ro 33 d/m/I1 in 1956 but rose to between 137 and 370 d/m/1 in 1957 (presumably becauseofslight fallout from a test series). As part of the 3rd annual survey, severalof the Marshallese people were brought back to Argonne National Laboratory for whole-body gamma-ray spectroscopystudies.’*' At that time the presence of Zn’”” as an internally deposited radioisotope was first noted, and the importance of similar studies on the entire Rongelap population was recognized. Since it was not feasible to bring large numbersof Marshallese back to the States for such a study, it was decided that for the 4th annual surveythe necessary equipment would be transported to Rongelap. (In view of the frequency of breakdown of the complex electronic equipment even under laboratory conditions, and the severe additional stresses associated with transportation andtropical conditions, complete spare units of the majorelec- tronic items were taken, as well as completesets of spare tubes and other small components.) Equipment and Procedures. “The 1957 measure- ments at Argonneindicated that, although a good shield would be needed to lower the background, there would be enoughradioactivity in the Rongelap subjects to makethe shielding requirementsless stringent than the criteria used at Argonne for very low body burdens. Accordingly, a steel room was used similar in design to the one at Argonne,* but with the walls and top only 4 in. thick and with the bottom only 2 in. thick. The steel deck of the LST and the water underneath were ex- pected to compensate for the relatively thin bottom shield. With outside dimensions of 5 ft 8 in. by 5 ft 8 in. by6 ft 6% in., the steel room weighed 21 tons. The crvstal found to be most useful as a detector nel pulse height analyzer. Commercial models* of the analyzer designed by Chase* were used. A fan and a phonograph contributedto the subject’s comfort within the steel room.** Before entering the steel room, the subjects took a shower bath and donned paperoveralls and slippers. A special facility had been constructed aboardthe ship for the shower and dressingsta- tion. The subjects were usually counted for 10 minutes. In order that direct comparisons of body bur- dens with urinary excretion rates could be made, individual, rather than pooled, 24-hr urine speci- mens were obtained. The radiochemical analyses of the urines were conducted at the Walter Reed ArmyInstitute of Research.*** One of the subjects died, and in this case the additional comparison of bone radionuclide concentration with whole-body and urine data was made. The gamma-rayspectral data and mostof the electronic equipment from the March 1958 trip were lost at sea, but prominent Cs*** and Zn" peaks had been observed in thefield, and it was felt that the expedition had provedthefeasibility of conducting such measurements underfield conditions. Assoonas possible, therefore, the lost equipment was replaced and a second survey was conducted in May. By then, however, the 1958 series of weapons tests had begun at Eniwetok. This addedto the difficulties because the steel room was taken to Rongelap byship from Eniwetok,andit was not discovered until arrival at Rongelap that the ship being used (an LCU) wassufficiently con- taminated with radioactivity to raise the background enoughto interfere with the measure- ments. In fact, the deck underneath the steel room Within the steel room the subjects sat in a semireclining chair in a position similarto that used at Argonne.’*-"* The crystal, photomultiplier tube, and preamplifier were suspended above the sub- had been painted with a nonskid paint which evidently included radioactive sand from Eniwetok. The use of a paint remover and generous washing down of the ship reduced the background from 50,000 to 20,000 cpm, which, though still very high, did permit the measurements to be made. In March the background had been 1200 cpm. the preamplifier to a linear amplifier outside the room and subsequently analyzed with a 100-chan- *Technical Measurements Corp., New Haven, Conn. **Additional information on gamma-ray spectroscopy and was a sodium iodide (thallium activated) crystal in the form of a right cylinder 5 in. in diameter and 5 in. deep. ject’s abdomen. The signal was conducted from *The authors wish to express their gratitude to Dr. C.E. Miller, Dr. L.D. Marinelli, and Mr. J.E. Rose of Argonne National Laboratory for generous assistance in planning the steel room. including their supplving drawings of the Argonne iron room. sources of data may be foundin references 79 to 90. ***We are grateful to Col. James Hartgering, (MC) USA, Maj. Kent T. Woodward, (MC) USA, and Lt. Ariel Schrodt of the Walter Reed Army Medical Center; Dr, John Harley and Mr. Edward Hardy of the New York Operations Office of the AEC; and Dr. Stanton H. Cohn of Brookhaven National Labo- ratory for assistance in the radiochemical analyses. ae