Effect Of Fast Neutron Damage Research Articles

Quantifying yield behaviour in metals by X-ray nanotomography.

Nanoindentation of engineering materials is commonly used to study, at small length scales, the continuum mechanical properties of elastic modulus and yield strength. However, it is difficult to measure strain hardening via nanoindentation. Strain hardening, which describes the increase in strength with plastic deformation, affects fracture toughness and ductility, and is an important engineering material property. The problem is that the load-displacement data of a single nanoindentation do not provide a unique solution for the material’s plastic properties, which can be described by its stress-strain behaviour. Three-dimensional mapping of the displacement field beneath the indentation provides additional information that can overcome this difficulty. We have applied digital volume correlation of X-ray nano-tomographs of a nanoindentation to measure the sub-surface displacement field and so obtain the plastic properties of a nano-structured oxide dispersion strengthened steel. This steel has potential applications in advanced nuclear energy systems, and this novel method could characterise samples where proton irradiation of the surface simulates the effects of fast neutron damage, since facilities do not yet exist that can replicate this damage in bulk materials.

Effects due to a Pu-C source on a HPGe detector and the corresponding neutron shielding

A gamma spectrum of a Pu-C source is measured using a p-type HPGe detector, whose three peaks (full energy, single-escape and double-escape peak) can be used as a calibration source for the beam energy measurement system of BEPCII. The effect of fast neutron damage on the energy resolution of the HPGe detector is studied, which indicates that the energy resolution begins to deteriorate when the detector is subject to 2×107 n/cm2 fast neutrons. The neutron damage mechanism and detector repair methods are reviewed. The Monte Carlo simulation technique is utilized to study the shielding of the HPGe detector from the fast neutron radiation damage, which is of great significance for the future commissioning of the beam energy measurement system.

Effect of fast neutron damage on the performance of a high resolution HPGe coaxial detector

The effect of fast neutron damage on the energy resolution and the full energy peak efficiency (FEPE) of a 157 cm3 coaxial HPGe detector is studied. When the detector is subjected to approximately 5*108 fast neutrons, the energy resolution deteriorates from 1.85 keV to 11.65 keV at 1332 keV. The FEPE decreases by approximately 28% at 80.997 keV and approximately 8% at 1332 keV with a dose of approximately 4*108 fast neutrons. With the same dose of fast neutrons the total detection efficiency decreases by approximately 13%, and the peak to Compton ratio (for 1408.03 keV 152Eu peak) reduces to 11.7 from its original value of 70.6.

Magnetization studies of YBa 2Cu 3O 7−x irradiated by fast neutrons

Studies of the effect of fast neutron damage on the magnetic hysteresis of YBa 2Cu 3O 7−x ceramic samples subjected to fluence of neutrons of 2∗10 16 n/cm 2 up to 6∗10 17 n/cm 2 have been performed. irradiation up to dose of 1∗10 17 did not cause any change in the critical temperature. However it causes a strong increase of the magnetic hysteresis which is presumably connected with the creation of defects. The critical current density at 77 K in H = 10 k0e for the sample irradiated with the dose 1∗10 17 n/cm 2 was estimated to be 520 A/cm 2 as compared to 29 A/cm 2 for the reference non-irradiated sample, non-irradiated sample.

Fast Neutron Damage Studies of La1.85Sr0.15CuO4

The effect of fast neutron damage on the superconducting transition temperature Tc and the critical current density jc of the compound La1.85Sr0.15CuO4 has been investigated. Irradiation to a fluence of 1.3×1018 n/cm2 (E > 0.1 MeV) resulted in a decrease of Tc of about 3 K while jc at 4.2 K and H = 2 T increased by a factor of two to 1.2×104 A/cm2.

Laser‐monitored electrothinner for preparation of ultrathin metal foils

Apparatus and techniques are described which allow the preparation of metal foils several square centimeters in area with thickness as small as 2 μm. The foils retain the microstructure of the 25–50‐μm‐thick starting material and are especially useful in experiments utilizing charged particle bombardment to simulate the effects of fast neutron damage on mechanical, electrical, thermal, and mass transport properties. The thinning rate is controlled by monitoring the transmittance of 6328‐Å light passed through the electrolyte. Intermittent specimen rotation, dc voltage pulsing, and periodic adjustments in electrolyte composition permit reproducible thinning rates with point‐to‐point variations in foil thickness smaller than 20%.

Effects of fast-neutron damage from 0 to 42 × 10 21 neutrons/cm 2 on the physical properties of nearisotropie grades of graphite

Effects of fast-neutron damage from 0 to 42 × 10 21 neutrons/cm 2 on the physical properties of nearisotropie grades of graphite

Effect of neutron irradiation on the tensile properties of zircaloy-2 and zircaloy-4

The effect of fast-neutron damage on the room-temperature tensile properties of zircaloy-2 and zircaloy-4 irradiated at low temperature ( < 100 °C) up to a fluence of 1.43 × 10 20 n/cm 2 ( > 1 MeV) and at elevated temperature (320–360 °C) up to 1.53 × 10 21 n/cm 2 (> 1 MeV) was investigated. The irradiation conditions at elevated temperature simulated those of fuel elements. The behaviour of irradiation-hardening of zircaloy-2 was similar to that of zircaloy-4. Considerable irradiation-hardening and loss of ductil'ty were observed. The rate of hardening for low-temperature irradiation was higher than that for elevated-temperature irradiation. Irradiation-induced changes in yield stress, Δσ y , showed saturation at a fluence of 4 × 10 19 n/cm 2 (> 1 MeV) for zircaloy-2 and 5 × 10 19 n/cm 2 (> 1 MeV) for zircaloy-4 for low temperature, while no saturation was observed after elevated-temperature irradiation up to a fluence of 1.53 × 10 21 n/cm 2 (>1 MeV) . Low-temperature irradiation showed Δσ y ∞ . (φt) case1 3 below saturation while elevated-temperature irradiation showed Δσ y ∞ . (φt) 0.1 . The amount of irradiation-hardening decreased in zircaloy-4 as the pre-irradiation yield stress was increased either by increasing the amount of cold work or decreasing the grain size. The results are discussed in terms of recent results in electron microscopy of irradiated materials.

Neutron Damage in GaAs Laser Diodes: At and above Laser Threshold

The effects of fast neutron damage on GaAs laser diodes have been examined with the following results: (1) Infrared photomicrographs of laser output for diodes operating above threshold at 300 K reveal that neutron irradiation does not have a significant effect on the near-field spatial distribution. (2) Neutron irradiation of a group of laser diodes of different cavity lengths demonstrates that the damage-induced increase in threshold current at 300 K is due primarily to a decrease in gain factor. The rate of decrease of the gain factor with neutron fluence agrees with that predicted by a previously determined damage constant. (3) Preliminary measurements of total light output as a function of diode current at 300 K and 76 K show that the lasers are much less sensitive to neutron damage at currents significantly above threshold. In fact, for some diodes the light output at 76 K increases at a given current with neutron irradiation for fluences as high as 3 × 1014 n/cm2.

Neutron Irradiation Effects on Diffused GaAs Laser Diodes

The effects of fast neutron damage on diffused GaAs laser diodes have been studied by observing the pre- and post-irradiation current-voltage characteristics and electroluminescence (EL) spectra at several temperatures between 75°K and 300°K. The pre-irradiation diode current at high temperature is dominated by nonradiative space-charge region recombination. The principal emission band at 300°K results from band-to-acceptor recombination in the p-region. A secondary band at 1.28 eV occurs via donor-acceptor pair recombination in the depletion region. At low temperature the dominant diode current flow is by nonradiative tunneling while the principal emission band contains radiative tunneling and band-filling components. Neutron irradiation increases the constant-voltage diode current. The additional current is due to space-charge region recombination (SC) at high temperatures and both SC and tunneling at low temperatures. The room-temperature damage constant is somewhat larger than that found in epitaxial GaAs laser diodes and in silicon p+n diodes. The constant-voltage principal emission band intensity decreases with fluence at a rate such that the resultant damage constant is about half that of the SC current damage constant. Irradiation to a fluence of 1.8 × 1015 n/cm2 (> 10 keV) has no effect on the constant-voltage secondary emission band intensity.

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The effect of fast neutron damage on the deformation of Copper-Tin alloys

The deformation behaviour of several copper-tin alloys was examined before and after irradiation with fast neutrons. It was found that the first measurable change in all of the alloys occurred at a dose between 10 16 and 10 17 n.v.t. and, although the initial flow stress of unirradiated alloys decreased with tin content, all of the alloys reached the same maximum flow stress at a saturation dose of approximately 3 × 10 19n.v.t. The dependence of the flow stress upon grain size was examined and it was found that the friction stress of irradiated alloys decreased linearly with strain and that the initial dislocation sources were heavily jogged. The jogged sources were eliminated by a few percent of strain. A simple theory for irradiation hardening, which predicts a complex relationship between stress and fast neutron dose and between stress and temperature, is proposed. The agreement of the experimental results with this theory is good.