Section III. Nuclear physics
Analysis of fissionable material using delayed gamma rays from photofission

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Abstract

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched 235U, natural uranium, and 93% enriched 239Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four isotopes studied reveal a distinctive intensity distribution. For example, the intensity ratio of the pair of gamma rays at 1436 keV (138Cs) and 1428 keV (94Sr) is 1.9 for 235U, 2.4 for 238U, 1.7 for 232Th and 1.4 for 239Pu.

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