High-altitude polar NM with the new DAQ system as a tool to study details of the cosmic-ray induced nucleonic cascade

TL;DR

This paper introduces a new data acquisition system for neutron monitors at the Antarctic station, enabling detailed analysis of cosmic-ray induced atmospheric cascades through pulse shape and timing data.

Contribution

The study presents a novel DAQ system that digitizes and analyzes pulse characteristics, revealing new insights into atmospheric cascades and secondary particle spectra.

Findings

Identification of distinct pulse types related to secondary neutrons, noise, and muons.

Detection of two peaks in waiting time distributions indicating different cascade processes.

Potential to study cosmic-ray spectra and atmospheric cascades at a single location.

Abstract

A neutron monitor (NM) is, since the 1950s, a standard ground-based detector whose count rate reflects cosmic-ray variability. The worldwide network of NMs forms a rough spectrometer for cosmic rays. Recently, a brand-new data acquisition (DAQ) system has been installed on the DOMC and DOMB NMs, located at the Concordia research station on the Central Antarctic plateau. The new DAQ system digitizes, at a 2-MHz sampling rate, and records all individual pulses corresponding to secondary particles in the detector. An analysis of the pulse characteristics (viz. shape, magnitude, duration, waiting time) has been performed, and several clearly distinguishable branches were identified: (A) corresponding to signal from individual secondary neutrons; (B) representing the detector's noise; (C) double pulses corresponding to the {shortly separated nucleons of the same} atmospheric cascades; (D) very-high multiple pulses which are likely caused by atmospheric muons; and (E) double pulses potentially caused by contamination of the neighbouring detector. An analysis of the waiting time distributions has revealed two clearly distinguishable peaks: peak (I) at about 1 msec being related to the intra-cascade diffusion and thermalisation of secondary atmospheric neutrons; and peak (II) at 30--1000 msec corresponding to individual atmospheric cascades. This opens a new possibility to study spectra of cosmic-ray particles in a single location as well as details of the cosmic-ray induced atmospheric cascades, using the same dataset.