Pierre-Simon Mangeard

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

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, 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, from time delay histograms. Using data taken during 2000-2007 by a ship-borne neutron monitor latitude survey, we observe strong dependences 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 Earths 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.

Cosmic Ray Modulation Observed by the Princess Sirindhorn Neutron Monitor at High Rigidity Cutoff

Solar modulation refers to Galactic cosmic ray (GCR) variations with the

Impulsive Increase of Galactic Cosmic Ray Flux Observed by IceTop

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

11-year sunspot cycle and

Observations and Monte Carlo Simulation of the Princess Sirindhorn Neutron Monitor at a Vertical Rigidity Cutoff of 16.8 GV

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Monte Carlo simulation of the neutron monitor yield function

22-year solar magnetic cycle, and is relevant to the space radiation environment and effects on Earths atmosphere. Its complicated dependence on solar and heliospheric conditions is only roughly understood but has been empirically modeled in terms of a single modulation parameter. Most analyses of solar modulation used neutron monitor (NM) data from locations with relatively low geomagnetic cutoff rigidity, i.e., the threshold for cosmic rays to penetrate Earths magnetic field. The Princess Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand has the highest cutoff rigidity (

Measurement and simulation of neutron monitors count rate dependence on surrounding structure

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Distinct Pattern of Solar Modulation of Galactic Cosmic Rays above a High Geomagnetic Cutoff Rigidity

17 GV) where observations span a complete solar modulation cycle (since late 2007). The pattern of solar modulation at Doi Inthanon during 2011-2014 was qualitatively very different from that at low geomagnetic cutoff, and is not well described by the same modulation parameter. At other times, NM count rates from Doi Inthanon and McMurdo, Antarctica (cutoff

Bare Neutron Counter and Neutron Monitor Response to Cosmic Rays During a 1995 Latitude Survey

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GeV Solar Energetic Particle Observation and Search by IceTop from 2011 to 2016

0.01 GV) are linearly correlated and confirm the observation from latitude surveys in the previous solar cycle that the slope of the correlation changes with solar magnetic polarity. Low solar magnetic tilt angles (