in total dose assignment in the NTPR program (Reference C.13.2).

After a badge was returned to the Radsafe Section, the photometrists of the Radiological Safety Technical Service Units developed the film in it, and measured the film's optical density. This was a measure of the amount of radiation to which the film had been exposed. The film number, the wearer's last name, and the exposure date and time were written on a line on the left-hand page of an open ledger book of the type then widely used by Federal agencies. Sometimes the individual's first name, initials, or rank were written in. Sometimes the name of the ship where he was quartered or, more often, the target ship on which he had worked that day was entered. If the badge had been used on an island or ship as a radiation recorder, the location information was recorded instead of a person's name. Optical densities under the lead cross and on the corners of the badge were entered on the right-hand page. The radiation exposure was calculated from these densities and recoded as the final beta and gamma readings at the page's far right. Years later, the pages were removed from the ledgers and microfilmed. Information from badges work during September, October, November, and December of 1946 was recorded on large (5- x 8-inch) cards for each individual.

Neither the detached pages nor the microfilm is easy to work with. The penmanship of the radsafe staff is not always legible, and incomplete identification of the badge wearers and inconsistent ship identifiers are additional problems. In 1968 the Reynolds Electrical and Engineering Company (REECo) transferred the information from the ledgers to a computer data base, allowing easier manipulation and analysis of the material. The REECo list is used as the basis of the personnel exposure in this report.

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