NMs record primarily the secondary nucleonic component (mostly neutrons) of the cosmic-ray induced atmospheric cascade with a small fraction of counts caused by muons. Its count rate is defined by the flux of primary (impinging on the top of the atmosphere) cosmic rays, as a combination of the cosmic-ray energy spectrum, detector's yield function and geomagnetic rigidity cutoff (Clem & Dorman, 2000;Mishev et al., 2020). The NM is an energy-integrating detector, with the effective energy ranging from about 12 GeV for polar NMs to 35 GeV for equatorial ones (Asvestari et al., 2017). The sensitivity of NMs to low-energy cosmic rays is highest in polar regions (low or no geomagnetic shielding) and high altitudes (lower atmospheric shielding) and decreases toward equatorial latitudes. The worldwide network of NMs can act as a giant spectrometer able to roughly estimate the spectrum of both galactic cosmic rays (e.g., Dorman, 2004) and relativistic solar protons (e.g., Duggal, 1979;Mishev et al., 2014). Along with the count rate, the multiplicity of NM counts (the average number of pulses within a short time interval) is sometimes studied (Balabin et al., 2011;Dorman, 2004) as a rough index of the spectral hardness of cosmic rays. Sometimes NM are accompanied by separate muon detectors to measure high-energy cosmic rays. This work is focused at two mini-NMs, DOMC and DOMB, located at the Concordia Antarctic Research station on top of Dome C, Central Antarctic plateau (75°06′S, 123°23′E, 3,233 m above sea level) (Poluianov et al., 2015). They are ones of the most sensitive NMs to lower energy cosmic rays (including solar energetic particles) thanks to the highly elevated polar location. Each NM has one BF 3 -filled detector surrounded by reflecting and moderating layers of polyethylene. In addition, DOMC has a layer of lead serving as a neutron 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 neighboring detector. An analysis of the waiting-time distributions has revealed two clearly distinguishable peaks: peak (I) at about 1 ms being related to t...

Two high-altitude polar neutron monitors DOMC and DOMB (Dome C, Concordia station, Antarctic plateau, 3233 m a.s.l.) received a major electronics upgrade in 2019. While a typical standard neutron monitor data acquisition (DAQ) system only registers the number of pulses from a cosmicray particle detector, the new system digitizes all pulses with 2 MHz sampling rate and stores this information in raw data files. This feature makes it possible to conduct a pulse height-length analysis of the neutron monitor data on a routine basis. In this study, we have analysed several months of the cosmic-ray data recorded with the new DAQ system during 2019-2020 (more than 10 million pulses). We identified several pulse branches corresponding to different processes: (a) secondary particles from individual cosmic-ray cascades, (b) noise, (c) double pulses originated from particles of the same local cascade, (d) high multiple pulses likely related to atmospheric muons, (e) double pulses potentially caused by contamination by neutrons scattered in the neighbouring instrument. We also studied the waiting time distributions of pulses and have shown that two peaks can be clearly distinguished: (1) at about 1 millisecond, which is related to the intracascade particles, and (2) at 30-1000 milliseconds related to different uncorrelated cosmic-ray cascades. Our conclusions are supported by theoretical estimates of the waiting times in different scenarios.

A pair of neutron monitors (NMs) is installed on the high Central Antarctic plateau, at the Concordia station (3200 m altitude) and measures the nucleonic component of nucleonic-muon-electromagnetic cascades in- duced by high-energy cosmic rays in the atmosphere. The installation includes two NMs: DOMC, a standard mini-NM, and a bare (lead-free) DOMB NM. The newly installed data acquisition (DAQ) system records in- dividual pulses corresponding to mostly neutrons in the detector’s counting tube. Here we analyze different types of pulses and study the distribution of the waiting times between individual pulses as well as the pulse height, recorded by the DOMC NM during a quiet period of January 2020. The distribution appears double- peaked with peaks corresponding to the frequency of individual atmospheric cascades and the intra-cascade variability, respectively. We discuss also the nature of different components contributing to the pulses and se - paration of the signal from noise. It is shown that the waiting-time distribution has distinguished timescales, >30 ms defined by the cosmic-ray induced atmospheric cascades, and < 10 ms reflecting the intra-cascade variability. The new DAQ system allows one to study the development of the atmospheric cascade.