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
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.