was only 5.8 per cent. This correlation was maintainea even wnen tne relative concentration of the nuclides were changed by a factor of 20. Subsequent analysis of the fallout from TEAPOT indicate a variation of less than 14 per cent between a radiochemical separation of Bal40 Lat49 ang 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 Rul03, 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 2e3<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 in= 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 Axe1.20/ These calcula- tions predicate a ratio of escape to non-escape of 0.14 compared with the present result of 0.15. Below the 35~kev peak there is seen a sharp rise in the pulseheight 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- sis can be carried out on fallout ézhrough a study of the gamma-ray spectrum. In future work, use should be made of the fact that short lived isotopes almost invariably emit the higher~energy gamma raysSe For instance, Na*4, which is produced in large quantities in a nuclear detonation near sea water, has a 2.76 kev gamma ray and 15-hr half life. At a tims of about one day after the shot this is the only gamma ray of apprecia days after a shot, Ba intensity and La in this energy region. About ten are in transient-equilibrium. 1a140 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, 2r9 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 procedures. The external radiation hazard, (gamm dose rate) is an energy dependent phenomenon, with the effects of gamma 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. 84 Not enough isotopes were