Ge Encapsulated Detectors

Encapsulated Germanium Detectors for Gamma Measurements

Features

• Total reliability
• Easy handling and exchange
• For compact construction of multi-element detectors
• Easy regeneration in standard ovens, without pumping, in case of radiation damages
• In situ annealing in space applications
• Long detector life time
• Wide range of shapes (pentagonal, hexagonal) for compact matrix assemblies
• Essential for complex cryostat development, particularly with segmented detectors

Description

Mounting and operation of several detectors in a common vacuum with a minimum spacing between consecutive elements are difficult. Encapsulation techniques have been developped to minimized such problems.

Putting into vacuum each encapsulated detector in an individual aluminum cap makes it possible to separate the vacuum of each detector from the cryogenic vacuum shared by all detectors. Encapsulation drastically enhances the germanium detector reliability.

This technology is of general interest for many applications, in space in particular. Encapsulated germanium detector may be easily handled by the users ; they may be stored, exchanged or rearranged so to be adapted to different applications with different types of cryostats. A capsule may be regenerated many times and can be thermal annealed in an ordinary oven from neutron radiation damages, without pumping.

The life time of such a device may be estimated to a minimum of 7 years without service. Encapsulated detectors hardiness enable a wide application range, such as part of the payload of nacelles, space launchers, etc...

Compact arrays may be designed. The capsules manufactured for EUROBALL offers a typical wall thickness of 0.7 mm with a distance between cap and crystal of only 0.7 mm. Those encapsulated detectors may be in contact to each other offering thus a 3 mm distance between consecutive crystals and a 1.4 mm total aluminum wall thickness.

For a better follow-up of the scientific progress, some segmented crystals were encapsulated so to offer, in addition to preceeding advantages, a high granularity.
The detector granularity qualifies the number of independent cells constituting this detector. Such detectors allow a significant reduction or gamma ray broadening ue to the Doppler effect. Moreover, the use of internal and external contacts of the crystal provides an information on the interacting position:
- Vertically and transversally, by analyzing siglals induced by mirror charges,
- Radially by making a pulse shape analysis.
Accurate localization of the interaction points allows not only reduction of the Doppler effect broadening, but also gamma ray tracking.
In addition of these advantages, the segmented detector encapsulation allows the design of complex cryostats, thus signal optimization which is of much interest for pulse shape analysis.