The Karlsruhe 4π BaF2 detector

The Karlsruhe 4π BaF₂ detector is composed of 42 crystals of 1.5-l volume, shaped as hexagonal or pentagonal truncated pyramids, forming a spherical shell of 20-cm inner diameter and 15-cm thickness. Each crystal is covered by a thin reflector and viewed by a phototube, thus representing a complete gamma-ray detector. The energy resolution of the individual detector modules is 10-11% at 662- keV and 4-5% at 6.13-MeV gamma-ray energy, while the time resolution as measured with a ⁶⁰Co source is 400-500 ps. The overall efficiency of the entire detector is about 100% for gamma-rays up to 10 MeV. Compared to 4π detectors with comparable efficiency made from NaI (TI), the present setup offers five times better time resolution at similar resolution in gamma-ray energy. The detector will be used for the accurate determination of neutron capture reactions in the neutron energy range from 3 to 200 keV primarily for astrophysical applications. The performance of the detector under experimental conditions is demonstrated in various test measurements on gold samples