Overview of the Gamma Ray Tracking Project

Modelling of gamma-ray interactions in Germanium
A project student at University of Surrey is setting up a commercial Monte Carlo code for modelling electron-hole transport in Germanium which will work with existing code for simulation of Compton interaction during scattering. The effectiveness of the segmented detector used in this project, and other possible detector designs, in true 3-d position determination for tracking can then be modelled. In parallel, a post-doc has developed Compton scattering algorithms for gamma ray track reconstruction and is verifying the simulation. This initial work will later be exploited by applying the modelling and simulation techniques to novel detector designs (asymmetrical or offset contacts, resistive contacts etc.) with the aim of optimising tracking performance in the following generation of segmented detectors.

Design and Procurement of Detectors
Physicists and engineers from Daresbury, Liverpool and Surrey have produced designs and specifications for two segmented coaxial Germanium detectors. One has regular 6x6 segmentation and the other 6x4 with smaller segments nearer the front of the detector. Both detectors have warm FETs and fast preamplifiers. Both detectors have been delivered and are under test using a data acquisition system which digitizes pulse shapes from all segments simultaneously.

Data Acquisition and electronics
Measurements are being made at Universities of Surrey and Liverpool on the segmented Ge detectors using a simple Compact PCI electronics and DA system which stores a short period of raw data from flash ADCs sampling the preamplifier charge outputs. During the second phase of the project, electronics is being designed by Daresbury Laboratory to implement gamma ray position determination algorithms based on the simulation work and on analysis of pulse shapes recorded during extensive tests of a segmented Germanium detector at University of Liverpool. The algorithms will be checked and improved in tests conducted using prototype electronics attached to a segmented detector before building VME electronics to enable experimental data to be collected from the segmented detectors. New timing algorithms will also be implemented and tested based on simulation results.

Software will be developed at Daresbury and Liverpool in parallel with the first and second phases of the project to gain match the data ready for tracking and to implement the tracking algorithms as and when they become available. Software will also be developed for controlling the VME electronics and analysing the data, including the visualisation of tracked data.

Testing in a "real" Physics experiment
The third phase of the project will be to use the detectors, electronics and software to perform experiments. Fine tuning to optimise the tracking algorithms will continue during this phase where necessary.

More details are available from the project manager, Ian Lazarus.

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