Speaker
Description
The High Efficiency Neutron Spectrometry Array (HENSA) project focuses on the development and scientific application of high-efficiency neutron spectrometers [1], with uses in underground laboratories, rare-events experiments, cosmic-ray neutron studies, space weather research, and environmental dosimetry. The detection principle of HENSA is based on the Bonner Spheres System (BSS) [2], but incorporates a topological modification in detector geometry, achieving up to a tenfold increase in overall detection efficiency compared to standard BSS [3]. The extended-energy-range version of HENSA is sensitive to neutrons from thermal energies up to 10 GeV, enabling full-spectrum measurements of cosmic-ray neutrons. Its high efficiency and wide energy sensitivity allow for the determination of the neutron spectrum and the ambient neutron dose equivalent within 30–60-minute intervals, complementing ground data from the Neutron Monitor Network [4]. This capability enables near real-time analysis of spectral fluctuations throughout the solar cycle and during high-intensity solar events, such as Ground Level Enhancements (GLEs) and Forbush Decreases (FDs).
In 2020, a HENSA detector was deployed in a measurement campaign to study the cosmic-ray neutron spectrum under quiet solar conditions at the beginning of Solar Cycle 25. This campaign enabled the mapping of cosmic-ray neutrons across magnetic rigidities from 5.5 to 8.5 GV and altitudes from sea level to 3000 m, complementing previous studies [5]. Building on these results, a new spectrometer, HENSA++, has been developed with optimized energy resolution for cosmic-ray neutron studies. Since 2024, HENSA++ has begun commissioning, first in Valencia city (sea level, Rc = 7.5 GV) and later at the Observatorio Astrofísico de Javalambre (OAJ) in Teruel, Spain (1957 m above sea level, Rc = 7.07 GV) [6].
In this talk, we present an overview of the HENSA project for cosmic-ray neutron studies, including results from the 2020 measurement campaign and preliminary findings from the commissioning phase. These include an analysis of the temporal evolution of the neutron spectrum over the measurement period, as well as a preliminary investigation of selected solar events, including the latests observed Ground Level Enhancement (GLE). Finally, we discuss future perspectives for continuous cosmic-ray neutron monitoring with HENSA++ during the second half of Solar Cycle 25.
References
[1] https://www.hensaproject.org/
[2] D.J. Thomas and A.V. Alevra (2002). NIMA, 476, p. 12–20.
[3] B. Wiegel, A.V. Alevra (2002). NIMA 476 (2002) 36–41.
[4] https://www.nmdb.eu/
[5] M. S. Gordon, et al. (2004). IEEE Transactions on Nuclear Science, 51(6)
[6] https://www.cefca.es/observatorio/descripcion
