The PRISMA-36 array for studying variations of the thermal neutron flux

From 2012 to 2023, the PRISMA-32 array operated at the Experimental Complex NEVOD (MEPhI, Moscow). The purpose of the array was to study extensive air showers detecting their neutron and electron-photon components using unshielded neutron detectors. To expand the capabilities of this facility, including the study of cosmic and geophysical phenomena with a neutron flux, its upgrade was carried out. In this upgrade, a measurement channel to study the variations of the neutron background and the processes affecting them was added. To achieve this, the photomultipliers, the integrating amplifiers, the digitalizing electronics and the high-voltage power supply system were replaced. The paper describes the structure of the upgraded array, which was named PRISMA-36, and presents the results of studying the characteristics of the main elements of its “variation” channel. A method for identifying signals caused by neutron capture and the determined criteria for their selection are discussed. An example of a Forbush decrease, caused by a X1.1-class flare and recorded with the variation channel of the PRISMA-36 array, is given.