Abstract
Low background experiments place stringent constraints on amount of radioactive impurities in the materials used for their assembly. Often these are in conflict with the constraints placed on the materials by their roles in the experiment. This is especially true for certain electronic components. A high value, high voltage capacitor for use in low background experiments has been developed from specially selected radiopure materials. Electroformed copper foils are separated by polyethylene napthalate (PEN) foils and supported within a PTFE teflon spiral coil tube. The electrical performance as well as radiopurity are scrutinized here. With some minor modifications to tune the performance for the application, this capacitor can be well suited for a variety of applications in low background experiments. Here the use of the capacitor for high voltage (HV) decoupling in the operation of high purity germanium (HPGe) detectors is demonstrated.
Highlights
Low-background physics experiments are searching for events with rare signals
The breakdown voltage of polyethylene napthalate (PEN) is 300 MV/m [4]. This suggests that the capacitor with 50 μm of PEN separating the conducting planes could be operated with a voltage as high as 15 kV
A good resolution achievable in high purity germanium (HPGe) detectors is of O(0.77) keV or an equivalent noise charge (ENC) of 112 electrons r.m.s [17]
Summary
Low-background physics experiments are searching for events with rare signals. The signals are often rarer than typical backgrounds. The materials that are in close contact to a low background detector typically have one or more of several functions: mechanical support, electronic support, shielding. There are potentially many uses for such a capacitor in low background experiments This may be used as a filter capacitor in the HV supply line or as a decoupling capacitor to measure the charge collection on a high voltage plane of a detector. To demonstrate the necessity of this work, a measurement of the radioactivity of a sample of commercially available 1.2 nF NP0 type capacitors was performed. These capacitors are specified to meet the electrical requirements both at room temperature as well as at liquid nitrogen temperatures.
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