Investigation of Differential Energy and Angle for ¹³⁷Cs Gamma Rays in Water and Air

Differential energy and angle spectra from a point isotropic ¹³⁷Cs source in an effectively infinite medium of water have been determined for γ-ray penetrations of 1, 2, 3, and 4 mean-free-paths at 15° intervals. The spectra were unfolded from scintillation spectrometer measurements by an analytic method based on the Scofield iteration scheme. An integration of the results over all angles yielded differential energy spectra which were consistent with multigroup transport calculations. The measurements were also carried out in a condensed, air-like medium. A comparison of the results with those obtained in water showed that the differences in attenuation coefficients between the two materials caused spectral differences only at very low energies for small separations between source and detector, which were consistent with theoretical calculations.