Measurement and simulation of neutron monitor count rate dependence on surrounding structure
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Date
2015Author
Aiemsa-ad, N.
Krüger, H.
Moraal, H.
Ruffolo, D.
Sáis, A.
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Show full item recordAbstract
Neutron monitors are the premier instruments for precise measurements of time variations
(e.g., of solar origin) in the galactic cosmic ray (GCR) flux in the range of ∼1–100 GeV. However, it has proven
challenging to accurately determine the yield function (effective area) versus rigidity in order to relate a
neutron monitor’s count rate with those of other monitors worldwide and the underlying GCR spectrum.
Monte Carlo simulations of the yield function have been developed, but there have been few opportunities
to validate these observationally, especially regarding the particular environment surrounding each
monitor. Here we have precisely measured the count rate of a calibration neutron monitor near the Princess
Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand (18.59∘N, 98.49∘E, 2560 m altitude), which
provides a basis for comparison with count rates of other neutron monitors worldwide that are similarly
calibrated. We directly measured the effect of surrounding structure by operating the calibrator outside
and inside the building. Using Monte Carlo simulations, we clarify differences in response of the calibrator
and PSNM, as well as the calibrator outside and inside the building. The dependence of the calibrator count
rate on surrounding structure can be attributed to its sensitivity to neutrons of 0.5–10 MeV and a shift of
sensitivity to nucleons of higher energy when placed inside the building. Simulated calibrator to PSNM
count rate ratios inside and outside agree with observations within a few percent, providing useful
validation and improving confidence in our ability to model the yield function for a neutron monitor station
URI
http://hdl.handle.net/10394/18401http://dx.doi.org/10.1002/2015JA021249
http://onlinelibrary.wiley.com/doi/10.1002/2015JA021249/full