Monitoring Short-Term Cosmic-Ray Spectral Variations Using Neutron Monitor Time-Delay Measurements

Ruffolo, D.; Sáiz, A.; Mangeard, P.-S.; Kamyan, N.; Muangha, Pradiphat; Nutaro, Tanin; Sumran, Supon; Chaiwattana, C.; Gasiprong, N.; Channok, Chanruangrit; Wuttiya, C.; Rujiwarodom, M.; Tooprakai, P.; Asavapibhop, B.; Bieber, J. W.; Clem, J.; Evenson, P. A.; Munakata, K.

doi:10.3847/0004-637x/817/1/38

Cited by 51 publications

(90 citation statements)

References 18 publications

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“…A seasonal wave in the leader fraction (ratio of the number of SPs giving counts by the total number of counts) at PSNM, which is related to the time delay between counts and represents an inverse multiplicity, was observed by Ruffolo et al []. The results shown in the present work used an atmospheric profile for January (dry season).…”

Section: Yield Functionssupporting

confidence: 59%

Monte Carlo simulation of the neutron monitor yield function

et al. 2016

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Neutron monitors (NMs) are ground‐based detectors that measure variations of the Galactic cosmic ray flux at GV range rigidities. Differences in configuration, electronics, surroundings, and location induce systematic effects on the calculation of the yield functions of NMs worldwide. Different estimates of NM yield functions can differ by a factor of 2 or more. In this work, we present new Monte Carlo simulations to calculate NM yield functions and perform an absolute (not relative) comparison with the count rate of the Princess Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand, both for the entire monitor and for individual counter tubes. We model the atmosphere using profiles from the Global Data Assimilation System database and the Naval Research Laboratory Mass Spectrometer, Incoherent Scatter Radar Extended model. Using FLUKA software and the detailed geometry of PSNM, we calculated the PSNM yield functions for protons and alpha particles. An agreement better than 9% was achieved between the PSNM observations and the simulated count rate during the solar minimum of December 2009. The systematic effect from the electronic dead time was studied as a function of primary cosmic ray rigidity at the top of the atmosphere up to 1 TV. We show that the effect is not negligible and can reach 35% at high rigidity for a dead time >1 ms. We analyzed the response function of each counter tube at PSNM using its actual dead time, and we provide normalization coefficients between count rates for various tube configurations in the standard NM64 design that are valid to within ∼1% for such stations worldwide.

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Section: Yield Functionssupporting

confidence: 59%

Monte Carlo simulation of the neutron monitor yield function

et al. 2016

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“…The modulation due to changes in solar activity also impacts the value of L, as found by Ruffolo et al [2016] for a fixed station. At low R c , a variation up to ∼0.004 is observed between the different surveys with a larger L for survey years 2005 and 2006, which correspond to a period of low solar activity, weaker solar modulation, and softer GCR spectra.…”

Section: Observational Resultsmentioning

confidence: 81%

“…As reported in Ruffolo et al [2016], the dead time in the time delay electronics is about ∼62 μs larger than the dead time in the count rate electronics. The dead time of the time delay electronics (known for each tube thanks to the time delay histograms) is then imposed.…”

Section: Response To Secondary Particlesmentioning

confidence: 79%

“…For more details about the experimental determination of the histograms, we refer to Ruffolo et al [2016]; in particular, the present measurements used the 600 series electronics described there. It has been shown by Ruffolo et al [2016] that it is possible to extract a parameter from the time delay histograms, the leader fraction L, which is the statistically determined fraction of neutron counts that did not follow a related count due to the same primary cosmic ray. The short time histogram, which is actually a zoom in the long time histogram, shows the nonexponential excess at short time delays that can be attributed to the time delays between neutrons produced in the same secondary particle interaction in the lead.…”

Section: Time Delay Distributionsmentioning

confidence: 99%

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Dependence of the neutron monitor count rate and time delay distribution on the rigidity spectrum of primary cosmic rays

et al. 2016

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Neutron monitors are the premier instruments for precisely tracking time variations in the Galactic cosmic ray flux at GeV‐range energies above the geomagnetic cutoff at the location of measurement. Recently, a new capability has been developed to record and analyze the neutron time delay distribution (related to neutron multiplicity) to infer variations in the cosmic ray spectrum as well. In particular, from time delay histograms we can determine the leader fraction L, defined as the fraction of neutrons that did not follow a previous neutron detection in the same tube from the same atmospheric secondary particle. Using data taken during 2000–2007 by a shipborne neutron monitor latitude survey, we observe a strong dependence of the count rate and L on the geomagnetic cutoff. We have modeled this dependence using Monte Carlo simulations of cosmic ray interactions in the atmosphere and in the neutron monitor. We present new yield functions for the count rate of a neutron monitor at sea level. The simulation results show a variation of L with geomagnetic cutoff as observed by the latitude survey, confirming that these changes in L can be attributed to changes in the cosmic ray spectrum arriving at Earth's atmosphere. We also observe a variation in L with time at a fixed cutoff, which reflects the evolution of the cosmic ray spectrum with the sunspot cycle, known as solar modulation.

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“…PSNM is operated at DI with a complete set of 18 BP-28 ( 10 BF 3 ) neutron counter tubes with the standard NM64 configuration (18NM64). Further details are available from [22]. The present study considers monthly or Carrington (solar) Rotation (CR) averages.…”

Section: Solar Modulation At High Cutoff Rigiditymentioning

confidence: 99%