X-Ray Induced Luminescence of Sapphire and Ruby

Over the past decade the luminescence properties of sapphire (∝-AL2O3) and ruby (Al2O3:Cr2O3) have been the subject of many investigations because of their importance in materials technology. Sapphire and ruby are at present used as lasing materials, radiation dosimeters, and as optical windows. In order that these operations may be made more efficient, and that other useful luminescent properties may be systematically explored and developed, much attention has been given to understanding the luminescent mechanisms from the standpoint of the physics of the solid state. However, mechanisms have not yet been proposed that describe in detail the known luminescent properties of sapphire and ruby. The luminescence experiments which have been previously reported in the literature on sapphire and ruby fall into two classes: experiments in which the exciting energy is stored in the crystal by some defect mechanism and subsequently released by perturbing the crystal, and experiments in which the luminescence is observed while the crystals are being excited. Thermoluminescence, in which energy is stored in the crystals by exposing it to ionizing radiation and subsequently released by raising the temperature of the crystal, is the most extensively used technique of the former class. The facts concerning the thermoluminescence of sapphire and ruby are well documented. (11,12) Numerous experiments in the latter class have been reported in which the exciting radiation was in the visible or ultraviolet energy region. (16, 17) These latter experiments have a disadvantage; the amount of exciting energy absorbed is not independent of two important parameters, temperature and chromium concentration. It was the primary intent of these investigations to resolve the difficulty of the dependence of the absorbed energy by exciting sapphire and ruby crystals with x-rays. Because the energy of the x-ray photons incident on and within the crystal is more than an order of magnitude more energetic than is necessary to produce highly mobile or free electrons within the crystal, the number of such electrons produced is independent of the temperature and chromium concentration over the range that these parameters were varied. The program of experiments reported herein was designed to answer the following questions: (1) How does the intensity of the total luminescence depend on the temperature? (2) How does the emission spectrum depend on temperature and chromium concentration? (3) How does the luminesce yield depend on temperature? The answers to these questions were obtained by observing the luminescence of sapphire and ruby, subjected to continuous x-ray excitation, as a function of temperature and chromium concentration. The total x-ray-induced luminescence and emission spectra of two crystals, one nominally pure sapphire and the other sapphire containing 0.005% Cr2O3, were observed as the temperature of the crystals was raised and lowered between 25°C and 400°C. The results for other chromium concentrations (0.05% and 0.5% Cr2O3) may be found in Mr. Wayne Cooke’s masters’ thesis (21) The thermoluminescence total emission and emission spectra were observed between 25°C and 400°C after x-ray exposure at room temperature. It should be noted that there is one experiment in the literature in which the x-ray-induced luminescence of ruby was observed as a function of temperature.(19) The investigators observed the luminescence as the temperature increased; hence, much of the emission as the temperature decreases because the energy stored in a crystal at a particular temperature has a decreasing probability of being released at lower temperatures

A Comparison of Minority and Non-Minority Engineering Students on Selected Personality and Program Variables

The purpose of this study was to investigate whether there are common characteristics associated with 226 Hispanic, African American, and White engineering students who persist at predominantly White colleges and universities. A personality profile of minority and non-minority engineering students was developed. Information regarding factors influencing choice of major, university, study, work and extracurricular involvement, possible reasons for withdrawal from college, awareness and satisfaction with student support services and selected academic courses was also compiled. Components of Minority Engineering Programs (MEPs) which are most used or valued by minority engineering students were identified. Analysis of Variance identified four of the thirty-seven ACL scales that were statistically significantly different between groups. MEP results indicate that students attending universities with formal MEP\u27s in place are more aware of MEP and other services offered by the university than students attending universities without formal MEP\u27s. Engineering Survey results indicate minorities as deciding on college and college major much earlier than their non-minority counterparts. Minorities were employed more hours per week than non-minorities and spend less time studying outside of class

Teachers’ Perceptions of a Multiple High-Risk Behavior Prevention Program and Delivery of Universal Programming

Much of the success of high-risk behavior prevention programs rests with teachers who deliver the curriculum however; few studies have investigated teachers\u27 perceptions of program implementation. The objective of this phenomenological study was to answer the question, “What are the experiences of teachers who are asked to be involved in the implementation process when their school adopts a multiple high-risk behavior prevention program”? Participants included 10 teachers at a local, private high school in the Southern United States. Five themes emerged: (a) lack of consistent historical effort, (b) need for program, (c) positive but tentative perceptions, (d) challenges with implementation, and (e) review of program counselor. The qualitative results identified factors that can promote or hinder success of the program

Supersonic boundary-layer transition on the LaRC F-106 and the DFRF F-15 aircraft. Part 1: Transition measurements and stability analysis

For the case of the F-15 flight tests, boundary layer transition was observed up to Mach numbers of 1.2. For very limited and specific flight conditions, laminar flow existed back to about 20 percent chord on the surface clean up glove. Hot film instrumentation was effective for locating the region of transition. For the F-106 flight tests, transition on the wing or vertical tail generally occurred very near the attachment line. Transition was believed to be caused by either attachment line contamination or strong cross flow development due to the high sweep angles of the test articles. The compressibility analysis showed that cross flow N-factors were in the range of 5 to 12 at transition

Vagotomy with Pyloroplasty or Antrectomy: A Comparison of Results in the Treatment of Duodenal Ulcer

During the years 1970-73, 776 operations were performed for the relief of duodenal ulcer. Truncal vagotomy was done in all cases, and to this was added antrectomy in 92 cases and pyloroplasty in 24 cases. In the followup, three-fourths of the patients in both groups said they were satisfied with the result. There were four recurrences in the smaller pyloroplasty group. In this series, antrectomy with vagotomy appears to be the best operation for duodenal ulcer disease

Laminar-flow flight experiments

The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time