Thermal neutron detection based on resistive gaseous devices

Abstract

In the framework of the uRANIA (u-Rwell Advanced Neutron Imaging Apparatus) project, we are developing innovative thermal neutron detectors based on resistive gaseous devices such as micro-Resistive WELL (μ-RWELL) and surface Resistive Plate Counter (sRPC).

The μ-RWELL is a single amplification stage resistive MPGD developed for HEP applications. The amplification stage, based on the same Apical® foil used for the manufacturing of the GEM, is embedded through a resistive layer in the readout board. The resistive layer is realized by sputtering the back side of the Apical® foil with DiamondLike-Carbon (DLC). A cathode electrode, defining the gas conversion/drift gap, completes the detector mechanics. The deposition of a thin layer of ¹⁰B4C on the cathode surface allows the thermal neutrons conversion into ⁷Li and α ions, which can be easily detected in the active volume of the device. Results from tests performed with different detector layouts show that a thermal neutron (25 meV) detection efficiency up to 7% can be achieved with a single detector. A comparison between experimental data and the simulation of the detector behaviour has been performed. In parallel, we are proposing the development of thermal neutron detectors based on a novel RPC concept. The sRPC is a revolutionary RPC based on surface resistive electrodes realized by exploiting the well-established DLC sputtering technology on thin (50µm) polyimide foils, the same used in the manufacturing of the µ-RWELL. The DLC foil is glued onto a 2 mm thick float-glass. The 2 mm gas gap between the electrodes is ensured by spacers made of Delrin®, inserted without gluing at the edges of the glass supports. By replacing DLC with ¹⁰B4C sputtered electrodes, the device becomes sensitive to thermal neutrons. Different layouts of ¹⁰B4C coated electrodes have been tested, allowing to achieve efficiency up to 6%. The robustness, ease of construction, and scalability of the sRPC technology should allow the construction of cost-effective large area detector units as required by applications in homeland security (such as Radiation Portal Monitor).