Prototype of Deep Sea In-situ Neutron Activation Spectrometer for Polymetallic Nodules and Crusts Exploration

In-situ exploration of deep-sea seabed resources is a valuable research direction. Neutron activation-based in-situ exploration methods for seabed polymetallic nodules or crust resources are theoretically feasible due to the high content and high neutron capture cross-section of manganese elements in the nodules or crusts. However, there are only a few relevant studies. In this paper, a prototype deep-sea in-situ neutron activation spectrometer for resource exploration is designed. Through the analysis of the principles of the spectrometer, combined with Monte Carlo simulations of physical principles and finite element simulations of deep-sea pressure, the structure and fundamental components of the spectrometer were determined. The inner core of the spectrometer comprises three components: a compact neutron generator for neutron production, gamma-ray detectors, and an electronics system. The gamma-ray detector array of the spectrometer consists of LaBr3 and BGO scintillation crystals coupled with silicon photomultiplier (SiPM) arrays. The electronics system is divided into two modules implementing SiPM readout and digital signal analysis along modular design lines. Testing with radiation sources shows that the spectrometer achieves energy resolution results of 3.2% at 662 keV for the LaBr3 detector and 5.5% at 2.5 MeV for the BGO detector. The experimental activation of neutron beamlines at China Spallation Neutron Source (CSNS) demonstrated the spectrometer detectors' capability in detecting activated gamma rays. The laboratory model experiment tested the functionality of the spectrometer prototype on one hand, and the Geant4 simulation of the experiment verified the reliability of the Monte Carlo method on the other.