Design of a Prototype in-situ Gamma-ray Spectrometer for Deep Sea

Research on the in-situ environment in deep sea is a new focus in marine science. In this work, a prototype in-situ gamma-ray spectrometer was designed in order to measure the gamma-ray spectrum of the environment at about 5000 meters underwater in the South China Sea. The new spectrometer consists of an NaI(Tl) crystal, a photomultiplier tube (PMT), and its electronics. The full digital processing method is implemented in the electronics system, including waveform digitization and digital filtering, to build a general readout platform for various scintillator material based gamma-ray detection. The prototype electronics system is comprised of three modules, which are responsible for analog signal conditioning and high-speed high-resolution waveform digitization, as well as digital filtering, data buffering and transferring based on the field programmable gate array (FPGA). Tests were also conducted to evaluate the system performance. The results indicate that this gamma-ray spectrometer prototype achieves energy range from 60 keV to 3 MeV and full width at half maxima (FWHM) resolutions of 7.5% at 662 keV and 8.8% at 511 keV, which are above the application requirement.