Balloon Flight Test of a Compton Telescope Based on Scintillators with Silicon Photomultiplier Readouts

摘要

We present the results of the first high-altitude balloon flight test of aconcept for an advanced Compton telescope making use of modern scintillatormaterials with silicon photomultiplier (SiPM) readouts. There is a need in thefields of high-energy astronomy and solar physics for new medium-energygamma-ray (~0.4 - 10 MeV) detectors capable of making sensitive observations. Afast scintillator- based Compton telescope with SiPM readouts is a promisingsolution to this instrumentation challenge, since the fast response of thescintillators permits the rejection of background via time-of-flight (ToF)discrimination. The Solar Compton Telescope (SolCompT) prototype was designedto demonstrate stable performance of this technology under balloon-flightconditions. The SolCompT instrument was a simple two-element Compton telescope,consisting of an approximately one-inch cylindrical stilbene crystal for ascattering detector and a one-inch cubic LaBr3:Ce crystal for a calorimeterdetector. Both scintillator detectors were read out by 2 x 2 arrays ofHamamatsu S11828-3344 MPPC devices. Custom front-end electronics providedoptimum signal rise time and linearity, and custom power supplies automaticallyadjusted the SiPM bias voltage to compensate for temperature-induced gainvariations. A tagged calibration source, consisting of ~240 nCi of Co-60embedded in plastic scintillator, was placed in the field of view and provideda known source of gamma rays to measure in flight. The SolCompT balloon payloadwas launched on 24 August 2014 from Fort Sumner, NM, and spent ~3.75 hours at afloat altitude of ~123,000 feet. The instrument performed well throughout theflight. After correcting for small (~10%) residual gain variations, we measuredan in-flight ToF resolution of ~760 ps (FWHM). Advanced scintillators with SiPMreadouts continue to show great promise for future gamma-ray instruments.