Reverse-Electrode Coaxial Ge Detectors

Features

• Ultra-thin ion implanted contacts
• Spectroscopy from 3 keV up
• Radiation damage resitiant
• Excellent timing resolution
• High energy rate capability
• Diode FET protection
• Warm-up/HV shutdown
• High rate indicator

Description

The Reverse-Electrode detector (REGe) is similar in geometry to other coaxial germanium detectors with one important difference. The electrodes of the REGe are opposite from the conventional coaxial detector in that the p-type electrode, (ion-implanted boron) is on the outside, and the n-type contact (diffused lithium) is on the inside. There are two advantages to this electrode arrangement – window thickness and radiation damage resistance.

The ion-implanted outside contact is extremely thin (0.3 mm) compared to a lithium-diffused contact. This, in conjunction with a thin cryostat window, extends the response to below 5 keV, giving this detector a dynamic range of 2000:1. Needless to say, this dynamic range exceeds the 100:1 offered by most analysis systems so the detector is unlikely to be covering the range of 5 keV to 10 MeV at once.

The radiation damage resistance properties of the REGe detector come about for the following reason. It has been found that radiation damage, principally due to neutrons or charged particles, causes hole trapping in germanium. Unlike the case of the conventional coaxial detector, holes are collected by the outside electrode of the REGe detector. Since a much greater amount of the active detector volume is situated within a given distance, D R, of the outside contact, than of the inside contact (Volume » R²) it follows that, on average, holes have less distance to travel if they are attracted to the outside contact than if they are attracted to the inside contact. With less distance to travel, they are less likely to be trapped in radiation damaged material. The extent of the improved resistance to radiation damage depends on other facts, of course, but experimental evidence suggests that the REGe detector may be 10 times as resistant to damage as conventional Coaxial Ge detectors.