高自旋同质异能态束流及其在核谱学中的应用

介绍了在日本理化学研究所利用高自旋同质异能态束流装置上取得的核谱学研究结果。强调了可利用重离子核反应中逆运动学产生高自旋同质界能态束流,并用其进行二次核反应,描述了首次利用高自旋同质异能态束流完成的物理实验． The study of nuclear spectroscopy by using the High spin isomer Beam(HSIB)facility in RIKEN was introduced.The production of HSIB based on the inverse kinematics in heavy ion nuclear reaction,and its application for secondary nuclear reaction were stressed The first experimental result by using HSIB was also briefly discribed.     

126Ce的EC/β+衰变

利用187 MeV的40Ca离子轰击同位素靶92Mo, 由熔合蒸发反应生成目标核126Ce。 藉助氦喷嘴快速带传输系统和X-X-t与X-γ-t符合测量, 首次建立了126Ce的EC/β+衰变纲图。 建议了可能属于126Ce一个高自旋同核异能态的衰变, 其β衰变后布居在与126La的高自旋同核异能态相关的低位能级区, 测定的半衰期是57(9) s。 也建议了可能属于126Ce基态的衰变, 其β衰变后布居在与126La的低自旋同核异能态相关的低位能级区,它的半衰期被测定为12(4) s。 但偶偶核126Ce存在高自旋同核异能态的物理原因还有待进一步探究。 Ce was produced by bombarding an enriched target of 92Mo with 187 MeV 40Ca beam and studiedby using a helium jet fast tape transport system in combination with X-γ and γ-γ coincidencemeasurements. An EC/β+ decay scheme of 126Ce was proposed for the first time. A group of low lying states associated with the low spin isomer in 126La feeding by β decay was possibly from the ground state EC/β+ decay of 126Ce with the measured half-life 12(4) s. Another group of low lying states associated with the high spin isomer in 126La feeding by β decay was possibly from a high spin isomer EC/β+ decay of 126Ce with the measured half-life 57(9) s. However, the physical reason for the existence of a high spin isomer in even-even nucleus 126Ce is still an open problem.     

原子核高K同质异能态的诱发γ辐射

介绍了原子核高K同质异能态潜在的应用价值及国内外研究的进展。 总结了形成同质异能态的3种主要物理机制。 说明了高K同质异能态的应用原理是将其激发到更高的不稳定的K混合态上, 再发生诱发退激, 形成γ瀑, 释放其存储的能量。 同时又介绍了K混合态的3种主要产生机制。 最后分析了178Hfm2诱发退变的实验, 讨论了这些实验的区别和与角动量投影壳模型计算结果的差异。The nuclear isomer states have great potential value of application. The important experimental and theoretical researches are presented here. There are three kinds of physics mechanism for the formation of the isomer states. The principle of releasing the energy stored in the isomer is to excite it to higher states, K mixing states, which can spontaneously decay to the ground state forming the γ cascade. After introducting the three ways to form the K mixing states, we analyzed experiments on the most prospective isomer 178Hfm2, discussed the key differences between these experiments and suggested that the Projected Shell Model (PSM) can be helpful to confirm the occurrence of the  K mixing states and would work out characteristics of the induced decay.     

混合对称态对Majorana相互作用的依赖性(英文)

在 IBM2中研究了混合对称态 .发现某些较高自旋的混合对称态随着 Majorana相互作用很快变化 .这个结果改变了传统的关于混合对称态的观点 :最大 F旋态的能量最低 ,F旋越小 ,能量越高 .Fmin或 Fmin- 1的态会成为 yrast或 yrare态 .这些态很难向下衰变 ,因而很稳定.这个研究的结果表明可能存在一种由于质子和中子自由度的特殊性质而引起的新的同质异能态. Mixed symmetry states were studied in the framework of the neutron proton interacting boson model(IBM2). It was found that some of the mixed symmetry states with moderate high spins changed very fast with respect to the Majorana interaction. This changes our traditional picture that the maximum F spin states are the lowest in energy, the smaller the F spin, the higher the energy. The minimum F spin states or the state with F spin next to minimum may become the yrast or...     

高自旋同质异能态束流及其在核谱中的应用

介绍了在日本理化学研究所利用高自旋同质异能态束流装置上取得的核谱学研究结果，强调了可利用重离子核反应中逆运动学产生自旋同质异能态束流，并用其进行了二次核反应，描述了首次利用高自旋同质能态束流完成的物理实验。     

HI－13串列加速器上的核结构研究

本文综述了中国原子能科学研究院ＨＩ－１３串列加速器上的核结构研究．在原于核高自旋态方面．简要地介绍了稀土区奇质子核带交叉反常现象研究,质量数为Ａ＝９０和Ａ＝１３０核区的高自旋态研究、原子核高自旋能级寿命研究和三轴形变研究．在原于核巨共振方面介绍了矮共振区的ＧＤＲ研究,形变核的ＧＤＲ以及高温转动核的ＧＤＲ研究． The nuclear structure studies carried out at the HI-13 tandem in China Institute of Atomic Energy are reviewed. Brief introductions in the field of high spin state physics are given, such as the anomolous band crossing for odd-proton rare earth nuclei, high spin state studies in the mass 90 and 130 regions, nuclear high spin state life time study and the investigation of the triaxial de formation. Brief introductions in the field of GDR studies of pygmy resonance and GDR studies in deformed...     

准幻核中的近似广义辛弱数守恒（英文）

对称性在了解诸如原子核的转动、自旋和宇称、及同位旋等核结构性质中都起着重要的作用,并且使复杂的原子核结构问题得以简化。辛弱数就是由于原子核的对相互作用中的对称性所导出的众所周知的好量子数。通过对丰中子和缺中子核素及核素的高自旋态的衰变数据分析来揭示辛弱数的近似守恒性质。研究结果表明,在准幻核的高自旋同质异能素链中,无论所涉及的价空间的核子轨道有何不同,广义辛弱数总是近似的好量子数。Symmetry plays an important role in understanding the nuclear structure properties from the rotation of a nucleus to the spin, parity and isospin of nuclear states. This simplifies the complexity of the nuclear problems in one way or the other. Seniority is also a well known quantum number which arises due to the symmetry in the pairing interaction of nuclei. We present empirical as well as theoretical evidences based on decay rates which support the goodness of seniority at higher spins as well as in nrich or, n-deficient nuclei. We find that the generalized seniority governs the identical trends of high-spin isomers in different semi-magic chains, where different set of nucleon orbitals from different valence spaces are involved.     

Response of Alanine Dosemeter to Heavy Ions

The amino acid L-α-alanine has been investigated for use as a radiation detector in low and high LET radiation fields[1]. The radiatioa detector is cheap and easy to handle. The radiation inducing free radicals are stable at normal laboratory conditions for doses below 10^4 Gy over a long period of time, which makes the detector useful for intercomparison and documentation purposes. The dosimetric features of alanine-based electron spin resonance (ESR) detectors in high energy electron beams used in radiotherapy were considered[2]. The 5 mm long alanine detectors were found to be the most suitable for carrying out in vivo dosimetry on patients undergoing electron beam radiotherapy. However, data concerning dosimetry of the alanine dosemeter to heavy charged particles are lacking, especially in China.     

The physics of spin rectification and its application

A coherent nonlinear coupling between the charge and spin dynamics of electrons results in the rectification of microwaves,which is enhanced through resonant magnetization dynamics such as ferromagnetic resonance.This property,known as the spin rectification effect,enables the spin dynamics within a material to be electrically detected with a high sensitivity.Techniques utilizing this property have been widely used to study the magnetization dynamics of various ferromagnetic materials and structures in the past decade.Additionally,the coherent nature of spin rectification opens the door for spintronic devices to be used in phase-resolved microwave sensing techniques.In this work we review the physics of spin rectification and its applications in several interesting topics of magnetism and spintronics.     

Probing Shell Correction at High Spin by Neutron Emission of Doubly Magic Nuclei 208Pb and 132Sn

Shell effects in particle emission for two doubly magic nuclei ^132Sn and ^208pb were studied in the framework of Smoluchowski equation taking into account temperature and spin-dependent shell correction. It is shown that the shelle ffects in the emission of pre-scission neutrons are sensitive to the spin dependence of the shell correction at a moderate excitation energy. Therefore, we propose to use neutron multiplicity as an observable to probe the shell correction at high spins.     

The decay of the 560 ns Isomer at 8.6 MeV in 64 147 Gd83

In (α,xn) and (¹²C, 5n) in-beamγ-ray experiments with pulsed beams the decay of the 560 ns high-spin isomer in¹⁴⁷Gd has been investigated. Extensive coincidence measurements identified in the isomeric decay more than eightyγ-rays which almost all were placed in the level scheme. Of crucial importance for establishing the highly complex decay was the comparison of data from the different reactions and the identification of transitions which bypass the 27 ns isomer at 3.58 MeV. Our data determine the excitation of the 560 ns isomer as 8.588 MeV and suggest 47/2 as its most probable spin.     

Tilted foil polarization of radioactive beam nuclei

Tilted foil polarization has up to now been mostly applied to nuclear reaction products recoiling out of a target traversed by a primary particle beam. Being a universal phenomenon it can be applied equally well to beams of particles, primary or secondary, radioactive or other. There are however some technical considerations arising from the nature of the beam particles. Radioactive beams are associated with ground state nuclei. They usually have low nuclear spin and as a consequence-as will be shown later-low polarization. Secondary beams are usually low in intensity and do not impose any constraints on the foils they traverse; unlike intense primary heavy ion beams which, if they traverse the foils, essentially limit the foil material to carbon. We review here briefly the tilted foil polarization process and then discuss an experiment with an isomer beam. Finally we review experiments with radioactive beams, past, present and planned for the future.     

Experimental Observation of High Spin States in 146Sm Nucleus

High spin states of ¹⁴⁶Sm have been experimentally studied by using ¹³C(95MeV) beam bombarding natural Ba target.Seventeen new γ-rays and eleven new levels were found and assigned to the level scheme of ¹⁴⁶Sm which extends up to 10.2MeV excitation energy.Level structure still shows the characteristics of particle configurations.No long-lived high spin isomer was found up to such high excitation region.     

Coulomb excitation paths of high-K isomer bands in 178Hf

Three distinctly different mechanisms are shown to populate the K(pi)=6(+) (t(1/2)=77 ns), 16(+) (31 yr), and 8(-) (4 s) isomer bands of 178Hf by Coulomb excitation. High spin states of the three isomer bands were populated by Coulomb excitation of a hafnium target with a 650 MeV 136Xe beam. Although direct population of high-K bands is highly K-forbidden, isomer bands in 178Hf were populated up to spins 13(+)(K=6), 20(+)(K=16), and 14(-)(K=8) with in-band gamma yields of approximately 10(-4) of the ground state band. The data are consistent with a rapid increase in K mixing with increasing spin in the isomer bands.     

Polarization of high spin nuclear levels via tilted multifoil interaction

It has been demonstrated that with suitably spaced carbon foils, tilted with respect to the particle momentum, a large polarization can be generated in high spin nuclei by the tilted foil atomic polarization. Two experiments have been carried out with such polarized high spin isomers: a measurement of the sign of the quadrupole moment of the 10⁺ isomer in⁵⁴Fe, and a new attempt of higher sensitivity at detecting a possible positive parity admixture to the 17/2^– isomer in⁹³Tc.On leave from the Hahn-Meitner Institut, Berlin, W. Germany.On leave from Physics Department, Brooklyn College of the City of New York, Brooklyn, New York.     

Polarised targets for 4<Emphasis Type="Bold">π</Emphasis> detectors at MAMI

The spin, as a fundamental property of a particle, has been a main object of investigation in particle and nuclear physics research in recent decades. Consequently, the investigation of polarisation observables has become more and more important. Nowadays cw beams with high duty cycles are standard technology. In parallel, the development of detectors with full angular acceptance, so called 4π detectors, has kept pace with the accelerator technology to allow for precise determination of the final state of the reaction under investigation. The availability of high speed data acquisition systems has enabled an increase in the luminosities by orders of magnitude. For complete spin investigation, one requires a polarised target in additon to polarised beams and recoil polarimeters. The advent of advanced beam and large acceptance detector technologies has driven the development of highly polarised, full angular acceptance targets.     

Relativistic electron vortex beams: angular momentum and spin-orbit interaction

Motivated by the recent discovery of electron vortex beams carrying orbital angular momentum (AM), we construct exact Bessel-beam solutions of the Dirac equation. They describe relativistic and nonparaxial corrections to the scalar electron beams. We describe the spin and orbital AM of the electron with Berry-phase corrections and predict the intrinsic spin-orbit coupling in free space. This can be observed as a spin-dependent probability distribution of the focused electron vortex beams. Moreover, the magnetic moment is calculated, which shows different g factors for spin and orbital AM and also contains the Berry-phase correction.     

Neutron beam effects on spin-exchange-polarized 3He

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal spin-exchange-polarized 3He cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable 3He polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at Los Alamos Neutron Science Center and Institute Laue-Langevin. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as sqrt[phi_{n}], where phi_{n} is the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the concentration of electron-ion pairs but is much larger than expected from earlier work.     

Triggering of nuclear isomers via decay of autoionization states in electron shells (NEET)

Nuclear excitation by an electron transition (NEET) may be used for triggering the decay of nuclear isomers only when there are compensations between energies (ΔE) and multipolarities (ΔL) of the nuclear transition and the transition in an electron shell. It is shown that using the autoionization states (AS) allows one to compensate for the ΔE and ΔL differences. Laser radiation may be used for the excitation of AS with energies up to 10–15 eV and ^229m Th (3.5 eV) nuclear isomer excitation by NEET via AS decay. Ion beams, electron beams, and X rays may be used for the excitation of the trigger nuclear levels with energies up to 150 keV by NEET via AS and for the triggering of the nuclear isomer decay. For excitation of AS with the energies up to 150 keV, two or more hole states in deep inner electron shells must be excited. The cross section for such two-hole state excitation in electron shells by ion beams may be sufficiently high. The possibilities of NEET via AS for the triggering of nuclear isomer decay are discussed.