Speaker
Description
Helium-3 gas-filled proportional counters are extensively used as neutron detectors for measurements in a wide range of applications. A recent example are ($\alpha$,n) reactions measured by the MANY collaboration using the miniBELEN detector [1]. This kind of neutron counters are also commonplace as neutron monitors, both for the study of cosmic rays and solar weather [2], as well as background monitors for rare-event experiments and detectors.
One such experiment is the International Axion Observatory (IAXO) [3], a planned gaseous detector helioscope designed to detect axions, hypothetical particles proposed as a solution for the strong CP problem, which have also been theorised to be dark matter candidates. A smaller prototype, BabyIAXO [4], is currently in manufacturing and is expected to be installed at DESY (Hamburg, Germany). A baseline detector prototype, IAXO-D0, is at present undergoing tests at the premises of the Universidad de Zaragoza. The prototype is sensitive to background that could induce false positive axion detections, and in particular to ambient neutrons of high energy.
A neutron monitor has been proposed as a way to provide a continuous measurement of ambient neutrons and its variability. Neutron Monitors typically consist of several neutron counter detectors surrounded by a series of layers that act as reflector, multiplier and moderator for the neutrons.
In this work a prototype neutron monitor was designed and assembled. It consists of three identical LND He-3 proportional counter tubes, surrounded by a high density polyethylene (HDPE) moderator, a layer of lead that acts as multiplier, and an outer layer of HDPE as reflector. The neutron monitor has been in operation since March 2024, producing an almost continuous measurement of the count rate of neutrons detected inside the laboratory where IAXO-D0 is being commissioned.
We will present the Monte Carlo simulations performed to characterise the monitor and the first results of the neutron count rate during the Forbush decrease observed in May 2024, once noise and pile-up have been taken care of, and atmospheric pressure effects have been corrected.
The information obtained from this prototype neutron monitor, as well as the data from IFIC’s High Efficiency Neutron Spectrometry Array (HENSA) measured at the same location, will guide the design of a neutron monitor optimised for neutrons of around >100 MeV tailored to the IAXO-D0 needs. The design of the new device will be briefly presented.
