A combination of two 4π-detectors for neutrons and charged particles

A combination of two 4π-detectors for neutrons and charged particles is employed for the event-by-event determination of the thermal excitation energy of nuclei produced in spallation reactions. Here the highly efficient charged particle detector BSiB is described while the neutron detector is presented in the preceding paper (Jahnke et al., Nucl. Instr. and Meth. A, this issue). The Berlin Silicon Ball (BSiB) consists of 162 500 μm thick silicon detectors forming a self-supporting complete sphere with a diameter of 20 cm . By means of time of flight and energy H, He, IMFs, FFs, and HRs are identified. The lower detection thresholds are about 2 MeV for all detectors and about 0.5 MeV for 16 selected detectors in the forward direction. In addition, 6 ancillary four-fold detector-telescopes are employed with isotopic resolution up to C, and Z-identification up to Na. The geometric efficiency of BSiB has been determined experimentally to 80.4±1.0% for the standard configuration with 151 mounted detectors. Efficiency losses due to energy thresholds, target shadow, multiple hits and reaction kinematics are calculated for protons, helium, fission fragments, and heavy residues released in 1.2 and 2.5 GeV proton-induced spallation reactions on Fe and Au. The results are supported by experimental data for binary fission, which have been analysed as a function of excitation energy.