Resonance Energy Region Research Articles

Americium-241 phase I: reevaluation for JEFF-3.1.1 and a step forward

This article reviews the low energy neutron cross section revision and the capture isomeric ratio evaluation of the 241Am neutron data performed for JEFF-3.1.1. It covers the history of the anterior evaluation made for JEF-2.2 and gives the consistent path used for re-evaluating the resolved resonance parameters from differential measurements and “integral” data feedback. This article highlights the procedure pursued to evaluate the 241Am capture ISOmeric ratio (ISO γ) from 0 to 20 MeV in parallel with a valuable estimation of the associated variances. Monte Carlo-type calculations have been made which predict ISO γ fluctuations over the energy region of the resolved resonances due to the presence of 2 s-wave types exhibiting well separated individual values (estimated to (90 ± 3)% and (76 ± 3)%, respectively, for a 2− and a 3− resonance) and well-resolved γ-multiplicities ( and ). Arguments are developed for using directly pointwise ISO γ data in reactor codes in the form of resonant partial capture cross sections, possibly from extended multi-level Breit–Wigner resonance parameterization, allowing systematic ISO γ Doppler broadening for a better comparison between experimental, differential, and integral measurements. This work corrects the fission widths of the lowest resonances inadequately treated during the JEFF-3.1.1 revision with an attempt of spin assignment supported by the present ISO γ study. Part of this work was also the preamble for the design of a new differential data program at the IRMM/Geel. This article shows the present status on the 241Am evaluated neutron data in terms of low energy cross sections and ISO γ data and, proposes some directions for the next JEFF-3.2 stage.

Nonresonance Compton scattering of an X-ray photon by a Ni-like atomic ion

The absolute values and the shape of the double differential cross section for nonresonance Compton scattering of an X-ray photon by an atomic ion with d symmetry in the core are studied theoretically beyond the impulse approximation for the example of the Ni-like atomic ions Zn2+, Kr8+, and Mo14+. It is established that, as the nuclear charge of an ion increases, (a) in all the scattering channels, the leading harmonics of transition to states of the continuous spectrum are concentrated and (b) the integral intensities of nonresonance Compton scattering are increasingly redistributed to the energy region of resonance Lands-berg-Mandelstam-Raman scattering between the threshold of termination of the Compton profile and the line of elastic (Thomson and Rayleigh) scattering. The calculated results are predictive in character.

Level density of 2+states in40Ca from high-energy-resolution (p,p′) experiments

The level density of 2${}^{+}$ states in ${}^{40}$Ca has been extracted in the energy region of the isoscalar giant quadrupole resonance from a fluctuation analysis of high-energy-resolution ($p,{p}^{\ensuremath{'}}$) data taken at incident energies of 200 MeV at the K600 magnetic spectrometer of iThemba LABS, South Africa. Quasifree-scattering cross sections were calculated to estimate their role as a background contribution to the spectra and found to be small. The shape of the background was determined from the discrete wavelet transform of the spectra using a biorthogonal wavelet function normalized at the lowest particle separation threshold. The experimental results are compared to widely used phenomenological and microscopic models.

Mechanisms of electron acceleration in the excitation of nuclear reactions in solid-state laser plasmas

Investigation of nuclear reactions in a solid-state plasma generated by modern high-intensity sources of ultrashort-wavelength laser radiation is undoubtedly of interest for establishing nuclear-reaction yields versus the intensity of laser radiation and for efficiently exciting new nuclear and photonuclear reactions—in particular, in the resonance energy region. The present article is devoted to describing, for laser plasmas, various mechanisms of electron acceleration, which triggers the acceleration of atomic ions and the excitation of subsequent nuclear reactions.

Pion induced reactions on 4He in the Δ resonance energy region

Measurement of the in-medium modifications of the Δ resonance, signatures of the excitation of nuclear collective states and the first experimental evidence for a thermal emission of photons have been obtained from the analysis of new π±4He data at Tπ = 106 MeV at PAINUC experiment.

Measurement and Analysis of Reactivity Worth of 241Am Sample in Water-Moderated Low-Enriched UO2 Fuel Lattices at TCA

The reactivity worths of 22.82 grams of 241Am oxide sample were measured and theoretically analyzed in water-moderated UO2 fuel lattices in seven cores of the Tank-Type Critical Assembly (TCA) at the Japan Atomic Energy Agency for an integral test of 241Am nuclear data. These cores provided a systematic variation in the neutron spectrum between the thermal and resonance energy regions. The sample reactivity worth was measured with an uncertainty of 2.1% or less. The theoretical analysis was performed using the JENDL-3.3 nuclear data by a Monte Carlo calculation method. Ratios of calculation to experiment (C/Es) of the reactivity worth were between 0.91 and 0.97, and showed no apparent dependence on the neutron spectrum. In addition, sensitivity analysis based on the deterministic calculation method was carried out to obtain the impact of changing the 241Am capture cross section on the sample reactivity worth. The result of this analysis showed that the C/E could be significantly improved by almost uniformly increasing the 241Am capture cross section of JENDL-3.3 by 25–30%.

SKYRME–HARTREE–FOCK DESCRIPTION OF THE DIPOLE STRENGTH IN NEUTRON-RICH TIN ISOTOPES

Low-energy E1 strength in neutron-rich 132-164 Sn isotopes is analyzed in the framework of the Skyrme random phase approximation (RPA) with different Skyrme forces. A double folding procedure is applied to take into account the energy-dependent width effects beyond RPA. All the considered Skyrme forces indicate a soft prolate deformation in the open shell isotopes 142-164 Sn . The integrated E1 strength in the energy region of the pygmy resonance grows with the neutron number. The influence of deformation on the integrated strength near the particle emission thresholds (which is of a keen astrophysical interest) is strictly suppressed by the mutual compensation effect for the branches of the giant dipole resonance. The results obtained are in a good agreement with the previous findings of the relativistic mean field model.

Resonant Angle-Resolved Photoelectron Spectroscopy of Substitutional Solid Solutions of CeRu2Si2

Angle-resolved photoelectron spectroscopy was measured in the Ce 3 d →4 f resonance energy region for the paramagnetic state of CeRu 2 Si 2 , Ce 0.84 La 0.16 Ru 2 Si 2 , and LaRu 2 Si 2 to investigate a variation of band structures around the quantum critical point (QCP). While the results clearly demonstrate the difference of the band structures between CeRu 2 Si 2 and LaRu 2 Si 2 , the observed band structures of CeRu 2 Si 2 and Ce 0.84 La 0.16 Ru 2 Si 2 resemble each other. The results indicate that the Ce 4 f electrons in the paramagnetic state have an itinerant character in either side of the critical composition, and Ce 1- x La x Ru 2 Si 2 near QCP is similar to CeRu 2 (Si 1- x Ge x ) 2 .

Measurement and Analysis of Reactivity Worth of 241Am Sample in Water-Moderated Low-Enriched UO2 Fuel Lattices at TCA

The reactivity worths of 22.82 grams of 241Am oxide sample were measured and theoretically analyzed in water-moderated UO2 fuel lattices in seven cores of the Tank-Type Critical Assembly (TCA) at the Japan Atomic Energy Agency for an integral test of 241Am nuclear data. These cores provided a systematic variation in the neutron spectrum between the thermal and resonance energy regions. The sample reactivity worth was measured with an uncertainty of 2.1% or less. The theoretical analysis was performed using the JENDL-3.3 nuclear data by a Monte Carlo calculation method. Ratios of calculation to experiment (C/Es) of the reactivity worth were between 0.91 and 0.97, and showed no apparent dependence on the neutron spectrum. In addition, sensitivity analysis based on the deterministic calculation method was carried out to obtain the impact of changing the 241Am capture cross section on the sample reactivity worth. The result of this analysis showed that the C/E could be significantly improved by almost uniformly increasing the 241Am capture cross section of JENDL-3.3 by 25–30%.

Test of Universal Rise of Hadronic Total Cross Sections Based on πp, Kp, \-pp and pp Scatterings

Abstract There are several evidences of the hadronic total cross section σtot to be proportional to B log2s consistent with the Froissart unitarity bound. The COMPETE collaboration has further assumed σtot ≃ B log2(s/s0) + Z to extend its universal rise with the common value of B for all hadronic scatterings to reduce the number of adjustable parameters. The coefficient B is suggested to be universal in the arguments of color glass condensate (CGC) of QCD. There has been, however, no rigorous proof yet based only on QCD. We attempt to investigate the values of B for πxxxp, Kxxxp and p¯p, pp scatterings respectively through the search for the simultaneous best fit to the experimental σtot and ρ ratios at high energies. The σtot at the resonance and intermediate energy regions has also been exploited as a duality constraint based on the special form of finite-energy sum rule (FESR). We estimate the values of B individually for πxxxp, Kxxxp and p¯p, pp scatterings without using the universality hypothesis. It turs out that the values of B are mutually consistent within one standard deviation, and the universal rise of hadronic total cross sections is strongly suggested. It has to be stressed that we cannot obtain such a definite conclusion without the duality constraint.

Measurement of theAm241(γ,n)Am240reaction in the giant dipole resonance region

The photodisintegration cross section of the radioactive nucleus $^{241}\mathrm{Am}$ has been obtained using activation techniques and monoenergetic $\ensuremath{\gamma}$-ray beams from the HI$\ensuremath{\gamma}$S facility. The induced activity of $^{240}\mathrm{Am}$ produced via the $^{241}\mathrm{Am}$$(\ensuremath{\gamma},n)$ reaction was measured in the energy interval from 9 to 16 MeV utilizing high-resolution $\ensuremath{\gamma}$-ray spectroscopy. The experimental data for the $^{241}\mathrm{Am}$$(\ensuremath{\gamma},n)$ reaction in the giant dipole resonance energy region are compared with statistical nuclear-model calculations.

N 1s photoelectron angular distributions from fixed-in-space NO2 molecules: Stereodynamics and symmetry considerations

Angular distributions of N 1s photoelectrons from fixed-in-space NO(2) molecules have been measured over the energy region of shape resonance and above. A multiple-coincidence velocity-map imaging technique for observation of molecular frame photoelectron angular distributions (MF-PADs) has been extended to nonlinear molecular targets. Density functional theory calculations have also been conducted to elucidate the photoionization dynamics and shape resonance in the N 1s photoionization of NO(2). Results show that the N 1s MF-PADs exhibit strong shape variation as a function of both photoelectron kinetic energy and symmetries of final states, whereas asymmetry parameters of laboratory frame PADs show a local minimum around the shape resonance region and increase monotonically as the photon energy increases. Over the shape resonance, the spatial shape of the photoelectron wave function with b(2)-symmetry closely resembles that of 5b(2)(∗) unoccupied molecular orbital of NO(2), although the MF-PAD pattern for b(2)-symmetry does not correspond directly to the 5b(2)(∗) orbital shape. At higher kinetic energy of 90 eV, MF-PADs become less structured, but still show a significant dependence on the symmetry of final states.

Electronic structure of self‐assembled Sm nanostructure on HOPG studied by in‐situ photoemission spectroscopy and scanning probe microscopy

AbstractIn‐situ photoemission spectroscopy of Sm over‐layer on HOPG in the coverage regime of 0.3∼10.0 Å has been performed at room temperature in the 4d–4f resonance energy region by using monochromatic synchrotron radiation light. Based on analysis of the spectra taken at hν = 134 eV (close to divalent samarium resonance), it is indicated that the divalent feature predominates the valence band spectra for the coverage below than 1.0 Å, while the trivalent structures are enhanced for Sm over‐layer coverage higher than the 1.0 Å. However, in the case of valence band spectra are excited with the photon of energy of 141 eV at trivalent samarium resonance, the trivalent feature dominates the spectra across over the 0.6∼10.0 Å coverage of Sm over‐layer. The mixed valence in the present Sm over‐layer system might be heterogeneous in nature. Our first result indicates that the VUV irradiation of Sm makes an important role for stimulating the degeneration of divalent multi‐configuration during the vacuum ultraviolet photoemission spectroscopy. Copyright © 2010 John Wiley & Sons, Ltd.

Running sums for2νββ-decay matrix elements within the quasiparticle random-phase approximation with account for deformation

The $2\nu\beta\beta$-decay running sums for $^{76}$Ge and $^{150}$Nd nuclei are calculated within a QRPA approach with account for deformation. A realistic nucleon-nucleon residual interaction based on the Brueckner G matrix (for the Bonn CD force) is used. The influence of different model parameters on the functional behavior of the running sums is studied. It is found that the parameter $g_{pp}$ renormalizing the G matrix in the QRPA particle-particle channel is responsible for a qualitative change in behavior of the running sums at higher excitation energies. For realistic values of $g_{pp}$ a significant negative contribution to the total $2\nu\beta\beta$-decay matrix element is found to come from the energy region of the giant Gamow-Teller resonance. This behavior agrees with the results of other authors.

Band structures of CeRu2(Si1−xGex)2 studied by resonant soft X‐ray ARPES

AbstractAngle‐resolved photoelectron spectroscopy (ARPES) measurements were made in the Ce $3d \to 4f$ resonance energy region for the paramagnetic state of CeRu2Si2, CeRu2(Si0.82Ge0.18)2, and LaRu2Si2 to investigate a variation of band structures around the quantum critical point (QCP). The observed band structures are very similar between CeRu2Si2 and CeRu2(Si0.82Ge0.18)2. The results indicate that the Ce 4f electrons in the paramagnetic state have an itinerant character and participate in the formation of energy bands both in CeRu2Si2 and CeRu2(Si0.82Ge0.18)2, and the change of the band structures in the paramagnetic states should be continuous around the QCP of the CeRu2(Si1−xGex)2 system.

Bremsstrahlung target for studying photonuclear reactions in the giant dipole resonance energy region

Studying the interaction mechanism between gamma-quanta and atomic nuclei in the giant dipole resonance energy region gives us significant information about atomic nuclei. A large number of experiments for studying giant dipole resonance structure were accomplished using bremsstrahlung gamma-quanta. In such experiments cross sections of interactions are retrieved from reaction yields. To retrieve cross sections one needs to know the shape of the bremsstrahlung spectrum and to choose the optimal characteristics of the bremsstrahlung target. The purpose of this article is to choose the optimal characteristics of the bremsstrahlung target for experiments in the energy region E < 30 MeV. The analysis that was carried out based on numerical simulation showed that the optimal bremsstrahlung target consists of two parts. The first part is a tungsten plate 2.5 mm thick. The second part is aluminum plate 3 cm thick.

Photoionization of the Ce3+@C60

Photoionization of the Ce3+@C60 has been studied using our recently developed model potential for the C60 [1] and the random phase approximation with exchange (RPAE) method [2]. The results demonstrate the new resonance peak near the threshold energy region and a great suppression effect of the carbon cage in the energy region of the giant resonance.

Pygmy dipole resonance in nuclei

A brief survey of the state of the modern microscopic theory of the so-called pygmy dipole resonance in nuclei is given—in particular, some unresolved problems are listed. It is emphasized that, in order to explain the pygmy dipole resonance, it is necessary but not sufficient to take into account the coupling of single-particle degrees of freedom to photon degrees of freedom. The results of the calculations performed for the first time for the isovector pygmy dipole resonance and the isovector electric giant dipole resonance in 124Sn within a self-consistent approach involving, in addition to the standard quasiparticle random-phase approximation, a single-particle continuum and quasiparticle-phonon coupling of single-particle degrees of freedom to phonon degrees of freedom are presented. The results are found to be in satisfactory agreement with experimental data. The calculation of the isoscalar strength function in the energy region of the pygmy dipole resonance revealed that the nuclear-structure mechanism does not provide the isoscalar-strength suppression observed at energies in excess of 7 MeV in (α, α′γ) reactions; therefore, this suppression may stem from the reaction mechanism.

Calculation of resonances in the H+H2 reaction using the faddeev-AGS method

The H+H2 reactive collision is described quantum mechanically in terms of valence–bond electronic states and the Faddeev–AGS equations for three-body collisions. The permutational symmetry of identical nuclei is considered within the present approach, which appears to avoid some of the difficulties associated with the use of electronically adiabatic states. A procedure based on the eigenvalue analysis of the K-matrix is used to locate resonances. Calculations probing the energy region of the lowest resonance in the H3 system revealed one with an energy in good agreement with previous work.

Measurement and Analysis of Reactivity Worth of 237Np Sample in Cores of TCA and FCA

The reactivity worth of 22.87 grams of 237Np oxide sample was measured and analyzed in seven uranium cores in the Tank-Type Critical Assembly (TCA) and two uranium cores in the Fast Critical Assembly (FCA) at the Japan Atomic Energy Agency. The TCA cores provided a systematic variation in the neutron spectrum between the thermal and resonance energy regions. The FCA cores, XXI and XXV, provided a hard neutron spectrum of the fast reactor and a soft one of the resonance energy region, respectively. Analyses were carried out using the JENDL-3.3 nuclear data library with a Monte Carlo method for the TCA cores and a deterministic method for the FCA cores. The ratios of calculated to experimental (C/E) reactivity worth were between 0.97 and 0.91, and showed no apparent dependence on the neutron spectrum.