was only 5.8 per cent. This correlation was mintainea even wnen tne relative concentration of the nucl§des were changed by a factor of 20. Subsequent analysis of the fallout from TEAPOT indicate a variation of lege than 14 per cent between a radiochemical separation of Bal40 Lat40 and the gamma spectral analyses. The peak at 750 kev remaining after subtraction of Ba and la decayed as if an isotope of 7-day half-life and an isotope of 35-day half-life were present. Both activities are unassigned. The peak at 500 kev left after subtracting the contributions due to the higher-energy gamma rays decayed with half lives of 11 and 40 dayse These activities are assigned to Ndl47and RulO3, At low energies, peaks were found at 104, 209, 264, and 340 kev, decaying with an average half-life of about 5.5 days. These gamma rays are believed due to the combined effects of 6.7-day U237 and 2.3-day Np239. The predominant peak at 104 kev is due to the 105kev gamma ray reported for Np239 and to the x-rays following the ine ternal conversion of a gamma ray of 207~-kev in U 37, Unfortunately, data earlier than 10 days were not available and the data covering the period 10 to 40 days were not extensive enough to permit the separation of the two isotopes. Because of the 29-kev energy difference and about equal decay half lives, the peak at 35 kev is believed to be the iodine x-ray escape peak of the 64-kev gamma ray. Also, the related number of counts in the two peaks is in agreement with that expected from the theoretical calculations of Axel.20/ These calcula- tions predicate a ratio of escape to non-escape of the present result of 0.156 0.14 compared with Below the 35~kev peak there is seen a sharp rise in the pulse- height distribution. These counts are believed to be due to the Bremsstrahlung radiation formed in stopping high-energy beta particles. Since the beta rays were stopped in aluminum rather than in some more dense material the number was kept to a minimum. The actual amount formed has not been evaluated. This work indicates that, within limitations, isotopic analy- eis can be carried out on fallout zhrough a study of the gamm-ray spectrum. In future work, use should be made of the fact that short lived isotopes almost invariably emit the higher-energy gamma rayse For instance, Na24, which is produced in large quantities in a nuclear detonation near sea water, has a 2.76 kev gamm ray and 15-hr half life. At a tims of about one day after the shot this is the only gamma ray of apprecia intensity in this energy region. About ten days after a shot, Ba and La are in transient-equilibriun. 1al40 emits a 1.6-Mev gamma which is the only gamma ray in that energy ‘region at that time after the shot. At a period of about 60 days after a shot, Zr?5 may be analyzed with a gamma ray at 730 kev. Also, at this time, an analysis can be made of Rul03 with a gamma energy of 498 kev by subtraction procedurese The external radiation hazard, (gamm dose rate) is an energy dependent phenomenon, with the effects of gamm rays increasing as the energy increases. Analysis of the gamm spectrum of fallout used in conjunction with the known decay schemes of the individual isotopes could yield data showing the contribution of the gamm dose rate from all isotopes of any consequence in fallout. Not enough isotopes were 84