[Illustration: Figure 14 _Whole body counter record of evidence that a cyclotron worker has picked up higher-than-average quantities of radioactive zinc-65. Note how the graph shows peaks at specific energy levels identifying the radionuclides._] [Illustration: Figure 15 _Graphic evidence that a radioactive gas accidentally inhaled by a worker at an experimental reactor contained 3 radioactive isotopes of iodine._] [Illustration: Figure 16 _The number of 1.38-Mev gamma rays emitted by sodium-24 in the body of a reactor accident victim indicates he received about 900 rads of neutron irradiation._] _Figures 14 through 16 illustrate the kind of data that whole body counters provide to help physicians care for people involved in accidents._ Similarly, neutron bombardment of natural sodium (²³Na) atoms in the body produces sodium-24. This reaction is written: ²³Na(n, gamma ray)²⁴Na. The 1.38-Mev gamma rays emitted by sodium-24 are detected effectively by whole body counters. Since a given neutron dose converts a known proportion of ²³Na atoms to ²⁴Na, it is possible to determine how much neutron exposure a worker has received by obtaining his body count of radioactive sodium. Crystal type counters also were used in an interesting special case of excessive radiation exposure. Seven natives of the Marshall Islands were examined by the whole body counter at the Argonne National Laboratory in 1957. Another whole body counter, mounted in a Navy amphibious landing ship, was taken to Rongelap Atoll in the Marshalls several times to check on the health of all the residents of the atoll. These people had accumulated zinc-65 in their bodies as a result of contamination of crabs and other food items by fallout from the March 1954 atomic bomb tests at the Pacific Proving Ground. Although normal radioactive decay progressively reduced the total amount of radioactivity in the area, the Marshallese still were carrying this nuclide in their bodies after several years. (See _Atoms, Nature, and Man_, another booklet in this series, for a more complete report of this study.) SPECIAL USES Studies of New Babies Study of the transfer of nutrients and other substances from an expectant mother’s body to that of her unborn child is one of the most challenging areas of biological research. A team of scientists headed by N. S. MacDonald has used a whole body counter at the University of California at Los Angeles to study one aspect of this problem by comparing the concentrations of radioactive materials in newborn infants, in babies who are born dead, and in tissues of the mothers-to-be. In these studies the scintillation crystal was placed directly beneath a plastic bassinet holding the babies. Twenty-eight infants, 6 to 24 hours old, were counted for 45 minutes each. The only radionuclide found was the ever-present potassium-40.