Next Generation Gamma/Neutron Detectors for Planetary Science.

Gamma ray and neutron spectroscopy are well established techniques for determining the chemical composition of planetary surfaces, and small cosmic bodies such as asteroids and comets; however, new technologies with the potential to significantly improve the performance of planetary nuclear spectroscopy are emerging in response to demands in other fields such as homeland security. We propose to develop new gamma-ray and neutron detectors based on wide-band-gap solid state photomultiplier (SSPM) photodetectors coupled to emerging scintillation materials such as Cs2YLiCl6:Ce (CLYC), and CeBr3 for gamma and neutron spectroscopic studies of planet surfaces and small cosmic bodies. CLYC is most promising for neutron spectroscopy and can provide high efficiency detection of thermal and epithermal neutrons. In addition, it has excellent pulse height resolution for gamma ray spectroscopy. CeBr3 is also well suited for precision gamma ray spectroscopy. Its extremely high light output, excellent energy resolution, as well as zero self activity, can enable precise measurements of geochemically-significant elements. The proposed SSPM photodetector for scintillation readout is based on AlGaAs, a wide-band-gap compound semiconductor with aluminum concentration between 60% to 90%. The band-gap energy of this material is engineered to provide high photo sensitivity between 300nm to 500nm, which matches well with the emission spectrum of both CLYC and CeBr3. The wide-band-gap nature of AlGaAs also provides much lower dark noise and better radiation tolerance than Si-based detectors. Compared to conventional PMTs, the compact size, low voltage operation, and lighter weight of AlGaAs SSPM is more ideal for spaced based instruments. The advantages of AlGaAs-based SSPM and the excellent detection properties of CLYC and CeBr3 scintillation materials make them a perfect match in the development of next generation gamma neutron spectrometers for planetary science.

The proposed innovative technology is a suitable component for a gamma-ray and neutron spectrometer that can be used for Earth science missions, planetary missions, exploration of small cosmic bodies such as asteroids and comets, satellite radio-imaging, and space exploration probes. The nature of the detectors, as having a high signal-to-noise ratio, excellent energy resolution, low power consumption, and resiliency to harsh radiation environments, can open the door for improved gamma and neutron spectroscopy in future NASA planetary missions.

The development of the new gamma-ray and neutron detectors has a myriad of applications in the science, homeland security, and medical fields. The AlGaAs SSPM, with its low thermal noise and radiation hardness, makes it an excellent photodetector for scintillation detection of high energy x-rays, gammas, neutrons, and protons in nuclear and high energy physics experiments. The instrument can also be used for detecting and monitoring of radioactive materials for homeland security, and in medical imaging applications such as Postron Emission Tomography and Single Photon Emission Computed Tomography.