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 sources 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 new detector concept of a thermal detector provides a fundamental advantage over conventional ionization-mediated detectors, in particular for heavier particle masses at low energies. Using fissile targets of U-235, Pu-239 and Pu-241, nuclear-charge separation was studied in the mass 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 light-mass group of 241Pu. Towards mass-symmetry, known Z-yield data were supplemented in the range A = 110 to 113 for Pu-241 and Pu-239. Extended data sets were cumulated for A = 92 and 96 due to a recent request from studies on the reactor anti-neutrino spectrum. Furthermore, considerable progress was achieved to extend isotopic yield measurements up to the heavy-mass region, hardly accessible until now.