Speaker
Description
Andy Buffler1, Marco Caresana2, Andrea Cirillo2, Massimiliano Clemenza3 and Luna Pellegri4,5
1Metrological and Applied Sciences University Research Unit (MeASURe),
Department of Physics, University of Cape Town, South Africa, 7700
2Department of Energy, Politecnico di Milano”, Via Lambruschini 4, 20156 Milan, Italy
3INFN sezione di Milano Bicocca, Piazza della Scienza 3, 20126 Milan, Italy
4School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa
5 iThemba Laboratory for Accelerator Based Sciences, Somerset West 7129, South Africa
Measurements of high-energy cosmic-ray neutrons are typically carried out using neutron monitors located around the world. These measurements have a wide range of applications, including space weather observation, solar cycle analysis, and radiation protection at flight altitudes. The flux of cosmic-ray neutrons is also responsible for inelastic reactions that produce isotopes such as ²⁶Al in rocks—used to date the age of rocks and minerals that have been exposed to these neutrons over extended periods.
However, several aspects of cosmic-ray neutron measurements remain under investigation, including the spatial heterogeneity of the particle flux across the Earth and its relationship with other secondary cosmic-ray particles, such as muons. On the one hand, studies in this field would greatly benefit from widespread measurements of secondary cosmic rays at the Earth’s surface; on the other hand, neutron monitors are generally heavy, non-portable systems. Additionally, environmental factors such as snow cover can significantly affect neutron flux intensity at ground level, especially for low-energy neutrons (below 10 MeV). As a result, cosmic-ray observations typically achieve high sensitivity only for neutron energies above 20 MeV.
For these reasons, Politecnico di Milano and INFN are developing a portable neutron monitor for ground-level cosmic-ray neutron measurements. The system is based on a commercial thermal neutron counter with high sensitivity, housed within a modular moderator made of polyethylene and lead. This work presents the characterization of the neutron detector in a mixed neutron/gamma radiation field and the Monte Carlo simulations used to determine the optimal moderator dimensions. These efforts are preparatory steps toward the device's calibration in quasi-monoenergetic neutron fields at iThemba LABS.
Calibration of moderator-based detectors is typically performed using the shadow-cone technique in monoenergetic fields to suppress the background from scattered neutrons. According to ISO 8529, this technique is a standard for neutron energies up to 20 MeV; however, its application becomes more complex at higher neutron energies. That said, the low sensitivity of neutron monitors to neutrons below 10 MeV may allow for a relaxation of the stringent requirements for background suppression. This work includes Monte Carlo simulations evaluating the effectiveness of the shadow-cone technique for high-energy neutron measurements.
