Large, High Resolution CdTe Gamma Ray Sensors

An important need of the nuclear industry is an uncooled, high resolution nuclear spectrometer which would be useful in many applications including post accident monitoring, pipe inspection and health physics. Cadmium telluride detectors with high atomic number and ability to operate at room temperature, have for years been recognized as having the potential to fill the requirements of such an instrument. Previous work indicated that excellent high energy spectroscopy could be achieved using CdTe detectors with rise time discrimination. However, the resulting loss of efficiency was often unacceptable. Recently, a program h as been conducted to develop a CdTe spectrometer intermediate in resolution between NaI and HPGe systems using a PIN diode structure. This allows a much larger operating voltage and therefore a much increased photopeak fraction. By combining this device structure with the pulse discrimination technique, both high resolution and good sensitivity can be achieved. In addition the low noise and leakage current of the PIN devices, makes practical the assembly of an array with a single preamp to further increase the sensitivity.