Performance of multi-element CdZnTe detectors

Single-element CdZnTe detectors are limited in size, and therefore efficiency, by the poor hole transport, even with a coplanar grid. We are investigating the possibility of a 27-element (3 × 3 × 3) array using 15 mm × 15 mm × 15 mm elements for gamma-ray energies to 10 MeV for NASA planetary missions. We present experimental results for combinations of various size coplanar grid detectors using NIM electronics and energies to 6.1 MeV. Summation of the signals after linear gating and requiring coincidence produces only a small increase in the energy resolution. Our results indicate that good efficiency and a spectrum not complicated by a large Compton continuum can be achieved by simply summing the spectra from 15 × 15 × 15 mm detectors for gamma-ray energies below about 2 MeV. Above 2 MeV, 2-fold coincidence might be required, depending on the spectrum, to suppress the Compton continuum and escape peaks. We use a Monte Carlo calculation to predict the performance of the 27-element array for a lunar highlands spectrum. Such ambienttemperature, high-efficiency, good-resolution arrays will facilitate new NASA missions to determine elemental composition of planetary bodies and terrestrial applications requiring high-efficiency, good-resolution portable instruments.