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Magnetic Properties of Insulators : Quarterly Report No. 1 Covering the Period from February 15, 1961 to May 15, 1961

Description: "The magnetic properties of color centers were studied to obtain information regarding electron traps in insulators. Experiments designed to determine the equation governing the recovery of resonance after saturation were carried out. Relatively large samples were prepared by the method of additive coloration. KCl and RbCl crystals were used. Resonance saturation as a function of concentration was investigated and no significant dependence found. Measurements of the unsaturated susceptibility were made at liquid nitrogen and liquid helium temperatures. The bleaching of the F-center to form the B-band produced a different resonance. The equipment for observing the saturation and recovery of a portion of the resonance at 4 deg K is described. A theoretical examination was made of the interaction between the vibration of the ions around a negative-ion vacancy in an alkali halide and an electron trapped at that site. (M.C.G.)."
Date: May 29, 1961
Creator: Markham, Jordan J.
Partner: UNT Libraries Government Documents Department

Magnetic Properties of Insulators : Quarterly Report No. 6 Covering the Period from May 16, 1962 to August 15, 1962

Description: The following quarterly report covers the period from May 16 to August 15, 1962. This report summarizes the progress being made on the study of the saturation and recovery of the hole which can be burned into the magnetic resonance band associated with the F-center in KCl.
Date: August 15, 1962
Creator: Markham, Jordan J.
Partner: UNT Libraries Government Documents Department

Magnetic Properties of Insulators : Quarterly Report No. 7 Covering the Period from August 16, 1962 to November 15, 1962

Description: The following quarterly progress report covers the period of August 15 to November 15, 1962. It summarizes three activities of the group. The first part is the optical study of the absorption band associated with the F-center in RbCl. The second part discusses some elementary calculations of the spin-lattice relaxation times, the primary purpose of this step is to indicate the nature of the theoretical problem faced and show the large gap between the value calculated theoretically and measured experimentally. The last section includes more data on the shape and recovery of the hole in a EPR band associated with the F-center in KCl.
Date: December 1, 1962
Creator: Markham, Jordan J.
Partner: UNT Libraries Government Documents Department

Magnetic Properties of Insulators : Quarterly Report No. 8 Covering the Period from November 16, 1962 to February 15, 1963

Description: The following quarterly progress report covers the period from November 16, 1962 to February 15, 1963. This report summarizes three activities that study the ratio of the maximum absorption of the K band to the maximum absorption of the F band has been made in additively colored and [gamma]-irradiated rubidium chloride.
Date: March 1, 1963
Creator: Markham, Jordan J.
Partner: UNT Libraries Government Documents Department

Magnetic Properties of Insulators : Quarterly Report No. 9 Covering the Period from February 16, 1963 to May 15, 1963

Description: The following quarterly report covers the period during February 16 to May 15, 1963. This report is divided into sections covering the separate activities during this period, studying the thermal behavior of the F-center in RbCl.
Date: June 5, 1963
Creator: Markham, Jordan J.
Partner: UNT Libraries Government Documents Department

Magnetic Properties of Insulators : Quarterly Report No. 2 Covering the Period from May 15, 1961 to August 15, 1961

Description: Abstract: "The electron paramagnetic resonance (EPR) of color centers in additively colored KCl crystals is measured to observe the effects of optical bleaching at room temperature. Earlier measurements on the F-center are confirmed and the susceptibility is measured at 78 and 300 deg K over five decades of power, including the very low power region. The width and the saturation properties of the individual multiplets are studied in detail and the technique of making EPR measurements on inhomogeneously broadened lines is discussed. A calculation is presented which shows that a slight departure from a Lorentzian multiplet shape can account for the saturation data. The bleached crystals show a resonance which has a width of 35 gauss and a different rate of saturation than the F- center. This resonance is associated with the B-band which appears in the optical absorption."
Date: August 30, 1961
Creator: Markham, Jordan J. & Noble, Gordon A.
Partner: UNT Libraries Government Documents Department

Radiation-Induced Coloration in Glass

Description: General aspects of radiation-induced coloration in glass are discussed. It is considered that the most significant initial effect of the radiation is to produce free electrons and positive holes in a track. The decay of the track from the initial condition is described in some detail, assuming that the rate of diffusion of electrons from the track is small compared to the rates of other processes, and that primary'' processes which form color centers can be considered independent of secondary'' processes which cause destruction of color centers. A method of calculation is described which gives the concentration of color centers formed at various doses. With plausible assumptions for the parameters, agreement with the data of Schulman on a silver phosphate glass is obtained. The treatment of glasses less simple than the silver phosphate case is also discussed. (auth)
Date: August 1, 1959
Creator: Cropper, W. H.
Partner: UNT Libraries Government Documents Department

Transient Radiation Darkening Features in VISAR Window

Description: We have studied and characterized radiation-induced changes in the index of refraction of materials used in Z experiments. Interferometric measurements of the radiation-induced change in the real part, n, of the complex index of refraction, N = n + iK, have been made in lithium fluoride (LiF), sapphire, and fused silica samples. Our results indicate that the index changes are small, with {delta}n/n {approx} 1 x 10{sup -5}/kGy. In addition, we have characterized the dose dependence of the radiation-induced transient radiation darkening (TRD) of these materials, which is related to K, the imaginary part of the refractive index. We have also measured time-resolved spectral profiles of TRD in LiF and sapphire, and have examined the results in terms of known color centers and possible colloid aggregation.
Date: June 2001
Creator: Stevens, G. D. & Moy, K. J.
Partner: UNT Libraries Government Documents Department

Thermal Stability of Photosensitive Bragg Gratings in Sputter-Deposited Germanosilicate Glass

Description: The thermal stability of photo-imprinted Bragg gratings formed in reactive-atmosphere, RF-magnetron sputtered germanosilicate thin films was evaluated in terms of point defect modifications observed during isochronal annealing. Optical and magnetic spectroscopes were utilized to evaluate structural relaxation in these sputtered glasses on both a local and medium-range size scale. Depending upon the substrate temperature used during deposition, significant structural rearrangement was found to occur with increasing post-deposition anneal temperature to 600 C. This resulted in changes in the photobleaching response of the material itself as the identity of optically active structural defects evolved. Based on a color center model for photosensitivity in these materials and measured changes in optical absorption with annealing, the thermal stability of a photo-imprinted Bragg grating was modeled. Good qualitative agreement with experiment was observed.
Date: July 24, 2000
Creator: POTTER JR.,BARRETT G.; POTTER,KELLY SIMMONS & DUNBAR,TIMOTHY D.
Partner: UNT Libraries Government Documents Department

Boron-Loaded Silicone Rubber Scintillators

Description: Silicone rubber received attention as an alternative to polyvinyltoluene in applications in which the scintillator is exposed to high doses because of the increased resistance of the rubber to the formation of blue-absorbing color centers. Work by Bowen, et al., and Harmon, et al., demonstrated their properties under gamma/x-ray irradiation, and Bell, et al. have shown their response to thermal neutrons. This last work, however, provided an example of a silicone in which both the boron and the scintillator were contained in the rubber as solutes, a formulation which led to the precipitation of solids and sublimation of the boron component. In the present work we describe a scintillator in which the boron is chemically bonded to the siloxane and so avoids the problem of precipitation and loss of boron to sublimation. Material containing up to 18% boron, by weight, was prepared, mounted on photomultipliers, and exposed to both neutron and gamma fluxes. Pulse height spectra showing the neutron and photon response were obtained, and although the light output was found to be much poorer than from samples in which boron was dissolved, the higher boron concentrations enabled essentially 100% neutron absorption in only a few millimeters' thickness of rubber.
Date: May 12, 2003
Creator: Bell, Z.W.; Maya, L.; Brown, G.M. & Sloop, F.V.Jr
Partner: UNT Libraries Government Documents Department

Development of radiation stable plastic scintillator. Final technical report, July 1991--July 1993

Description: The Detector Development Group at the University of Florida has identified the only known optically radiation hard polymer, scintillator and wavelength shifter materials. The authors summarize their findings here. They conducted an extensive study of siloxane polymers using monomers of dimethyl, diphenyl and methylphenyl siloxanes. An important finding of that study was that polymethylphenylsiloxane is a candidate polymer for use at the SSC. However, the most important result of that work was the demonstration of the existence of optical polymers with extreme resistance to radiation damage. It held out the promise that other possibly more convenient polymers with similar properties could be identified. The first high viscosity, transparent, radiation hard siloxane with high fluor solubility was processed into prototype plates. The authors propose a mechanism to account for radiation induced annealable color center formation in commercial scintillator polymers such as PS and PMMA. The authors produced analogues of these polymers with T{sub g} < room temperatures. These polymers are optically radiation hard. The University of Florida has applied for a patent on this breakthrough discovery. It was found that dye mobility for radiation hard elastomers (T{sub g} < room temperature) was unacceptable over a period of one year. Dyes would tend to crystallize on the surface of the plates. The work concentrated therefore on thermoplastic polymers which had T{sub g} {approximately} 50 C (i.e., high enough for structural stability) and with high color center annealing rate such as polyisobutylmethacrylate. These polymers were both radiation hard and had minimal dye migration. The University of Florida has a patent on these materials. These materials were extruded and tested for stability and found adequate for operation up to 10 Mrad at the SSC.
Date: July 22, 1998
Partner: UNT Libraries Government Documents Department

MAGNETIC PROPERTIES OF INSULATORS. Quarterly Report No. 1, Covering Period February 15, 1961 to May 15, 1961

Description: The magnetic properties of color centers were studied to obtain information regarding electron traps in insulators. Experiments designed to determine the equation governing the recovery of resonance after saturation were carried out. Relatively large samples were prepared by the method of additive coloration. KCl and RbCl crystals were used. Resonance saturation as a function of concentration was investigated and no significant dependence found. Measurements of the unsaturated susceptibility were made at liquid nitrogen and liquid helium temperatures. The bleaching of the F-center to form the B-band produced a different resonance. The equipment for observing the saturation and recovery of a portion of the resonance at 4 deg K is described. A theoretical examination was made of the interaction between the vibration of the ions around a negative-ion vacancy in an alkali halide and an electron trapped at that site. (M.C.G.)
Date: May 29, 1961
Creator: Markham, J. J.
Partner: UNT Libraries Government Documents Department

Cathodoluminescence of uranium oxides

Description: The cathodoluminescence of uranium oxide surfaces prepared in-situ from clean uranium exposed to dry oxygen was studied. The broad asymmetric peak observed at 470 nm is attributed to F-center excitation.
Date: August 9, 1984
Creator: Winer, K.; Colmenares, C. & Wooten, F.
Partner: UNT Libraries Government Documents Department

Far infrared spectroscopy of solids. I. Impurity states in Al$sub 2$O$sub 3$. II. Electron-hole droplets in Ge

Description: Far infrared Fourier transform spectroscopy was used to study the low lying vibronic states of Mn$sup 3+$ in Al$sub 2$O$sub 3$ and the plasma absorption of electron-hole droplets in Ge. The transmission of Mn-doped samples of Al$sub 2$O$sub 3$ was measured in the frequency range from 3 to 30 cm$sup -1$ in applied magnetic fields up to 50 kG. Absorption lines were observed due to both ground and excited state transitions. Polarization measurements established that these absorption lines were due to electric dipole transitions. Temperature dependence measurements were used to derive a level diagram for the low lying states of Mn$sup 3+$. A phenomenological model based on an electronic Hamiltonian was developed which successfully describes the data. The empirically determined trigonal field and spin-orbit quenching parameters of this model are 0.7 and 0.1 respectively. This quenching is attributed to the dynamic Jahn-- Teller interaction. The plasma absorption of small ($alpha$) electron-hole drops in Ge was measured in the frequency range from 30 to 300 cm$sup -1$. The observed absorption is in good agreement with measurements by Vavilov and other workers. A theoretical model which includes both intraband and interband contributions to the dielectric constant in the Rayleigh limit of Mie theory is used to describe the observed lineshape. Measurements of plasma absorption of large ($gamma$) drops in inhomogeneously stressed Ge were made in magnetic fields up to 50 kG. The lineshape at zero applied field was calculated in the large sphere limit of Mie theory including intraband terms and a zero-strain interband term. Qualitative agreement with experiment was obtained. The peak absorption shifted quadratically with applied magnetic field and the total plasma absorption increased. No oscillatory structure was observed in the field-dependence of the total absorption. (auth)
Date: September 12, 1975
Creator: Aurbauch, R.L.
Partner: UNT Libraries Government Documents Department

Single Ion Implantation and Deterministic Doping

Description: The presence of single atoms, e.g. dopant atoms, in sub-100 nm scale electronic devices can affect the device characteristics, such as the threshold voltage of transistors, or the sub-threshold currents. Fluctuations of the number of dopant atoms thus poses a complication for transistor scaling. In a complementary view, new opportunities emerge when novel functionality can be implemented in devices deterministically doped with single atoms. The grand price of the latter might be a large scale quantum computer, where quantum bits (qubits) are encoded e.g. in the spin states of electrons and nuclei of single dopant atoms in silicon, or in color centers in diamond. Both the possible detrimental effects of dopant fluctuations and single atom device ideas motivate the development of reliable single atom doping techniques which are the subject of this chapter. Single atom doping can be approached with top down and bottom up techniques. Top down refers to the placement of dopant atoms into a more or less structured matrix environment, like a transistor in silicon. Bottom up refers to approaches to introduce single dopant atoms during the growth of the host matrix e.g. by directed self-assembly and scanning probe assisted lithography. Bottom up approaches are discussed in Chapter XYZ. Since the late 1960's, ion implantation has been a widely used technique to introduce dopant atoms into silicon and other materials in order to modify their electronic properties. It works particularly well in silicon since the damage to the crystal lattice that is induced by ion implantation can be repaired by thermal annealing. In addition, the introduced dopant atoms can be incorporated with high efficiency into lattice position in the silicon host crystal which makes them electrically active. This is not the case for e.g. diamond, which makes ion implantation doping to engineer the electrical properties of diamond, ...
Date: June 11, 2010
Creator: Schenkel, Thomas
Partner: UNT Libraries Government Documents Department

Emission spectra of sensitized and unsensitized LiF; TLD-100

Description: It was found in a study of the emission spectra of LiF powders, the glow curve shape appears to be independent of wave length. Data indicate that any recombination centers created by radiation could not have an optical transition significantly different from that of the recombination center originally present. (FS)
Date: January 1, 1965
Creator: Pearson, D. & Cameron, J.R.
Partner: UNT Libraries Government Documents Department

Radiation effects on organic scintillators: Studies of color center annealing

Description: The interaction of ionizing radiation with organic, polymer-based scintillators results in the discoloration of the material, which reduces the scintillation efficiency. This phenomenon can be described in terms of two types of color centers: annealable and nonannealable. For many common materials, at doses of a few Mrad, the annealable color centers account for a large fraction of the observed radiation-induced absorption. We are conducting studies to understand the mechanisms and kinetics of the annealing process. By conducting experiments on polystyrene in which polymerization of the monomer, {gamma}-irradiation, and post-irradiation annealing were all carried out in a sealed, degassed tube, we have been able to resolve the question of whether annealing can occur in the absence of oxygen. We find that annealing does indeed occur under inert conditions. The rate of inert annealing at room temperature is drastically slower than oxygen-mediated annealing, whereas the rates for the two processes is only slightly different at 80{degree}C. We have measured the annealing rate of color centers in {gamma}-irradiated polystyrene in air over the temperature range of 30 to 90{degree}C, and find a large increase in annealing rate with increasing temperature. Arrhenius plots of the annealing data show strong non-linearity, which can be ascribed to two different annealing mechanisms of very different activation energy: presumably oxidative and nonoxidative. Ongoing work involves deconvolution of the two annealing processes, and construction of a model for long-term annealing kinetics in these materials. 6 refs., 4 figs.
Date: January 1, 1990
Creator: Clough, R.L. & Wallace, J.S.
Partner: UNT Libraries Government Documents Department