Application of Calorimetric Low-Temperature Detectors for the Investigation of Z-Yield Distributions of Fission Fragments

In recent experiments, the new concept of calorimetric low-temperature detectors (CLTDs) was applied for the first time for the investigation of isotopic yields of fission fragments. Fragments from neutron-induced fission were mass-separated by the LOHENGRIN spectrometer at the ILL Grenoble and, after passing silicon nitride membranes used as degraders, detected in a CLTD array. The concept of a CLTD provides a fundamental advantage over conventional ionization-mediated detectors, in particular for heavier particle masses at low energies. Using fissile targets of 235 U, 239 Pu and 241 Pu, nuclear charge separation was studied for selected masses in the region 82 ≤ A ≤ 139. For light fragments, the Z-resolution matches historically best values with conventional techniques, while for heavier masses substantial improvement was attained. We have gained first LOHENGRIN data on the isotopic yields in the range A = 91 to 112 of 241 Pu(n,f). Towards mass-symmetry, known Z-yield data were extended to the range A = 110 to 113 for 239 Pu(n,f). Extended data sets were cumulated for A = 92 and 96 because of a recent request from studies on the reactor antineutrino spectrum. Furthermore, considerable progress was achieved to extend isotopic yield measurements up to the heavy-mass region, hardly accessible until now.