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

Santwana Dubey,Werner Lauterfeld,Manfred Mutterer,Stefan Stolte,Jose Gomez,Ulli Köster,Saskia Kraft-Bermuth,Patrick Grabitz,Peter Egelhof,Pascal Scholz,Aurelien Blanc,Shawn Bishop,Artur Echler,Friedrich Gönnenwein,U Köster

doi:10.1051/epjconf/201819304002

Abstract

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 of235U,239Pu and241Pu, 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 of241Pu. Towards mass-symmetry, known Z-yield data were supplemented in the range A = 110 to 113 for241Pu and239Pu. 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.

Highlights

For the light fragment group, good Z-resolution was obtained, sufficiently high to clearly separate individual nuclear charges in the residual-energy spectra and, as expected, with the resolving power improving towards higher energy losses
Known Z-yield data were supplemented in the range A = 110 to 112 for 241Pu, and A = 111 to 113 for 239Pu
The investigation of isotopic yields for the heavier masses A > 108 (Fig. 5c) was started with the aim to study the onset of even-odd effects in the transition region from the light fragment group towards the symmetry region, which is of high interest for verification of nuclear models [19]

Summary

Introduction

Due to its perfect mass resolution, LOHENGRIN has contributed more high resolution data sets on mass, nuclear charge and energy distributions than any other method, with the isotopic yields, being restricted to the region of light fragment masses [5]. We have applied a new experimental approach to determine isotopic yields at LOHENGRIN by the passive absorber method using an array of calorimetric lowtemperature detectors (CLTDs) instead of an ionization chamber for the residual energy measurement.

Results

Conclusion