Ge Segmented Coaxial Detectors

Features

• For gamma tracking, polarimetry, Doppler effect correction, b decay suppression
• Longitudinal and transversal segmentation of the outer contact by photolithography (up to 36 segments), on all N type crystal geometries
• Neither dead zone nor absorbing material between segments
• Monolithic detectors
• No crosstalk effects
• Increase of granularity of multidetector systems
• Localisation of the interaction and gamma ray tracking capability through coincidence between internal and segment contacts.

Description

Already available on planar detectors, the segmentation provides high quality information signals coming from each detector cell, while taking benefits from the total detection volume.

The segmented coaxial Germanium offer, in addition to the characteristics of coaxial detectors (High efficiency and excellent resolution), the potential due to a good granularity.

Granularity of segmented coaxial detectors qualifies the number of independent cells constituting this detector. Longitudinal and transversal crystal segmentation in 2 or 4 drastically increases the granularity (up to 36 output channels are possible).

Such detectors allow an important reduction of gamma ray broadening due to the Doppler effect.

Moreover, the use of internal and external contacts of the crystal (in case of detector segmentation) gives us an interaction position information:
- Vertically and transversally by analyzing signals induced by mirror charges
- Radially, by making a pulse shape analysis

Accurate location of the interaction points allows not only reduction of the Doppler broadening, but also gamma ray tracking.

The external contact of a detector can be longitudinally or transversally segmented without dead zone generation. All segmentations are possible, on the front face (like a checker-board for example) and laterally (in one or two directions).

For a given n-segment detector, n+1 preamplifiers are used : one for each external segment plus one for the central contact. This design allows a better use of the full detection volume by AC coupling.

Segment separation is such that no cross-talk effect occurs between consecutive channels. Under particular conditions, inner contact segmentation makes it possible to decrease the number of output channels. An externally segmented crystal, 6-fold longitudinally and 2-fold transversally, will offer 2 x 6 = 12 output channels, whereas a 6-fold crystal externally segmented (longitudinally) and 2-fold segmented internally (transversally) will have 6 + 2 = 8 output channels.