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Measurement of the Low-Energy Portion of the Primary Cosmic Ray Spectrum

Entry ID: gov.noaa.ngdc.G00599

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Summary

Abstract: ABSTRACT: Most cosmic rays come from the galaxy, though some are produced by eruptive events on the Sun's surface. These high energy cosmic ray particles can affect satellites, causing single event upsets. Scientists have postulated that cosmic rays can affect the earth by causing changes in weather. Cosmic rays can cause clouds to form in the upper atmosphere, after the particles collide with ... other atmospheric particles in our troposphere. The process of a cosmic ray particle colliding with particles in our atmosphere and disintegrating into smaller pions, muons, and the like, is called a cosmic ray shower. These particles can be measured on the Earth's surface by neutron monitors.Ground-based neutron monitors detect variations in the approximately 500 Mev to 20 GeV (low energy) portion of the primary cosmic ray spectrum. This class of cosmic ray detector is more sensitive in the approximate 500 Mev to 4 GeV portion of the cosmic ray spectrum than are cosmic ray muon detectors. The portion of the cosmic ray spectrum that reaches the Earth's atmosphere is controlled by the geomagnetic cutoff which varies from a minimum (theoretically zero) at the magnetic poles to a vertical cosmic ray cutoff of about 15 GV (ranging from 13 to 17) in the equatorial regions. (Note: GeV is a unit of energy, GV is a unit of magnetic rigidity). The primary cosmic ray particles interact with the atmosphere and generate secondaries, some of which will reach the surface of the Earth. In high latitude regions of the Earth, where the geomagnetic cutoff is low, the lower threshold response of the neutron monitor is controlled by the atmospheric mass (about 1030 grams at sea level) which limits the response threshold of the neutron monitor to primary radiation of about 430 MeV. (At the South Pole, where the surface is 2820 M above sea level, the reduced atmospheric mass lowers the primary radiation detection threshold to about 300 MeV). At mid-latitudes or equatorial latitudes, the detection threshold is controlled by the geomagnetic cutoff. Neutron monitors at high altitudes have higher counting rates than neutron monitors at lower altitudes because of the atmospheric absorption of the cosmic ray secondaries generated near the top of the atmosphere. When the secondary cosmic rays interact in the monitor, (actually in lead surrounding the counters) they cause nuclear disintegrations, or stars. These stars are composed of charged fragments and neutrons typically in the energy range of tens to hundreds of MeV, even up to GeV energies. As a result of these high energy nuclear interactions, there will be more secondary fragments generated than incident particles and hence there is a multiplier effect for the counters. The neutrons are moderated and then counted using Boron tri-fluoride (BF3) proportional counters which are efficient thermal neutron detectors; hence the name neutron monitor. The original design is often designated as an IGY neutron monitor. A description of this type of instrument is given by Simpson, (Annals of the IGY, Vol. 4, pp. 351-373, 1957). The NM-64 or super neutron monitor was developed for the IQSY (International Quiet Sun Years 1964-65) when instruments with a higher counting capacity were required. A description of this type of neutron monitor is given by Carmichael (Annals of the IQSY, Vol. 1, pp. 178-197, 1968). Super neutron monitors are often designated as xx-NM-64 where xx is the number of tubes in the monitors. An 18-NM-64 at high latitude has a counting rate of approximately 1 million counts per hour or 0.1 percent statistics. The neutron monitor and supermonitor digital data for the time period 1953 to present are available at http://spidr.ngdc.noaa.gov and consist of over 100 stations' hourly (UT) values of: (a) counting rates corrected for atmospheric pressure effects; (b) uncorrected counting rates; and (c) atmospheric pressure data. If it is not possible to have all three types of data, the most important is the counting rate corrected for atmospheric pressure.NGDC also holds paper archives for some cosmic ray Ionization Chamber monitors and some meson telescopes, mostly during the period of the International Geophysical Year (IGY) and International Quiet Sun Years (IQSY) 1957-1968.

CURRENTNESS REFERENCE: Ground Condition

DATA SET CREATORS: DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce (comp)

Purpose: PURPOSE: Cosmic Ray Research

Related URL

Link: GET DATA

Description: Get data

Geographic Coverage

(Click for Interactive Map)

Spatial coordinates

N: 90.0

S: -90.0

E: 180.0

W: -180.0

Data Set Citation

Dataset Originator/Creator: Please See Summary

Dataset Title: Measurement of the Low-Energy Portion of the Primary Cosmic Ray Spectrum

Dataset Series Name: Solar Terrestrial Physics

Dataset Release Date: 1953

Dataset Release Place: Boulder, CO

Dataset Publisher: National Geophysical Data Center

Version: First

Issue Identification: 'STP-93-3, Neutron Monitor Data on CD-ROM'

Online Resource: http://www.ngdc.noaa.gov/stp/SOLAR/COSMIC_RAYS/cosmic.html

Temporal Coverage

Start Date: 1953-01-01

Science Keywords

SUN-EARTH INTERACTIONS > SOLAR ENERGETIC PARTICLE PROPERTIES

ISO Topic Category

GEOSCIENTIFIC INFORMATION

Project

ESIP > Earth Science Information Partners Program

Access Constraints ACCESS CONSTRAINTS: No Constraints

DISTRIBUTION LIABILITY: While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by any errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.

CUSTOM ORDER PROCESS: Contact data center for information

Use Constraints None

Ancillary Keywords

Atmosphere

Aurora

Data Set Progress

IN WORK

Data Center

National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce

Data Center URL: http://www.ngdc.noaa.gov/
Dataset ID: ______COSMIC_RAY_-_NEUTRON_MONITOR ____

Data Center Personnel
Name: EDWARD H. ERWIN Phone: (303) 497-6133 Fax: (303) 497-6513 Email: Edward.H.Erwin at noaa.gov Contact Address: NOAA/NESDIS/NGDC E/GC2 325 Broadway City: Boulder Province or State: CO Postal Code: 80303 Country: USA

Distribution

Distribution Size: 507.800000

Distribution Format: ASCII

Fees: Depends on the Data Set Depends on the Data Set

Personnel

EDWARD H. ERWIN

Role: TECHNICAL CONTACT

Role: DIF AUTHOR

Phone: (303) 497-6133

Fax: (303) 497-6513

Email: Edward.H.Erwin at noaa.gov

Contact Address:

NOAA/NESDIS/NGDC

E/GC2

325 Broadway

City: Boulder

Province or State: CO

Postal Code: 80303

Country: USA

Creation and Review Dates

DIF Creation Date: 2009-07-14

Last DIF Revision Date: 2011-03-07

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