Dynamic nuclear polarization and nuclear orientation in an antiferromagnet

Dynamic nuclear polarization is a well established technique which has been used to produce polarized targets for experiments in nuclear physics. This paper suggests experiments of a similar type but involving the nuclear magnetic resonance of two isotopes, one stable and the other radioactive. The substance is an antiferromagnet, dysprosium phosphate, at temperatures below the Néel point, where line widths are comparatively small. The effect may be detected through changes in the rate of gamma ray emission observed by a nuclear orientation experiment.     

Dynamic nuclear polarisation in metallic silver

Dynamic nuclear polarisation is a well established technique, which has been used to produce polarised targets for experiments in nuclear physics. This paper suggests that the nuclei spins in metallic silver may be polarised by inclusion of erbium as a small impurity with an electronic spin.     

关于原子核电荷半径的研究

结合原子核电荷半径实验数据, 对885个中子数N≥8和质子数Z≥8的核电荷半径做了系统的研究. 对于单参数核电荷半径公式, Z^1/3律公式计算的结果优于A^1/3律的结果, 而对于两参数和三参数公式, Z^1/3律和A^1/3律的结果基本相当. 考虑到壳效应及奇偶摆动现象, 在原有的三参数公式基础上提出了加入Casten因子项和δ项的核电荷半径新公式. 利用该公式计算得到的核电荷半径理论值和实验值符合得非常好, 均方根偏差仅为σ=0.0266 fm, 此值比常用的三参数公式的结果下降了近50%, 理论计算值能更好地反映出壳效应及核电荷半径奇偶摆动的变化趋势.     

Direct photons,dimuons and nuclear effects

Largep _T direct photon and dimuon production in experiments using nuclear targets have been studied in detail. We show that, by a careful choice of kinematic configurations in these experiments, very good estimates of nuclear quark and gluon densities can be obtained. Information on the cumulative region of the nuclear structure functions i.e. the regionx>1 can also be obtained by considering semi-integrated cross sections.     

J/ψ production as a probe of charge symmetry violations and nuclear corrections in parton distributions

We investigate the sensitivity of J/Ψ production in proton-neutron and proton-deuteron collisions to charge symmetry violations in the parton distributions as well as to nuclear corrections. It is found that the effects of charge symmetry violations in the quark distributions are confined to large x _F and difficult to measure in experiments currently being planned. However, from proton-deuteron experiments it should be possible to isolate nuclear corrections to the gluon distribution.     

The case of RIB at intermediate energies: Isospin effects on nuclear dynamics

In the reaction dynamics of intermediate-energy radioactive beams we can probe highly asymmetric nuclear matter in compressed as well as dilute phases. In this report some predictions are presented, based on analytical results as well as on reaction simulations. We suggest a series of experiments with RIB aimed to shed light on isospin properties of nuclear interactions in the medium. Received: 1 May 2001 / Accepted: 4 December 2001     

The impact of nuclear magnetism on superconductivity

The influence of nuclear magnetism on the superconducting critical field B_c has been measured in the nuclear magnets Al, AuIn₂, and Sn, at ultralow temperatures, 17 μKT1 K. The materials have been chosen in respect to their distinctive Korringa constants κ(Al, AuIn₂, Sn)=(1.8, 0.1, 0.05) Ks. Both in the weakly and in the strongly coupled nuclear magnets, Al and Sn, a reduction of B_c is observed being proportional to the nuclear magnetization at T4 mK. However, using the high resolution of the experiment performed on Sn, the decrease of B_c at cooling down to 70 μK is found to be nonmonotonic. The features of the recently measured B_c(T) curve of Sn which are not understood yet as well as the formerly observed results of the interplay of nuclear ferromagnetism and superconductivity in AuIn₂ have motivated ongoing experiments which try to clear up the pair breaking contribution of nuclear magnetism.     

Extending and refining the nuclear mass surface with ISOLTRAP and MISTRAL

Through the nuclear binding energy, the atomic mass gives us important information about nuclear structure. Viewing the ensemble of mass data over the nuclear chart, we can examine the hills and valleys that form this surface and make hypotheses about the effects of certain nuclear configurations. To unveil these effects, mass measurements of very high precision (<10⁻⁶) are required. Two experiments at ISOLDE pursue this effort of nuclear cartography: the tandem Penning trap spectrometer ISOLTRAP and the radiofrequency transmission spectrometer MISTRAL. Between them, the masses of almost 150 nuclides have been measured from stable isotopes to those with half-lives as short as 30 ms. Both experiments rely on good optical properties of a low energy ion beam and are thus well suited to the ISOLDE facility. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-body correlations in nuclear systems

Correlations in the nuclear wave-function beyond the mean-field or Hartree-Fock approximation are very important to describe basic properties of nuclear structure. Various approaches to account for such correlations are described and compared to each other. This includes the holeline expansion, the coupled cluster or “exponential S” approach, the self-consistent evaluation of Greens functions, variational approaches using correlated basis functions and recent developments employing quantum Monte-Carlo techniques. Details of these correlations are explored and their sensitivity to the underlying nucleon-nucleon interaction. Special attention is paid to the attempts to investigate these correlations in exclusive nucleon knock-out experiments induced by electron scattering. Another important issue of nuclear structure physics is the role of relativistic effects as contained in phenomenological mean field models. The sensitivity of various nuclear structure observables on these relativistic features are investigated. The report includes the discussion of nuclear matter as well as finite nuclei.     

Cold nuclear fusion

Recent accelerator experiments on fusion of various elements have clearly demonstrated that the effective cross-sections of these reactions depend on what material the target particle is placed in. In these experiments, there was a significant increase in the probability of interaction when target nuclei are imbedded in a conducting crystal or are a part of it. These experiments open a new perspective on the problem of so-called cold nuclear fusion.     

Application of microscopic transport model in the study of nuclear equation of state from heavy ion collisions at intermediate energies

The equation of state (EOS) of nuclear matter, i.e., the thermodynamic relationship between the binding energy per nucleon, temperature, density, as well as the isospin asymmetry, has been a hot topic in nuclear physics and astrophysics for a long time. The knowledge of the nuclear EOS is essential for studying the properties of nuclei, the structure of neutron stars, the dynamics of heavy ion collision (HIC), as well as neutron star mergers. HIC offers a unique way to create nuclear matter with high density and isospin asymmetry in terrestrial laboratory, but the formed dense nuclear matter exists only for a very short period, one cannot measure the nuclear EOS directly in experiments. Practically, transport models which often incorporate phenomenological potentials as an input are utilized to deduce the EOS from the comparison with the observables measured in laboratory. The ultrarelativistic quantum molecular dynamics (UrQMD) model has been widely employed for investigating HIC from the Fermi energy (40 MeV per nucleon) up to the CERN Large Hadron Collider energies (TeV). With further improvement in the nuclear mean-field potential term, the collision term, and the cluster recognition term of the UrQMD model, the newly measured collective flow and nuclear stopping data of light charged particles by the FOPI Collaboration can be reproduced. In this article we highlight our recent results on the studies of the nuclear EOS and the nuclear symmetry energy with the UrQMD model. New opportunities and challenges in the extraction of the nuclear EOS from transport models and HIC experiments are discussed.     

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.     

锕系核靶制备与应用北大核心CSCD

基础核物理、核能开发、超重元素研制等领域对精确、值得信赖的核参数的需求日益增大,锕系核靶作为核数据测量实验的核心部件,其产品种类及关键质量参数的优劣直接制约核数据测量的发展水平。系统介绍了国内外锕系核靶制备及检测方法以及国内外核靶研究团队技术储备及发展方向。     

Generating entanglement and squeezed states of nuclear spins in quantum dots

We present a scheme for achieving coherent spin squeezing of nuclear spin states in semiconductor quantum dots. The nuclear polarization dependence of the electron spin resonance generates a unitary evolution that drives nuclear spins into a collective entangled state. The polarization dependence of the resonance generates an area-preserving, twisting dynamics that squeezes and stretches the nuclear spin Wigner distribution without the need for nuclear spin flips. Our estimates of squeezing times indicate that the entanglement threshold can be reached in current experiments.     

Magnetic structure determined by nuclear orientation

Conclusion In conclusion we suggest that nuclear orientation is a useful technique for determining nuclear spin structures. For a known hyperfine interaction atomic magnetic structures may also be deduced. Measurements on antiferromagnets and the rare earth magnet holmium demonstrate the method, although in the latter case the turn angle cannot be determined because of the limitation of L2 radiation. These experiments show that nuclear orientation can at least complement neutron diffraction and at best furnish information about magnetic structure when the latter technique is not applicable. We intend to study other rare earth magnets and more complicated antiferromagnetic structures.     

Experimental studies of the gamma resonances of long-lived nuclear isomers

Studying the gamma resonances of the long-lived nuclear isomers started at ITEP in the 1960s–1970s. The first experiments were conducted with silver isotopes. Its results did not contradict the existing theoretical ideas of large broadening of Mössbauer gamma lines via the interactions of nuclear magnetic moments. However, the data obtained in 11 experiments performed up until now with gamma sources made of silver metal doping by ¹⁰⁹Cd showed that there is no large broadening of ^109mAg Mössbauer gamma line with energy of 88.03 keV, that is the theoretically predicted gamma line broadening by ～10⁵ times is absent. The instrument of quite a new type—“gravitational gamma spectrometer”, designed at ITEP, allowed one to determine the form of ^109mAg gamma resonance, which proved to be ～10⁸ times narrower than that of well known nuclide ⁵⁷Fe. Some ideas are discussed as an attempt to explain this situation.     

Nucleon mean free path in nuclear matter

In calculations of nuclear reaction yields at incident energies of some tens of MeV consistently better agreement with experiments is obtained by assuming a nucleon mean free path in nuclear matter longer than that deduced from the Fermi gas model and free nucleon-nucleon cross sections.     

Surface physics with nuclear probes

A series of typical experiments using nuclear moments as microscopic probes for hyperfine fields on surfaces are discussed: Mössbauer spectroscopy, perturbed angular correlation studies, nuclear magnetic resonance, nuclear spin relaxation due to spin-lattice relaxation, and low-dimensional diffusion. Experiments are selected which deal mainly with well-characterized surfaces. Out of a wealth of data, particularly those that contribute to currently discussed topics in surface science are selected.Supported partly by the Bundesministerium für Forschung und Technologie (contract 06 MR 853 I) and the Deutsche Forschungsgemeinschaft (contract Fi 311-1 and Fi 311-1)