Information from the abstract
Abstract Neutron monitors serve as the premier instruments for continuous, precise, real-time count rates of secondary particles from cosmic-ray showers, and recently developed techniques provide measures of the spectral index as well. We investigate the rigidity dependence of two such measures, the leader fraction and the count-rate ratio between leaded and unleaded counters, from the transportable semileaded neutron monitor “Changvan” during 2018–2019 and 2019–2020 latitude surveys on board the Chinese icebreaker Xue Long . Changvan comprises two outer leaded counters and one central counter without a lead producer, allowing simultaneous measurements of leaded and unleaded responses within a common moderator–reflector structure. Because the unleaded counter is embedded in the same assembly, its response is very different from that of an isolated bare detector. We examine the behaviors of the count-rate ratio C Leaded / C Unleaded and leader fractions L Leaded and L Unleaded over a wide range of geomagnetic cutoff rigidity. The count-rate ratio and both leader fractions decrease systematically with increasing cutoff rigidity, and Monte Carlo calculations reproduce the observed trends in leader fraction. Comparison with an earlier 2006–2007 fully leaded latitude survey suggests a consistent physical interpretation in which neutrons escaping from the leaded counters contribute to both count-rate and leader-fraction behavior. The unleaded counter acquires enhanced high-rigidity response through neutrons originating from lead around neighboring counters. This study confirms that the count-rate ratio and leader fractions serve to measure spectral variations, and the variations in leader fraction are well modeled by Monte Carlo simulations.
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Related topics: Astrophysics and Cosmic Phenomena · Radiation Therapy and Dosimetry · Solar and Space Plasma Dynamics
Thai researcher and institutional participation
P. Yakum · Achara Seripienlert · Waraporn Nuntiyakul · D. Ruffolo · A. Sáiz · Siramas Komonjinda · Chiang Mai University · Mahidol University
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