High energy resolution array

DIAMOND Berkeley High Energy Resolution Array... 

The addition of the gas detector offers significant improvements over the bare phoswich - approximately a factor of two in energy resolution and improved spatial resolution. For single events, around 1mm is achievable at 25 keV, compared with 16 mm for the bare crystal. For fluorescent pairs (section 2.1) simulations show that the very high light yield from the chamber still permits the true position of each event to be deconvolved from the overlapping light distributions despite the coarse 7x7 photomultiplier array [13]. 

An imaging high-pressure detector can be envisioned from an array of vertically cylindrical ionization chambers, with spatial resolution set by each tube diameter. It may further be possible to segment the collection anode, to derive an azimuthal co-ordinate within each detector and to use signal risetime to get a radial co-ordinate. The precision of such techniques, and the low-energy performance of such detectors is critically dependent upon the preamplifier noise. It may be possible to achieve around 50 electrons rms with modern (optical feedback, or no feedback) amplifiers resulting in an energy resolution of a few percent at 100 keV. 

The detection efficiency of silicon is low above 20 keV. A higher-Z, pixellated, detector is therefore included behind the silicon CCD. The silicon is therefore thinned down to the active thickness to minimise unwanted absorption. Due to the depth of focus of the optics, the second detector may be up to 15 mm beJiind the silicon CCD. In order to determine changes in source continua above 20 keV and to resolve cyclotron lines, we require to combine high detection efficiency with an energy resolution of between 1-2 keV over the energy band 20-60 keV. We envisage the use of a hybrid array of diodes constructed on... 

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