Page:Operation Crossroads 1946.pdf/122

 contamination were made by removing samples to laboratories where analyses could be made. Field assessments were made by assuming that the alpha emitter plutonium was mixed with the other weapon debris, made up of fission products and activated materials. The ratio of this mixture was apparently assumed to be constant so that there was a ratio between the measurable radiations, gamma and beta, emitted by the fission products and activated materials and the unmeasurable alphas from the unfissioned plutonium. Since the emissions from the beta and gamma emitters decayed while the alpha emissions remained nearly constant, this ratio changed with the passage of time -- but in a way that was predictable.

The laboratory on Kwajalein operated by Los Alamos informed the Radsafe Advisor that on BAKER day + 13 (7 August) 4.5 alpha counts [per minute] per square centimeter of contaminated area could be expected when a survey meter gave a reading of 1 R/24 hours (presumably gamma) (Reference C.10.16). This theoretical determination was made in conjunction with samples that had been taken on 7 August from the forward lookout platform of New York. These samples had been collected by using concentrated hydrochloric acid to dissolve the paint and surface material, which were then collected for analysis. The result was forwarded by teletype to the Chief of the Radsafe Section on 10 August and stated that the reading in the collected material was 25 alpha counts [per minute] per square centimeter [of the contaminated platform] for a [gamma] reading of 3 R/24 hours. The laboratory said that this count was twice as high as expected due to "washing." By this it is presumed the laboratory meant that the fission and activation products had been more easily washed away during decontamination activities before 7 August than had the plutonium particles. It should be noted that this analysis took three days from sample collection to report.

The account from the DSM report continues (Reference C.9.185, p. 13): "A conference was called by the Task Force Commander on 10 August to discuss the matter [Prinz Eugen contamination]. As a result of this conference, continuation of detailed decontamination was considered unsafe under the selecting conditions, and all further decontamination work on the targets by ship's force was ordered discontinued. Subsequently, all further work on these vessels by Task Force Personnel was limited to recovery of instruments, limited surveys, salvage work and preparations for towing from the area."

Judging from the time required to analyze and report the New York samples, it does not appear that the samples from Prinz Eugen taken on 9 August could have been analyzed by the next day.

There is a further difficulty with this sole surviving account of the discovery. It appears in the last sentence of the first quotation wherein "widespread presence... in spaces not obviously contaminated" is deemed "probable." If "not obviously contaminated" means not easily measured with existing field survey meters, than the statement is not confirmed by surviving records of the measurements that were taken of alpha contamination. Reports available after 4 September on alpha contamination in samples taken from the target vessels and sent back to Los Alamos for analysis show that alpha emissions were always reported in conjunction with gamma and beta emissions.

117