With the knowledge of the scattered electron's energy and direction, the possible directions of the incident gamma ray describe a small arc on the sky, rather than a complete ring, greatly reducing potential source confusion and increasing sensitivity. First and foremost, the use of SSDs gives the potential to track the Compton recoil electron. The time of flight of the photon from D1 to D2 can also be measured to discriminate downward from upward (background) events.Īnother feature of TIGRE is that it was also designed to overcome many of the common limitations of Compton telescopes. The locations of the interactions in D1 and D2 are found by timing and pulse height analysis, and can be used to give the direction of the scattered photon. The Compton scatter formula can then be used to calculate the scatter angle of the gamma ray. The gamma ray is then absorbed in the bottom layer (D2).
Ideally, an incoming gamma ray Compton scatters in the top layer (D1), with the energy of the recoil electron being measured there.
This capability greatly enhances the instrument's efficiency, as well as providing the ability to perform as a gamma-ray polarimeter. This design feature is new for Compton telescopes, and allows TIGRE to detect large angle Compton scatter events. The CZT is arranged to form a five-sided box surrounding D1. The second component, D2, consists of 5 to 10 layers of cadmium zinc telluride (CZT) strip detectors. These detect charged particles passing through the detector, giving X and Y coordinates of the interaction location with a resolution of less 1 mm. The first, called D1, consists of 50 or more layers of double sided silicon strip detectors (SSDs). This facilitates background rejection, improved sensitivity, and image reconstruction.Īt left we can see an scheme of his configuration (click to enlarge).īasically is composed by two major elements. When combined with the direction and energy of the Compton scattered gamma ray a unique incident direction for each photon event is determined.
It uses multi-layers of thin silicon detectors to track and measure the energy losses of Compton recoil electrons. This instrument is a balloon-borne telescope of a new kind for making gamma-ray observations in the MeV energy range.
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