Demonstration of a dual-range photon detector with SDD and La[Br.sup.3]([Ce.sup.3+]) scintillator

A novel concept for improving gamma ray spectroscopy in compact instruments is presented. The dual-range photon detector (DRPD) consists of a silicon drift detector (SDD) which is optically coupled with a La[Br.sup.3]([Ce.sup.3+]) crystal. In contrast to similar configurations investigated so far the SDD points to the radiation source. Pulse shape discrimination allows separating the distinct detection mechanisms which correspond to gamma absorption in the SDD or in the scintillator, respectively. This arrangement combines for the first time the excellent performance of an SDD as X-ray detector on its own with the striking energy resolution of a La[Br.sub.3] ([Ce.sup.3+]) scintillator read out by an SDD. The concept was successfully demonstrated with two experimental SDD-La[Br.sub.3]([Ce.sup.3+]) systems. An energy resolution (FWHM) of 2.7% and 2.9% at 662 keV was measured with the two distinct systems operated in scintillator mode whereas scintillator-photomultiplier combinations with the same crystals yielded only 3.3% and 3.1%, respectively. The SDD mode provided an energy resolution surpassing the scintillator resolution by about one order of magnitude in the limited energy range up to 100 keV. Measurements with various radioactive sources demonstrated that this mode uncovers line structures which could never be resolved with scintillators or CZT detectors. Homeland security programs could profit from the proposed detector concept. Index Terms--Energy resolution, gamma-ray spectroscopy, homeland security, pulse shape discrimination, radioisotope identification, scintillation detectors, silicon detectors.