Computer Science – Performance
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........42m&link_type=abstract
PhD Dissertation, Massachusetts Inst. of Tech. Cambridge, MA United States
Computer Science
Performance
1
Gamma Ray Bursts, Radiation Detectors, Ultraviolet Radiation, Imaging Techniques, Charge Coupled Devices, Neutron Stars, Stellar Activity, Stellar Evolution, Applications Programs (Computers), Stellar Physics, Quantum Efficiency, Stellar Structure, Performance Tests, Surface Properties, Astronomical Models, Thermodynamics, Nuclear Reactions, Thermal Conductivity, Algorithms
Scientific paper
In the first part of this dissertation I present experimental research which contributes to the development of a UV-sensitive solid-state imaging detector for the HETE satellite. The detector is a thinned, backside-illuminated charge-coupled device (CCD). The ultraviolet (UV) quantum efficiency (QE) is very sensitive to the results of the back-surface treatment, which stabilizes and protects that surface. As part of the detector development I designed and built an instrument to measure the quantum efficiency of a CCD over the wavelength range of 200-500 nm. With this instrument I measured the QE of seven prototype devices that were manufactured with three different back-surface technologies. I derived a statistical test to measure the mean number of electrons per photon which increases from unity with increasing photon energy above a threshold of approximately 3.65 eV (340 nm). This effect is critically important when making photometric measurements at these wavelengths with solid state detectors. I also developed a simple physically-motivated model of the back surface which provides adequate fits to the measured QE. I find that the best back-surface technology yields CCD's that have stable QE's of greater than 40% in the HETE UV band of 220-310 nm. This is somewhat better than the QE of 20% required by the HETE UV instrument (Ricker et al. 1992). Slowly-accreting neutron stars should exist in the galaxy and their evolution is the focus of the second part of this dissertation. I present computational research on the evolution of this class of slowly accreting neutron stars. I describe an evolution code, which simulates the crust of a slowly accreting neutron star, and report on the evolution of the stored energy, density inversions, structure, and composition of fifteen different simulated models. This evolution code is a version of ASTRA, an evolution code originally developed by Rakavy et al. (1967). It is based on the version developed by Joss (1978) to simulate thermo-nuclear flashes in the crust of accreting neutron stars. The major changes are a new set of thermodynamic equations, a new nuclear reaction network, and a new thermal conductivity algorithm. I find that the crust of a slowly-accreting neutron star stores approximately 1045 ergs in the non-equilibrium nuclear composition. One possible trigger mechanism for releasing this energy is the density inversions which occur naturally during the evolution of the crust.
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