E.G. Adelberger and H.E. Swanson

We built an integral module containing the detector, preamp and thermoelectric cooler element for use in an ultrahigh vacuum system. The module is shown in the following figure. The detector plugs directly into the front of the preamp box which accepts either 9mm X 9mm or 20mm X 20mm Hamamatsu PIN diodes. Both the detector and preamp are cooled by a thermoelectric element. Temperature is sensed at the detector and an external feedback circuit holds the temperature constant to better than 0.1 deg C. This is important for long term stability as the module runs in a cold shroud and the signals from both preamp and detector have a temperature dependence. The preamp electronics uses a small hybrid developed for the emiT PIN diode detector (see Section 1.9). It was necessary to reduce the gain so the dynamic range included 6 MeV protons. The preamp box seals the electronics from the vacuum. The copper rod conducts heat generated by the thermoelectric element to a heat sink external to the vacuum. The module is placed in an ion-pumped ultrahigh vacuum system to avoid condensing material on the detector surface.

The detector was operated at 10° C. which reduced the leakage current to less than 0.01 microamps. Under these conditions the resolution for 3 MeV Protons was about 6 keV, while the pulser resolution was about 5 keV.