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Relationship between the neutron time delay distribution and the rigidity spectrum of primary cosmic rays up to 16.8 GV


Mangeard, P-S and Ruffolo, D and Saiz, A and Nuntiyakul, W and Madlee, S and Nutaro, T and Bieber, JW and Clem, J and Evenson, P and Pyle, R and Duldig, ML and Humble, JE, Relationship between the neutron time delay distribution and the rigidity spectrum of primary cosmic rays up to 16.8 GV, Proceedings of Science, 30 July - 06 August, The Hague, Netherlands, pp. 1-8. ISSN 1824-8039 (2015) [Non Refereed Conference Paper]

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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. In addition to the count rate, recording and analyzing the time delays between successive counts allows us to infer variations in the cosmic ray spectrum as well. In particular, 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 nuclear interaction, from time delay histograms. By analyzing data taken during 20012007 by a ship-borne neutron monitor latitude survey we confirm a strong dependence of L on the geomagnetic cutoff up to 16 GV. The data of the Princess Sirindhorn Neutron Monitor located in Thailand at a higher vertical cutoff of 16.8 GV have also been analyzed for the period 20072014. We have developed Monte Carlo simulations of cosmic ray interactions in the atmosphere and in both neutron monitors. Both data and simulations show that the absolute value of L depends significantly of the configuration of the detector and that experimental conditions such as the electronic dead time must be well monitored. The simulation results show a change in L with the geomagnetic cutoff as observed by the latitude survey, confirming that this change in L can reasonably be attributed to changes in the cosmic ray spectrum.

Item Details

Item Type:Non Refereed Conference Paper
Keywords:cosmic rays: neutron monitor, rigidity spectrum, neutron time delay
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:110303
Year Published:2015
Deposited By:Mathematics and Physics
Deposited On:2016-07-23
Last Modified:2016-08-05

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