Fast Neutron Damage Research Articles

Irradiation-induced defects in amorphous Fe 40Ni 40P 20

During fast neutron damage, defects are generated in amorphous Fe 40Ni 40P 20. These defects cause a macroscopic swelling, but the crystallization enthalpy, the crystallization temperature and the ductility remained unchanged. Moreover, since specimens which had been thermally embrittled prior to irradiation became completely ductile again after low dose neutron irradiation, these defects appear to be beneficial for ductile behaviour. From small-angle neutron scattering experiments the average radius of the irradiation-induced defects, which are not visible in the transmission electron microscope, is 10 nm. The nature of these defects can be described as density fluctuations. A phase separation or the formation of crystallites during neutron irradiation can be ruled out.

The Critical HTGR Test Facility KAHTER–An Experimental Program for Verification of Theoretical Models, Codes, and Nuclear Data Bases

The critical facility KAHTER was used to verify and to adjust theoretical models describing the physics of pebble-bed high-temperature gas-cooled reactors. Using methods such as evaluating critical masses, flux mappings, and reaction rate measurements, more sophisticated experimental and theoretical methods have been developed to get exact information and interpretation of control rod efficiency, power determination, and fast neutron damage.

Effect of charge carrier trapping on germanium coaxial detector line shapes

A theoretical method to predict and quantify the effects of charge carrier trapping on germanium coaxial detector line shapes has been developed. This model was used to calculate line shapes which closely matched the measured line shapes of both conventional and reverse electrode high-purity germanium coaxial detectors that had suffered fast neutron damage. In accordance with experimentally established behavior, the theory predicts that reverse electrode detectors are vastly more resistent to the effects of neutron damage than conventional electrode detectors. The theory also predicts that the energy resolution and line shape of neutron-damaged conventional electrode detectors are far more dependent on detector diameter than are detectors of the reverse electrode configuration. The generally observed variation of the energy resolution and line shape as a function of bias voltage is shown to arise from an ¢E −1 dependence of the trap cross section on electric field.

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.

Structural damage in MgAl 2O 4 spinel after high dose electron irradiation at elevated temperatures

Crystals of stoichiometric magnesium aluminate spinel, pre-implanted with 1000 ppm helium, have been bombarded by intense 1 MV electron beams to simulate fusion reactor irradiation damage. The spinel proved to be much more resistant to conventional lattice structural damage than either MgO or Al2O3, no dislocation loops or voids being nucleated after doses exceeding 10 and 30 dpa on the respective cation and anion sublattices at temperatures in the range 800–1300 K. Discontinuities in the material, e.g. specimen surfaces, or inhomogeneities in the flux intensity of the irradiating beam however produced segregation of the ionic species, non-stoichiometry, precipitation of metal and non-equilibrium phases, volumetric contraction, fracture and surface erosion. Degradation rates increase rapidly (2.1 eV activation energy) with temperature. The damage process is interpreted as an internal electrolysis induced by charge segregation derived from the dynamic motion of secondary electrons. Fast neutron damage cannot be simulated because electron irradiation is unable to nucleate dislocation loops, in stoichiometric spinel.

Promising copper alloys for high heat load applications in neutron environments

Four candidate copper alloys and two elemental coppers were irradiated in the Experimental Breeder Reactor to damage levels of about 3 and 15 dpa at 385°C. The irradiated and control samples were evaluated to determine swelling, room temperature tensile properties, transmutation product levels, and electrical resistivity. Transmission electron microscopy was used to characterize the damaged microstructures. Among the six materials studied, the alumina-dispersed copper alloys (Glidcop Al-20 and Al-60 sheet material) exhibited the best, overall resistance to fast neutron damage as they had minimal swelling and retained their original values of yield strength and electrical resistivity (corrected for transmuted elements) after irradiation. The two cold-worked and age-hardened alloys (AMZIRC and MZC) suffered loss of yield strength after irradiation at 385°C. The two elemental coppers and the AMZIRC alloy showed large swelling (3.6–6.8 vol%) due to void formation after the high neutron fluence. Further study is needed to understand microstructural alterations caused by neutron damage of the alumina-dispersed copper alloy.

Radiation damage ininsulators at high doses

Abstract Radiation damage at high doses (approaching or exceeding one displacement per atom) has been studied widely in metals and alloys in view of its importance in fission and fusion reactor technology. Insulators have received less attention, but their use-actual or potential-in reactors and as host materials for radioactive waste has stimulated recent studies. Insulators present conceptual problems compared with metals: electronic as well as atomic processes may contribute to radiation damage and different sub-lattices may not be affected by radiation in the same way. Ionization damage (radiolysis) in NaCl at high doses and temperatures provides a model system where the production of metal and halogen-based defect clusters can be studied experimentally and theoretically in some detail. It also has direct practical relevance to the storage of high-level radioactive waste in salt repositories. Fast neutron damage to high doses will be sustained by insulators used in any future fusion reactors. Basic st...

The mechanical properties of irradiated pitchcoke graphite

Small specimen measurements of dynamic Young's Modulus E, flexural strength S and critical stress intensity factor K Ic of pitchcoke graphite irradiated to a high fuel burn-up in a Civil Advanced Gas-cooled Reactor are reported. Previous data indicate that the fractional change in S due to fast neutron damage alone follows the corresponding fractional change in √ E and due to radiolytic oxidation alone approximately follows the corresponding changes in E. No comparative measurements of K Ic have previously been made. Thus, up to now it has been assumed that the fractional changes in K Ic are identical to the corresponding fractional changes in S. The new K Ic data support the fast neutron damage relation but suggest that K Ic is reduced to a slightly lesser extent than E or S with radiolytic oxidation. A comparison with a previous thermal oxidation study is made.

Fast neutron damage in tetrahedral ANB8− N Compounds: Effects of ionicity

Irradiation of crystals with neutrons of high energy leads to the formation of different types of defects, such as point defects or extended defects, like clusters or even amorphous regions in the displacement spike. Their nature and their creation yields depend on the chemical nature of the compound. In order to investigate some of the trends within the A N B 8− N compounds with a tetrahedral coordination, a typical covalent binary (GaAs) has been compared to the most ionic members of this family which are the cuprous halides (CuX). Comparative experiments have been performed using room temperature irradiation with fast neutrons (1–2 MeV). Defect assessment has been made by means of electron paramagnetic resonance (EPR). Whereas in GaAs the irradiation generates strong EPR signals, no similar effect is observed in the CuX. Particularly, the corresponding defect of the anionic antisite As Ga in GaAs is absent in the CuX; instead, they present only weak lines ascribed to extrinsic and extended defects. These results are discussed and we stress that the relevant parameter is the cation self-diffusion rate, itself related directly to the ionicity of the bond.

Artifacts in the measurement of fast-neutron damage rates at liquid-helium temperature

Abstract The simultaneous fast-neutron irradiation of thin copper foils immersed in liquid helium has shown an unexpected increase in the damage production rate with decreasing foil thickness. This effect can be attributed to the damage produced in the near-surface region of the foils by energetic helium atoms that result from the neutron bombardment.

Mercuric iodide (HgI 2) semiconductor devices as charged particle detectors

The properties of HgI 2 semiconductor devices as charged particle detectors have been investigated. Nearly linear energy response with fwhm resolution of 5–15% is observed for 1,2H and 3,4He ions, E < 40 MeV. Fast proton damage is observed for 10 10 protons/cm 2. However, based on measurements with two HgI 2 detectors, little fast neutron damage is apparent at fluences up to 10 15 neutrons/cm 2. This suggests considerably greater resistance to radiation damage than is observed for Si and other solid state devices.

Accelerated irradiation testing of SYNROC and its constituent minerals using fast neutrons

Fast neutron irradiation is being used to produce displacement damage in SYNROC B, SYNROC C, barium hollandite, zirconolite and perovskite, to simulate the actinide decay damage which will accumulate during long term disposal of SYNROC containing radioactive waste. Fast neutron and actinide decay damage is correlated by equating the calculated displacements per atom for the two cases, on the basis of 10 wt% waste addition. The macroscopic, microscopic and crystal structure effects are being measured on all five materials for ‘SYNROC ages’ up to 10 6 years, obtained by irradiating to a fast neutron dose of 4.8 × 10 20 n/ cm 2 (⩾ 1 MeV). Materials variables include the fabrication method and the presence or absence of simulated radwaste. All materials have exhibited a volume expansion and a corresponding decrease in density with increasing fast neutron dose. For the same dose, the volume expansions increase in the order barium hollandite ≅ hot pressed SYNROC B < perovskite ≅zirconolite ≅ SYNROC C< cold pressed and sintered SYNROC B. Microcracking occurs in SYNROC at expansions greater than 4 vol%, producing only a small increase in open porosity. For SYNROC C the neutron dose is equivalent to a SYNROC age of 2 × 10 5-years.

Processing of semiconductor materials and devices by neutron irradiation

Large volume neutron irradiation processing of semiconductor materials and devices has stimulated a renewed interest in neutron damage in semiconductors. Recent neutron damage experiments in Si are presented. Thermal neutron irradiation for industrial transmutation doping of float zone Si and fast neutron damage for the reduction of soft errors in Si computer memories are discussed.

Primary recoil spectra and subcascade effects in ion bombardment experiments

Abstract The motivation of this work is to compare atomic damage configurations associated with neutron and fast-ion damage. The question we set out to answer was: Which choice of ion mass and kinetic energy provides the best simulation of fast neutron damage? The answer which emerges is that the primary damage state, i.e. the statistical distribution of free defects, and subcascade regions before annealing, is remarkably independent of the ion species and its PKA spectrum. This conclusion is sufficiently surprising to warrant careful examination, and is presented together with a variety of qualifications.

A comparison of 252Cf and 238Pu, Be neutron sources for partial-body in vivo activation analysis

A comparison is made of the isotopic neutron sources 252Cf and 238Pu, Be for partial-body in vivo neutron activation analysis. Depth distributions of thermal neutron fluences in a water phantom are very similar for the two sources. The peak depth occurs at 5 cm. This value is approximately 2 cm less than the values obtained with uncollimated neutrons produced in broad-beam irradiations. With respect to the fluence-to-dose ratio, the 252Cf neutrons have an advantage of approximately 1.4 over the 238Pu, Be source. The use of 252Cf offers two additional advantages for the investigator. First, it minimises the on-line fast-neutron damage in Ge(Li) semiconductor detectors. Secondly, it is subject to much less stringent transport regulations than 238Pu, Be. The latter feature takes on particular importance in view of the increasing usefulness of transportable instruments for in vivo cadmium measurements at the workplace.

Potentiation by Caffeine of Potentially Lethal Fast-Neutron Damage in Cultured Human Cells

Caffeine was found to potentiate single-dose fast-neutron-induced killing of human T-1 cells when present at 2 mM for 60 hr or more after (and 10 hr before) irradiation. Analyses of survival curves of cells treated with neutrons or X rays with and without caffeine indicate that only the linear, low-dose portion of survival curves is modified. Potentiation of lethality by caffeine is attributed mainly to its effects on single-hit potentially lethal lesions, possibly certain DNA double-strand breaks.

Comparison of fission fragment damage with fast neutron damage in metals

Comparison of fission fragment damage with fast neutron damage in metals

Reply to “comparison of fission fragment damage with fast neutron damage in metals”

Reply to “comparison of fission fragment damage with fast neutron damage in metals”

Mechanism for fast neutron damage of Ge(HP) detectors

The effect on high purity germanium detectors of the disordered regions (r ∼ 100 A ̊ ) created by fast neutrons is theoretically and experimentally addressed. The hole trapping cross section of these defects is a function of their net negative charge and the applied electric field. We estimate σ ≈ 10 −9 – 10 −10 cm 2 immediately after biasing an n-type detector and σ ≈ 10 −10 – 10 −12 cm 2 as hole trapping and detrapping reach a steady state in the depleted detector. Resolution transients observed immediately after biasing n-type and p-type Ge(HP) coaxial detectors are reported and are shown to be consistent with the neutralization (n-type) or the charging (p-type) of the thermal equilibrium state. However on the basis of these transients we cannot exclude the possibility that point defects play a decisive role in the steady state resolution degradation. The ionization or activation of traps after cycling the p-type detector off/on can be consistently interpreted as due to an acceptor level near E v + 0.27 eV. The duration of the transient observed in n-type germanium was reduced to less than 1 h by placing a 6.5 μCi 60Co source on the end cap. Thus this transient does not significantly diminish the advantage of the contracting polarity employed on n-type coaxial detectors in reducing the effect of the hole trapping on resolution.

Defect clusters in heavy-ion irradiated nickel and nickel alloys

Low-dose (≲1012ions/cm2) heavy-ion irradiation gives a convenient method of studying some aspects of fast-neutron radiation damage and has now been studied using transmission electron microscopy in a wide variety of metals and alloys (e.g. see the reviews by Eyre 1973 and Wilkens 1975). From these studies a consistent picture of the development of the damage structure has emerged. In most cases small vacancy loops are observed, produced heterogeneously at the sites of displacement cascades by the collapse of vacancy-rich ‘depleted zones’. The interstitial component of the damage is usually lost to the foil surfaces and is not observed. There have been surprisingly few investigations of heavy-ion damage in materials of technological importance. However, it has been noted that cascade collapse appears to take place less readily in complex alloys such as steels than in pure metals such as copper (e.g. Williams and Eyre 1976) but few attempts have been reported to explore this effect systematically.