New Experimental Results on the Cumulative Yields From Thermal Fission of $^{235} {\rm U}$ and $^{239}{\rm Pu}$ and From Photofission of $^{235} {\rm U}$ and $^{238} {\rm U}$ Induced by Bremsstrahlung

Abstract

The yields of fission products are one of the main characteristics of the fission process. In the field of nuclear waste package characterization, using Photon Activation Analysis (PAA), these yields are needed in order to optimize a technique enabling the identification of actinides ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">238</sup> U, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">239</sup> Pu), based on the detection of delayed gamma-rays. As the lack of data in the field of photofission is strongly penalizing for the tuning of this technique, we designed several measurement campaigns in order to determine the yields of various photofission products. The experiments were based on the detection of delayed gamma-rays and delayed neutrons emitted during the same measurement. The feasibility of this technique was first verified in the context of active neutron interrogation, by comparing experimental results for the thermal fission of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">239</sup> Pu with reference values provided by several recent databases (ENDFB 6.8, JEFF 3.1). The method was then applied to active photon interrogation, in order to obtain the yields of nuclides formed by the photofission of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">238</sup> U. This paper presents the experimental results obtained with these measurements.