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THE USE OF COLOR CENTERS FOR THE DETECTION AND MEASUREMENT OF RADIATION INDUCED DEFECTS

Description: The use of color centers showed that the number of defects produced in NaCl by fast reactor neutrons is consistent with existing theories on radiation damage. Color centers were also used to siudy the growth and annealing of defects formed in Al/sub2/O/sub 3/ and fused silica by reactor irradiations. Overall, as the amealing temperature was raised for Al/sub 2/O/sub 3/, the number of reactor-induced defects decreased and at 700 and 730 un. Concent 85% C they disappeared entirely. Reactor-irradiated samples, which were fully annealed, did not color any more than virgin ones even with gamma ray doses of 10/sub 9/ r. Defects detected by color centers in fused silica were not removed until the samples were heated to 700 un. Concent 85% C or slightiy higher. The techniques used to determine defects are described. (P.C.H.)
Date: January 1, 1963
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Recent developments in thermoluminescence kinetics: applications to other thermally stimulated processes

Description: Recent thermoluminescence (TL) studies indicate that many kinetic properties are not in accord with the well known 1st and 2nd order TL kinetic equations. For example, the usual equations do not describe: (1) the shape of certain single glow peaks. (2) The shape of glow peaks in many glow curves containing more than one glow peak. (3) The dependence of the peak temperature, the FWHM, the shape, and other properties on the pre-measurement dose. However, the properties of some single glow peaks are precisely described, or closely approximated by, the more general basic equation from which the usual 1st and 2nd order equations are obtained as special cases. Furthermore, glow curves containing more than one glow peak are described by a system of equations that includes interactions between different types of traps and is a straightforward extension of the general one peak equation. This system - called Interactive Kinetics - accounts for most properties, and explains many anomalies, associated with glow curves containing more than one glow peak. It is particularly convenient for computerized analysis procedures. Lastly, it is suggested that other thermally stimulated processes depend on analogous interactions and are describable by similar sets of kinetic equations that are convenient for computer analysis. 11 refs., 2 figs.
Date: August 7, 1985
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Thermoluminescence systems with two or more glow peaks described by anomalous kinetic parameters

Description: The usual first and second order TL kinetic expressions are based on a number of assumptions, including the usually unstated assumption that charges released from one type of trap, giving rise to one glow peak, are not retrapped on other types of traps, associated with other glow peaks. Equations have been developed describing TL systems in which charges released from one type of trap may be retrapped in other types of traps. Called interactive kinetic equations, they are quite simple but have been studied by numerical methods. In particular, glow curves computed from the interactive kinetic equations have been regarded as data and analyzed by fitting them to the usual first and second order kinetic expressions. All of the anomalous features described above are reproduced. For example, usually the computed glow peaks are well fitted by the first and second order expressions over their upper 60 to 80% but not in the wings. This explains why the usual analysis methods, especially those utilizing peak temperature, full width, etc. appear to describe such peaks. Often unrealistic kinetic parameters are often obtained. Furthermore, the computed glow curves often reproduce the observed dependence on dose.
Date: January 1, 1983
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Thermoluminescence kinetics in materials exposed to the low doses applicable to dating and dosimetry

Description: Thermoluminescence (TL) kinetics have been investigated for low dose situations applicable to dating, dosimetry, and recent geological deposits. Studied were the general one-trap kinetic equation, which reduces to the well known 1st and 2nd order kinetic equations when various assumptions apply, and the interactive kinetic equations, which describes TL in materials exhibiting more than one glow peak. In materials with one glow peak area varies linearly with dose; however, peak height is not linear with dose unless the TL obeys 1st order kinetics at all doses. In materials with two or more glow peaks neither peak height nor peak area varies linearly with dose, except in special situations. In fact, many peak height vs dose curves will be supralinear with the initial low-slope region occurring at relatively low doses. These considerations indicate: (1) Dating and dosimetry technique based on assumed linear peak height vs dose curves will usually underestimate the accumulated dose. (2) Dating techniques can be improved and/or made more reliable by determining the TL kinetics of the glow peaks measured.
Date: November 1, 1984
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Radiation damage studies on natural rock salt from various geological localities of interest to the radioactive waste disposal program

Description: As part of a program to investigate radiation damage in geological materials of interest to the radioactive waste disposal program, radiation damage, particularly radiation induced sodium metal colloid formation, has been studied in 14 natural rock salt samples. All measurements were made with equipment for making optical absorption and other measurements on samples, in a temperature controlled irradiation chamber, during and after 0.5 to 3.0 MeV electron irradiation. Samples were chosen for practical and scientific purposes, from localities that are potential repository sites and from different horizons at certain localities.
Date: January 1, 1981
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Facilities for studying radiation damage in nonmetals during irradiation

Description: Two facilities have been developed for making optical absorption, luminescence and other measurements on a single sample before, during and after irradiation. One facility uses /sup 60/Co gamma rays and the other 0.5 to 3 MeV electrons from an accelerator. Optical relays function as spectrophotometers, luminescenc detectors, etc. All radiation sensitive components are outside of walk-in irradiation chambers; all measurement control and data recording is computerized. Irradiations are made at controlled temperatures between 5K and 900/sup 0/C. The materials studied include glasses, quartz, alkali halides (especially natural rock salt), organic crystals, etc. As determined from color center measurements the damage formation rate in all materials studied at 25/sup 0/C or above is strongly temperature dependent. The defect concentration during irradiation is usually much greater than that measured after irradiation. The fraction of defects annealing after irradiation and the annealing rate usually increases as the irradiation temperature increases. The completed studies demonstrate that, in most cases, the extent of maximum damage and the damage formation and annealing kinetics can be determined only by making measurements during irradiation.
Date: August 1, 1984
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Characteristics of thermoluminescence glow curves for materials exhibiting more than one glow peak

Description: The properties of thermoluminescence glow curves, containing one or more glow peaks, have been determined for situations where the assumptions invoked to obtain the usual first and second order kinetics do not apply. First order kinetics occurs only when retrapping is negligible. If more than one glow peak is present and retrapping occurs between different types of traps the glow peaks can be approximated, except in the wings, by the usual first and second order expressions; but often physically unrealistic parameters are obtained. These studies indicate that dating is best accomplished with minerals exhibiting first order kinetics. 6 figures, 1 table.
Date: January 1, 1982
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Space--time-temperature profiles for conductive heat flow in country rock surrounding hot intrusive bodies

Description: Temperature vs distances profiles during geological time were calculated for a variety of realistically shaped magmatic bodies intruded into country rock. The calculations were made with a computerized finite difference formulation of the classical time dependent conductive heat-flow equation. The formulation can be adopted to numerous situations. These include: emplacement at different rates, variations in the shape of the intrusion, e.g., domed cylinders, cones, or even arbitrary shapes as determined by field measurements. The intrusions may remain in contact with or become isolated from the magma pool. Also, the thermodynamic properties of the intrusion may be adjusted, e.g., to include latent heat of fractional crystallization. The surrounding rock may be homogeneous or strata of different kinds of rock. The surface above the intrusion may assume any reasonable shape. Faulting in the surrounding rock is being included and magma convection will be added in the future. Completed calculations of the surface heat-flow gradients are consistent with those found in regions of known geothermal activity. This calculational procedure, in conjunction with local surface and subsurface temperature and heat-flow measurements appears to provide a useful approach to evaluating geothermal energy sources and new techniques for geothermal exploration and characterization.
Date: January 1, 1977
Creator: Spergel, M.S. & Levy, P.W.
Partner: UNT Libraries Government Documents Department

Geological applications of thermoluminescence measurements made with equipment for simultaneously determining intensity, wavelength, and temperature

Description: Thermoluminescent spectra measurements at closely spaced temperatures were used to study the TL of carbonate rock near lead-zinc deposits, apparently a useful exploration tool; the radiation--induced TL of quartz, useful for uranium exploration; and thermally--induced modifications of the feldspar albite.
Date: January 1, 1978
Creator: Levy, P W
Partner: UNT Libraries Government Documents Department

Radiation damage studies on natural and synthetic rock salt. [1 to 3 MeV electrons]

Description: Radiation damage studies are being made on natural rock salt from various localities, including potential repository sites and on synthetic melt-grown crystals. Sufficient information will be obtained to compute the radiation damage in repository salt at any point as a function of time, temperature, canister temperature and radiation levels, strain in the rock, salt, backfill materials, and other parameters. Most of the completed measurements have been made with unique equipment at BNL for making optical and other measurements on samples before, during, and after irradiation with 1- to 3-MeV electrons. Samples are irradiated in temperature-controlled chambers containing an inert exchange gas. Radiation damages on natural rock salts and synthetic melt-grown crystals, characterized by determining the radiation-induced F-center, colloid, and V-region absorption, are described in detail.
Date: January 1, 1980
Creator: Levy, P W & Swyler, K J
Partner: UNT Libraries Government Documents Department

Effects of gamma-ray irradiation on dislocations in sodium nitrate single crystals

Description: The topography of the etch pits formed on the (100) cleavage surfaces of unirradiated and irradiated NaNO/sub 3/ single crystals has been studied. The principal etch pit alignments are consistent with dislocation families of the type (100) (011), (211) (011), and (111) (011). The pit density increases from 1.4 (+-0.2) x 10/sup 4//cm/sup 2/ at zero dose to 7.3 (+-0.2) x 10/sup 5//cm/sup 2/ at 5.0 x 10/sup 8/ rad. With increasing dose the pit density distribution narrows and clusters at 1.0 x 10/sup 6/ pits/cm/sup 2/ at doses above 5.0 x 10/sup 8/ rad. Above this dose radiolytic-induced micro bumps or structures are observed that precede the onset of radiolytic decomposition that is visible at 2.5 x 0/sup 9/ rad. These asymmetric structures appear to nucleate at the same sites as the chemically created etch pits and are aligned in the same principal directions. These observations indicate that dislocations are important sites for nucleating radiation induced decomposition and internal radiolytic gas generation. 12 references, 9 figures, 1 table.
Date: December 1, 1984
Creator: Solnick-Legg, H.; Herley, P.J. & Levy, P.W.
Partner: UNT Libraries Government Documents Department

CaF/sub 2/:Mn thermoluminescence: a single glow peak not described by 1st or 2nd order kinetics

Description: The thermoluminescence (TL) of CaF/sub 2/:Mn has been studied using photon counting and digital recording. For doses of 10 rad or less the TL glow curves appear to consist of a single glow peak. However, there are indications - which are pronounced at larger doses - that one additional low intensity peak (area less than or equal to one percent) is superimposed on each side of the central peak. The intense peak is not described by 1st or 2nd order kinetics but is well described by the more general kinetics from which these kinetics are derived. These observations, and the results of additional kinetic analysis, demonstrate that retrapping is not negligible and may include all three peaks. In such systems, which are likely to include other dosimeter materials and minerals, peak height will not increase linearly with dose; an important factor for dosimetry and dating applications.
Date: December 1, 1984
Creator: Hornyak, W.F.; Levy, P.W. & Kierstead, J.A.
Partner: UNT Libraries Government Documents Department

Radiation induced F-center and colloid formation in synthetic NaCl and natural rock salt: applications to radioactive waste repositories. [1 to 3 MeV electrons]

Description: Radiation damage, particularly Na metal colloid formation, has been studied in synthetic NaCl and natural rock salt using unique equipment for making optical absorption, luminescence and other measurements during irradiation with 1 to 3 MeV electrons. Previous studies have established the F-center and colloid growth phenomenology. At temperatures where colloids form most rapidly, 100 to 250 C, F-centers appear when the irradiation is initiated and increase at a decreasing rate to a plateau, reached at doses of 10/sup 6/ to 10/sup 7/ rad. Concomitant colloid growth is described by classical nucleation and growth curves with the transition to rapid growth occurring at 10/sup 6/ to 10/sup 7/ rad. The colloid growth rate is low at 100 C, increases markedly to a maximum at 150 to 175 C and decreases to a negligible rate at 225 C. At 1.2x10/sup 8/ rad/h the induction period is >10/sup 4/ sec at 100 C, <3000 sec at 150 to 175 C and >10/sup 4/ sec at 275 C. The colloid growth in salt from 14 localities is well described by C(dose)/sup n/ relations. Data on WIPP site salt (Los Medanos, NM, USA) has been used to estimate roughly the colloid expected in radioactive waste repositories. Doses of 1 to 2x10/sup 10/ rad, which will accumulate in salt adjacent to lightly shielded high level canisters in 200 to 500 years, will convert between 1 and 100% of the salt to Na colloids (and Cl) if back reactions or other limiting reactions do not occur. Each high level lightly shielded canister may ultimately be surrounded by 200 to 300 kg of colloid sodium. Low level or heavily shielded canisters may produce as little as 1 kg sodium.
Date: January 1, 1983
Creator: Levy, P.W.; Loman, J.M. & Kierstead, J.A.
Partner: UNT Libraries Government Documents Department

Radiation damage studies on synthetic NaCl crystals and natural rock salt for waste disposal applications. [1. 5-MeV electrons]

Description: Radiation damage studies are being made on synthetic NaCl and natural rock salt crystals from various localities, including potential repository sites. Measurements are being made with equipment for recording the radiation induced F-center and colloid particle absorption bands during irradiation with 1.5 MeV electrons at various temperatures. A technique has been developed to resolve the overlapping F-center and colloid bands. The resulting spectra and curves of absorption vs. dose provide information on colloid particle size and concentration, activation energies for processes occurring during colloid formation, and additional data suggesting that both strain and radiation induced dislocations contribute to the colloid formation process.
Date: January 1, 1979
Creator: Klaffky, R.W.; Swyler, K.J. & Levy, P.W.
Partner: UNT Libraries Government Documents Department

Radiation-induced sodium-metal-colloid formation in natural rock salt from different geological localities

Description: Radiation damage has been studied in natural rock salt from various localities, including potential repository sites. In the 100 to 300 C range the damage consists of point defects, primarily F-centers, and colloidal metal sodium particles. With increasing dose the F-centers grow to a saturation level, reached at 10/sup 7/ to 10/sup 8/ rad, that decreases with increasing temperature to a negligible level at 300 C. Colloid concentration vs. irradiation-time curves follow nucleation and growth curves accurately described by C t/sup n/, or C(dose)/sup n/, relations at large irradiation times. For fourteen samples, n = 1.85 +- 0.18 but the values of C vary by a factor of more than 10/sup 3/. The constant C is related to the sample strain, the impurity and void content, dose rate, and possibly other factors. The currently available data indicate that rock salt adjacent to radioactive waste canisters, at a temperature of 150 C, will contain between 0.01 and 10 mole percent of sodium metal when the total dose reaches 10/sup 10/ rad.
Date: January 1, 1981
Creator: Loman, J.M.; Levy, P.W. & Swyler, K.J.
Partner: UNT Libraries Government Documents Department