Engineering topics

Gibson, W. M.

Publications and source records attributed to Gibson, W. M..

3 records

NASA NTRS1999

Polycapillary X-Ray Optics for X-Ray Astronomy

High-energy x-ray spectrometry from astronomical sources is difficult due to low flux rates and high background. Polycapillary x-ray optics can be used to increase the signal-to-noise ratio by focusing photons onto a small energy dispersive detector. Two optics, both designed for x-ray astronomy, have been built and tested as collimating optics with a microfocus x-ray source for x-ray energies up to 70 keV and as focusing optics with parallel x-rays up to 50 keV. Results from these tests show that polycapillary x-ray optics have transmission efficiencies ranging from 5% to 40% and signal gains ranging from 5 to over 100 for energies up to 50 keV. Furthermore the results show that these optics have potential for use up to 100 keV. The experimental results as well as simulations for the measured and for optimized optics will be discussed.

Russell, C. H.↗

NASA NTRS1997

Stationary Crystal Diffraction with a Monochromatic Convergent X-Ray Source and Application for Macromolecular Crystal Data Collection

A diffraction geometry utilizing convergent X-rays from a polycapillary optic incident on a stationary crystal is described. A mathematical simulation of the resulting diffraction pattern (in terms of spot shape, position and intensity) is presented along with preliminary experimental results recorded from a lysozyme crystal. The effective source coverage factor is introduced to bring the reflection intensities onto the same scale. The feasibility of its application to macromolecular crystal data collection is discussed.

Ho, J. X.↗

NASA NTRS1986

Studies of implanted iron in silicon by channeling and Rutherford backscattering

Different amounts of 100-keV iron ions have been implanted into high-resistivity p-type FZ-silicon samples. The implantation damage, recovery of damage during various annealing periods and temperatures, movement of iron atoms under annealing and oxidation, and the kinds of defects created after implantation, annealing, or oxidation are all investigated by channeling and backscattering measurements. It is found that the critical fluence of 100-keV iron implanted into silicon at room temperature is about 2.5 x 10 to the 14th Fe/sq cm, and that iron atoms are gettered by silicon oxidation. In this supersaturated region, iron atoms diffuse slightly towards bulk silicon during high-temperature annealing (greater than or equal to 1100 C) but not at all during low-temperature annealing (less than or equal to 1000 C) in dry nitrogen ambient.

Wang, P. W.↗