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Results for “time-dependent neutron transport”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

AXAF Detector Backgrounds Produced By Cosmic Ray Protons

One of the science instruments on the Advanced X-ray Astrophysics Facility (AXAF), planned for launch in 1998 into a highly elliptical (10,000 km x 140,000 km) orbit, is a microchannel plate High Resolution Camera (HRC). This detector is designed to provide imaging and spectroscopic observations of x-rays emitted by stellar sources in the 0.1 to 10 keV energy range. Described here are analyses made to determine the expected time-dependent detector background from prompt and delayed (activation) radiation initiated by galactic cosmic-ray (GCR) proton interactions in the spacecraft and payload. Numerical simulations were made using the coupled set of Monte Carlo radiation transport codes, analysis software, and data bases shown. The major codes are HETC for nucleon-meson transport, EGS for simulating electromagnetic cascades, and MORSE for low-energy (less than 15 MeV) neutron transport. The simulation follows the transport history of photons in the energy range from - 100 GeV down to approx. 0.1 keV due to gamma-ray sources from neutral pion decay, high-energy (spallation) collisions, and low-energy neutron inelastic scattering and capture reactions. Also included is radioisotope production and the tracking of gamma-rays, electrons, and positrons from induced radioactivity.

Armstrong, T. W.↗
NASA NTRS1986

Characteristic recovery times of Forbush-type decreases in the cosmic radiation. I - Observations at earth at different energies

Data on 30 asymmetric Forbush decreases recorded by the IMP spacecraft at 1 AU and the Mt. Washington neutron monitor over the period 1972-84 are examined to characterize the recovery characteristics of cosmic rays after the events. The spacecraft data are concentrated at energies of 1.7 GV, while the terrestrial instruments recorded events at 5 GV. Attention is paid to the relative amplitudes of the recorded transient decreases, the characteristic recovery times, and the energy dependence of the amplitudes and recovery time. The recovery times were found to be equal at both energy levels, supporting a concept of energy independence for the recoveries. Also, no correlations were found between the recovery times and the occurrences of a solar magnetic field reversal or with phase in the solar modulation cycle. A time-dependent, two-dimensional model is defined, which expresses the cosmic ray particle distributions as a function of the decay of the disturbance, with a small dependence on the transport parameters of the cosmic rays.

Lockwood, J. A.↗