Cosmic rays, originating from celestial phenomena such as stars, supernovae, and other astrophysical sources, are composed of high-energy particles that enter Earth’ s atmosphere. Upon interaction with atmospheric nuclei, these primary cosmic rays generate an array of secondary particles, with muons constituting the dominant component at ground level. Muons, due to their relative abundance, stability, and well-characterized energy loss mechanisms, serve as critical probes for investigating the fundamental properties of cosmic rays. Studies of muon energy distribution, diurnal anisotropy, and their modulation by solar activity provide essential insights into the mechanisms of particle acceleration in cosmic ray sources and the influence of solar and atmospheric effects.
This study aims to characterize the counting spectrum and anisotropic properties of cosmic ray muons using a plastic scintillator detector system. The experiment was conducted over a three-month period, from December 2023 to February 2024, leveraging long-bar plastic scintillator detectors equipped with dual-end photomultiplier tubes (PMTs) and a high-resolution digital data acquisition system. A dual-end coincidence measurement technique was implemented to enhance the signal-to-noise ratio by suppressing thermal noise and other background interferences. Comprehensive calibration of the detection system was performed using standard gamma-ray sources, including ¹³⁷Cs, ⁶⁰Co, and ⁴⁰K, ensuring precise energy scaling and reliable performance.
The observed energy spectrum of cosmic ray muons showed excellent agreement with theoretical predictions, accounting for the energy losses incurred as muons traverse the detector. Diurnal variations in muon count rates revealed a pronounced pattern, with a systematic reduction observed between 8:00 AM and 1:00 PM. This phenomenon is attributed to solar shielding effects, wherein enhanced solar activity during daytime hours modulates the flux of galactic cosmic rays reaching Earth’ s surface. To account for atmospheric influences, meteorological corrections were applied using temperature and pressure adjustment functions derived from regression analysis. These corrections revealed that atmospheric pressure and temperature are significant factors influencing muon count rates, with clear linear relationships observed.
The study further corroborated these findings through cross-comparisons with data from the Yangbajing Cosmic Ray Observatory. Minor discrepancies, primarily in low-energy muon count rates, were attributed to variations in detector sensitivities and local atmospheric conditions. These observations underscore the robustness of the plastic scintillator detector system for capturing detailed muon spectra and anisotropic patterns.
In conclusion, this research establishes a reliable experimental framework for analyzing cosmic ray muons and their modulation by solar and atmospheric phenomena. The results contribute to a deeper understanding of cosmic ray anisotropy and the interplay between astrophysical and geophysical processes. Furthermore, the findings provide valuable insights for optimizing detection technologies and enhancing the accuracy of cosmic ray studies.