. cc, Preliminary results indicate that the installation and operation of the filter-material samplers was satisfactory for obtaining an adequate sample for the determination of filter efficiency against cloud contaminants, The filter efficiency of two of the five types of filter material tested approximites that determined by standard Laboratory test mothods using non-radioactive aerosols. The decay of sel- ected samples from one shot taken at the site closely followed the expected early decay of gross fission products. 8, CONTAMINATION AND DECONTAMINATION STUD LEO a. The objectives of this part of the program were to study the contamina- tion charactoristics of standard materials; to determine the efficiencies of decontaminating agonts and methods; and to determine the capabilities of those methods in full-scale operations, b, The radioactive decay rates of the samples collected for study seemed to show significant differences for different shots, Some doubt exists whether the gen- erally used decay oxpression is accurate cnough for the clese estimation of expected dose which might be accumulated as a result of a military opcration during or follow ing an atomic attack, This point is being studicd now, A slight decrease in decon- tamination efficiency of various materials was notcd, both through aging and as the result of alternate wetting and drying. The decrease was not enough, however, to have a significant bearing on military or field operations, ec, it has been found that the order of efficiency of different decontamina- ting agents was about the same for the removal of contamination from samples obtained | at Operation GREENHOUSE, as far the removal of synthetic aerosols on which labora~ tory testing is based, However, the laboratory contaminants were removed inuch more efficiontly than were the GREENHOUSE contaminants, It is concluded,therefore, that laboratory testing can assess relative merits of cleaning agents, but cannot pre. diet their actual ficld efficiency at present. d. Of the various factors which affect the contaminebility of materials it was found that details of cxposure overshadowed differences duc to the character istics of the material, composition, There seemed to bo little offeet duc to hardness or chemical A notiecable decrease in contaminebility was observed if the surface WAS very smooth, However, this effect was of relatively little importance after the surface became only slightly rough, 8. No consistent trend was found in the study of the fifteen proposed in- dustrial decontaminating processes studied, except that stcam cleaning without chemi-~ be — Mir”