Executive Summary Chapter 1 History, heritage and operation

With regards to Galactic Cosmic Radiation

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  Neutron monitors are used for observing solar modulation in real time, including Forbush decreases.
  
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  High resolution (hourly) data covers practically the entire jet age of civilian flight (starting in the late 1950s).
  
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  Useful for both long term monitoring (solar cycle) and short term variations (Forbush effects).
  
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  One monitor with many tubes is enough for basic GCR modelling, if statistics are good and magnetic drift of the cutoff is accounted for, but more monitors add more insight, and may be needed to get adequate statistics if monitors have only a few tubes each.
  

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  NMs provide the best data for reconstructing SPE particle spectrum anisotropy, which is needed to drive the most accurate and sophisticated SPE flight dose models.
  
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  To reconstruct global anisotropic particle flux spectra requires multiple NM at different altitudes and geomagnetic latitudes, both N and S.
  
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  NMs are the only data source providing insight into multi-GeV proton and alpha spectra during a SPE; satellite instruments simply do not have enough shielding to discriminate well.
  

Bartol Research Institute (2015). http://neutronm.bartol.udel.edu/listen/main.html#tell, accessed 10 Oct 2015.

Bureau of Labor Statistics (2016). Occupational Outlook Handbook. Available at: www.bls.gov/ooh/, accessed 11 May 2016.

Copeland, K; Sauer, HH; Duke, FE; Friedberg, W. Cosmic radiation exposure of aircraft occupants on simulated high-latitude flights during solar proton events from 1January 1986 through 1 January 2008. Advan Space Res, 2008, 42(6), 1008-1029.

Dwyer JR, et al. Estimation of the fluence of high-energy electron bursts produced by thunderclouds and the resulting radiation doses received in aircraft. J Geophys Res, 2010; 115: D09206, doi:10.1029/2009JD012039.

Federal Aviation Administration. Order 3900.19B, Chapter 14, Part 1406, Paragraph ‘a’. Washington, DC: Department of Transportation, Federal Aviation Administration, 26 August 2008.

International Commission on Radiological Protection. The 2007 Recommendations of the International Commission on Radiological Protection, Report No. 103. London: Elsevier, 2007.

ISO (International Standards Organization). Space environment (natural and artificial) --Galactic cosmic ray model. ISO 15930:2004. Geneva, Switzerland: ISO; 2004. Available from: www.iso.org/iso/home/store/catalogue_tc/ catalogue_detail.htm?csnumber=37095&commid=46614, accessed 12 June 2013.

MEXT (2011). Radiation in daily life. Available from www.mext.go.jp/component/english/__icsFiles/afieldfile/ 2011/04/26/1305115_001.pdf, accessed 10 May 2016.

National Council on Radiation Protection and Measurements. Ionizing Exposure of the Population of the United States, NCRP Report No. 160. Bethesda, MD, 2009.

O’Brien, K., Smart, D.F., Shea, M.A., Felsberger, E., Schrewe, U., Friedberg, W., Copeland, K. World-wide radiation dosage calculations for air crew members. Advan. Space Res. 31(4), 835-840, 2003.

O'Niel, P.W., Golge, S., and Slaba, T.C. Badhwar - O'Neill 2014 Galactic Cosmic Ray Flux Model Description, NASA/TP-2015-218569. Houston, TX: Johnson Space Center, 2015.

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). Sources and Effects of Ionizing Radiation: United Nations Scientific Committee on the Effects of Atomic Radiation: UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes Volume I: Sources. New York, NY: United Nations, 2000.

Warner-Jones, SM; Shaw, KB; Hughes, JS. Survey into the Radiological Impact of the Normal Transport of Radioactive Material by Air. Report NRPB-W39. National Radiation Protection Board (UK); Apr 2003. Available from: www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947310807, accessed 29 Jul 2014.

Ian Howat

Byrd Polar and Climate Research Center of The Ohio State University
Direct, continuous measurements of ice sheet surface mass balance are lacking, particularly in the accumulation zone where the surface snow and firn varies in density. Nearly all of our knowledge of surface mass variability comes from snow pit and ice core stratigraphy, providing annual resolution with relatively large uncertainties that are inadequate for constraining meteorological models. Further, little information is available on how the density of the firn layer changes with time, hampering efforts to estimate mass change from altimetry measurements. We are testing cosmic ray sensing technology to obtain the first high-accuracy (mm-scale) and continuous measurements of ice sheet mass balance that can be directly compared with models. The technology is simple in concept: we measure the attenuation of neutrons impacting a sensor as it is buried by accumulating mass. To obtain accurate measurements of mass accumulation, however, this signal must be corrected for variations due to atmospheric pressure and solar fluctuations. For the later, the neutron monitors maintained by the Bartol Research Institute provide a critical reference series. Following the successful pilot deployment of our snow mass balance sensors, we aspire to deploy a large network of sensors in both Greenland and Antarctica. The Bartol monitors at Thule, Labrador, South Pole and McMurdo Station will be critical for this effort.

Old Summary

The advent of the neutron monitor came after the discovery by Simpson [1948] that the latitude variation of the intensity of nucleonic component in cosmic ray air showers is several times larger than that of the electromagnetic and muon components. In 1952 the first neutron monitor stations were established at Chicago, Climax, Huancayo and Sacramento Peak. In 1954 a sea-level latitude survey by Rose et al. [1956] confirmed that the neutron monitor responded to lower energy primary particles than an ionization detector, and during the International Geophysical Year in 1957 a global network of roughly fifty neutron monitor stations was established. The reliability and basic simplicity of neutron monitors provide a means for studying the longer-term variations, while the sensitivity to low energy primary cosmic rays and high count rates make possible the measurement of short term intensity changes.

Because the intensity of cosmic rays hitting Earth is not uniform, it is important to place neutron monitors at multiple locations to form a complete picture of cosmic rays in space. Networking neutron monitors at different locations provides additional information such as cosmic ray arrival anisotropy, the energy spectrum and possible detection of relativistic solar neutrons. Furthermore the network constitutes a unique “instrument” in a fleet of particle detection and measurement facilities in space now and to be deployed in the future. The network has a detection threshold of order 500 MeV, extending up to 17 GeV, above which no variation over the Earth surface is expected. The network provides a full-sky field of view continuously making dozens of pointed measurements in key directions.

As the result of the long term reliability and on-line availability of neutron monitor data, users outside the traditional circles of Space Sciences have discovered innovated ways to utilize these data for new and unforeseen investigations, radiation monitoring or for improving real-time background knowledge. This includes understanding the background, important for the problem of detecting of illicit nuclear materials, monitoring soil moisture changes, monitoring biological hazards from radiation variation in the aerospace environments, microelectronics single event upsets in avionics and additional inputs for space weather forecasting. Over past decades neutron monitor data have become an operational resource in many different areas.