Development of a silicon gamma ray spectrometer

We present the initial results obtained with double-sided silicon strip detectors used as a non-imaging gamma ray spectrometer. Silicon detectors have previously been proposed as sensors for the scatterer of a regular Compton telescope, or as sensors for a multiple scatter Compton imager where three or more interactions in the silicon are used to image and determine the energy of a gamma ray, even if all the energy is not absorbed. This work extends that concept to the case where the source location is known, as in solar physics, and where the main interest is a high-resolution spectrum. With the source location known, only two interactions are required to reconstruct a spectrum of the source. We made a proof of concept demonstration using two small silicon detectors. The detectors were 63 x 63 mm in area and 2 mm thick, with 0.9 mm orthogonal strips on both faces. A full-energy peak with an energy resolution of ∼ 40 keV was obtained at 662 keV. This was in good agreement with our simulations. Using detectors with a finer strips pitch an energy resolution of 15 keV (68% containment) can be achieved at 662 keV. This is limited by the momentum distribution of the electrons in silicon. The energy resolution can be improved by kinematically selecting events, although at the cost of detector efficiency. Another unique feature of this approach is the fact that a spectrum is reconstructed with a full energy peak but without any Compton continuum.