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

conference contribution
posted on 2023-05-23, 18:23 authored by Mangeard, P-S, Ruffolo, D, Saiz, A, Nuntiyakul, W, Madlee, S, Nutaro, T, Bieber, JW, Clem, J, Evenson, P, Pyle, R, Marcus DuldigMarcus Duldig, John Humble
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 2001–2007 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 2007–2014. 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.


Publication title

Proceedings of Science






School of Natural Sciences


Scuola Internazionale Superiore di Studi Avanzati (S I S S A), International School of Advanced Studies

Place of publication


Event title

34th International Cosmic Ray Conference (ICRC 2015)

Event Venue

The Hague, Netherlands

Date of Event (Start Date)


Date of Event (End Date)


Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the physical sciences