Physics & Astronomy ETDs

Publication Date

6-21-1974

Abstract

The University of New Mexico High-Energy Neutron Experiment flown aboard NASA Satellite OS0-6 in 1969 was designed and built to study neutrons at an altitude of 􀀄500 km, above the earth's dense atmosphere. The detector was a proton recoil telescope with directional discrimination and was sensitive to protons as well as neutrons. Neutron data from August, 1969 to January, 1971 was analyzed in the energy range 40-120 Mev. Proton data in the energy range 60-170 Mev obtained during October and November of 1969 was also analyzed. Analysis was limited to the region of space known as the South Atlantic Radiation anomaly. This investigation was carried out to study source and loss mechanisms of the Van Allen radiation belts.

The omnidirectional proton flux as a function of B and L at ~500 km altitude in the anomaly (latitude limit -33°) was presented. The results compared favorably with previous mea­surements. Atmospheric energy loss scale heights were deter­mined from the east-west asymmetry of mirroring protons and compared with previous experiments and model atmosphere calculations. The results cover minimum mirroring altitudes from 50 to 550 km and L from 1.1 to 1.8. Pitch angle distributions of trapped protons were observed and fitted with gaussian functions. The half-widths of the gaussians were compared with predicted values for protons in a dipole magnetic field and an exponential atmosphere. The neutron data was studied to determine if there is enhanced neutron production in the South Atlantic anomaly.

Results in the 200-400 km minimum mirroring altitude range gave good agreement with previous effective atmospheric loss computations indicating that coulomb interactions are the prime loss mechanism for inner belt protons. The effects of pitch angle scattering and/or radial diffusion were evident in the 50-150 km minimum mirroring altitude results. These may also be significant source and loss mechanisms for inner belt protons. Results in the 400-500 km minimum mirroring altitude range indicated possible problems with the high alti­tude constituents of the model atmospheres considered here. The east-west ratios of the neutrons near the anomaly indicated that more neutrons are being generated in the anomaly than elsewhere. These additional neutrons are most likely being produced by high-energy trapped protons colliding with the atmosphere in the anomaly.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Christopher Pratt Leavitt

Second Committee Member

Derek B. Swinson

Third Committee Member

Roy Thomas

Language

English

Document Type

Dissertation

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