A technique for the nondestructive assay of fissionable nuclides is described which utilizes a californium-252 neutron source, cyclic activation, and delayed gamma ray analysis. Ihe results of preliminary experiments with uranium-235 samples are presented, comparing the effects of various cyclic activation sequences and sample enrichments on the high energy gamma ray spectra of the short-lived fission products. The quantitative accuracies of the method are also presented. : t • Thit report wa»

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... raparad as an account of work aponaoNd by,the United SUM Govarnaent. Nattier the United StMM act MM United StttM Atonic Eawgy ComatfMkM, aor aay of tlMir aKptoyMt, Mr any of UI aoMracton, tabcoatcacton, or flwfc awployaa, _»" -~-•» UapM«d, or aawwa any mtfc-s any warranty, axpnta or lapHta*, or tmm y tatnl HabBHy or raaponatMUty for tto accuracy, com-Matai or nuMnan of any iaforauti t t BHy or raaponatMUty for tto accuracy, com iMiaitai or nuMnan of any iaforaution, apoatatua, arodact or proeaai daictoaa*. or raataaanta tast Ka MM wo«ldnotiafria|*|>clTaUlyoWiMdrifhtt. As part or the Californium-252 Market Evaluation Program, xe.searchers at the Nuclear Reactor Laboratory at The University, of Texas at Austin are investigating measurement techniques .for the. nondestructive assay of special nuclear materials. One technique showing promise is based upon the very discriminating gamma ray spectra of the short-lived fission products, observed following interrogation of fissionable ; .samples by neutrons from a californium-252 neutron source. rCyclic activation is used in this technique to enhance the -detection of gamma radiation from the shorter-lived fission products. ' ' In this paper, the bases of the proposed technique will be presented, followed by the results of experiments performed with a moderated spectrum of interrogation neutrons. pases of Proposed Technique The main features of the proposed active interrogation involve use of the following: 1) Cf-252 neutron*interrogation, 2) cyclic activation" and 3) gamma ray analysis.