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 ²³⁵U, ²³⁹Pu and ²⁴¹Pu, 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 ²⁴¹Pu(n,f). Towards mass-symmetry, known Z-yield data were extended to the range A = 110 to 113 for ²³⁹Pu(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.