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Woolf RS, Sinclair LE, Van Brabant RA, Harvey BJA, Phlips BF, Hutcheson AL, Jackson EG. Measurement of secondary cosmic-ray neutrons near the geomagnetic North Pole. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2019; 198:189-199. [PMID: 30640033 DOI: 10.1016/j.jenvrad.2019.01.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 12/27/2018] [Accepted: 01/02/2019] [Indexed: 06/09/2023]
Abstract
The spectrum of cosmogenic neutrons at Earth's surface covers a wide energy range, from thermal to several GeV. The flux of secondary neutrons varies with latitude, elevation, solar activity, and nearby material, including ground moisture. We report the results from a campaign to measure count rates in neutron detectors responding to three different energy ranges conducted near the geomagnetic North Pole at CFS Alert, Nunavut, Canada (82.5°N, 62.5°W; vertical geomagnetic cutoff rigidity, RC = 0 GV) in June of 2016. In November 2016, we performed a follow-on measurement campaign in southern Canada at similar RC (1.5 GV) and elevations. We conducted these measurements, at varying elevation and ground moisture content, with unmoderated and moderated 3He detectors for thermal and epithermal-to-MeV sensitivity, and with EJ-299-33 pulse shape discrimination plastic scintillator detectors for fast neutrons. Background gamma rays were monitored with NaI(Tl) detectors. Using these data sets, we compared the measured count rates to a predictive model. This is the first ever data set taken from this location on Earth. We find that for the thermal and epithermal-to-MeV neutron measurements the predictive model and data are in good agreement, except at one location on rock-covered ground near 1 km elevation. The discrepancy at that location may be attributable to ground moisture variability. Other measurements, during this campaign and prior, support the assertion that ground moisture plays a critical role in determining neutron flux.
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Affiliation(s)
- Richard S Woolf
- Space Science Division, U. S. Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC, 20375, USA.
| | - Laurel E Sinclair
- Natural Resources Canada, Government of Canada, 930 Carling Ave (CEF, Bldg 7, Observatory Cr.), Ottawa, Ontario, K1A 0Y3, Canada.
| | - Reid A Van Brabant
- Natural Resources Canada, Government of Canada, 930 Carling Ave (CEF, Bldg 7, Observatory Cr.), Ottawa, Ontario, K1A 0Y3, Canada.
| | - Bradley J A Harvey
- Natural Resources Canada, Government of Canada, 930 Carling Ave (CEF, Bldg 7, Observatory Cr.), Ottawa, Ontario, K1A 0Y3, Canada.
| | - Bernard F Phlips
- Space Science Division, U. S. Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC, 20375, USA.
| | - Anthony L Hutcheson
- Space Science Division, U. S. Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC, 20375, USA.
| | - Emily G Jackson
- Formerly: NRC Research Associate Resident at the U. S. Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC, 20375, USA.
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Kanbach G, Reppin C, Schönfelder V. Support for Crand Theory from measurements of Earth albedo neutrons between 70 and 250 MeV. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja079i034p05159] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Preszler AM, Simnett GM, White RS. Angular distribution and altitude dependence of atmospheric neutrons from 10 to 100 MeV. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja079i001p00017] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Iles RHA. Effect of solar energetic particle (SEP) events on the radiation exposure levels to aircraft passengers and crew: Case study of 14 July 2000 SEP event. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003ja010343] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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O'Brien K, Sauer HH. The atmospheric radiation response to solar-particle-events. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 2003; 32:73-80. [PMID: 14727666 DOI: 10.1016/s0273-1177(03)90373-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
High-energy solar particles, produced in association with solar flares and coronal mass ejections, occasionally bombard the earth's atmosphere. resulting in radiation intensities additional to the background cosmic radiation. Access of these particles to the earth's vicinity during times of geomagnetic disturbances are not adequately described by using static geomagnetic field models. These solar fluxes are also often distributed non uniformly in space, so that fluxes measured by satellites obtained at great distances from the earth and which sample large volumes of space around the earth cannot be used to predict fluxes locally at the earth's surface. We present here a method which uses the ground-level neutron monitor counting rates as adjoint sources of the flux in the atmosphere immediately above them to obtain solar-particle effective dose rates as a function of position over the earth's surface. We have applied this approach to the large September 29-30, 1989 ground-level event (designated GLE 42) to obtain the magnitude and distribution of the solar-particle effective dose rate from an atypically large event. The results of these calculations clearly show the effect of the softer particle spectra associated with solar particle events, as compared with galactic cosmic rays, results in a greater sensitivity to the geomagnetic field, and, unlike cosmic rays, the near-absence of a "knee" near 60 degrees geomagnetic latitude.
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Affiliation(s)
- K O'Brien
- Northern Arizona University, Flagstaff, AZ 86011-6010, USA. keran.o'
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