Showing papers on "Fluence published in 1973"

Laser‐induced shock effects in Plexiglas and 6061‐T6 aluminum

Abstract: The mass removal per unit area from Plexiglas and 6061‐T6 aluminum targets irradiated in air with a giant pulsed laser is presented as a function of incident fluence. This quantity appears to be a strong function of the focal length of the focusing lens. Air breakdown in the presence of a target occurs at fluences greater than 380 J/cm2 for Plexiglas targets and 159 J/cm2 for aluminum targets. Photographic evidence of the back‐face spallation of a 0.1‐cm‐thick aluminum sample irradiated in vacuum is presented. The mirror‐finished target was inclined at 45° to the incident beam and irradiated with a fluence of approximately 5000 J/cm2.

Optical Waveguides Fabricated by Ion Implantation

Abstract: Optical waveguides are formed by implantation of various ions (H+, H2+, He+, Li+, and B+) in fused quartz and the properties of mode propagation are investigated at 6328 A. The origin of the refractive index change is discussed from the ESR measurement. The depth distribution of defects is measured by ESR measurements and the effective thickness of the high-refractive index region is estimated from the measured depth distribution of defects. In as-implanted samples, the propagation loss decreases with decreasing fluence, but a minimum fluence is required for a given implantation energy for the lowest mode to be propagated. The propagation loss is explained to be internal absorption due to color centers introduced by ion implantation. It is shown that the propagation losses are different for various implanted ions. Annealing behavior of the propagation loss and the refractive index change is also presented.

Swelling and Tensile Property Evaluations of High-Fluence EBR-II Thimbles

Abstract: The effects of very high neutron fluences on tensile properties and swelling of 300-series austenitic stainless steel were evaluated by destructive examination of several EBR-II thimbles that had accumulated fluences approaching 1.2 x 10 2 3 n/cm 2 (E n > 0.1 MeV). Irradiation temperatures ranged from 370 to 470 C (698 to 878 F). Immersion density measurements on control or safety rod thimbles 3D1, 5C3, 5A3, and 3A1 indicate that swelling increases with neutron fluence. Maximum measured volume changes are about 11 percent at 1.1 x 10 2 3 n/cm 2 (E n > 0.1 MeV) and temperatures near 420 C (788 F). No indications of saturation were observed; in fact, swelling rates increase with increasing fluence over the whole range of fluences investigated. Anomalous swelling behavior was observed in control rod thimble 5A3. In this component, which may have been subjected to mechanical constraint, swelling gradients were found to be much lower than anticipated on the basis of the corresponding gradients in irradiation conditions. This behavior may be the result of an effect of stress on swelling not previously encountered. Tensile property changes are similar to those classically observed. When irradiation and test temperatures are equivalent, yield strength (0.2 percent offset) increases rapidly at low fluences and becomes fluence-independent at high fluence levels ( > 7 x 10 2 2 n/cm 2 , E n > 0.1 MeV). Uniform elongation correspondingly decreases with increasing fluence and appears to saturate near 0.5 percent at higher fluence levels. This transition in fluence dependence of the properties is associated with a transition in fracture mechanism. The transition occurs from the usual homogeneous plastic dimpling fracture at low fluences to an extremely heterogeneous channel fracture at high fluence levels.

Effect of 80‐keV Ne+ ion implantation on acoustic surface wave attenuation in LiNbO3

Abstract: Acoustic surface wave attenuation in LiNbO3 caused by ion implantation was studied as a function of fluence and surface wave frequency. 80‐keV Ne+ ions were implanted at five fluences covering the range 1014–1016 ions/cm2. The yz Rayleigh surface waves were generated spanning the interval 100–1000 MHz by interdigital transducers operating at odd harmonics. Attenuation was measured directly by a standard laser probe using reflected light. At low acoustic power densities, the data can be fit by P(z)/P0=10−Af2z, where P is acoustic power, f is the surface wave frequency, and A is a constant for each fluence used. The values of A show a definite peak with fluence at around 1015 ions/cm2, where A=9 × 10−5 dB cm−1 MHz−2±10%. This is about twenty times the value of A for an unimplanted surface.

Neutron irradiation damage in a precipitation-hardened aluminum alloy

Abstract: A 6061 aluminum alloy target sleeve from the high flux isotope reactor, originally in a precipitation-hardened condition, was examined for neutron radiation damage after exposure to a maximum fast fluence of 9.2 x 102 2 n/cm2 (E >0.1 MeV) and a thermal fluence of 1.38 x 10 2 3 n/cm 2 at 60 C (140 F). Voids and a transmutation-produced silicon precipitate were found to cause about 1.1 percent internal swelling; a surface oxide scale contributed additional swelling. Irradiation-induced strength increases were measured at test temperatures in the range 25 to 200 C (77 to 392 F) and are accounted for in terms of the observed silicon precipitate and an associated dislocation structure. There was also a loss of ductility that was most severe at 200 C. The fracture mode appeared to remain transgranular over the range of test temperatures.

Defect Aggregation in Ion-Implanted GaAs

Abstract: An (hν)2 dependence of the ion-Implantation induced near-band-edge optical attenuation on photon energy has been measured in GaAs. This relationship is observed for relatively high Xe+ ion fluence and ion flux levels and is more readily induced at elevated implant temperatures. The present optical attenuation results are analogous to those previously observed for heavily neutron irradiated GaAs. The dependence of the (hν)2 relationship on fluence, flux, and ion-implantation temperatures lends strong support to a model for which scattering and absorption is due to the formation of metallic-like defect aggregates. This dependence is not observed for low fluence Xe+ ion implantation or for heavy proton implantation.

Temperature, illumination and fluence dependence of current and voltage in electron irradiated solar cells

Abstract: Emperical equations have been derived from measurements of solar cell photovoltaic characteristics relating light generated current, IL, and open circuit voltage, VO, to cell temperature, T, intensity of illumination, W, and 1 Mev electron fluence, phi both 2 ohm-cm and 10 ohm-cm cells were tested. The temperature dependency of IL is similar for both resistivities at 140mw/sq cm; at high temperature the coefficient varies with fluence as phi 0.18, while at low temperatures the coefficient is relatively independent of fluence. Fluence dependent degration causes a decrease in IL at a rate proportional to phi 0.153 for both resistivities. At all intensities other than 560 mw/sq cm, a linear dependence of IL on illumination was found. The temperature coefficient of voltage was, to a good approximation, independent of both temperature and illumination for both resistivities. Illumination dependence of VOC was logarithmic, while the decrease with fluence of VOC varied as phi 0.25 for both resistivities.

Effect of refuelling on dose rate in an irradiation facility

Abstract: The effects of core rearrangement on the dose rate, gamma -contamination and the neutron spectrum were studied by physical measurements and biological experiments. The neutron spectrum was characterized by the ratio of effective neutron fluence rates measured with In and S. This fluence ratio, the neutron fluence and dose rate normalized to unit MW reactor power, as well as gamma -contamination are characteristic of the shielding. Physical measurements are consistent with the percentage survival patterns of CFLP white mice.

Effects of room temperature proton radiation damage on the conductance of reactively sputtered tantalum thin-Film resistors for fluences up to 2 × 1018 p/cm2

Abstract: Tantalum thin-film resistors reactively sputtered in oxygen and nitrogen simultaneously have been irradiated by 150-kev protons at 286°K. For discontinuous films consisting of metallic islands largely surrounded by Ta2O5, the conductance initially increases with fluence until a dopant-dependent threshold fluence is reached, at which point the conductance decreases rapidly with fluence. The conductance increase is attributed to an enhanced tunneling current resulting from radiation-produced defects within the inter-island oxide regions. The non-linearity in this conductance increase is ascribed to mobile defects annihilating at the gap-island interfaces during irradiation. The subsequent conductance decrease may be accounted for by an increase in the inter-island tunneling barrier as a result of unequal concentrations of donor and acceptor defects annihilating at gap-island interfaces, thus producing a radiation-produced shift in the Fermi level. In contrast to this behavior, the conductance of co...