Caltech Gamma Ray Imaging Payload (GRIP)
The Gamma Ray Imaging Payload (GRIP2) is a balloon borne coded-aperture telescope designed for imaging observations of galactic and extragalactic gamma-ray sources. GRIP2 incoorporates a rotating hexagonal coded aperture mask and a 70 cm diameter NaI(Ti)/CsI(Na) phoswich detector. It is optimized for imaging observations in the energy range 30 keV to 500 keV, with usable sensitivity to 2 MeV. The instrument was most recently flown from Alice Springs, NT Australia in early October 1995.
GRIP-2 Data Analysis/Results
Alice V Campaign Galactic Plane Image
30 - 75 keV
75 - 150 keV
The GRIP-2 detector is a large-area
imaging phoswich detector, and provides a substantial collecting area
and sensitivity improvement over the original GRIP detector. The
NaI(Ti)/CsI(Na) detector is optimized for imaging observations in the
energy range 30 keV to 600 keV, with usable sensitivity up to 2 MeV.
The 1.5 cm thick NaI(Ti) detection element is fabricated from a single
crystal, while the CsI(Na) Compton shield backing the NaI is composed
of a mosaic of hexagonal scintillator pieces. The detector is
instrumented with 119 photomultiplier tubes (Hamamatsu 2.5" diameter
R1410) which view the scintillator through a lead glass optical
window. The lead glass reduces the rate of low energy events in the
CsI, easing the requirements on the electronics for phoswich
discrimination. The PMT's are mechanically constrained against the
lead glass window by a rigid aluminium strong back structure, assuring
a uniform optical coupling between the PMT's and the glass.
Sixty-nine light fibers, each coupled to an individual LED are
symmetrically located in the strong back. These provide a programmed
sequence of individual light pulses over the full active area of the
detector for both ground and in-flight calibration of the instrument.
Photos from Alice V