Cross Sections Of Nuclides Research Articles

Measurements of neutron capture cross-section for nuclides of interest in decommissioning (II): 58Fe(n,γ)59Fe

ABSTRACT As nuclear facilities are dismantled in decommissioning, large amounts of various waste are generated. Even more inconveniently, such waste is radioactive due to neutron activation. Thus, the neutron capture cross-sections of nuclides targeted in decommissioning are required to evaluate the radioactivity produced. In this work, 58Fe nuclide was selected among objective nuclides for decommissioning, and its thermal-neutron capture cross-section was measured by a neutron activation method at the graphite thermal column of Kyoto University Research Reactor in 5-MW operation. The thermal-neutron capture cross-section was derived using Westcott’s convention. The present work obtained 1.36 ± 0.03 barns for the58Fe(n,γ)59Fe reaction. The present result supports the JENDL-5 evaluation within 2σ. If updated with currently recommended nuclear data, some of the reported past data would support the present result.

Measurements of neutron capture cross-sections for nuclides of interest in decommissioning: 45Sc, 63Cu, 64Zn, 109Ag, and 113In

ABSTRACT As nuclear facilities are dismantled in decommissioning, various and large amounts of waste are generated. Even more inconveniently, they are radioactive waste due to neutron activation. Thus, the neutron capture cross-sections of nuclides targeted for decommissioning are required to evaluate the radioactivity produced. The present study selected 45Sc, 63Cu, 64Zn, 109Ag and 113In among targeted nuclides, and performed the measurements of thermal-neutron capture cross-sections by an activation method at the Kyoto University Research Reactor. The thermal-neutron capture cross-sections were derived on the basis of Westcott’s convention. The present results were obtained as follows: 27.18 ± 0.28 barn for 45Sc(n,γ)46Sc, 4.34 ± 0.06 barn for 63Cu(n,γ)64Cu, 0.719 ± 0.011 barn for 64Zn(n,γ)65Zn, 4.05 ± 0.05 barn for 109Ag(n,γ)110mAg and 8.53 ± 0.27 barn for 113In(n,γ)114Inm1+m2 reactions. The results for 45Sc and 64Zn support evaluated cross-section data within the limits of uncertainties, while those for the other nuclides were slightly different from evaluated ones. The obtained results are useful not only for the evaluation of isotope production, but also for the consideration of those nuclides as flux monitors, as an alternative to Au and Co.

Fragment production in proton–induced reaction on Bi209 target at intermediate energy range

We used the phasotron of the Laboratory of Nuclear Problems at JINR to irradiate isotopically pure $^{209}\mathrm{Bi}$ target with 660 MeV protons. Cross sections of the fragment production with mass numbers $24\ensuremath{\le}A\ensuremath{\le}210$ u were measured for the first time using the direct $\ensuremath{\gamma}$-spectrometry method with a high-resolution HpGe detector. The $\ensuremath{\gamma}$ lines of the fragments have been identified, and the cross sections determined by the deimos code. The results of the measured nuclide cross section have been parametrized in terms of a three-parameter equation in order to reproduce the real isobaric distribution. Fission and spallation mass yields have been reconstructed on the base of charge distribution of reaction products. The main reaction results have been compared with other experimental data obtained from the proton-induced reaction at 600 MeV as well as with theoretical model calculations using the crisp code.

How were the heavy chemical elements beyond iron made in the Universe?

Nuclear astrophysics, which is an interdisciplinary branch of nuclear physics (micro scale) and astrophysics (macro scale), addresses some of the most compelling questions in the universe. Research efforts have been devoted to many topics such as the origins of the chemical elements, the unique conditions of earth that makes life possible, and the formation and evolution of the sun, stars, and galaxies. Nuclear processes play an extremely important role in cosmic evolution after the Big Bang, and they are the only known mechanisms that synthesize heavy elements, in addition to providing the energy for stars to resist the force of gravity. Over the past 50 years, scientists have developed a deep understanding of Big-Bang primordial nucleosynthesis and the mechanisms for synthesizing heavy elements. However, the astrophysical models have yet to adequately reproduce the observed solar abundances of those elements beyond iron (referred to as ultra-iron elements). It is widely believed that these ultra-iron elements were primarily synthesized via the slow neutron capture process (s-process) and the fast neutron capture process (r-process). The fundamental s-process component is thought to originate from thermally pulsing low-mass AGB stars, with reaction pathways closed after the stable nuclides. About half of the heavy elements (up to bismuth) were produced via the s-process. The r-process is thought to occur in the explosive burning of core-collapse supernova and/or neutron-star mergers. Although the r-process site remains a mystery, experts believe that more than half of the ultra-iron elements (up to thorium and uranium) were produced via the r-process. In addition, there are 35 neutron-deficient stable isotopes, which are present in significantly less abundance in our solar system. These so-called p-nuclei are likely produced in Type II supernova, through the photo-dissociation (referred to as p-process or r-process) of existing s- or r-process seeds, or through the recently proposed neutrino-proton v p-process. Astrophysical models require a huge amount of nuclear-physics input data. The most essential data include nuclear mass, structure, decay and fission characteristics, and related nuclide cross-sections along the various nucleosynthesis paths. Thus far, the lack of systematic and precise nuclear inputs is one of the main reasons scientists have not been able to reproduce the observed solar abundances of ultra-iron elements. Published by Discover magazine in 2002, the American National Research Council ranked the question, how were the heavy elements from iron to uranium made? as one of the 11 Greatest Unanswered Questions of Physics in this Century . More complete and precise nuclear physics inputs are therefore urgently needed to improve astrophysical models and decode the observations. This paper introduces the most important nucleosynthesis processes that are responsible for the ultra-iron elements production in the universe, while also summarizing the relevant key nuclear-physics inputs required in the astrophysical models. Finally, the frontier in this field study includes the origins of ultra-iron elements, and the future of nuclear astrophysics research in China is examined.

On-the-fly Doppler broadening method based on optimal double-exponential formula

As temperature changes constantly in nuclear reactor operation, on-the-fly Doppler broadening methods are commonly adopted for generating nuclear cross sections at various temperatures in neutron transport simulation. Among the existing methods, the widely used SIGMA1 approach is inefficient because it involves error function and Taylor series expansion. In this paper, we present a new on-the-fly Doppler broadening with optimal double-exponential formula based on SuperMC to improve efficiency with given accuracy. In this method, double-exponential formula in 1/16 steps is used for broadening cross section at low energy, with both accuracy and efficiency. Meanwhile, the Gauss–Hermite quadrature of different orders is used for broadening cross section at resonance energy. The method can generate neutron cross section rapidly and precisely at the desired temperature. Typical nuclide cross sections and benchmarking tests are presented in detail.

Fast spectrum reactor fuel assembly sensitivity analysis

The Experimental Breeder Reactor-II was a sodium-cooled, metal-uranium-fueled fast-neutron reactor designed and built by Argonne National Laboratory. The reactor achieved initial criticality September 30, 1961, and continued operation until 1994. The reactor thermal power limit was 62.5MW with a corresponding electrical output of 19MW. To preserve important EBR-II reactor physics information, a benchmark evaluation is underway for proposed inclusion in the International Handbook of Evaluated Reactor Physics Benchmark Experiments. Coupled with development of the reactor physics benchmark evaluation, sensitivity analysis has been performed. Individual nuclide cross-section sensitivities for heterogeneous and homogeneous fuel assembly models were calculated using the multi-group adjoint method, the iterated fission probability (IFP) method, and the Contribution-Linked eigenvalue sensitivity/Uncertainty estimation via Track length importance Characterization (CLUTCH) method. Good agreement between the three methods was observed except for the sodium total and elastic cross-section and the uranium-235 total cross-section sensitivity coefficients where the multi-group adjoint method produced results approximately 14% and 7% lower than the IFP and CLUTCH methods, respectively.

Production and testing of the ENEA-Bologna VITJEFF32.BOLIB (JEFF-3.2) multi-group (199 n + 42 γ) cross section library in AMPX format for nuclear fission applications

The ENEA-Bologna Nuclear Data Group produced the VITJEFF32.BOLIB multi-group coupled neutron/photon (199 n + 42 γ) cross section library in AMPX format, based on the OECD-NEA Data Bank JEFF-3.2 evaluated nuclear data library. VITJEFF32.BOLIB was conceived for nuclear fission applications as European counterpart of the ORNL VITAMIN-B7 similar library (ENDF/B-VII.0 data). VITJEFF32.BOLIB has the same neutron and photon energy group structure as the former ORNL VITAMIN-B6 reference library (ENDF/B-VI.3 data) and was produced using similar data processing methodologies, based on the LANL NJOY-2012.53 nuclear data processing system for the generation of the nuclide cross section data files in GENDF format. Then the ENEA-Bologna 2007 Revision of the ORNL SCAMPI nuclear data processing system was used for the conversion into the AMPX format. VITJEFF32.BOLIB contains processed cross section data files for 190 nuclides, obtained through the Bondarenko (f-factor) method for the treatment of neutron resonance self-shielding and temperature effects. Collapsed working libraries of self-shielded cross sections in FIDO-ANISN format, used by the deterministic transport codes of the ORNL DOORS system, can be generated from VITJEFF32.BOLIB through the cited SCAMPI version. This paper describes the methodology and specifications of the data processing performed and presents some results of the VITJEFF32.BOLIB validation.

Eigenvalue implicit sensitivity and uncertainty analysis with the subgroup resonance-calculation method

Response sensitivity coefficients with respect to nuclide cross sections consist of two parts, explicit sensitivity coefficients and implicit sensitivity coefficients. The explicit sensitivity coefficients, which account the direct impact of cross sections on the responses through neutron transport equation, can be calculated efficiently with the classical Perturbation Theory. The implicit sensitivity coefficients, which account the indirect impact of cross sections on the responses through resonance self-shielding, are either omitted in most sensitivity analysis codes, or accounted for based on simple resonance-calculation methods which are not applicable for complex fuel designs. In order to expand the implicit sensitivity analysis method to wider application domain, a method based on the Generalized Perturbation Theory (GPT) is proposed in this paper to calculate the implicit sensitivity coefficients by using the subgroup method in the resonance self-shielding calculation. Based on the in-house-developed 2-D general-geometry method-of-characteristic neutron-transport code AutoMOC and subgroup resonance self-shielding code SUGAR, the proposed method has been implemented in the COLEUS code for the sensitivity and uncertainty analysis. Numerical analysis is then performed to investigate the impact of the implicit sensitivity coefficients of eigenvalue on non-resonance nuclide cross sections in two single-cell cases with different enrichments. The eigenvalue sensitivity coefficients predicted by the COLEUS code are consistent with those calculated by the direct-perturbation method, the reference solution. The results show that the implicit sensitivity has an important impact on both sensitivity and uncertainty in some analyzed cases.

Spallation of197Au with 4.4-GeV deuterons

A comprehensive set of 110 radioactive nuclide cross sections with mass num- bers 22 ≤ A ≤ 198 amu in the interaction of 4.4-GeV deuterons with 197 Au have been measured for the first time. The results including charge distributions have been parame- terized in term of a 3-parameter equation in order to reproduces the isobaric distributions. Using data from the charge distributions, the total mass-yield distribution was obtained. The new experimental data of the recoil properties of reaction products were also ob- tained. Kinematical characteristics of the reaction products obtained from measurements of the residuals emitted in the forward and backward directions exhibit different behav- ior depending on the mass region. The kinematical features of reaction products have been analyzed on the basis of the two-step model of high-energy nuclear reactions and discussed in terms of the different reaction mechanisms.

A facility for fast-neutron irradiations at Jyväskylä and its use for nuclide cross-section measurements in fission

An efficient and reliable transport system for fast-neutron irradiations has been built at the Physics Department, Jyväskylä, Finland. It is constructed from commercial bicycle components and is driven by a computer-controlled stepping motor. It can be operated in single or cyclic mode. The neutron irradiated targets are moved within 1.2s (full stop to full stop) to a well-shielded position 3m away where they can be removed or directly investigated by γ spectroscopy. The system has been built with the aim to experimentally verify the calculated production rates of neutron-rich nuclei in the SPIRAL2 uranium target. However, the facility can be used for various kinds of fast-neutron irradiations, with a neutron spectrum up to 60MeV produced by stopping a deuteron beam of several μA in a thick target. Examples of applications are activation and integral cross-section measurements, evaluation of damages in materials and biological cells.

Measurements of nuclide yields in neutron-induced fission of natural uranium for SPIRAL2

Cross-sections for nuclide production in fast-neutron induced fission of natural uranium are part of the input for predictions of yields of neutron-rich nuclides obtainable at Radioactive Ion Beam facilities. We first describe the neutron spectra produced according to the scheme once envisaged for SPES (protons on an enriched 13C target) and the one adopted for SPIRAL2 (deuterons on natural carbon), which both have been measured at JYFL. We then present the measurements of Z-splits in isobaric chains performed at IGISOL. When coupled with the fission cross-section and A-splits for the relevant neutron spectrum, they allow estimates of nuclide cross-sections. It looks that calculations, even those based on modern libraries, are too optimistic by about a factor of two.

Analysis of the (n,f) Reaction in the Plutonium Isotopes

This paper describes the modified Hauser-Feshbach formalism used to com- pute accurately fission cross sections for low-energy neutrons (from a few keV up to 5.5 MeV) in presence of intermediate structure in the second well. Application to the large plutonium isotope family (236 to 244) has been made with in particular reliable predic- tions of the cross sections of the short-lived nuclides. Special attention is paid to the choice of the model parameters entering in the calculations. The decay of a compound nucleus by fission is a complex multi-dimensional problem, whose de- scription still requires many model parameters. The elucidation and physical understanding of these parameters is an ongoing research process, and this paper reports our progress in the study of the fis- sion cross-sections for a long sequence of plutonium isotopes. Our ultimate goal is to replace many fitting parameters ubiquitous in current data evaluations with physically sound theory with fewer pa- rameters. If successful, such an approach would lead to reliable predictions of the fission cross-sections of nuclides for which measurements are unavailable or very poor, while at the same time deepen our understanding of the fission process. Here we present results obtained with a modern version of the AVXSF code (AVerage Cross Sec- tion of Fission), which treats in great detail the intermediate structure due to the presence of a sec- ond well on the fission path. The correct modeling of the class-II states properties and in particular, their coupling with the levels present in the first well as well as to the continuum, is crucial to infer meaningful barrier heights. Experimentally, those barrier heights can be inferred from an analysis of low-energy neutron-induced fission cross sections in the case of fertile nuclei, and transfer reactions leading to fission, e.g., ( t, p f ), in the case of fissile nuclei. The AVXSF code can treat both situations adequately in order to extract fission barrier heights. In the following, the theory and main equations implemented in the AVXSF code are introduced. Approximate formulae valid in specific situations are also discussed. A Monte Carlo option is used when analytic approximations fail and a full sampling of the level characteristics distributions is needed. We then present preliminary results on the neutron-induced fission cross sections obtained for a suite of plutonium isotopes, for which a consistent set of model input parameters was devel- oped. Our analysis encompasses neutron incident energies from a few keV up to 5.5 MeV, just below the onset of second-chance fission. The importance of fission barrier heights, nucleon pairing gaps and level densities is emphasized. This paper concludes on some examples of predicted cross sections with some reliability for the short-lived nuclides of the Pu series.

Production and testing of HENDL-2.1/CG coarse-group cross-section library based on ENDF/B-VII.0

A coarse-group coupled neutron and photon (27 n + 21γ) cross-section library HENDL-2.1/CG, based on ENDF/B-VII.0 evaluate data source, has been produced by FDS Team in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). HENDL-2.1/CG containing 350 nuclide cross-section files (from 1H to 252Cf) was generated in MATXS format with the NJOY processing system and then by compiling coarse-group problem-dependent format using the TRANSX code. In order to verify the availability and reliability of the HENDL-2.1/CG data library, requisite benchmark calculations were performed and compared with HENDL-2.0/MG fine-group coupled neutron and photon (175 n + 42γ) cross-section library. In general, results using the coarse-group library showed similarly believable as fine-group library.

Experimental investigation of the residues produced in the136Xe+Pband124Xe+Pbfragmentation reactions at1AGeV

The nuclide cross sections and longitudinal velocity distributions of residues produced in the reactions of {sup 136}Xe and {sup 124}Xe at 1A GeV in a lead target were measured at the high-resolution magnetic spectrometer, the fragment separator (FRS) of GSI. The data cover a broad range of isotopes of the elements between Z=3 and Z=56 for {sup 136}Xe and between Z=5 and Z=55 for {sup 124}Xe, reaching down to cross sections of a few microbarns. The velocity distributions exhibit a Gaussian shape for masses above A=20, while more complex behavior is observed for lighter masses. The isotopic distributions for both reactions preserve a memory on the projectile N/Z ratio over the whole residue mass range.

An improved photo-absorption cross section model for the physics models regime in MCNPX

The photo-nuclear physics model capabilities utilising the CEM2k model implemented in the MCNPX code were improved > 100 MeV photon energy by basing the photon transport on experimental photo-absorption cross sections of nuclides rather than on free nucleon cross sections. Below 100 MeV, the photo-nuclear physics model now uses isotope-specific giant dipole resonance (GDR) photo-absorption cross sections that are provided to the code in a parameterised form on a data file. Adjustments of the photo-fission cross sections were implemented to match the BOFOD evaluated data through a CEM2k internal parameter. The physics models with these improvements are better equipped to supplement the tabulated data based photo-nuclear MCNPX capability for isotopes with missing tabulated data evaluations especially in the GDR region, and has improved its predictive power at energies above the GDR resonances.

Nuclide cross-sections of fission fragments in the reaction 208Pb + p at 500 A MeV

The isotopic distributions and recoil velocities of the fission fragments produced in the spallation reaction 208Pb + p at 500 A MeV have been measured using the inverse-kinematics technique, a lead beam onto a liquid-hydrogen target, and the high-resolution spectrometer FRS at GSI. The shapes of the different distributions are found in good agreement with previously published data while the deduced total fission cross-section is higher than expected from existing systematics and some previous measurements. From the experimental data, the characteristics of the average fissioning system can be reconstructed in charge, mass and excitation energy, and the average number of post-fission neutrons can be inferred. The results are also compared to different models describing the spallation reaction. The intranuclear cascade code INCL4 followed by the de-excitation code ABLA is shown to describe reasonably well the evolution of the isotopic distribution shapes between 500 and 1000 A MeV.

Universal curve of epithermal neutron resonance self-shielding factors in foils, wires and spheres

The presence of a nuclide sample in an epithermal neutron field of a nuclear reactor creates a perturbation of the local neutron flux. This effect can be very important, especially if the nuclide cross-section exhibits a prominent resonance peak. To take into account the effect of the neutron flux perturbation in the sample activation, a resonance neutron self-shielding factor ( G res ) must be considered. This factor depends on the geometry and dimension of the sample, as well as on the physical and nuclear properties of the nuclide. On the basis of a dimensionless variable which includes the relevant characteristics of the sample, an universal curve is proposed, which enables the determination of the factor G res for isolated resonances of any nuclide and samples of various geometries (foils, wires and spheres). The proposed universal curve is in very good agreement with experimental and calculated values obtained from the literature.

Benchmark Model of Critical Experiment at TCA for Integral Evaluation of Fission Product Nuclide Cross Sections

Benchmark models of the critical experiments which measured reactivity effects of main fission product elements (Rh, Cs, Nd, Sm, Eu, and Gd) and of an important burnable poison element, erbium, were presented. These elements were dissolved in a vessel which was inserted into the central region of a fuel rod array of TCA (Tank-Type Critical Assembly). The atomic number densities of aqueous solutions in the vessel were calculated. Using these number densities, criticality calculations with MCNP 4A, TWOTRAN code, and JENDL-3.2 cross section library were performed for these experiments.

Benchmark Model of Critical Experiment at TCA for Integral Evaluation of Fission Product Nuclide Cross Sections.

Benchmark models of the critical experiments which measured reactivity effects of main fission product elements (Rh, Cs, Nd, Sm, Eu, and Gd) and of an important burnable poison element, erbium, were presented. These elements were dissolved in a vessel which was inserted into the central region of a fuel rod array of TCA (Tank-Type Critical Assembly). The atomic number densities of aqueous solutions in the vessel were calculated. Using these number densities, criticality calculations with MCNP 4A, TWOTRAN code, and JENDL-3.2 cross section library were performed for these experiments.

Strong nonstatistical effects in neutron capture at the 2p size resonance region.

This paper investigates the nonstatistical effects in radiative neutron capture cross sections for nuclides at the 2p size resonance region of neutron strength function, specifically /sup 27/Al(n,..gamma..) and /sup 28/Si(n,..gamma..) reactions. The neutron energies studied range from thermal up to 2 MeV. The calculated results show that in comparison with medium and heavy nuclei, the nonstatistical fractions in the total capture cross sections for the two lighter nuclides are extremely large. In the thermal energy region, the fractions are about 50%. In the resonance energy region, the averaged contributions from the nonstatistical processes are considerably larger than that from the statistical mechanism. The physical significance of the results was briefly discussed. It was also indicated that this conclusion is qualitatively consistent with the fact that the measured capture data show significant correlations in both nuclides.