Diamond Scattering Detectors for Compton Telescopes

Abstract

We present our work to demonstrate the suitability of artificial single-crystal diamond detectors (SCDDs) for use as the scattering medium in Compton telescopes for medium-energy gamma-ray astronomy. SCDDs offer the possibility of position and energy resolution comparable to those of silicon solid-state detectors (SSDs), combined with efficiency and timing resolution so-far only achievable using fast scintillators. It has been shown that SCDDs fabricated using chemical vapor deposition (CVD) show good energy resolution (~7 keV FWHM), comparable to SSDs, with much faster time response (~ns rise time) due to higher electron/hole mobilities. They are also temperature- and light-insensitive, and radiation hard. In addition, diamond is lowZ, composed entirely of carbon, but relatively high-density (3.5 g cm-3) compared to silicon or organic scintillator. SCDDs are therefore an intriguing possibility for a new Compton scattering element: if patterned with ~mm-sized readout electrodes and combined with a calorimeter composed of fast inorganic scintillator, such as CeBr 3 , read out by silicon photomultipliers (SiPMs), SCDDs will enable a compact and efficient Compton telescope using time-of-flight (ToF) discrimination to achieve low background. Such an instrument offers the exciting potential for unprecedented sensitivity, especially at energies < 1-2 MeV, on a small-scale mission utilizing recently available SmallSat buses (payload mass < 100 kg). We present the status of our laboratory development effort to design, fabricate, and test a small prototype Compton telescope.