Answer to Question #14473 Submitted to "Ask the Experts"
Category: Instrumentation and Measurements
The following question was answered by an expert in the appropriate field:
We did not use HPGe detectors for at least 10 years. what are the expected troubles if we use them again?
As you are likely aware, storing an HPGe detector for long periods at room temperature is not a generally recommended procedure.
If you have a typical coaxial type detector, one degradation that will most likely have occurred has to do with the fact that the n-contact may be a lithium-diffused electrical contact, and over extended times, months to years, the lithium ions will drift in the contact, resulting in an effective increase in thickness, which represents a dead layer to incoming photons, that will typically degrade the efficiency of the detector, most notably at lower photon energies.
Other effects are also possible. An obvious possibility relates to physical damage resulting from rough/improper handling. A knock on the end cap could produce a defect in the vacuum seal, requiring special service. A less obvious but observed defect in the vacuum integrity may result from diffusion of ambient gases, especially low mass gases such as helium, through the vacuum seals producing a loss of vacuum.
Of course, the longer a detector is left in storage at room temperature, the more likely it typically is that it will encounter some negative impacts that could alter performance, and 10 years is a long time.
In an earlier question we have discussed considerations that apply in recooling the detector, and you can review that question and response at this link.
I wish you well as you attempt to resurrect your detector(s).
George Chabot, PhD, CHP