Site-specific incoming correction based on muons: a comparison with cosmic neutrons measurements at JUNG at OULU.

Cosmic Rays Neutron Sensing (CRNS) opened the possibility to measure water content in the environment by neutrons absorption overcoming the need of an artificial radioactive source of neutrons. While the exploitation of a naturally available source of radiation is a fundamental feature that allows the widespread deployment of permanent sensors on-field, it intruduces the need of monitoring the natural variation of the incoming radiation to correct the signal accordingly.

This so-called “incoming correction” for CRNS is usually obtained by referring to the public data provided by the Neutron Monitor DataBase (NMDB) observatories, with the Jungfraujoch (JUNG) often being the preferred one, due to its position in central Europe on the Swiss Alps. In fact, a critical factor affecting the incoming flux of cosmic rays at the ground is the geomagnetic cutoff rigidity parameter, which is site-specific with a strong dependence on the latitude. The site-specificity of the incoming correction, together with the need to rely on an external source of data, makes it a crucial topic for the CRNS community.

Finapp developed a patented detection technology with the feature of contextually detecting neutrons and muons. Muons are also generated by cosmic rays, but they are not backscattered by the soil like neutrons, which makes them suitable for monitoring the incoming flux itself. In order to provide a fair, site-specific comparison between the variations of muons counts by Finapp and cosmic neutrons counts by NMDB observatories, we installed a sensor at the NMDB-JUNG site in January 2024 and one at the NMDB-OULU site in Finland in October 2024. In this presentation we will report preliminary results of this project and its impact on CRNS applications.

We acknowledge the NMDB database (www.nmdb.eu), founded under the European Union's FP7 programme (contract no. 213007) for providing data. Jungfraujoch neutron monitor data were kindly provided by the Physikalisches Institut, University of Bern, Switzerland. Oulu neutron monitor data were kindly provided by the Sodankyla Geophysical Observatory (https://cosmicrays.oulu.fi).