Production of neutron-rich actinide isotopes in isobaric collisions via multinucleon transfer reactions

We systematically calculated the multinucleon transfer reactions of ^(208)Os,^(208)Pt,^(208)Hg,^(208)Pb,^(208)Po,^(208)Rn,^(208)Ra,and ^(132,136) Xe when bombarded on ^(232) Th and ^(248) Cm at Coulomb barrier energies within the dinuclear system model.These results are in good agreement with the available experimental data.The influence of Coulomb and shell effects on actinide production in these reactions has been rigorously studied.We calculated and analyzed the potential energy surface (PES) and total kinetic energy (TKE) mass distributions for the reactions involving ^(208)Hg,^(208)Pb,and ^(208) Po with ^(248) Cm and ^(232)Th.The PES and TKE spectra shed light on the fragment formation mechanisms in multinucleon transfer reactions,with clear indications of isospin and shell effects.The production cross sections for multinucleon transfer products show a strong dependence on isobar projectiles with a mass number A=208.Isobar projectiles with high N/Z ratios are advantageous for generating neutron-rich target-like fragments.Conversely,products induced by isobar projectiles with larger charge numbers tend to shift toward proton-rich regions.The intertwining of the Coulomb potential and shell effect is evident in the production cross sections of actinide isotopes.Drawing from reactions induced by radioactive projectiles,we anticipate the discovery of several new actinide isotopes near the nuclear drip lines,extending our reach into the superheavy nuclei domain.

Prediction of synthesis cross sections of new moscovium isotopes in fusion‑evaporation reactions

In the framework of the dinuclear system model,the synthesis mechanism of the superheavy nuclides with atomic numbers Z=112,114,115 in the reactions of projectiles 40,^(48)Ca bombarding on targets^(238)U,^(242)Pu,and^(243)Am within a wide interval of incident energy has been investigated systematically.Based on the available experimental excitation functions,the dependence of calculated synthesis cross-sections on collision orientations has been studied thoroughly.The total kinetic energy(TKE)of these collisions with fixed collision orientation shows orientation dependence,which can be used to predict the tendency of kinetic energy diffusion.The TKE is dependent on incident energies,as discussed in this paper.We applied the method based on the Coulomb barrier distribution function in our calculations.This allowed us to approximately consider all the collision orientations from tip-tip to side-side.The calculations of excitation functions of^(48)Ca+^(238)U,^(48)Ca+242Pu,and^(48)Ca+^(243)Am are in good agreement with the available experimental data.The isospin effect of projectiles on production cross-sections of moscovium isotopes and the influence of the entrance channel effect on the synthesis cross-sections of superheavy nuclei are also discussed in this paper.The synthesis cross-section of new moscovium isotopes 278−286 Mc was predicted to be as large as hundreds of pb in the fusion-evaporation reactions of^(35,37)Cl+^(248)Cf,^(38,40)Ar+^(247)Bk,^(39,41)K+247 Cm,^(40,42,44,46)Ca+^(243)Am,45 Sc+^(244)Pu,and^(46,48,50)Ti+237Np,51 V+^(238)U at some typical excitation energies.

低能电子穿越玻璃直管时倾角依赖的输运动力学

采用900 e V能量的电子对直玻璃管进行了穿透实验,测量了玻璃管在倾角为–0.15°,–0.4°和–1.15°时充电过程角分布的时间演化,以及平衡态下出射电子能谱.发现穿透率随时间先下降后上升最后趋于平稳,下降的时间随倾角的增大而减小.当倾角为–0.4°和–1.15°时,电子穿透率下降到最低点时几乎看不到穿透电子(穿透率小于3‰),这种穿透率最低点状态保持时间随倾角增大而增大.穿透电子的角分布中心随着时间变化.在平稳状态时,发现穿透电子的能量损失随倾角增大而增大.采用蒙特卡罗方法模拟了电子经过管壁不同次数反射后的能谱,与测量能谱进行对比,发现–0.15°,–0.4°和–1.15°倾角下,穿透电子分别经历了管壁的一次、两次和三次与表面的反射过程.基于此,本文对电子穿越玻璃管的充电过程动力学给出了物理解释.实验结果和理论分析表明,在小倾角下玻璃管内能形成宏观负电荷累积,排斥后续电子形成反射,增加电子出射概率,这对应用绝缘体微结构,例如玻璃锥管产生稳定的电子微束具有重要的参考意义.

离子在近电子能损阈值能区诱发云母表面小丘形成

利用0.65 MeV的He^+离子轰击白云母膜,并在大气环境下用原子力显微镜(AFM)的轻敲模式分析了辐照后的膜表面。实验结果显示,在不同温度下离子诱导的小丘高度在小于1 nm到几nm之间,且室温条件下能诱发小丘生成的He^+离子电子能损阈值在0.44 keV/nm以下。此外,升高温度至973 K并在其中选取不同温度进行表面辐照来验证观测到的小丘结构。实验发现,相比于室温,小丘直径和高度的统计分布在更高温度下表现出了更大的歧离。分别利用分析热峰模型和双温热峰模型计算了辐照过程中的核能损与电子能损,并选取了用能损在阈值附近的离子辐照所产生的小丘的实验数据与模拟结果相比较,发现实验结果与双温热峰模型吻合较好。

低能电子在玻璃管中的稳定传输

分别对裸的直玻璃管和外壁与出入口两端面涂导电银胶的直玻璃管进行了低能电子穿透实验.穿透电子的倾角分布显示,穿透电子强度随倾角增大而减少,并且穿透倾角不会超过玻璃管的几何张角.还测量了玻璃管在倾角为-0.2°时的充电过程.对于裸玻璃管,在充电过程中,穿透率和角分布有显著的振荡现象.整体来看,穿透率随时间先下降后上升,最后在某个平均值附近振荡;角分布随穿透率变化同步变化,先向正角度移动再向负角度移动,最后在玻璃管的倾角附近振荡.对于涂导电胶的玻璃管,在充电过程中,穿透率和角分布稳定变化.穿透率随时间先下降后上升最后平稳,角分布随时间先向负角度移动再向正角度移动,最后在玻璃管倾角附近稳定.通过模拟电子与SiO;材料的碰撞过程,提出了电子在裸玻璃管和涂导电胶玻璃管中的充电过程的物理图像.该物理图像能很好地解释电子在裸玻璃管和涂导电胶的玻璃管中充电过程的实验结果.最后,依据实验结果和物理图像给出了低能电子在玻璃毛细管中稳定输运的条件.

低能Cl^-在Al2O3绝缘微孔膜中的输运过程

研究了10 keV Cl^-离子穿越Al2O3绝缘微孔膜的物理过程,发现穿越的Cl^-其分布中心在初束中心即0°附近,Cl^-离子穿透率下降与几何穿透一致,这是典型的直接几何穿越有一定角发散的微孔导致的结果;而出射的Cl0和Cl^+以微孔轴向为中心分布,Cl^+和Cl0穿透率下降慢于几何穿透.模拟计算发现沉积电荷会使出射粒子中Cl^-占主要成分,并使出射Cl^-角分布中心移动到微孔轴向方向而随微孔膜倾角移动;而在不考虑沉积电荷的情况下,计算结果较好地符合了实验结果.通过分析在不同倾角下散射过程对出射粒子的角分布和电荷态分布的影响,发现绝大部分的Cl0是通过一次和两次散射出射的,其中一次散射出射的Cl0占主要成分,从而导致出射的Cl0沿微孔轴向出射而Cl^+主要是经过一次碰撞出射.这导致了随倾角增大,出射的Cl0穿透率下降速度比Cl^+小,Cl0所占比例相对增大较快,从而导致观测到的Cl^+/Cl0的比例下降.本文结果更仔细地描述了低能离子穿越绝缘体微孔的物理机理,印证了之前实验和理论工作的结果,发现在10 keV以上能区的Cl^-离子穿越绝缘微孔膜的过程中,沉积电荷并未起到主要作用,其主要穿透特征是散射过程造成的.

Contributions of optimized tensor interactions on the binding energies of nuclei

The tensor parts of Skyrme interactions are constrained from the collective charge-exchange spin-dipole and Gamow-Teller excitation energies in 90Zr and 208Pb,together with the isotopic dependence of energy splitting between proton h11=2 and g7=2 single-particle orbits along the Z=50 isotopes.With the optimized tensor interactions,the binding energies of spherical or weakly deformed nuclei with A=54-228 are studied systematically.The present results show that the global effect of tensor interaction is attractive and systematically increases the binding energies of all these nuclei and makes the nuclei more bound.The root mean squared deviation of the calculated binding energies from the experimental values is significantly improved by the optimized tensor interactions,and the contribution of the tensor interaction to the binding energy is estimated.

Progress in the R&D Experiments About a Novel Method of Electr Scattering off Short-lived Nuclei

A novel method has been established to realize the experiment of electron scattering off short-lived nuclei. The method was based on the well known ＂ion trapping＂ phenomenon in electron storage rings. In the R^D experiments at Kyoto University, stable nucleus, 133^Cs, was employed as the target nucleus. The luminosity of scattering experiment was nearly 1026 cm^-2s^-1 at electron beam current around 75 mA. The angular distribution of elastically scattered electrons from trapped Cs ions was measured and the result was well fitted by theoretical calculation. It was indicated that higher luminosity can be reached with larger electron beam current.

Negative Parity States in ^(39)Cl Configured by Crossing Major Shell Orbits

Traditional "magic numbers" were once regarded as immutable throughout the nuclear chart. However, unexpected changes were found for unstable nuclei around N = 20. With both proton and neutron numbers around the magic number of 20, the neutron-rich ^(39)Cl isotope provides a good test case for the study of the quantumstate evolution across the major shell. In the present work, the negative parity states in ^(39)Cl are investigated through the β decay spectroscopy of 39 S. Newly observed γ transitions together with a new state are assigned into the level scheme of ^(39)Cl. The spin parity of 5/2^- for the lowest negative parity state in ^(39)Cl is reconfirmed using the combined γ transition information. These systematic observations of the negative parity states in ^(39)Cl allow a comprehensive comparison with the theoretical descriptions. The lowest 5/2^- state in ^(39)Cl remains exotic in terms of comparisons with existing theoretical calculations and with the neighboring isotopes having similar single-particle configurations. Further experimental and theoretical investigations are suggested.

Inelastic Scattering of ^(32)Mg at 190 MeV/Nucleon from a Thick Proton Target

The first excited 2^(+)state(885 keV)of ^(32)Mg and its corresponding deformation parameterβ_(2) are studied with proton inelastic scattering at 190 MeV/nucleon using in-beamγtechnology with a thick target.Angular distributions of the inelastic scattering cross sections are analyzed with coupled-channel calculations.The deformation parameterβ_(2)=0.41(3)obtained in this work agrees with the earlier experimental results obtained at lower beam energies.Our work demonstrates that the structure of unstable nuclei can be studied with proton inelastic scattering at high incident energies in the vicinity of 200 MeV/nucleon using thick targets.

The Wheat Plastochron Mutant, fushi-darake, Shows Transformation of Reproductive Spikelet Meristem into Vegetative Shoot Meristem

In wheat plants at the vegetative growth stage, the shoot apical meristem (SAM) produces leaf primordia. When reproductive growth is initiated, the SAM forms an inflorescence meristem (IM) that differentiates a series of spikelet meristem (SM) as the branch. The SM then produces a series of floret meristem (FM) as the branch. To identify the mechanisms that regulate formation of the reproductive meristems in wheat, we have investigated a leaf initiation mutant, fushi-darake (fdk) which was developed by ion beam mutagenesis. The morphological traits were compared in wild type (WT) and fdk mutant plants grown in the experimental field. WT plants initiated leaves from SAM at regular intervals in spiral phyllotaxy, while fdk plants had 1/2 alternate phyllotaxy with rapid leaf emergence. The fdk plants have increased numbers of nodes and leaves compared with WT plants. The time interval between successive leaf initiation events (plastochron) was measured in plants grown in a growth chamber. The fdk plants clearly show the rapid leaf emergence, indicating a shortened plastochron. Each tiller in fdk plants branches at the upper part of the culm. The fine structure of organ formation in meristems of fdk plants was examined by scanning electron microscopy (SEM). The SEM analysis indicated that fdk plants show transformation of spikelet meristems into vegetative shoot meristems. In conclusion, the fdk mutant has a heterochronic nature, i.e., both reproductive and vegetative programs were simultaneously in operation during the reproductive phase, resulting in a shortened plastochron and transformation of reproductive spikelets into vegetative shoots.

Relativistic Brueckner-Hartree-Fock Theory for Finite Nuclei

Starting with a bare nucleon-nucleon interaction, for the first time the full relativistic Brueckner Hartree-Fock equations are solved for finite nuclei in a Dirac-Woods-Saxon basis. No free parameters are introduced to calculate the ground-state properties of finite nuclei. The nucleus 160 is investigated as an example. The resulting groundstate properties, such as binding energy and charge radius, are considerably improved as compared with the non-relativistic Brueckner-Hartree-Fock results and much closer to the experimental data. This opens the door for ab initio covariant investigations of heavy nuclei.

Proton Spectroscopic Factors Deduced from Helium-3 Global Phenomenological and Microscopic Optical Model Potentials

Global phenomenological GDP08 and microscopic hefium-3 optical model potentials have been recently derived. We evaluate these two potential sets by comparing the elastic scattering data of 25 MeV 3He on 160, 180, 19F, 23Na, 24Mg, 25Mg, 26Mg, 27A1, 28Si, 30Si, 31p, 32S, 34S, 35Cl, 3761, and 39K isotopes. Using the deuteron angular distributions calculated with the distorted wave Born approximation model, we extract the ground-state proton spectroscopic factors from （3He, d） reactions on the same set of nuclei. The extracted proton spectroscopic factors are compared with the large-basis shell-model calculations.

Odor-Active Volatile Compounds from the Gonads of the Sea Urchin <i>Mesocentrotus nudus</i>in the Wild in Miyagi Prefecture, Tohoku, Japan

Background and Aims: Mesocentrotus nudus is commercially harvested from shallow rocky bottoms in northern Japan. The gonads are targeted as an edible product. The objective of this study was to identify odor-active volatile organic compounds (VOCs) from the gonads of adult M. nudus collected at a fishing ground in Miyagi Prefecture, Tohoku, Japan. Methods and Results: Gas chromatography-mass spectrometry analysis and gas chromatography-sniffing techniques identified 42 compounds categorized as alcohols, aldehydes, aromatic hydrocarbons, esters, halomethanes, hydrocarbons, ketones, sulfur-containing compounds, and nitrogen-containing compounds. GC-sniffing analysis characterized four compounds with preferable odors of sea urchin gonads;limonene, propyl acetate, acetone, dibromochloromethane. On the other hand, the analysis characterized three compounds with unpreferable odors;methyl mercaptane, dimethyl sulfide, and s-methyl thioacetate. Several VOCs from the gonads were derived from seaweeds, terrestrial plants, and fish flesh as food because M. nudus is omnivorous. Conclusion: This is the first study to identify VOCs from edible sea urchin gonads in the wild in Japan. These VOC data comprise a typical standard in order to evaluate a higher quality of sea urchin gonads.

Observation of New Isotope^(131)Ag via the Two-Step Fragmentation Technique

We report on the first observation of the neutron-rich nucleus^(131)Ag.This isotope was produced via fragmentation reactions of intense secondary radioactive ion beams,including 134,135Sn.The secondary beams were produced from induced fission reactions from a stable 238U beam at 345 MeV/nucleon.Secondary reaction residues were selected by the ZeroDegree spectrometer and identified by measuring their magnetic rigidity,time of flight,energy loss,and total kinetic energy.

Light Microbeams by Tapered Glass Capillaries for Biological Irradiation

Microbeams of visible light were studied using a tapered glass capillary. Transmittance of laser light through capillaries with different inlet and outlet diameters was measured. About several % of the transmittance was obtained and larger than 80% was achieved in combining with an optical lens. It was found that the obtained transmittance considerably depended on the capillary shape, i.e., the taper angle. Density enhancement of the extracted beam was derived and showed a strong focusing ability for the tapered glass capillary. Propagation of visible light through the capillary was discussed.

2-25 Gas-phase Chemistry of Short-lived Re Carbonyl Complexes Part 1: Adsorption Enthalpy on Teflon Surface

In the collaboration of RI Applications Team from RIKEN (Japan) and the Nuclear Chemistry Group from IMP (China), the short-lived Re carbonyl complexes were synthesized and investigated. As the lighter homologs of superheavy element Bh, Re belongs to period 6, group 7 of the periodic table. Short-lived Re isotopes with half-lives of several minutes were produced in the reactions of natGd(23Na7+, xn) 172?177Re at Nishina center of RIKEN.

2-26 Gas-phase Chemistry of Short-lived Re Carbonyl Complexes Part 2: Chemical Yields in Gas-phase Reactions

After the volatile Re carbonyl complexes were synthesized and their volatility was studied we performed another experiment to measure their chemical yields when He were used as the carrier gas. The same experimental setups were used except the low temperature isothermal chromatography device[1]. The natGd2O3 target and 23Na7+ion beam were used to produce short-lived Re isotopes, and the Gas-filled Recoil Ion Separator (GARIS) was employed to separate the evaporation residues[2]. High purity He gas and CO gas were used as the mixed gas. The depth of recoil chamber was 100 mm because of the long stop range in He gas, and the gas pressure was around 80 kpa. The total gas flow rate was 1 L/min.