Measurement of Gamma Ray Energy Distribution of Fallout

Abstract

This paper describes the variation of gamma ray distribution and the average gamma energy of fallout due to nuclear detonation from September 1961 until September 1964.
Fallout samples were collected with continuous dust-samplers. The gamma ray spectra of the samples were measured by a 400-channel gamma ray spectrometer. The detecter was used the sodium iodide crystal 5inφ×4 in and it was set in the ion box about 20 cm thick.
Analysis of the gamma ray spectra were made by using the strip-off method. The energy ratio to the total gamma activities in the fallout was calculated from the net count-rate of the photo-peak. The ratio of gamma energy (0.76 MeV) from ⁹⁵Zr-⁹⁵Nb ranged from 50 percent to 88 percent in the period, The average gamma energy of the Fallout in the operiod was nearly constant. The average value was 0.68 MeV.