K. Wisshak, K. Guber, F. Käppeler, J. Krisch, H. Müller, G. Rupp, F. Voss

Kernforschungszentrum Karlsruhe, Institut für Kernphysik
D-7500 Karlsruhe, Federal Republic of Germany

The 4π array of 42 BaF2 crystals which has been set up at Karlsruhe over the past three years is intended for precise measurements of neutron capture cross sections in the energy range 3 < En < 200 keV, primarily for astrophysical applications. We present the essential features of the detector, e.g. mechanical construction, setup of the individual detector modules, and the stabilisation of the entire system, which is operated as a calorimeter summing all gamma-rays of the capture cascade. Time and energy resolution of the individual detector modules are 0.4 ns and 5.7% at 2.5 MeV gamma-ray energy, while the corresponding values for the system as a whole are 0.5 ns and 7.1%, respectively. The performance of the detector under experimental conditions is demonstrated in various test measurements on gold samples.

KEYWORDS: BaF2 scintillators, 4π gamma-ray detection, neutron capture cross sections, 3 < En < 200 keV