Performance study of a large CsI(Tl) scintillator with an MPPC readout for nanosatellites used to localize gamma-ray bursts
Abstrakt
We are designing a fleet of nanosatellites to perform accurate position determinations of short-duration gamma-ray bursts by measuring arrival time differences. To achieve sufficient photon statistics to measure the arrival times precisely under the severe limitations of size, mass and power consumption, we propose the use of large-area CsI(Tl) scintillators which provide a high light output and the use of a small-sized multipixel photon counters (MPPC), a kind of SiPM, that have low power consumption.
We plan to use one of the latest-model MPPCs provided by Hamamatsu Photonics, namely, S13360-6050CS, which has an active area of 6 x 6 mm(2). We have compared the performance of two scintillators of different sizes (150x75x5 mm(3) and 100x75x5 mm(3)); the bigger one is the maximum size that can be mounted on a three-unit satellite, according to CubeSat standards.
We have found that the light yield of the bigger scintillator is lower than that of the smaller one, but the difference is only approximately 13%, and each has an energy threshold of similar to 10 keV at 25 degrees C. We have tested one-and two-MPPC readout and confirmed the same energy thresholds.
The light yield for the two-MPPC readout is 1.4 times as high as that for the one-MPPC readout. We have also examined the position dependence of the light yield by using radiation from a Am-241 (59.5 keV) source, and confirmed that uniformity was improved, and energy resolution got better by similar to 7% for two-MPPC readout.