Gated-Dynode Photomultiplier Tube Assembly for the Boronated Scintillator Detector of the ISS-CREAM Experiment
We present the design of a four-photomultiplier tube (PMT) assembly for measuring light generation in theBoronated Scintillator Detector (BSD) of the Cosmic Ray Energetics And Mass experiment for the InternationalSpace Station (ISS-CREAM). The light produced in the scintillator includes a contribution from the captureof thermalized neutrons produced in cosmic ray interactions, as well as delayed fluorescence, in the range ofseveral microseconds following the incident cosmic ray impact. The BSD is held in an insensitive state until acosmic-ray trigger causes a rapid turn on of the PMTs to detect late light signals, several microseconds afterthe trigger. The design includes two pulsed high-voltage supplies, which serve to gate the first two dynodesof the Hamamatsu R1924A PMTs used in the assembly. When the dynode gates are held in the "off" state,this scheme is shown to suppress >105 photons from injection into the tube's multiplier stage, while beingcapable of rapid switching into a stable operating mode in less than 1 s. This mitigates any backgroundsfrom afterpulsing that might otherwise be present in the PMT response following the cosmic ray incidence.