沿Z=0.743N+11.6质子滴线分布的稀土区新核素的合成与研究

利用与延发质子符合的子核中已知的第一个２＋→０＋（基态）的γ跃迁来鉴别其β延发质子先驱核的方法已在实验中得到证实，并在兰州重离子加速器ＳＦＣ上用氦喷嘴快速带传输系统成功地合成与研究了沿Ｚ＝０．７４３Ｎ＋１１．６质子滴线分布的稀土区新β延发质子先驱核１３５Ｇｄ和１２１Ｃｅ．该鉴别方法在缺中子稀土区新核素合成中将具有很大的应用前景． It′s more and more difficult to synthesis and study new nuclei along the proton drip line by using on line isotope separator because of its low efficiency. A specific method of “p γ” coincidence measurement, using the known low lying “2+→0+(ground state)” γ transition of the “daughter” nucleus in coincidence with its β delayed proton, could increase the detection sensitivity ...     

对超重核基态性质的系统性研究

对有限力程小液滴模型计算的质子数z=101—130超重核同位素链核的基态性质进行了系统的分析，通过对这些同位素链中处于裂变稳定线上核的平均结合能、四极形变、单质子分离能、双质子分离能和a衰变能等性质的系统研究，显示了质子数Z=108，114，126和中子数N=162，180，196时壳幻数的存在，同时可以看到Z=127之后超重核的基态性质还需要进一步研究。The calculated data by the Finite Range Droplet Model (FRDM) for the ground state properties of super-heavy nuclear isotope chains from Z=101 to Z=130 are analyzed in a global systematic way. Some quantities of the super-heavy nuclei which lie on the line of stability agains fission, such as the mean binding energy, deformation, single and double proton separation energy, as well as the α decay energy indicate the existence of the shell closure positions at Z=108, 114 and 126 and N=162...     

145Er的β延发质子衰变性质研究

通过92Mo(58Ni, 2p3n)熔合蒸发反应生成了非常缺中子核145Er。利用氦喷嘴带传输系统把研究目标核传输到低本底测量站, 进行了质子 γ符合测量, 得到了不受同量异位素干扰的145Er的β延发质子谱。经过仔细分析与延发质子符合的γ谱, 发现了145Er的11/2-同核异能态具有β延发质子衰变性质。经拟合退激144Dy不同激发态γ跃迁的衰变曲线, 得出145Er的1/2+基态和11/2-同核异能态的半衰期分别为(1.6±0.6)和(0.6±0.1) s。最后, 简单介绍了中重质量区缺中子新核素的合成及衰变研究计划。The neutron deficient isotope 145Er was produced via the fusion evaporation reaction 92Mo(58Ni, 2p3n). The reaction products were transported to a low background counting area using a He jet tape transport system, and proton γ coincidence measurements were carried out. Based on the analysis of γ transitions in coincidence with β delayed protons, the β delayed proton decay of an νh11/2 isomer in 145Er was proposed. By fitting the decay curves of the γ transitions depopulating the low lying states in 144Dy, the half lives of the ground state and the νh11/2 isomeric state in 145Er were deduced to be (1.6±0.6) and (0.6±0.1) s, respectively. An experimental plan to synthesize new β delayed proton precursors in the medium heavy mass region has been presented.     

Three-Body Faddeev Approach to Two-Proton Emissions from iSNe Excited State

The proton drip line nucleus 18Ne is considered as a system of two protons and a 160 core. The excitation-energy spectrum of 18Ne and the relative-momentum distribution of the two protons emitted from the 6.15 MeV level of 18Ne are calculated using the Faddeev approach.     

Properties of the β-Delayed Proton Decay of 147Er

The β-delayed proton decay of 147Er is studied experimentally using the 58 Ni＋92Mo reaction at a beam energy of 383 MeV. Based on a He-jet apparatus coupled with a tape transport system, the β-delayed proton radioactivities both from the vδl/2 ground state and the vh11/2 isomer in 147 Er are identified by proton-7 coincidence measurements. By analyzing the time distribution of the 4＋ → 2＋-γ transition in the grand-daughter nucleus 146Dy, a half-life of 1.6 ± 0.2s is determined for the Vh11/2 isomer in 147 Er. The half-life for the ground state of 147Er is estimated to be 3.2±1.2 s.     

α结团模型在形变核区域的推广

将α结团模型推广至形变核,计算偶偶形变母核α衰变基态到子核基态和子核第一激发态的分支比,显示出α衰变精细结构的测量是提取核形变信息的有效手段.The cluster model of α-decay is extended to deformed nuclei. The branching ratios of α-decays from the ground state of a parent nucleus to the ground state 0~(+) of its deformed daughter nucleus and to the first excited state 2~(+) are calculated in the framework of the cluster model. The results indicate that a measurement of α spectroscopy is a feasible method to extract the information of nuclear deformation.     

远离稳定线核研究进展

近几年在对远离核的实验研究中,观测到了理论预言的新衰变模式,如45Fe的双质子衰变,β-缓发裂变;对中子滴线外一些核的存在可能性也进行了较多的实验探索和理论分析;开始了对人们一直关注的中子集团存在可能性的实验探索.远离核谱学和衰变性质研究逐渐深入,通过对一些远离核第一激发态能量的系统比较和许多远离核β衰变Q值的测量,以及核质量的精确测量,发现在远离核区,原有的一些幻数消失,代之产生了一些新的幻数,对其产生原因的理论分析做了简要的综述. Recently the predicted new decay model, for instance two-proton decay and β~(-)delayed fission have been observed in the investigations of the nuclei far from stability line. The existence of the nuclei located beyond the drip-line has already been studied experimentally and theoretically. It has been started to search for the neutron cluster in experiment by using neutron-rich nuclei. The researches of the spectroscopy and decay properties of the nuclei far from stability line are more and deeper, and...     

轻核区双中子滴线核的研究

运用形变相对论平均场（RMF）理论系统地研究了轻核区的元素O, Ne, Mg, Si, S, Ar和 Ca及Ni。 计算了这8个元素的偶 偶核基态的一些性质, 如结合能、 四极形变、 平均每核子结合能以及双中子分离能等。 计算中采用了NL3参数组, 并用BCS方法处理对关联。 限于篇幅, 文中只给出O和Mg元素的计算结果。 RMF理论计算的结果和实验值基本一致。 从双中子分离能的分析可知, RMF理论计算的各元素的双中子滴线核分别为 30O, 38Ne, 42Mg, 52Si, 54S, 60Ar, 80Ca和98Ni。 最后简单讨论了Ca和Ni同位素中的中子幻数情况。 The ground state properties of even even O, Ne, Mg, Si, S, Ar, Ca and Ni isotopes were studied with the self consistent deformed relativistic mean field theory with NL3 parameter set. The calculated results of O and Mg isotopes were presented in detail. The calculated binding energies and the two neutron separation energies were in good agreement with experimental values. By examining the two neutron separation energies, it was suggested that 30O, 38Ne, 42Mg, 52Si, 54S, 60Ar, 80Ca and 98Ni are the two neutron drip line nuclei. We also briefly discussed the possible changes of neutron magic numbers in Ca and Ni isotopes. Key words: relativistic mean field; drip line nucleus; two neutron separation energy     

Theoretical Analysis of the Exotic Structure of ^17F

The first excited state and the ground state of ^17F are studied with the asymptotic normalization coefficient method. The results show that the probabilities of the last proton being out of the binding-potential in both the states are P = 59.71% and P = 27.61%, respectively. This means that the last nucleon in both the states of ^17F is far-extended beyond the range of nuclear force, especially in the first excited state. This result is also verified by the calculation of the density distributions of the last proton in ^17F. It is quantitatively confirmed that the first excited state of^1TF is a nuclear halo state and its ground state is a proton skin state.     

β-delayed proton decays near the proton drip line

Simply speaking, the drip line is the margin in chart of the nuclides where the nu-clides with the lower limits of detectable lifetime survive. The N/Z ratios of the nuclides on the drip line are extreme. Synthesis of the nuclei near the drip line and study of their exotic decays deal with the physics under extreme conditions, and therefore become one of the frontiers in nuclear physics today. The rare-earth nuclei near the proton drip line have been predicted to be highly deformed[1]. They a…     

Proton radioactivity — spherical and deformed

The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically unbound to the emission of a constituent proton from their ground states. For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction of nuclear structure information from nuclei well beyond the proton drip line.     

Two-proton radioactivity search

Two-proton radioactivity, a spontaneous breakup of elements with emission of two protons, was predicted to exist near the proton drip line by V.I. Goldansky long time ago. The recent theoretical and experimental progress in a search for such an exotic nuclear decay is reviewed. In theory, the new three-body model which treats two-proton radioactivity as a genuine three-particle nuclear decay is considered. In experiment, the first evidence for two-proton decay of ⁴⁵Fe is described. Four atoms of ⁴⁵Fe, produced at the fragment separator of GSI, decayed via particle emission with a total energy of 1.1(1) MeV and a half-life of 3.2 _?1.0 ^+2.6 ms. A possible experiment for a direct observation of two-proton emission from the ground state of ¹⁹Mg is considered for its decay in-flight. The half-life of ¹⁹Mg, as well as proton-proton correlations, might be derived from the distribution of the ¹⁹Mg decay vertices extrapolated from the measured trajectories of all fragments.     

Ground State Structure of Hs Super-heavy Isotopes

The ground state properties of Hs nuclei studied in the framework of the relativistic mean field theory revealed that more stable isotopes are located on the proton abundant side of the chain.The last stable nucleus to the proton drip line is ~(256)Hs.The most stable unknown Hs nucleus may be ~(268)Hs.The density dependent delta interaction pairing is used to improve the BCS pairing correction,which results in more reasonable single-particle energy level distributions and nucleon occupation,and it is shown to be available to describe the properties of nuclei in the superheavy region.     

Empirical formulas for proton decay half-lives:Role of nuclear deformation and Q-value

Two empirical formulas for the proton decay half-lives including nuclear deformation are proposed. The formula with parameter set I gives the logarithm of the proton decay half-lives as an explicit function of the orbital angular momentum with eight adjustable parameters, whereas that with set II represents the logarithm of the reduced half-lives as an implicit function of the angular momentum with seven adjustable parameters. Experimental data for the half-lives of 44 proton emitters in the ground state or isomeric state were used to obtain the parameters. The experimental and calculated Q values were used. Different sets of parameters were obtained for the ground state transition, isomeric state transition, and all transitions for both deformed and spherical nuclei. The best agreement with experimental data was observed for set I for deformed proton emitters with experimental Q values.     

Reduced occupancy of the deeply bound 0d(5/2) neutron state in 32Ar

The 9Be(32Ar, 31Ar)X reaction, leading to the 5/2+ ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65.1 MeV/nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state.     

Shape transitions in proton-rich Ho and Tm isotopes

Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell e?ects. Ground-state shape changes from prolate to oblate at 143Ho and 145Tm in these two isotopes, which is due to the γ instability around N =76.     

Magnetic hyperfine anomaly in muonic193Ir

The nuclear decay of the 5/2⁺ 139 keV state to the 3/2⁺ ground state was observed in muonic¹⁹³Ir. The hyperfine splitting of the 3/2⁺ state and 5/2⁺ state was determined to be 640±100 eV and 1280±160 eV, respectively. The ground state splitting is about twice that of a point nucleus, an anomaly never observed this large. This is mainly due to the different radial distribution of spin and orbital magnetization of a d_3/2 proton configuration for which these contributions nearly cancel to zero in the magnetic moment. But calculations including configuration mixing and coupling to a vibrating or a deformed core show deviations. The groundstate anomaly is in line with that observed by the Mössbauer technique.     

New experimental results in proton radioactivity

A review of experimental data obtained recently on proton-radioactive nuclei is presented. The highlights include the observation of fine structure in proton emission, for the decays of ¹³¹Eu, ¹⁴⁵Tm and ¹⁴⁶Tm, and the studies of the excited states in proton-emitting nuclei. The observation limits are extended to few nanobarns cross-sections ( ¹⁴⁰Ho, ¹⁶⁴Ir and ¹³⁰Eu) and few microsecond half-lives (e.g., ¹⁴⁵Tm). Measured decay properties for thirty-nine proton-emitting ground and isomeric states contributed to the understanding of nuclear masses and evolution of single-particle states at and beyond the proton drip line. Experimental results have stimulated new theoretical approaches to proton emission and the structure of unbound narrow resonance states. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rykaczew@phy.ornl.gov