Shah, Kanai S. | Search NASA

DOE OSTI2017

History and current status of strontium iodide scintillators

Eu-doped strontium iodide single crystal growth has reached maturity and prototype SrI 2 (Eu)-based gamma ray spectrometers provide detection performance advantages over standard detectors. SrI 2 (Eu) offers a high, proportional light yield of >80,000 photons/MeV. Energy resolution of <3% at 662 keV with 1.5” x 1.5” SrI2(Eu) crystals is routinely achieved, by employing either a small taper at the top of the crystal or a digital readout technique. These methods overcome light-trapping, in which scintillation light is re-absorbed and re-emitted in Eu 2+ -doped crystals. As a result, its excellent energy resolution, lack of intrinsic radioactivity or toxicity, and commercial availability make SrI 2 (Eu) the ideal scintillator for use in handheld radioisotope identification devices. A 6-lb SrI 2 (Eu) radioisotope identifier is described.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Position sensitive solid-state photomultipliers, systems and methods

An integrated silicon solid state photomultiplier (SSPM) device includes a pixel unit including an array of more than 2.times.2 p-n photodiodes on a common substrate, a signal division network electrically connected to each photodiode, where the signal division network includes four output connections, a signal output measurement unit, a processing unit configured to identify the photodiode generating a signal or a center of mass of photodiodes generating a signal, and a global receiving unit.

42 ENGINEERING↗

DOE OSTI2013

Fast, Low Noise Photodetectors for Nuclear Physics

The overall goal of the Phase-II project was to construct and evaluate high performance SSPM technology for nuclear physics experiments. To achieve this overall objective, we first undertook optimization of the SSPM technology. This effort involved further enhancement of the optical quantum efficiency as well as the geometric efficiency (or fill-factor) of the SSPMs, which resulted in improvement of the photodetection efficiency of the SSPMs. Important SSPM parameters such as gain, dark count-rate, cross-talk, temporal response, after-pulsing, quantum efficiency and photodetection efficiency were evaluated for the optimized devices and these parameters were compared with those for Phase-I prototypes. Large area SSPMs (1 to 2 cm 2 ) were built using optimal design parameters. Noise analysis of large area SSPMs was performed. Upon coupling SSPMs to various scintillators (LSO/LYSO, LaBr 3 :Ce, NaI:Tl, LuAG:Ce etc.), energy resolution studies were carried. Timing resolution was also be measured with SSPMs coupled to fast scintillators (such as LaBr 3 :Ce, BaF 2 , LuAG:Ce, plastic and LSO/LYSO) using 511-keV gamma-rays ( 22 Na source). Multi-element SSPM arrays (6 x 6 format with ~1.5 x 1.5 mm 2 elements) were also designed and built using the CMOS process. These SSPM arrays were packaged and appropriate readout electronics was assembled. These SSPM arrays were operated with individual readout of each SSPM element. Large area (~1 cm 2 ) micro-pixel level PS-SSPMs with active and passive components to enable on-chip charge sharing for position sensing were also designed and built. Spatial, energy and timing resolution studies were conducted with the multi-element SSPM arrays as well as PS-SSPMs coupled to segmented scintillation arrays.

99 GENERAL AND MISCELLANEOUS↗