Stacked CdTe gamma-ray detector and its application to a range finder

Stacking several ten layers of thin CdTe devices is a new concept of a gamma-ray detector, featuring both good energy resolution and high efficiency. We have developed prototype models of the CdTe stacked detector which consists of 10 layers and 40 layers based on a newly-developed large CdTe diode. The energy resolution of the detector is measured to be 1–2% (FWHM) from 500 keV to 6 MeV. In addition to the gamma-ray spectroscopy, we propose to use the stack detector as a new type of range finder for gamma-ray sources below a few hundred keV. We demonstrate that the distance of a 57Co radio active source, which is located 5 cm from the detector surface, is measured within the accuracy of 1–2 mm.