Neutrinoless double beta decay

The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given.     

Superheavies and beyond

The extension of the periodic system into various new areas is investigated. Experiments for the synthesis of superheavy elements and the predictions of magic numbers are reviewed. Different ways of nuclear decay are discussed like cluster radioactivity, cold fission and cold multifragmentation. Further on, investigations on hypernuclei and the possible production of antimatter-clusters in heavy-ion collisions are reported. Various versions of the meson-field theory serve as effective field theories at the basis of modern nuclear structure and suggest structure in the vacuum which might be important for the production of hyper- and antimatter. A perspective for future research is given.     

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.     

Calculation of decay half-lives for superheavy elements using the double folding model

α decay half-lives of some new synthesized superheavy elements, possibly synthesized superheavy elements and decay products are calculated theoretically within the WKB approximation by using microscopic m-nucleus interaction potentials. These nuclear potentials between the α particle and daughter nuclei are obtained by using the double folding integral of the matter density distribution of the α particle and daughter nuclei with a density-dependent effective nucleon-nucleon interaction, in which the zero-range exchange term is supplemented. The calculated α decay half-lives are compared with those of the different models and experimental data. It is shown that the present calculation successfully provides the half-lives of the observed αdecays for some new superheavy elements and therefore gives reliable predictions for α decay of possibly synthesized superheavy elements in future experiments.     

Multiple parton scattering in nuclei: twist-four nuclear matrix elements and off-forward parton distributions

Multiple parton scatterings inside a large nucleus generally involve higher-twist nuclear parton matrix elements. The gluon bremsstrahlung induced by multiple scattering depends not only on direct parton matrix elements but also on momentum-crossed ones, due to the Landau–Pomeranchuk–Migdal interference effect. We show that both types of twist-four nuclear parton matrix elements can be factorized approximately into the product of twist-two nucleon matrix elements in the limit of extremely large nuclei, A→∞, as assumed in previous studies. Due to the correlative nature of the twist-four matrix elements under consideration, it is actually the off-forward parton distributions that appear naturally in this decomposition, rather than the ordinary diagonal distributions probed in deeply-inelastic scattering. However, we argue that the difference between these two distribution classes is small in certain kinematic regimes. In these regions, the twist-four nuclear parton matrix elements are evaluated numerically and compared to the factorized form for different nuclear sizes within a schematic model of the two-nucleon correlation function. The nuclear size dependence is found to be A^4/3 in the limit of large A, as expected. We find that the factorization is reasonably good when the momentum fraction carried by the gluon field is moderate. The deviation can be more than a factor of 2, however, for small gluon momentum fractions, where the gluon distribution is very large.     

超重原子核与新元素研究

当前,原子核物理研究的一个重要前沿是探索原子核的电荷与质量极限,研究超重原子核与超重元素的性质,以及合成超重原子核。20世纪60年代,基于量子壳效应,理论预言质子数为114、中子数为184的原子核及其相邻核具有较长的寿命,甚至可能是稳定的,形成一个超重稳定岛。这个理论预言促进了重离子加速器及相关探测设备的建造,推动了重离子物理的发展。到目前,已经合成到了118号元素,填满了元素周期表的第7行。然而,合成更重的超重元素或包含更多中子的超重原子核面临着很多挑战,需要理论与实验密切结合,探索超重原子核的性质与合成机制,以登上超重稳定岛。文章概要评述超重原子核与新元素研究。首先介绍超重原子核与超重元素研究的背景及理论预言,包括超重核存在的根源、理论预言的概况等。之后简要给出实验合成超重核取得的主要进展和新元素命名情况。关于合成更重的超重元素面临的挑战,文章将针对利用重离子熔合蒸发反应合成超重核的截面低、所合成的超重核缺中子等情况展开讨论。最后评述近年来超重原子核结构性质、衰变、裂变与合成机制等方面的理论研究进展,包括超重核区的幻数和超重岛的位置,超重核的稳定性,利用重离子熔合蒸发反应合成超重核的三步过程及其复杂性,利用多核子转移合成超重核的探索,等等。The exploration of charge and mass limits of atomic nuclei and the synthesis of long-lived or stable superheavy nuclei (SHN) are at the frontier of modern nuclear physics. In the 1960s, based on the stability originating from quantum shell effects, the possible existence of an island of stability around 298114 was predicted. This prediction advanced the construction of heavy ion accelerators and detectors and the development of heavy ion physics. So far, superheavy elements (SHE) with Z up to 118 have been synthesized via heavy ion fusion reactions in laboratories. Recently the IUPAC/IUPAP Joint Working Party (JWP) concluded that criteria for the discovery of new elements have been met for those with Z=113, 115, 117 and 118. Therefore the seventh period of the periodic table of elements is completed. To synthesize even heavier elements or more neutron-rich SHN by using heavy ion fusion reactions, one confronts many challenges. More efforts should be made to study the properties of SHN both experimentally and theoretically. In this short review on the study on SHN and SHE, we will first introduce the background and theoretical predictions of SHN, including the origin of the possible existence of SHN and the predicted island of stability of SHN, etc. Then we will present progresses made up to now concerning the synthesis of SHN and the naming of the four new elements. As for the challenges nuclear physicists confront in synthesizing even heavier SHEs, we will detail those connected with heavy ion fusion-evaporation reactions, namely, the tiny cross sections to produce SHN and the fact that only neutron-deficient SHNs can be synthesized. Finally we will discuss some theoretical progresses on the study of SHN, including the structure of SHN and proton and neutron magic numbers after 208Pb, the stability and the synthesis mechanism of SHN as well as what we should focus on in the future.     

Nuclear bremsstrahlung as a test of the optical model

Nuclear optical potential matrix elements occur off-the-energy shell in standard nuclear reaction analyses. The usefulness of bremsstrahlung for investigating such matrix elements is examined. Contributions from virtual nuclear excitations are included.     

The Search for Transuranium Elements and the Discovery of Nuclear Fission

The synthesis of new, artificial elements beyond uranium was at the cutting-edge of physical research in the 1930s, and nearly half a dozen transuranium elements were reported between 1934 and 1938. Nuclear physicists and radiochemists collaborated closely, but each field introduced fundamental assumptions that proved to be false: that nuclear changes would always be small, and that transuranium elements would resemble transition elements chemically. With its surprise ending in the discovery of nuclear fission, the misguided transuranium project can be viewed as an example of the illogical progress of scientific discovery. It is also an example of an interdisciplinary collaboration that was flawed yet crucial, for although chemists and physicists both contributed to the delay in discovering fission, their collaboration was essential in leading them to it in the end.     

Nuclear Physics Programs for the Future RIBs Facility in Korea

We present nuclear physics programs based on the planned experiments using rare isotope beams (RIBs) for the future Korean Rare Isotope Beams Accelerator facility(KRIA). This ambitious facility has both an Isotope Separation On Line (ISOL) and fragmentation capability for producing RIBs and accelerating beams of wide range mass of nuclides with energies of a few to hundreds MeV per nucleon. Low energy RIBs at Elab = 5 to 20 MeV per nucleon are for the study of nuclear structure and nuclear astrophysics toward and beyond the drip lines while higher energy RIBs produced by inflight fragmentation with the reaccelerated ions from the ISOL enable to explore the neutron drip lines in intermediate mass regions. The planned programs have goals for investigating internal structures of the exotic nuclei toward and beyond the nucleon drip lines by addressing the following issues: how the shell structure evolves in areas of extreme proton to neutron imbalance; whether the isospin symmetry maintains in isobaric mirror nuclei at and beyond the drip lines; how two-proton radioactivity affects abundances of the elements; what the role of the continuum states including resonant states above protondecay threshold in exotic nuclei is in astrophysical nuclear reaction processes, and how the nuclear reaction rates triggered by unbound proton-rich nuclei make an effect on rapid proton capture processes in a very hot stellar plasma.     

Systematic study of α decay half-lives for even–even nuclei within a deformed two-potential approach

In this work, we systematically study the α decay half-lives of 196 even–even nuclei using a two-potential approach improved by considering nuclear deformation. The results show that the accuracy of this model has been improved after considering nuclear deformation. In addition, we extend this model to predict the α decay half-lives of Z = 118 and 120 isotopes by inputting the α decay energies extracted from the Weizsacker–Skyrme-type (WS-type) mass model, a simple nuclear mass formula, relativistic continuum Hartree–Bogoliubov theory and Duflo-Zuker-19 (DZ19) mass model. It is useful for identifying the new superheavy elements or isotopes for future experiments. Finally, the predicted α decay energies and half-lives of Z = 118 and 120 isotopes are analyzed, and the shell structure of superheavy nuclei is discussed. It shows that the shell effect is obvious at N = 184, while the shell effect at N = 178 depends on the nuclear mass model.     

Trap-assisted studies of odd, neutron-rich isotopes from Tc to Pd

We review the present and future of trap-assisted structure studies of odd, neutron-rich Tc, Ru, Rh and Pd isotopes at the limits of present experimental techniques. These nuclei of refractory elements are produced in light-particle induced fission and filtered by their mass number with the IGISOL mass separator. Further mass separation with the JYFLTRAP Penning trap system provides a clean, monoisotopic beam perfectly suited for precise nuclear spectroscopy. Connecting the IGISOL and the JYFLTRAP facilities to the recently installed MCC30/15 cyclotron opens new prospects for post-trap spectroscopy of very exotic, neutron-rich nuclei.     

The democratic nuclear interaction in relative S states

A simple relative l=0 interaction is obtained by setting all relative matrix elements of a given spin equal to each other. The nuclear matrix elements are nearly equal for this interaction and the standard l=0 interactions such as the Kallio-Koltveit interaction, although the relative matrix elements are quite different.     

How well do we understand the synthesis of heavy elements by heavy-ion induced fusion?

Experimental cross sections to synthesize heavy ion induced fusion reactions are confronted with calculations using the conventional picture of complete fusion after passing the barrier plus statistical deexcitation after complete equilibration. The sensitivity of the calculations to some of the parameters is demonstrated. Despite this sensitivity, a single parameter set is found that reproduces well the large body of data from experiments using actinide targets. By comparison, for the more symmetric entrance channels using targets around²⁰⁸Pb, we find a fusion hindrance that increases steeply with increasing compound nuclear charge. Predictions for a few reactions of future interest for the synthesis of heavy elements are also presented.     

我国核天体物理前沿研究进展

核天体物理是研究微观世界的核物理与研究宏观世界的天体物理融合形成的交叉学科,其主要研究目标是:宇宙中各种化学元素核合成的过程、时间、物理环境、天体场所及丰度分布;核反应（包括带电粒子、中子、光子及中微子引起的反应、β衰变及电子俘获）如何控制恒星的演化过程和结局。近十多年来获得的大量实验和理论研究使核天体物理研究进入了一个蓬勃发展的新阶段。文章总结了以兰州重离子加速器、北京串列加速器和国家天文台为基础,结合国际合作,在核天体物理研究领域对直接测量、间接测量、衰变测量、质量测量、理论计算、网络计算、天文观测等关键科学问题进行的研究进展。也展望了核天体物理的关键科学问题,这些关键问题包括:（1）在地面实验室、尤其是地下实验室开展天体物理能区重要热核反应截面的直接测量;（2）高能区带电粒子反应截面向天体物理能区的合理外推;（3）恒星平稳核燃烧阶段和爆发性天体事件中关键核反应截面的间接测量;（4）爆发性天体事件中所涉及的大量远离稳定线核素的质量、衰变特性和共振态性质的研究;（5）建立并不断完善核天体物理数据库,发展网络模拟程序,系统研究元素核合成的天体场所、丰度分布;（6）宇宙中铁以上元素的来源之谜。Nuclear astrophysics is an interdisciplinary research field. It composes of nuclear physics, which studies micro phenomena, and astrophysics which studies macroscopic phenomena in our world. The main research goals of nuclear astrophysics are:(1) how, when and where chemical elements are synthesized and what is their final abundance distribution in the universe; (2) how nuclear processes (reactions induced by charged particles, neutrons, photons and neutrinos, beta decays and electron capture processes) determine the evolution and the ultimate fate of stars. At present, nuclear astrophysics has been developed into a new prosperous stage with a huge number of experimental and theoretical progresses. This paper summarized the current progress of nuclear astrophysics in China, in the subfiels of direct and indirect measurement of key reactions, measurement of mass and decay, as well as the theoretical calculation and network simulation. In present paper, the prospects to solve the key scientific nuclear astrophysics problems are represented. These key problems include (1) direct measurement of important reactions at astrophysical energies in the laboratory on the earth surface and in the underground laboratory; (2)extrapolation of cross sections at higher energies for the reactions induced by charged particles; (3) indirect measurement of key reactions in the hydrostatic and explosive nuclear processes; (4) study of the mass, the properties of decay and resonant states for the nuclides far from the stability line in explosive astrophysical events; (5) establish and improve the database for nuclear astrophysics, and develop network simulation codes, and systematically study astrophysical sites and abundance distribution of nucleosynthesis; (6) origin of the elements heavier than iron in the universe.     

关于M－3Y力等效G矩阵元在重核区的有效性

采用Ｍ—３Ｙ力等效Ｇ矩阵元，并利用折线图多体方法计算了２１０Ｐｂ、２０６Ｐｂ以及２０６Ｈｇ和２１０Ｐｏ的低能谱．结果表明，Ｍ—３Ｙ力等效Ｇ矩阵元基本上适用于此核区的核结构微观计算．     

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron. Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies. In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in r-process calculations. We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples. For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of r-process nuclides.     

MCNP程序在核技术中的应用研究

叙述了MCNP,所程序在核临界计算、核保障技术和中子慢化实验装置模拟等方面的成功应用以及为此所做的进一步开发工作.对MCNP的进一步开发做了简要讨论.     

直接鉴别超重元素Z和A的一种新的可能方法

随着合成的超重元素向超重岛逼近,合成截面越来越小,同时,合成的超重元素的寿命可能相对增长, 这对利用α衰变链的传统方法鉴别超重元素是非常不利的。 讨论了可能突破这个瓶颈的一种可以直接鉴别超重元素原子序数Z和质量A的新方法, 即与RFQ离子阱技术相结合的激光多步共振电离方法, 对实现这种方法的途径、 该方法所面临的困难和挑战、需要进行的前期研究工作以及该方法的可能性和可行性进行了较详细的讨论。 With the synthesis of heavy elements approaching the super heavy island, the production cross section becomes smaller and the lifetime of the super heavy element becomes longer, which results in the difficulties for identification of theelements by using conventional alpha decay chain technique. In order to overcome the difficulties, a novel approach to direct identification of atomic number Z and nuclear mass A for super heavy elements is proposed, namely, the multi step resonant laser ionization of singly charged ions in combination with RFQ trap. The routine for the experiment is presented, and the possibilities, feasibilities, as well as the problems to be faced, are discussed in detail.     

A new technique for calculating virtual photon spectra

A first-order matrix differential equation in energy is used to propagate radial matrix elements arising in DWBA of relativistic electron scattering from nuclei. Given an initial set of matrix elements at some value of the energy, this equation permits the evaluation of the radial matrix elements over the complete energy transfer range. A computer code has been written for this new procedure and the virtual photon spectra accompanying electron scattering from a point nucleus is calculated as a function of photon energy for various multipoles, nuclear charges, and incident electron energies.     

Nuclear β-decay. I

In order to clarify the validity of the theory of nuclearβ-transition a new formulation is given. The nuclear properties are contained in form factors, arising from a decomposition of the matrix element of the V-A operator for nuclear states. The connection of these form factors with nuclear physics matrix elements is tabulated. The total transition amplitude can be written as an integral over these form factors folded with off-shell amplitudes for elastic and inelastic electron scattering on nuclei.