THE EFFECTIVE DIRECTIONAL SENSITIVITY OF COSMIC-RAY NEUTRON MONITORS

The direction of maximum sensitivity of a neutron monitor is calculated numerically for a set of points on the same geomagnetic meridian but extending in latitude from the equator to the pole. This leads to two master curves, one for the longitude, the other for the latitude of this direction. From these curves this direction is obtained in geographic co-ordinates for some 20 cosmic-ray stations. The method of calculation is described taking into account atmospheric absorption and the energy spectrum of the incident particles. The aperture of the sensitive cone, or source width, is also calculated. Finally the accuracy of the results is discussed and the application of the concept of effective direction is described.

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The long-term variation of the cosmic radiation

Canadian Journal of Physics ◽

10.1139/p68-379 ◽

1968 ◽

Vol 46 (10) ◽

pp. S903-S906 ◽

Cited By ~ 4

Author(s):

J. A. Lockwood ◽

W. R. Webber

Keyword(s):

Neutron Monitor ◽

Cosmic Radiation ◽

Cosmic Ray ◽

Solar Modulation ◽

Neutron Monitors ◽

Cosmic Ray Intensity ◽

Direct Measurements ◽

Term Variation ◽

Primary Cosmic Radiation

The variation in the cosmic-ray intensity recorded by neutron monitors from 1958 to 1965 has been investigated to deduce the form of the solar modulation of the cosmic radiation. The observed changes in the intensity at the neutron monitor stations, averaged over quarter-year periods, were compared with changes calculated using modulation functions depending upon energy, rigidity, and velocity × rigidity. These calculations were based upon the revised differential response functions deduced by Lockwood and Webber (1967). The variance between the observed and calculated changes in the neutron monitor intensities at different stations was minimized to determine the best form of the solar modulation function. We find that the change of the primary cosmic radiation, deduced from the change in the neutron monitor intensity as well as from direct measurements of the primary flux, can be described by a modulation of the form exp(–K/P) in the rigidity range 0.5 < P < 50 GV. The change between 1959 and 1965 can be fitted with K = 1.94 ± 0.09 and between 1963 and 1965 with K = 0.36 ± 0.05.

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Decadal trends in the diurnal variation of galactic cosmic rays observed using neutron monitor data

Annales Geophysicae ◽

10.5194/angeo-35-825-2017 ◽

2017 ◽

Vol 35 (4) ◽

pp. 825-838 ◽

Cited By ~ 2

Author(s):

Simon Thomas ◽

Mathew Owens ◽

Mike Lockwood ◽

Chris Owen

Keyword(s):

Phase Change ◽

Diurnal Variation ◽

Neutron Monitor ◽

Cosmic Ray ◽

Galactic Cosmic Rays ◽

Energetic Particles ◽

Magnetic Polarity ◽

Neutron Monitors ◽

Neutron Monitor Data ◽

Monitor Data

Abstract. The diurnal variation (DV) in galactic cosmic ray (GCR) flux is a widely observed phenomenon in neutron monitor data. The background variation considered primarily in this study is due to the balance between the convection of energetic particles away from the Sun and the inward diffusion of energetic particles along magnetic field lines. However, there are also times of enhanced DV following geomagnetic disturbances caused by coronal mass ejections or corotating interaction regions. In this study we investigate changes in the DV over four solar cycles using ground-based neutron monitors at different magnetic latitudes and longitudes at Earth. We divide all of the hourly neutron monitor data into magnetic polarity cycles to investigate cycle-to-cycle variations in the phase and amplitude of the DV. The results show, in general, a similarity between each of the A < 0 cycles and A > 0 cycles, but with a phase change between the two. To investigate this further, we split the neutron monitor data by solar magnetic polarity between times when the dominant polarity was either directed outward (positive) or inward (negative) at the northern solar pole. We find that the maxima and minima of the DV changes by, typically, 1–2 h between the two polarity states for all non-polar neutron monitors. This difference between cycles becomes even larger in amplitude and phase with the removal of periods with enhanced DV caused by solar wind transients. The time difference between polarity cycles is found to vary in a 22-year cycle for both the maximum and minimum times of the DV. The times of the maximum and minimum in the DV do not always vary in the same manner between A > 0 and A < 0 polarity cycles, suggesting a slight change in the anisotropy vector of GCRs arriving at Earth between polarity cycles. Polar neutron monitors show differences in phase between polarity cycles which have asymptotic directions at mid-to-high latitudes. All neutron monitors show changes in the amplitude of the DV with solar polarity, with the amplitude of the DV being a factor of 2 greater in A < 0 cycles than A > 0 cycles. In most cases the change in timing of the maximum /minimum is greatest with the stations' geomagnetic cut-off rigidity shows little variation in the DV phase with latitude. We conclude that the change in the DV with the dominant solar polar polarity is not as simple as a phase change, but rather an asymmetric variation which is sensitive to the neutron monitor's asymptotic viewing direction.

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Energy spectrum of diffuse primary X rays up to 180 keV

Canadian Journal of Physics ◽

10.1139/p68-270 ◽

1968 ◽

Vol 46 (10) ◽

pp. S461-S465 ◽

Cited By ~ 17

Author(s):

J. A. M. Bleeker ◽

J. J. Burger ◽

A. J. M. Deerenberg ◽

A. Scheepmaker ◽

B. N. Swanenburg ◽

...

Keyword(s):

Energy Spectrum ◽

Power Law ◽

Plastic Scintillator ◽

Geomagnetic Latitude ◽

Cosmic Ray ◽

Rotating Disk ◽

The Other ◽

X Rays ◽

X Ray ◽

Good Agreement

Two balloon flights with identical X-ray detectors were carried out in the summer of 1966, one from De Bilt, the Netherlands (geomagnetic latitude 53 °N), and the other from Taiyomura, Japan (geomagnetic latitude 25 °N). The detector consists of a NaI(Tl) crystal, 12.5 mm thick and 50 mm in diameter, surrounded by an effective collimator-shield and a plastic scintillator guard counter. The rotating disk incorporated enables the separation of "forward" X rays from the cosmic-ray-induced background. The results of the flights are in very good agreement with each other. In view of the rather large difference in geomagnetic latitude in these two flights, this agreement supports the celestial origin of the primary X rays observed. The energy spectrum between 20 and 180 keV can be expressed by a power law:[Formula: see text]

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Effect of the Muon Contribution on the Barometric Coefficient of Neutron Monitors

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000014028 ◽

1974 ◽

Vol 2 (5) ◽

pp. 304-305 ◽

Cited By ~ 1

Author(s):

T. T. Quang ◽

A. G. Fenton ◽

K. B. Fenton

Keyword(s):

Neutron Monitor ◽

Counting Rate ◽

Cosmic Ray ◽

Atmospheric Depth ◽

Neutron Monitors ◽

The Real ◽

Obliquely Incident ◽

Coefficient Versus ◽

Depth Curve ◽

Barometric Coefficient

The barometric coefficient of a cosmic-ray neutron monitor is found to increase with atmospheric depth from ~ 150 mm Hg to 600 mm Hg and then to decrease slowly with depth down to 760 mm Hg (Bachelet et al. 1965; Carmichael and Bercovitch 1969). Bachelet et al. 1965) tentatively attributed this change in the slope of the barometric coefficient versus atmospheric depth curve at 600 mm Hg to the contribution made by muons to the neutron monitor counting rate. Carmichael and Bercovitch (1969) have shown that the contribution to the monitor counting rate made by obliquely incident nucleons may be the real cause. Singh et al. (1970) have derived an expression for the barometric coefficient for vertically incident particles in a neutron monitor which increases continuously with increasing atmospheric depth down to 760 mm Hg, demonstrating more definitely that the above explanation of Carmichael and Bercovitch is correct.

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The mini-neutron monitor: a new approach in neutron monitor design

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020038 ◽

2020 ◽

Vol 10 ◽

pp. 39

Author(s):

Du Toit Strauss ◽

Stepan Poluianov ◽

Cobus van der Merwe ◽

Hendrik Krüger ◽

Corrie Diedericks ◽

...

Keyword(s):

Neutron Monitor ◽

Radiation Risk ◽

Cosmic Ray ◽

Cost Effective ◽

Space Travel ◽

Neutron Monitors ◽

New Approach ◽

Effective Version ◽

Technical Details ◽

Cosmic Ray Flux

The near-Earth cosmic ray flux has been monitored for more than 70 years by a network of ground-based neutron monitors (NMs). With the ever-increasing importance of quantifying the radiation risk and effects of cosmic rays for, e.g., air and space-travel, it is essential to continue operating the existing NM stations, while expanding this crucial network. In this paper, we discuss a smaller and cost-effective version of the traditional NM, the mini-NM. These monitors can be deployed with ease, even to extremely remote locations, where they operate in a semi-autonomous fashion. We believe that the mini-NM, therefore, offers the opportunity to increase the sensitivity and expand the coverage of the existing NM network, making this network more suitable to near-real-time monitoring for space weather applications. In this paper, we present the technical details of the mini-NM’s design and operation, and present a summary of the initial tests and science results.

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Short-term periodicities observed in neutron monitor counting rates

NMDB@Home 2020 - Cosmic ray studies with neutron detectors ◽

10.38072/2748-3150/p9 ◽

2021 ◽

pp. 65-71

Author(s):

Alejandro López-Comazzi ◽

Juan José Blanco

Keyword(s):

Neutron Monitor ◽

Spectral Power ◽

Cosmic Ray ◽

Global Network ◽

Competitive Effect ◽

Neutron Monitors ◽

Short Term ◽

Cosmic Ray Intensity ◽

The One ◽

First Time

The main objective is to check whether the periodicities observed in the cosmic rays in the interval 2013-2018 are affected by the magnetic rigidity or the height at which the neutron monitors are placed. A Global Neutron Monitor (GNM) has been defined as representative of the neutron monitor global network. The Morlet wave - let analysis is applied to the GNM and the selected solar activity parameters to find out common periodicities. Short-term periodicities of 13.5, 27, 48, 92, 132 and 298 days have been observed in cosmic ray intensity. A clear inverse relationship between rigidity and spectral power has been obtained for the 13.5, 48, 92, 132-day periods. A not so clear but still observed direct relationship between the height of the neutron monitors and the spectral power for the 48, 92, 132-day periods has been also found. The periodicity of 92 days is the one which shows the highest dependence with rigidity cutoff and height. As far as we know, this is the first time that these dependencies are reported. We think that these observations could be explained by assuming some cosmic ray intensity energy dependence in such periodicities and a competitive effect between rigidity and height.

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