Potential and Application of Large-area Si(Li) Detectors Developed for the GAPS Project

The lithium-drifted silicon [Si(Li)] detectors that were newly developed for the General AntiParticle Spectrometer (GAPS) experiment features a large sensitive area and a thick active layer. This Si(Li) detector model was developed for compatibility with mass production and provides a high energy resolution for X-rays at −40℃, far above the liquid nitrogen temperatures required for conventional Si(Li) X-ray detectors. Here, we cooled the GAPS Si(Li) detector down to nearly −100℃ and found that its leakage current decreases exponentially as cooled and reaches sub pA below −80℃. This substantiates that much better energy resolution can be expected at around −100℃. By dividing the sensitive area into finer structure, the energy resolution will be further improved to sub-keV scale. The improved Si(Li) detector will be useful not only for next-generation scientific experiments beyond GAPS but also for imaging apparatus in other fields such as medical and biological applications as well as security inspections. As an example, a Compton-camera-type three-dimensional single-photon emission computed tomography (SPECT) is expected.