High-Altitude Polar NM With the New DAQ System as a Tool to Study Details of the Cosmic-Ray Induced Nucleonic Cascade

摘要

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 the intracascade diffusion and thermalization of secondary atmospheric neutrons;and peak (II) at 30-1,000 ms 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 data set.