Different types of CRNS (Cosmic-Ray Neutron Sensing) sensors were characterised at the PTB Ion Accelerator Facility (PIAF) during the week beginning 12 February 2024. In the natural environment, CRNS sensors are used to monitor soil moisture dynamics via continuous measurement of naturally occurring neutrons. In the laboratory, "artificial" neutrons with well-defined energies are created through various nuclear reactions. These so-called neutron reference fields are typically used in neutron metrology for calibrating or characterising various neutron-sensitive instruments, such as spectrometers, detectors, monitors and personal dosimeters.

During our beam time at PTB, the CRNS sensors were irradiated in well-known neutron reference fields that are SI-traceable to neutron metrology standards. This establishes the metrological basis for the CRNS methodology by improving our understanding of how sensitive the sensors are to neutrons and how they perform under laboratory conditions. Next, we will systematically research their performance under outdoor conditions.