Threshold effects in nuclear reactions

We explore the idea that between the colliding particles or the reaction products of a nuclear reaction the interaction in the immediate neighbourhood of the nuclear surface may be represented by a static attractive potential. The Wigner-Eisenbud theory of nuclear reactions is readily reformulated to take this ‘surface potential’ into account, whereupon quasi-bound states of the compound system are found to appear, with high probability, very close to the various thresholds for two-particle channels. Consequently, the cross section of a reaction close to any threshold should have a certain resonance-like behaviour. The relevant experimental data are reviewed and are found to support all the predictions of the theory.     

Neutron activation cross section data library

To satisfy the requirements of nuclear reaction cross sections in nuclear engineering applications and nuclear physics studies, the Neutron Activation Cross Section Data Library has been established. 818 target nuclei including unstable target or isomeric target nuclei are considered in this library. The induced neutron energy range region is between 10^-5 eV and 20 MeV. The standard ENDF-6 format is adopted, including general information, reaction cross sections, multiplicities, and so on. The recommended reaction cross sections were obtained using UNF code system and FDRR nuclear model codes or systematic analysis based on available experimental data. The full evaluated dataset containing the evaluated activation cross sections is openly available at http://doi.org/10.57760/sciencedb.j00113.00024.     

Analysis of evaluated nuclear structure data

General analysis of the consistency of nuclear data and verification of the optimal values of excited state energies, presented in the evaluated nuclear structure data file (ENSDF) (October 2005) have been performed. As optimality criteria, we chose the Pearson and Romanovsky criteria. As a result, along with finding some misprints, it was revealed that the level energies are not optimal for a large number of the ADOPTED LEVELS, GAMMAS sets included in the ENSDF. The use of the standard GTOL program (7.1a version), which calculates the optimal values of the nuclear level energies from the energies of the transitions positioned in a scheme, made it possible to significantly improve the statistical consistency of the schemes.     

The effect of uncertainties in nuclear decay data on coincidence summing calculations for gamma-ray spectrometry

All nuclear decay data have uncertainties. It is not obvious how these uncertainties affect the detection efficiencies in gamma-ray spectrometry performed with HPGe detectors and in close geometry with cascading gamma-rays. This paper presents examples based on Monte Carlo simulations. It shows that for certain cases the uncertainty in the detection efficiency can be significantly greater than the uncertainty of the nuclear decay. This should thus be taken into account when performing a complete uncertainty budget for close geometry measurements.     

Relaxation of polarized nuclei in superconducting rhodium

Nuclear spin lattice relaxation rates were measured in normal and superconducting (sc) rhodium with nuclear polarizations up to p = 0. 55. This was sufficient to influence the sc state of Rh, whose T(c) and B(c) are exceptionally low. Because B(c)相似文献   

Nuclear Level Density at High Spin and Excitation Energy

The intensive studies of equilibrium processes in heavy-ion reaction have produced a need for information on nuclear level densities at high energies and spins. The Fermi gas level density is often used in investigation of heavy-ion reaction studies. Some papers have claimed that nuclear level densities might deviate substantially from the Fermi gas predications at excitations related to heavy-ion reactions. The formulae of calculation of the nuclear level density based on the theory of superconductivity are presented, special attention is paid to the dependence of the level density on the angular momentum. The spin-dependent nuclear level density is evaluated using the pairing interaction. The resulting level density for an average spin of 52 ħ is evaluated for ¹⁵⁵Er and compared with experimental data. Excellent agreement between experiment and theory is obtained.     

Indirect interaction of solid-state qubits via two-dimensional electron gas

We propose a mechanism of long-range coherent coupling between nuclear spin qubits in semiconductor-heterojunction quantum information processing devices. The coupling is via localized donor electrons which interact with the two-dimensional electron gas. An effective interaction Hamiltonian is derived and the coupling strength is evaluated. We also discuss mechanisms of decoherence and consider gate control of the interaction between qubits. The resulting quantum computing scheme retains all the control and measurement aspects of earlier approaches, but allows qubit spacing at distances of the order of 100 nm, attainable with the present-day semiconductor device technologies.     

Microscopic approach to the antiproton-nucleus optical potential

By using the self-energy of an antiproton evaluated in nuclear matter, the antiproton effective interaction with a bound nucleon is derived and is found to have a drastic density dependence. The p?-nucleus optical potential constructed by folding the effective interaction well reproduces experimental data on the p?-nucleus absorption cross section as well as on the complex level shift of p?-atoms. In addition, it is pointed out that the strong spin-orbit interaction spreads each doublet and considerably affects the lower complex level shift.     

Proximity forces

We have generalized a theorem according to which the force between two gently curved objects in close proximity is proportional to the interaction potential per unit area between two flat surfaces made of the same material, the constant of proportionality being a measure of the mean curvature of the two objects. This theorem leads to a formula for the interaction pontential between curved objects (e.g., two smooth cylinders of mica or two atomic nuclei) which is a product of a simple geometrical factor and a universal function of separation, characteristic of the material of which the objects are made, and intimately related to the surface energy coefficient. We have calculated and tabulated this universal function for nuclear surfaces, using the nuclear Thomas-Fermi approximation. The results can be expressed by a simple cubic-exponential formula which gives the potential between any two nuclei in the separation degree of freedom. Even simpler expressions are found for the interaction energy associated with the “crevice” or neck in the nuclear configuration that would be expected immediately after contact of two nuclei. These “proximity energies” are used to supplement the usual expansion of the energy of a thin-skinned system into volume, surface, curvature, and higher-order terms. The resulting elementary formulas are tested against explicit models of interacting nuclei and against elastic scattering data, and are found to be useful for even quite small mass numbers.     

A simple explanation of correlation data in inclusive pp interactions at high energy

The existing integral and differential data for two-particle correlations between negative pions produced in high-energy pp collisions are discussed. They are shown to be explained in a simple wayby adopting the Feynmann-Wilson two-component picture. The diffractive part of distribution, which appears to be small, is evaluated from experimental data. For the non-diffractive interaction the conservation laws are assumed to play the dominant role in correlation effects.     

Heavy-ion fusion: Comparison of experimental data with classical trajectory models

Currently available data on fusion excitation functions for heavy-ion induced reactions over a wide mass range are compared to results calculated with a classical dynamical model based on the proximity nuclear potential of Blocki et al., the Coulomb potential of Bondorf et al., and one-body nuclear friction in the proximity formalism of Randrup. With these conservative and dissipative forces and the radial parameters of Myers, overall good agreement is obtained between the theoretical excitation functions and most of the available data. Extensive calculations have been performed to test the sensitivity of the calculated fusion cross-sections to a number of parameters, including the radial dependence of the Coulomb and nuclear potentials, the radial and tangential friction form factors as well as the projectile and target radii. The theoretical excitation functions for the lighter heavy-ion systems are rather insensitive to changes in either the conservative or dissipative forces. The calculations show that tangential friction sufficient to produce the rolling condition is necessary to explain the magnitude of the fusion cross-sections at high energies, which are also sensitive to the magnitude of the radial friction component. This is in contrast to the fusion cross-sections at low energies which are determined by the nuclear potential at larger separations, and to a lesser extent by tangential friction. The low energy fusion data are most sensitive to the nuclear radii. The calculations reveal the importance of more experimental measurements of fusion cross-sections at high energies, especially for heavy systems where the magnitudes of the fusion cross-sections are the most sensitive to the assumed forces. However, even for these cases the effects of the conservative and dissipative forces are similar and difficult to separate. These studies indicate, however, that it is possible to construct a conservative potential that will give calculated fusion excitation functions which are in good agreement with all experimental data over the entire mass range. The maximum fusion cross-sections as defined here exceed considerably the liquid-drop limiting value for heavy systems.     

Modeling complex networks of nuclear reaction data for probing their discovery processes

Hundreds of thousands of experimental data sets of nuclear reactions have been systematically collected, and their number is still growing rapidly. The data and their correlations compose a complex system, which underpins nuclear science and technology. We model the nuclear reaction data as weighted evolving networks for the purpose of data verification and validation. The networks are employed to study the growing cross-section data of a neutron induced threshold reaction (n,2n) and photoneutron reaction. In the networks, the nodes are the historical data, and the weights of the links are the relative deviation between the data points. It is found that the networks exhibit small-world behavior, and their discovery processes are well described by the Heaps law. What makes the networks novel is the mapping relation between the network properties and the salient features of the database: the Heaps exponent corresponds to the exploration efficiency of the specific data set, the distribution of the edge-weights corresponds to the global uncertainty of the data set, and the mean node weight corresponds to the uncertainty of the individual data point. This new perspective to understand the database will be helpful for nuclear data analysis and compilation.     

Pairing in exotic and in stable nuclei

The exchange of low-lying collective vibrations between pairs of nucleons moving in time reversal states close to the Fermi energy provides a conspicuous contribution to the nuclear pairing interaction, which accounts for 30-50% of the pairing gap in the case of nuclei along the stability valley, and to essentially all of the pairing correlations of the most loosely bound nucleons in the case of halo nuclei.Received: 30 October 2002, Published online: 23 March 2004PACS: 21.30.Fe Forces in hadronic systems and effective interactions - 21.60.Jz Hartree-Fock and random-phase approximations     

Intercombination transitions of the carbon-like isoelectronic sequence

Energy levels, wavelengths, transition rates, oscillator strengths, and lifetimes between the 2s22p23P1,2s22p23P2,and 2s2p35S2 levels of ions in the carbon-like (C-like) isoelectronic sequence (nuclear charges Z=7-92) are calculated in the valence and core-valence limits using the multiconfiguration Dirac-Fock method. The Breit interaction, quantum electrodynamics (QED), and finite nuclear mass effects are taken into account in subsequent relativistic configuration-interaction calculations. The calculated energies and transition rates are compared with the critically evaluated experimental values and other recent calculated results. Our calculated data are in good agreement with these data.     

Non-empirical pairing energy density functional

We perform systematic calculations of pairing gaps in semi-magic nuclei across the nuclear chart using the Energy Density Functional method and a non-empirical pairing functional derived, without further approximation, at lowest order in the two-nucleon vacuum interaction, including the Coulomb force. The correlated single-particle motion is accounted for by the SLy4 semi-empirical functional. Rather unexpectedly, both neutron and proton pairing gaps thus generated are systematically close to experimental data. Such a result further suggests that missing effects, i.e. higher partial waves of the NN interaction, the NNN interaction and the coupling to collective fluctuations, provide an overall contribution that is sub-leading as for generating pairing gaps in nuclei. We find that including the Coulomb interaction is essential as it reduces proton pairing gaps by up to 40%.     

核数据研究及应用的进展与展望

核数据包括核反应数据与核结构及放射性衰变数据。核反应数据是描述入射粒子与原子核发生相互作用的数据，核结构数据是反映核素自身基本性质方面的数据。核数据是核能利用、核工程建设、核技术应用以及核物理基础研究等方面不可缺少的基础数据，在核医学、材料分析、资源勘探、环境监测、宇航技术以及核天体物理研究领域也有着广泛的应用。本文简要介绍了核数据的种类、产生及应用，评述了国际核数据研究与应用现状以及发展动态、我国核数据研究现状及存在的问题，并对我国核数据工作未来发展方向提出了几点建议。     

Constraining Isovector Nuclear Interactions with Giant Dipole Resonance and Neutron Skin in ~(208)Pb from a Bayesian Approach

The remaining uncertainties in relation to isovector nuclear interactions call for reliable experimental measurements of isovector probes in finite nuclei.Based on the Bayesian analysis,although neutron-skin thickness data or isovector giant dipole resonance data in ~(208)Pb can constrain only one isovector interaction parameter,correlations among other parameters can also be built.Using combined data for both the neutron-skin thickness and the isovector giant dipole resonance helps to significantly constrain all isovector interaction parameters;as such,it serves as a useful methodology for future research.     

An optical potential for heavy ion interactions

An optical potential for nucleus-nucleus interactions is evaluated using a density-dependent effective two body force. The resulting interaction potential is then used to discuss elastic scattering cross sections using a quarter-point recipe from Fresnel diffraction theory. Fits to quarter points of cross sectional data are obtained with parameters for the effective interaction which fit properties of nuclear matter and with parameters for target and projectile densities obtained from electron scattering.     

A semi-empirical correlation energy for nuclei

A semi-empirical interaction is used to calculate higher order corrections to the binding energies of even—even nuclei close to the line of stability. These corrections are taken to come from two phonon configurations and are treated as a perturbation with respect to the BCS nuclear ground state which is obtained from applying the energy density method to finite nuclei. The overall correspondence between theory and experiment for the 60 nuclei calculated between A =52 and A =234 is good, with excellent agreement for the non-deformed nuclei situated within the regions A = 72 to 144 and A = 200 to 212. The large correction enegies (several MeV per nucleus on the average) indicate that these correlations are of importance for explaining nuclear binding energies and that it is necessary to include them within energy functional itself. The fact that these correlations come almost exclusively from nucleons close to the fermi surface is also discussed.