Neutron Irradiated Nickel Research Articles

Nano-crystalline zirconia: a viable adsorbent for the column chromatographic separation of 58Co from neutron irradiated nickel targets

This paper described the utility of tetragonal nano-zirconia (t-ZrO2) for the column chromatographic separation of 58Co from 58Ni(n, p) reaction in neutron irradiation of natural Ni target. A careful scrutiny of the adsorption parameters of t-ZrO2 was systematically carried out to arrive at the optimum separation conditions. The radiochemical procedure developed herein consisted of selective retention of 58Co from an acidic solution of neutron irradiated Ni target on a chromatography column containing t-ZrO2 followed by elution of 58Co in 0.1 M HCl, which was validated using real samples. The overall recovery of 58Co was >90 % with appropriate radiochemical and radionuclide purity.

Microstructure and swelling of neutron irradiated nickel and binary nickel alloys

Pure nickel in two starting cold-worked conditions and three solute-added binary nickel-based alloys in two other cold-worked conditions were irradiated in the BR-10 fast reactor at a range of temperatures between 673 and 823K. The microstructure and swelling developed under irradiation were compared with those of other fast reactors operating at higher dpa rates. It was shown that in agreement with earlier studies cold-working can increase void swelling. It also appears that swelling reaches higher values as the dpa rate decreases, a trend seen in other studies. Further, the action of solutes, especially silicon and aluminum, on swelling and microstructure was consistent with the behavior observed in earlier studies. Finally, the evolution of yield strength was easily modeled in terms of the radiation-induced evolution of void, dislocation, and loop microstructure using standard hardening models.

Influence of impurities on the evolution of vacancy-type defects in neutron-irradiated nickel

In order to investigate the effect of impurities on vacancy defect evolution in nickel, specimens with high (5N) and technical (3N) purity were neutron-irradiated at ∼330K in the IVV-2M reactor (Russia) to fluencies in the range of 1×1021–1×1023n/m2 (E>0.1MeV) corresponding to displacement dose levels in the range of about 0.0001–0.01dpa and subsequently stepwise annealed to about 900K. The specimens of Ni with different purities were characterized both in as-irradiated state as well as after post-irradiation annealing by positron annihilation spectroscopy. The formation of three-dimensional vacancy clusters (3D-VCs) in cascades was observed under neutron irradiation. The density and size of 3D-VCs depended not only on dose level, but also on purity. The population of 3D-VCs in the technical Ni is lower than that in the high-purity Ni. 3D-VCs collapse into secondary-type clusters (stacking fault tetrahedra (SFTs) and vacancy loops) during stepwise annealing at 350–450K (stage III in Ni). The suppression of secondary cluster formation in 3N Ni is attributed to an effective vacancy interaction with impurity carbon atoms, which based on a relatively large vacancy–carbon atom binding energy (0.32–0.35eV). The trapping of vacancies released at the collapse of 3D-VCs by the interstitial impurity atoms dominates at low irradiation dose level (10−4dpa). Thus, we found that carbon impurity atoms have strong effects both on the primary vacancy-type defect aggregation and on the secondary vacancy clusters and complexes formation.

Detection of hydrogen in neutron-irradiated nickel using positron lifetime spectroscopy

Hydrogen in nano-voids in neutron-irradiated nickel has been detected using positron annihilation lifetime spectroscopy (PALS). As positron lifetime is greatly affected by nano-voids bound with hydrogen, special attention was paid to the analysis. The positron lifetime of neutron-irradiated nickel at higher irradiation doses increased with the dose, which is an indicator for vacancy cluster (nano-void) formation in the lattice. The introduction of hydrogen in well-annealed nickel by electrical charging also resulted in an increase in positron lifetime due to vacancy formation. In neutron-irradiated nickel specimens, hydrogen charging shortened the positron lifetime from 456 to 334 ps (irradiation dose: 3 × 10−3 dpa). Isochronal annealing behaviour of hydrogen-charged nickel and neutron-irradiated nickel was also studied. Positron trapping rate was calculated using a simple trapping model. Thermal desorption spectroscopy was used for the investigation of hydrogen behaviour in non-irradiated hydrogen-charged nickel.

The Effect of Hydrogen-Charging in Neutron Irradiated Nickel Studied by Positron Annihilation Lifetime Spectroscopy (PALS)

The Effect of Hydrogen-Charging in Neutron Irradiated Nickel Studied by Positron Annihilation Lifetime Spectroscopy (PALS)

Role of solute atoms on microstructural evolution in neutron irradiated nickel

Fission reactor irradiation of nickel alloys with solutes of widely varying volume size factors 2 at% of Si, Cu, Ge and Sn, was performed for a wide range of irradiation temperature. At a lower temperature 473 K, a high density of small vacancy clusters are mixed with interstitial-type dislocation loops in all the alloys. At higher temperatures, in the alloys with solutes of negative volume size factor, Si, and extremely large positive factor, Sn, the unfaulting of interstitial-type dislocation loops during irradiation is suppressed, and the development of dislocation structures is moderate. In the alloys with solutes of positive but not large volume size factor, Cu and Ge, including pure Ni, unfaulting of loops strongly promotes the development of dislocation structures. As a consequence of the difference in these dislocation structure developments, void formation is almost completely suppressed in the first category and is enhanced strongly in the second.

Benchmark test of transport calculations of gold and nickel activation with implications for neutron kerma at Hiroshima.

A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a 252Cf fission neutron source to validate the use of the code for the energy spectrum analyses of Hiroshima atomic bomb neutrons. Nuclear data libraries used in the Monte Carlo neutron and photon transport code calculation were ENDF/B-III, ENDF/B-IV, LASL-SUB, and ENDL-73. The neutron moderators used were granite (the main component of which is SiO2, with a small fraction of hydrogen), Newlight [polyethylene with 3.7% boron (natural)], ammonium chloride (NH4Cl), and water (H2O). Each moderator was 65 cm thick. The neutron detectors were gold and nickel foils, which were used to detect thermal and epithermal neutrons (4.9 eV) and fast neutrons (> 0.5 MeV), respectively. Measured activity data from neutron-irradiated gold and nickel foils in these moderators decreased to about 1/1,000th or 1/10,000th, which correspond to about 1,500 m ground distance from the hypocenter in Hiroshima. For both gold and nickel detectors, the measured activities and the calculated values agreed within 10%. The slopes of the depth-yield relations in each moderator, except granite, were similar for neutrons detected by the gold and nickel foils. From the results of these studies, the Monte Carlo neutron and photon transport code was verified to be accurate enough for use with the elements hydrogen, carbon, nitrogen, oxygen, silicon, chlorine, and cadmium, and for the incident 252Cf fission spectrum neutrons.

Dislocation loop formation on a twin boundary in neutron-irradiated nickel dilute alloys

Dislocation loop formation on a twin boundary in neutron-irradiated nickel dilute alloys

Positron annihilation in 14 MeV neutron irradiated nickel and nickel containing 25 at% iron

The defect structure in fusion neutron irradiated Ni and Ni+25 at% Fe has been studied by positron lifetime spectroscopy. The positron trapping is used as a defect indicator. Two lifetime components τ 1 and τ 2 are resolved. It is found that the number of vacancies in vacancy clusters is larger than 11. The recovery stage in Ni+25 at% Fe is shifted from 750 to 850 K.

Positron lifetime measurement and latent vacancy clusters in 14 MeV neutron irradiated nickel

The existence of electron microscopically invisible uncollapsed small vacancy clusters (latent vacancy clusters) in MeV neutron irradiated Ni has been investigated by comparison between electron microscopy observation and positron lifetime measurement. In the specimen irradiated at 300 K, a long lifetime component ( > 300 ps) was observed. This component was not observed in specimens irradiated at 363 K but appeared again in specimens irradiated at 423 K and higher temperatures. Considering the observed defect structures (stacking fault tetrahedra and interstitial loops up to the irradiation temperature of 423 K, and voids in addition to these above 473 K), the long lifetime component at 300 K was reasonably assigned to be latent vacancy clusters and that above 423 K to be voids.

Coincidence summing corrections for positron emitters in germanium gamma spectrometry

For positron emitters, 511 keV annihilation quanta are in coincidence with other gamma rays in the decay scheme. If the positrons are not localized at the point of decay, annihilation quanta will be produced at a site some distance from the point of emission. The magnitude of the summing coincidence effect will depend upon the position of annihilation. A method for determining the magnitude of the summing effect for a single gamma of energy E in coincidence with the annihilation gammas from non-localized positrons has been developed which makes use of the counting data for the full energy peaks for both the gamma ray ( E) and the 511 keV annihilation gammas. With this data and efficiency calibration data one can determine the average total efficiency for the annihilation positions from which 511 keV gammas originate, and thereby obtain the summing correction factor, SCF, for gamma ray ( E). Application of the method to a 22Na NIST standard gave excellent agreement of observed emission rates for the 1275 keV gamma with the NIST value for wide ranging degrees of positron localization having summing correction factors ranging from 1.021 to 1.505. The method was also applied successfully to 58Co in neutron-irradiated nickel foils. The method shows promise as a check on the accuracy of the efficiency calibration for a particular detector geometry at the 511 keV energy and energies for other gammas associated with positron emission.

Defect structure evolution from cascade damage in 14 Mev neutron irradiated nickel and nickel alloys

Abstract D-T neutron irradiation of nickel and 4 nickel based 2 at.% alloys were performed using RTNS-II at 300 to 700 K and fluences up to 1023 n/m2. The role of free point defects was detected by the comparison of defect structures produced by irradiation of material as thin foil and those irradiated as bulk. The analysis of vacancy clusters in thin foil nickel gives the average distance between sub-cascades to be 10 nm and 14 keV as sub-cascade energy. In bulk samples interstitial loops were formed; the major clustered vacancy defects in nickel at the lower temperatures were stacking fault tetrahedra, and voids at the higher temperatures. This difference reflects the variation of the stability of tetrahedra with temperature. Under-sized solutes (Si) and extremely over-sized solutes (Sn) enhanced the formation of loops in matrix, whereas moderately over-sized solutes (Cu,Ge) enhanced the formation of loops near dislocations. In the latter case, voids were observed since free point defects can diffuse long distances.

Grain boundary deformation in neutron irradiated nickel

The authors studied grain boundary deformation in nickel irradiated with neutrons in a VVR-K reactor and mechanically tested at different temperatures and various neutron fluences. The degree of radiation embrittlement was found to be significant. Results show that the general nature of intergranular displacement occurred in the form of relative sliding and mutual rotation of grains. Neutron irradiation was also found to suppress grain boundary migration. These conditions are assumed to cause the formation of grain boundary microcracks during high temperature tensile deformation. The microcracks increase with increasing deformation and merge together to form a potential main crack leading to ductility loss and intergranular fracture.

A Study of Defect Structures in Fast Neutron Irradiated Nickel at Low Temperature Using Magnetic Anisotropy Measurements

Measurements of the magnetic anisotropy in pure nickel after fast neutron irradiation at 5 K and after successive isochronal annealings at various temperatures between 5 K and 300 K were carried out at liquid helium temperature. Observed torque curves after the irradiation consist of only a biaxial component. By analyzing the intensity and phase of the biaxial term after the irradiation and during isochronal annealings, it was found that the structure of interstitials in nickel is 100-dumbbell type and those interstitials are initially aggregated on (100) planes, then change their state gradually and finally onto (111) plane after isochronal annealings at 320 K. The intensity of induced torque curves in nickel was compared with the case of bcc iron.

Flow behavior of nickel irradiated with 15 MeV neutrons and 16 MeV protons

The yield strength of zone refined nickel that was irradiated at 300 K with T(d, n) and Be(d, n) neutrons and 16 MeV protons was found to increase by a similar amount when compared at equal fluence levels. A factor of 2.5 increase in the yield strength was determined for a 15 MeV neutron fluence of 1 × 10 22 m −2 and a 16 MeV proton fluence of 2 × 10 22 m −2 . The strength increase was associated with defect clusters or small prismatic loops and could be described by a strong barrier model for both neutron and proton irradiated nickel. Serrated plastic deformation was observed for samples irradiated with 15 MeV neutrons and 16 MeV protons to fluences higher than 3 × 10 21 m −2 . The similarity in the hardening process of 15 MeV neutron and 16 MeV proton irradiated nickel is consistent with their damage energy cross sections being equal at high primary knock-on energies (> 10 keV).

Microstructure and tensile properties of T (d,n) and Be (d,n) neutron irradiated nickel, niobium and 316SS

The radiation damage induced in nickel, niobium and 316SS by T (d,n) and Be (d,n) neutrons was evaluated by microstructural analysis and mechanical property measurements. Also, the neutron flux gradients in the Be (d,n) neutron source were compared to the positional dependence of the yield strength of niobium wires. The microstructure and yield stress increase of T (d,n) and Be (d,n) neutron irradiated nickel were similar while there were differences in niobium.

The ORNL 10-meter small angle X-ray scattering camera

A new small-angle X-ray scattering camera which utilizes a rotating-anode X-ray source, crystal monochromatization of the incident beam, pinhole collimation, and a two-dimensional position-sensitive proportional counter has been developed. Because the sizes of the X-ray focal spot, the sample and the resolution element of the detector are each approximately 1 × 1 mm, the camera was designed so that the focal spot-to-sample and sample-to-detector distances may each be varied in 0.5 m increments up to 5 m to provide a system resolution in the range 0.5 to 4.0 mrad. A large, general-purpose specimen chamber has been provided into which a wide variety of special-purpose specimen holders can be mounted. The detector has an active area of 200 × 200 mm and has up to 200 × 200 resolution elements. The data are recorded in the memory of a minicomputer by a high-speed interface which uses a microprocessor to map the position of an incident photon into an absolute minicomputer memory address. With this interface, over 105 events s−1 can be recorded. The data recorded in the computer memory can be processed on-line by a variety of programs designed to enhance the user's interaction with the experiment. Among these are routines for background and detector-sensitivity correction, contour and perspective plotting of the two-dimensional data, a variety of averaging schemes for determining circular averages and/or one-dimensional slices of the data, file-management programs to handle the large quantity of data produced by a two-dimensional detector, and an interactive package for communications with a central computing facility via a dedicated hardwired link. At the highest angular resolution (0.4 mrad) the flux incident on the specimen is 1.0 × 106 photons s−1 with the X-ray source operating at 45 kV and 100 mA. The performance of the instrument is demonstrated with several examples, among which are scattering patterns from voids in neutron-irradiated nickel, plastically deformed polyethylene and collagen fibrils. Results from a kinetic study of the crystallization of polyethylene are also reported.

The effect of carbon on void formation in neutron-irradiated nickel

Abstract The effect of carbon on void formation in neutron-irradiated high purity nickel was investigated using transmission electron microscopy. After irradiation to fluences ranging from 4.0 × 1018 to 2.0 × 1020 n/cm2 (E > 0.1 MeV) at 500 and 710°C, voids were found in specimens containing up to 84 wppm carbon, whereas void formation was not observed in specimens with 600 wppm carbon. The present results have thus revealed a pronounced suppressing effect of interstitial carbon atoms on void formation. A quantitative analysis on void size and density indicates that the effect of carbon is mainly on void nucleation, not on void growth. A trapping mechanism, based on a relatively large divacancy-carbon atom complex binding energy of 0.86 eV, is proposed in which the dissolved carbon atoms are assumed to effectively trap at least two vacancies per carbon atom. This trapping mechanism is dynamic in nature because “free” interstitial carbon atoms are quite mobile in the nickel lattice at and above 500°C.

Positron annihilation in neutron-irradiated nickel single crystals

Abstract Recently Mogensen et al1 and Cotterill et al2 have reported appreciable effects of voids on positron annihilation in polycrystalline molybdenum heavily irradiated by fast neutrons at elevated temperatures. These authors found that the voids cause change to the characteristics of annihilation process more severely than other lattice defects such as vacancies and dislocations. In order to study the annihilation behavior of positrons in fcc metals containing voids, it is aimed to investigate the effect of voids on the angular correlation curve and its recovery behavior by measuring positron annihilation in neutron-irradiated nickel single crystals. In the present study, a nickel in-situ activation method is used taking advantage of a nuclear reaction 58Ni(n, p)58 Co .

Separation of Carrier Free 54Mn and 58Co from Neutron Irradiated Iron and Nickel

Separation of Carrier Free ⁵⁴Mn and ⁵⁸Co from Neutron Irradiated Iron and Nickel