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Best Practices for HPGe Detector Handling and Maintenance

These suggestions herein are provided to ensure the performance of your HPGe detector is optimum and may provide you with early indications of issues with your system. The handling of a detector when installing in a shield should be done with extreme care. The end cap is made from a thin wall material. Lifting or handling the detector by the end cap with any force can cause the end cap to flex. Flexing the end cap should avoided in all cases. Many detectors have an entrance window fixed to the front of the end cap. This flexing could lead to a small vacuum leak at the entrance window.

Upon receipt of your HPGe detector the detector system should be cooled and tested for the expected performance.

Cool the system. Filling the dewar with liquid nitrogen should be done with care to prevent the cryostat and the detector capsule from prolonged exposure to cold gases. A simple fan or paper/cardboard shielding of any cold gases from the end cap or other exposed cryostat surfaces can prevent the rapid cooling of an O-ring seal which can prevent a vacuum breach.

Once the detector is cold we recommend recording the temperature of the end cap with respect to the ambient room temperature. This can give you a reference for the vacuum performance as the system ages. The vacuum should be good enough to ensure the difference in the end cap temperature is no more than 5 degrees C from the ambient room temperature.

Recording of the measured energy resolution is not only a check of performance, but a good reference should conditions change.

For storage of the system it should be kept cooled in liquid nitrogen. If stored at room temperature (not advised) then the system should be cooled to liquid nitrogen at least monthly for a minimum of 48 hours and tested to ensure the system performance is OK.

When installed in a shield the system should not be in electrical contact with the shield or table. Tape or insulating plastic may be required if the shield is very close to the cryostat. This includes the cable ends where the connectors can be in electrical contact with the shield or table. All power connections for the detector electronics and any PC should share the same circuit from the mains. Special care should be taken to ensure the HV cabling is well grounded and the cable is not in proximity to any known radiant sources for noise (i.e., motors or other high voltage switching supplies). Dirty cable connections are a common source of noise. Methanol or alcohol can be used to clean cable connections if newer cables are not an option.

If your detector system has a Be or Carbon Fiber window the protective cover should be kept in place when not making critical measurements.