Analysis of CdTe Probes

Probes have been fabricated from semiinsulating CdTe and their efficiency for photoevents compared with silicon devices of similar active volumes (?6 mm3). CdTe probes were found to be 150 times more efficient to 122 keV photons and about an order of magnitude more efficient for 60 keV x-rays. The resolution (FWHM) for probes was limited to ?15 keV by cable capacitance at lower photon energies and at higher energies by the escape of the photoelectron from the active volume. For uncapsulated devices of comparable active volumes 8 keV and 10 keV resolution was obtained for 24lAm and 57Co. For 50 mm3 devices, resolutions of 5% were obtained for 137Cs and 60Co and peak to total ratios were comparable to (137Cs) and smaller than (60Co) the ratio of the photoelectric to total absorption coefficients. The photoelectric absorption coefficient was measured for CdTe at 122 keV and found to be 5.4 ± 0.4 cm-1. Theoretical spectra were computed and were only in qualitative agreement with experimental results.