Coherent investigation of nuclear data at CEA DAM: Theoretical models, experiments and evaluated data

The domain of evaluated nuclear data involves at the same time, a close interaction between the field of nuclear applications and that of nuclear physics, and a close interaction between experiments and theory. The final product, the evaluated data file, synthesises vast amounts of information stemming from all of the above fields. In CEA DAM, all these aspects of nuclear data are investigated in a consistent way, making full use of experimental facilities and high-performance computing as well as numerous national and international collaborations, for the measurement, calculation, evaluation, and validation of nuclear data.     

Status of current nuclear structure data bases for gamma-ray laser applications

A search of two nuclear structure data bases, CDRL82 and ENSDF, was undertaken in order to identify nuclei attractive for gamma-ray laser applications. Level pairs for 32 such candidate nuclei were determined that had properties (spacings, half-lives) attractive for possible gamma-ray laser use. However, many of these pairs suffer from details (for example, required spin transfers) that may take their use difficult in actual laser concepts. To complicate the problem, present data bases are deficient in the formation needed to identify additional, more promising candidates. Nuclear model calculations are suggested as a way to remedy such deficiencies in the near term. Examples from nuclear structure analyses are provided that impact consideration of current nuclear candidates or that may help identify new ones.     

Neutron-deuteron scattering calculation for evaluated neutron data libraries

In the low-energy regime, differential cross sections for n + d elastic scattering are not well described in existing nuclear data libraries, such as ENDF/B-VII.0. Supporting experimental data in this energy region are old, sparse and often inconsistent. We have carried out calculations with the AGS three-body theory and the Bonn-B nucleon-nucleon potential at energies 50?keV to 10.0?MeV.     

Accuracy of the chemical data evaluated from one-atom-at-a-time experiments

Studies of chemistry of the transactinoid elements, which are available only as single atoms, by gas (thermo)chromatographic techniques can provide the adsorption enthalpies of the atoms or molecules. These values serve the ultimate goal—to characterize bulk volatility of the species in terms like sublimation enthalpies. The paper attempts an in-depth discussion of the statistical significance of the adsorption enthalpies derived in such experiments. Usually, the counting statistics are very poor and one faces nonstandard problems in evaluating the confidence intervals for the values of parameters. Here, a most efficient way seems to be the Bayesian approach, realized, when necessary, by Monte Carlo simulations of the counting results. Necessarily, the adsorption enthalpy is not evaluated based on the second law of thermodynamics but through accepting an a priori value of the adsorption entropy. More additional assumptions about the mechanisms and parameters involved are needed. This may produce systematic errors in the quantitative conclusions; the analysis of some recent works with elements 106 and 108 corroborates this concern. Despite such problems, it is possible to reveal qualitative differences in the adsorption behavior of a transactinoid and its expected known congeners as well as to use chemistry for an independent assignment of the atomic numbers of transactinoid nuclides.     

Extremes of nuclear structure

With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these exotic nuclei and some of their expected properties will also be touched upon.     

New data on nuclear subshells obtained from the analysis of the information from the international database on nuclear structure ENSDF

In the last decade, a large amount of experimental nuclear spectroscopy data was obtained. This is good progress really, but a new very serious problem appears. Due to significant systematic errors of the data, one is often forced to deal with very discrepant data and often it is difficult to obtain reliable information from them. To solve this problem and to remove the systematic errors, new technologies in working with the data were developed. Using these new technologies, one can obtain information with a high accuracy and reliability, and in many cases, new information has not been or could not be obtained experimentally. Below, an approach of this kind is presented concerning spectroscopic data on Ca and Zr isotopes. It is shown that the behavior of the energy of the first 2⁺ level in Zr isotopes can be explained in the framework of a shell-model approach. A separation of the 2d_5/2 subshell in ⁹⁶Zr (as is for the 1f_7/2 subshell in ⁴⁸Ca) is found, so that the neutron number N=56 becomes like a magic number for Z=40. To explain a similarity in decaying properties of ⁴⁸Ca and ⁹⁶Zr, an additional interaction between closed structures consisting of 20 and 28 nucleons is proposed. Irregularities of the ground-state spin values in the K isotopic chain are explained in the framework of the shell-model approach by the inversion of the proton 1d_3/2 and 2s_1/2 orbitals.     

基于随机抽样法的多群核数据不确定性影响分析

基于随机抽样方法,研究多群核数据不确定性对反应堆物理计算的影响。首先利用SCALE软件包中核数据协方差矩阵和自主开发的随机抽样模块SAMP,得到多群微观截面等核数据的抽样值,之后分别使用SCALE/TRITON和PARCS程序进行组件计算及堆芯稳态计算,最后通过统计分析得到组件和堆芯计算结果的不确定度。以Almaraz压水堆核电厂装载的燃料组件和首循环堆芯为对象,研究了不同燃耗下有效增殖因子、动力学参数、核素浓度和双群均匀化宏观截面等组件计算结果,以及堆芯功率分布等堆芯计算结果的不确定度。分析结果表明：组件计算结果不确定度多随燃耗变化,快群宏观截面不确定度总体高于热群;堆芯计算结果受核数据不确定性影响显著,其中稳态径向功率分布的最大不确定度为1.9%左右。     

基于随机抽样法的多群核数据不确定性影响分析

基于随机抽样方法,研究多群核数据不确定性对反应堆物理计算的影响。首先利用SCALE软件包中核数据协方差矩阵和自主开发的随机抽样模块SAMP,得到多群微观截面等核数据的抽样值,之后分别使用SCALE/TRITON和PARCS程序进行组件计算及堆芯稳态计算,最后通过统计分析得到组件和堆芯计算结果的不确定度。以Almaraz压水堆核电厂装载的燃料组件和首循环堆芯为对象,研究了不同燃耗下有效增殖因子、动力学参数、核素浓度和双群均匀化宏观截面等组件计算结果,以及堆芯功率分布等堆芯计算结果的不确定度。分析结果表明:组件计算结果不确定度多随燃耗变化,快群宏观截面不确定度总体高于热群;堆芯计算结果受核数据不确定性影响显著,其中稳态径向功率分布的最大不确定度为1.9%左右。     

The effect of conventional nuclear binding on nuclear structure functions

We show that Fermi motion (including the effect of nucleon binding energy), together with a simple ansatz for the dependence of the nucleon structure function on its invariant mass, can explain the major features of recent nuclear structure function data. The close relationship of this work to the earlier explanations of the EMC effect based on an enhancement of the virtual pion field of the nucleus is discussed.     

Oblate-prolate effects in nuclear structure and in nuclear reactions

We show that the nuclear structure wavefunctions emerging from Faessler and Greiner's rotation-vibration coupling theory are oblate-prolate sensitive. This oblate-prolate sensitivity can be tested experimentally by means of suitably selected nuclear reaction experiments. As a specific case, we demonstrate oblate-prolate effects in α-particle scattering at 104 MeV from ²⁶Mg.     

Nuclear orientation and nuclear structure

The purpose of this paper is to demonstrate how recent experimental results of¹⁵¹Eu and⁵⁷Fe high pressure Mössbauer studies in 4f and 3d metallic magnetic systems can contribute to a deeper understanding of the nature of local moment (4f) and itinerant (3d) magnetism in these systems. Special emphasis is given on the comparison of the experimental results with related theoretical models.     

Antiprotons for nuclear structure research

The interaction of antiprotons with nuclei is investigated in a model using the free space $\overline{p} N$ T-matrix and nuclear densities from HFB calculations. Elastic scattering and annihilation reactions are used as probes for nuclear sizes of exotic nuclei. The annihilation cross sections are related to the nuclear root-mean-square radii by a scaling law. A more detailed picture is obtained by detecting in coincidence a pion ejected from the annihilation zone.     

Nuclear moments and nuclear structure

Research activities of the Osaka Sugimoto group in the past 30 years are summarized. Developments of the perturbed angular correlation method and the new NMR method under the leadership of Sugimoto opened a wide variety of possibilities, not only in the nuclear structure study but also in studies of nuclear reactions, weak interactions and hyperfine interactions.