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


Mangeard, P-S and Ruffulo, D and Saiz, A and Nuntiyakul, W and Bieber, JW and Clem, J and Evenson, P and Pyle, R and Duldig, ML and Humble, JE, Dependence of the neutron monitor count rate and time delay distribution on the rigidity spectrum of primary cosmic rays, Journal of Geophysical Research: Space Physics, 121 pp. 11,620-11,636. ISSN 2169-9380 (2016) [Refereed Article]


Copyright Statement

2016. American Geophysical Union

DOI: doi:10.1002/2016JA023515


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 20002007 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.

Item Details

Item Type:Refereed Article
Keywords:cosmic rays, neutron monitors, spectrum
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:High energy astrophysics and galactic cosmic rays
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Duldig, ML (Dr Marc Duldig)
UTAS Author:Humble, JE (Dr John Humble)
ID Code:114565
Year Published:2016
Web of Science® Times Cited:22
Deposited By:Mathematics and Physics
Deposited On:2017-02-19
Last Modified:2017-11-03
Downloads:135 View Download Statistics

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