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PoRTIA
The Piggyback Room Temperature Instrument for Astronomy (PoRTIA) has two room temperature semiconductor detectors housed in a small pressure vessel. PoRTIA was flown on three balloon flights with three different shielding configurations. Initially, PoRTIA was flown without GRIS on a small balloon from Palestine, Texas in June 1995. During this flight, the detector was passively shielded with 2 mm of lead and collimated to a 5 x 5 deg FOV.
In October 1995, PoRTIA flew on GRIS in Alice Springs. It was mounted on top of the GRIS blocking crystal and the 15 cm thick NaI GRIS anticoincidence shield used veto background events. The detectors were passively shielded from above and collimated to a 10 x 10 deg FOV. In the third flight, the PoRTIA instrument was mounted inside the GRIS NaI shield and blocking crystal. A Ge detector served as a monitor of the radiation environment inside the shield. Completely enclosed in the GRIS active shield, PoRTIA used minimum passive shielding and no collimator. A large (2.5 x 2.5 x 0.19 cm) CdZnTe detector was flown in all three flights so that valid background comparisons could be made. During each flight, the PoRTIA pressure vessel was surrounded by an evaporative cooler to provide a stable operating temperature below 0 deg C during flight. Data from the larger CdZnTe detector are shown in the figure below. All three flights are included; the data from the two Alice Springs flights were divided by 0.72 to correct for the difference in background levels between Palestine and Alice Springs (Gehrels 1992). Clearly, active shielding that completely surrounds the detector is crucial to achieve a low background with CdZnTe detectors. Measured In-Flight CZT Backgrounds
PoRTIA Team
Steve Derdeyn Chris Miller Steve Snodgrass
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This file was last modified on 5-Dec-96 |
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