dorsal/arxiv
View SchemaSpatial and Temporal Variability of the Gamma Radiation from Earth's Atmosphere during a Solar Cycle
| Authors | Michael J. Harris, Gerald H. Share, Mark D. Leising |
|---|---|
| Categories | |
| ArXiv ID | physics/0308082 |
| URL | https://arxiv.org/abs/physics/0308082 |
| DOI | 10.1029/2003JA009958 |
| Journal | J.Geophys.Res. 108A12 (2003) 1435 |
Abstract
The Solar Maximum Mission satellite's Gamma Ray Spectrometer observed Earth's atmosphere for most of the period 1980-1989. Its 28deg orbit ensured that a range of geomagnetic latitudes (geomagnetic cutoff rigidities) was sampled. We measured the variation with time and rigidity of albedo gamma-ray lines at 1.6 MeV, 2.3 MeV and 4.4 MeV which are diagnostic of Galactic cosmic radiation penetrating the cutoff and of the secondary neutrons produced in the atmosphere. We found that the gamma-ray line intensities varied inversely with solar activity and cutoff rigidity, as expected. The line ratio (1.6 MeV + 2.3 MeV)/4.4 MeV was remarkably constant (close to 0.39) at all times and rigidities; the former two lines are produced by 5-10 MeV secondary neutrons causing excitation and de-excitation of 14N, while the latter is produced by more energetic (>20 MeV) neutrons inducing spallation. We infer that the shape of the secondary neutron energy spectrum is virtually constant everywhere and at all times. We also measured the intensity of the 0.511 MeV electron-positron annihilation line. This line too varies with solar cycle and cutoff rigidity, but its fall-off from low to high rigidity is less marked than that of the nuclear lines. This results from the energy dependences of the cross sections for positron production and for the hadronic processes which which produce secondary neutrons.
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"abstract": "The Solar Maximum Mission satellite\u0027s Gamma Ray Spectrometer observed Earth\u0027s\natmosphere for most of the period 1980-1989. Its 28deg orbit ensured that a\nrange of geomagnetic latitudes (geomagnetic cutoff rigidities) was sampled. We\nmeasured the variation with time and rigidity of albedo gamma-ray lines at 1.6\nMeV, 2.3 MeV and 4.4 MeV which are diagnostic of Galactic cosmic radiation\npenetrating the cutoff and of the secondary neutrons produced in the\natmosphere. We found that the gamma-ray line intensities varied inversely with\nsolar activity and cutoff rigidity, as expected. The line ratio (1.6 MeV + 2.3\nMeV)/4.4 MeV was remarkably constant (close to 0.39) at all times and\nrigidities; the former two lines are produced by 5-10 MeV secondary neutrons\ncausing excitation and de-excitation of 14N, while the latter is produced by\nmore energetic (\u003e20 MeV) neutrons inducing spallation. We infer that the shape\nof the secondary neutron energy spectrum is virtually constant everywhere and\nat all times. We also measured the intensity of the 0.511 MeV electron-positron\nannihilation line. This line too varies with solar cycle and cutoff rigidity,\nbut its fall-off from low to high rigidity is less marked than that of the\nnuclear lines. This results from the energy dependences of the cross sections\nfor positron production and for the hadronic processes which which produce\nsecondary neutrons.",
"arxiv_id": "physics/0308082",
"authors": [
"Michael J. Harris",
"Gerald H. Share",
"Mark D. Leising"
],
"categories": [
"physics.space-ph",
"astro-ph",
"physics.geo-ph"
],
"doi": "10.1029/2003JA009958",
"journal_ref": "J.Geophys.Res. 108A12 (2003) 1435",
"title": "Spatial and Temporal Variability of the Gamma Radiation from Earth\u0027s Atmosphere during a Solar Cycle",
"url": "https://arxiv.org/abs/physics/0308082"
},
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