Projected Shell Model Description for the Proton Emitters

Proton radioactivity is an important decay mode for nuclei near the proton drip-line. Studies of this decay mode can reveal valuable information on exotic nuclear structure and provide important information on the stucture of nuclei in extreme conditions. The new experimental data can let us understand the interactions in exotic systems, which motivate further theoretical development. The most recent application of the projected shell model (PSM) for proton emitters is represented. We study the rotational bands of the deformed proton emitter 141Ho by using the PSM. The experimental data are well reproduced. Strongly suppressed γ transition from the low-lying IΠ= 3/2+ state makes this state isomeric. Variations in the dynamical moment of inertia are discussed due to band crossings using the band diagram. The calculated results for proton emitter 151Lu shows it is oblately deformed     

丰中子锶同位素的投影壳模型研究

利用考虑跨壳激发的投影壳模型（PSM）方法,研究了质子数Z=38、中子数N=63和64大形变丰中子101,102Sr同位素的结构性质。主要计算了转动谱、转动惯量和电磁跃迁性质等（如B（E2）和g因子）,并与相应的实验数据进行系统比较和相关的理论预言。结果表明,PSM可以利用理论计算的能带图解释101,102Sr同位素的转动惯量、电磁跃迁随自旋的变化,分析晕带的结构。PSM理论可以很好地再现实验结果,说明PSM方法及其采用的有效相互作用可以外推研究丰中子核区101,102Sr同位素的原子核结构。对于101,102Sr同位素,核子开始填布质子g_9/2和中子h_11/2轨道,通过更为仔细地分析能带图中来自质子g_9/2和中子h_11/2轨道对各转动带的组态成分的贡献,清晰地表明丰中子核结构性质对不同核子填布的依赖。Recently, we have carried out systematically studies on the structural properties of proton number Z=38, neutron number N=63 and 64 neutron-rich isotopes 101,102Sr by using the projected shell model (PSM) with consideration of cross shell excitation. The rotation spectra, the moment of inertia and the electromagnetic transition properties (such as B(E2) and g-factor) are calculated and compared with the corresponding experimental data in this paper. Furthermore, more high spin states are predicted in the calculation and expected to be confirmed experimentally. The results show that the PSM can not only well analyze the structural properties of yrast bands in 101,102Sr but also interpret the variation of the moment of inertia, electromagnetic transition with spins in terms with the theoretical band diagram. The good agreement with the experimental data suggests that the PSM with the adopted effective interactions can be generalized to study the nuclear structure of 101,102Sr isotopes in neutron-rich mass region. For 101,102Sr isotopes, the nucleons begin to fill proton g_9/2 and neutron h_11/2 orbital, the dependence of nuclear structure and properties on the different orbital occupies is described by carefully analyzing the contribution from proton g_9/2 and neutron h_11/2 orbital to the configuration of rotational bands in band diagram.     

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.     

Laser spectroscopy of high spin isomers – a review

This review summarizes the experimental data on charge radii differences among ground state and high spin isomeric states determined by high-resolution laser spectroscopic methods. A comparison is presented between radii changes obtained from the isomeric shifts in the atomic spectra and from the quadrupole moments of both ground and isomeric states under the assumption that the radii changes are determined by the difference of the quadrupole deformations. Special attention is paid to isomers arising from the break-up of nucleon pairs and isomers of odd–odd nuclei. The characteristic features of the radii changes for isomeric states of different origin are discussed.     

New isomeric states in 152,154,156Nd produced by spontaneous fission of 252Cf

Isomeric states have been observed in fission-fragments produced by spontaneous fission of ²⁵²Cf. These states are found in neutron rich nuclei of different structure and deformations. About 50 isomeric nuclei have been observed using coincidences between γ-rays identified in EUROGAM II and fission fragments detected in photovoltaic cells (SAPhIR). Lifetimes in the range from 20 ns to 2μs have been measured. Presented calculations based on HFB +D1S force on new measured isomeric states in the ^152,154,156Nd show evidence for K-isomers. Received: 3 November 1997 / Revised version: 15 December 1997     

Mathematical modeling of photoisomerization with intramolecular proton transfer

A system of equations describing time changes in the matrix elements of the density operator of a seven-level model of a molecule interacting with a light pulse taking into account spontaneous (including collective) decays of molecule excited states is suggested. Model parameters were selected to allow us to perform modeling of the photoisomerization of a molecule with two isomeric states with different stable proton positions on an intramolecular H-bond by numerically solving the suggested system of equations for density operator matrix elements. An analysis of the characteristic time dependences of the population of states of the model under consideration showed that proton phototransfer in the collective decay of various isomeric states of a molecule in an excited electronic state can be one of effective mechanisms of the photoisomerization of molecules whose structure is described by the model.     

缺中子核素101In低位同核异能态的首次观测

在兰州重离子加速器冷却储存环（HIRFL-CSR）上,用初级束流112Sn35+轰击了靶厚约10 mm的Be靶,产生了101In的基态和低位同核异能态。这些实验产生的碎片每25 s经过放射性束流线RIBLL2的筛选后注入到实验环CSRe中,利用飞行时间探测器测量离子在CSRe中的回旋周期。在此次实验中,磁场晃动会导致离子在环内的循环周期发生改变,传统的离子鉴别方法难以完成大部分离子的鉴别。通过发展和运用单次注入离子鉴别这一新的离子鉴别方法,有效地消除了磁场晃动对于离子鉴别的影响,并清楚地将101In基态和低位同核异能态鉴别出来,从而首次在实验中观测到101In的低位同核异能态。实验得到的激发能与理论外推值在112 keV的误差范围内一致,其低位同核异能态的寿命大于200 μs。Isochronous mass spectrometry has been applied to 112Sn projectile fragments at the HIRFL-CSR facility in Lanzhou. To produce short-lived nuclei of interest, we used projectile fragmentation of 112Sn35+ primary beams in a~10 mm thick 9Be production target. The fragments were selected and analyzed by RIBLL2 and injected into the experimental storage ring(CSRe) every 25 s. To measure revolution times of stored ions,we used a Time-Of-Flight detector installed in CSRe. A new particle identification method was developed to distinguish ions on the measured revolution time spectrum for each injection. Based on this method, the shifts of the revolution time due to instable dipole magnet fields can be corrected and the ground and isomeric states of 101In have been well-resolved. The measured excitation energy is consistent with the theoretical value in the error range of 112 keV. The lifetime of the isomeric states of 101In is more than 200 μs.     

一些近期发现的同核异能态的壳模型解释

近期,在101In、123,125Ag和218Pa等核中,首次观测到同核异能态。本工作通过原子核壳模型解释In、Ag同位素和$N\!=\!127$同中素中的这些同核异能态及相关的同核异能态背后的物理原因。101-109In这五个奇A核In同位素中,观测到的$1/2^{-}$同核异能态的激发能非常接近。这可以通过引入中子近期,在101In、123,125Ag和218Pa等核中,首次观测到同核异能态。本工作通过原子核壳模型解释In、Ag同位素和$N\!=\!127$同中素中的这些同核异能态及相关的同核异能态背后的物理原因。101-109In这五个奇A核In同位素中,观测到的$1/2^{-}$同核异能态的激发能非常接近。这可以通过引入中子$0g_{7/2}$和$1d_{5/2}$轨道间的很强的组态混合来解释。更进一步分析表明,这些奇A核In同位素中,从$9/2^{+}$基态到$1/2^{-}$同核异能态,一个质子从$1p_{1/2}$轨道激发到$0g_{9/2}$轨道。这一质子组态变化可能引发中子$0g_{7/2}$和$1d_{5/2}$轨道的单粒子能变化。这样一个原子核内的组态依赖的壳演化被称为第二类壳演化。与In同位素类似,123,125Ag的同核异能态被发现是$1/2^{-}$态,对应着一个质子空穴在$1p_{1/2}$轨道。但之前观测到的115,117Ag的$1/2^{-}$态是基态。这意味着质子$1p_{1/2}$轨道和$0g_{9/2}$轨道在$N\!=\!72$附近发生了反转。壳模型分析表明张量力是造成这两个轨道反转的决定性原因。之前观测到的奇奇核$N\!=\!127$同中素210Bi、212At、214Fr和216Ac中,基态是$1^{-}$态,同时存在高自旋的同核异能态。然而,基于$\alpha$衰变性质和壳模型计算,推荐218Pa中的基态和新发现的同核异能态分别为$8^{-}$态和$1^{-}$态。奇奇核$N\!=\!127$同中素基态和同核异能态的演化是由质子中子相互作用从粒子粒子形式转化为空穴粒子形式以及质子组态混合所导致。总的来说,壳模型对这些双幻核100Sn、132Sn和208Pb附近核中新发现的同核异能态有较好的描述。双幻核附近核中的同核异能态,也称为壳模型同核异能态,是核结构研究中非常重要的。因为这些同核异能态常常提供了中重质量区域极端丰中子和缺中子原子核中的第一个谱学性质,并包含了丰富的物理信息,比如质子中子相互作用及其在壳演化中的作用。     

An investigation of the properties of single-particle states in the second minimum of 237Pu

In connection with the recent measurement of the magnetic moments of the fission isomeric states in ²³⁷Pu, we investigate the following subjects: (i) The spin alignment of the lowest-lying states in a potential minimum which are populated by (α, 2nγ) reactions, and the fragment angular distributions in fission from isomeric states. (ii) The single-particle level scheme in a very deformed Woods-Saxon potential. (iii) The spin polarizability as a function of the quadrupole deformation.     

High-resolution studies of the gamma rays from isomeric states with half-lives of 10 μs - 30ms in nuclei with Z = 63−83

Eight new isomeric states with half-lives in the range 10 μs-30 ms have been identified following bombardment with 17.5 MeV protons of the natural elements and separated isotopes of the elements Eu to Pb. Improved data on 14, previously reported, isomeric states have also been obtained. The energies, half-lives and multipolarities of the gamma rays from these states have been measured using an 8 cm³ Ge(Li) detector. In most cases, level schemes have been constructed, and the spin and parity of the isomeric level and intermediate levels populated in the decay have been determined. A group of hindered E2 transitions have been observed, all of which are retarded by approximately the same degree e.g. 3 × 10⁻³ Weisskopf units. The results are discussed in terms of the Nilsson model and in terms of the selection rules for transitions between Nilsson states.     

Continuum three-body states using the hyperspherical adiabatic basis set

In this paper we investigate the feasibility of employing the hyperspherical adiabatic (HA) basis set to describe continuum three-nucleon states. In particular, the HA expansion is compared with the simpler expansion on hyperspherical harmonics (HH). A practical numerical application is presented using the MT-III potential.     

Responses of a Hodgkin-Huxley neuron to various types of spike-train inputs

Numerical investigations have been made of responses of a Hodgkin-Huxley (HH) neuron to spike-train inputs whose interspike interval (ISI) is modulated by deterministic, semi-deterministic (chaotic), and stochastic signals. As deterministic one, we adopt inputs with the time-independent ISI and with time-dependent ISI modulated by sinusoidal signal. The R?ssler and Lorentz models are adopted for chaotic modulations of ISI. Stochastic ISI inputs with the gamma distribution are employed. It is shown that distribution of output ISI data depends not only on the mean of ISIs of spike-train inputs but also on their fluctuations. The distinction of responses to the three kinds of inputs can be made by return maps of input and output ISIs, but not by their histograms. The relation between the variations of input and output ISIs is shown to be different from that of the integrate and fire (IF) model because of the refractory period in the HH neuron.     

Force control between quantum dots by light in polaritonic molecule states

Photomediated force between quantum dots (QDs) is theoretically studied. An attractive (repulsive) interparticle radiation force (IRF) arises by selectively exciting the lower (higher) split state of coupled polaritons in QDs. Since these states are analogous to bonding and antibonding states of a diatomic molecule, we term this system the "polaritonic molecule (PM)". IRF in PM states is controlled by the photon energy, polarization, and phase at each QD. This mechanism can be used to probe internal quantum properties of nano-objects and to manipulate collective dynamics of QDs.     

Erzeugung neuer isomerer Kernzustände durch Kernphotoreaktionen am Antimon und Thallium

The systematic search for new short-lived isomeric states has been continued by irradiation of an additional 32 selected elements with 26 MeV bremsstrahlung. Isomeric transitions were detected using a conventional scintillation spectrometer. Irradiation of antimony led to the production of a new (530±50) μsec isomeric state which decays through emission of partially converted (62±2) keV and (76±3) keV gamma rays. The 530 μsec half-life is tentatively associated with the 136 keV level in Sb¹²². An apparent inconsistency in the previously proposed level scheme of Sb¹²² can be removed if the 3.5 min Sb¹²²-activity is assigned to an isomeric level in Sb¹²² lying less than 15 keV above the 136 keV isomeric state. A new measurement of the half-life of this level yielded a value of (4.1₅±0.2) min. Another new isomeric state with a (2.l±0.2) msec half-life was produced by irradiating thallium. The isomeric state decays by emission of two gamma rays of (335±8) keV and (597±12) keV which were found to be in coincidence. Irradiation of erbium led to the production of a short-lived isomeric transition which may be identical with a previously reported Ho-isomer. Results are discussed in the appendix.     

Isomer triggering via nuclear excitation by electron capture

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.     

Dominance of Fermi-surface holes in p-type tunneling

In-plane uniaxial stress is used to tune continuously the mixing between the heavy-hole (HH) and light-hole (LH) states in a p-type double-barrier structure. The LH1 and HH2 resonant tunneling peaks shift at almost the same rate with stress, in contrast to the corresponding exciton peaks observed by photoreflectance, which exhibit a strong Fano-related anticrossing. Comparison between the observed shifts and a four-band k x p calculation of the state energies in the well provides the first experimental proof that the flow of holes through off-zone center states dominates the resonant tunneling current in p-type structures.     

Special features of isomeric ratios in nuclear reactions induced by various projectile particles

Calculations for (p, n) and (α, p3n) reactions were performed with the aid of the TALYS-1.4 code. Reactions in which the mass numbers of target and product nuclei were identical were examined in the range of A = 44–124. Excitation functions were obtained for product nuclei in ground and isomeric states, and isomeric ratios were calculated. The calculated data reflect well the dependence of the isomeric ratios on the projectile type. A comparison of the calculated and experimental data reveals, that, for some nuclei in a high-spin state, the calculated data fall greatly short of their experimental counterparts. These discrepancies may be due to the presence of high-spin yrast states and rotational bands in these nuclei. Calculations involving various level-density models included in the TALYS-1.4 code with allowance for the enhancement of collective effects do not remove the discrepancies in the majority of cases.     

A k.p model for hole capture into a quantum well

A k.p model for hole capture into a quantum well has been applied to the calculation of the rates for capture via phonon and alloy scattering into a 30Å In_0.7Ga_0.3As-InGaAsP quantum well, a system which is suitable for lasers operating at 1.55 μm. The well has three subbands, derived from the HH1, LH1 and HH2 zone centre states. Capture of holes into the HH2 subband is predicted to be dominated by polar optical phonon emission, whereas scattering into the other two bands proceeds mainly by non-polar optical phonon emission or alloy scattering. There is structure in the capture rate plotted as a function of the energy and in-plane wavevector of the incident hole, which is attributed to instances where incident holes in barrier states undergo strong transmission into the well region. Mixing between the quantum well subbands is important through the effect upon the density of final states in capture transitions, but is less significant with respect to its effect on the scattering matrix elements.     

Static Moments of Neutron-Rich Ground States and Isomers Produced by Projectile Fragmentation

New achievements in nuclear moment measurements on nuclei produced and spin-oriented in intermediate energy (50–80 MeV/u) projectile fragmentation reactions are presented. By combining different types of spin-orientation with different experimental techniques, we show that the magnetic dipole moments and electric quadrupole moments of exotic neutron rich nuclei in their ground state as well as in their excited isomeric states can be measured. A selection of recent experiments performed at the LISE spectrometer at GANIL (Caen, France) is described. This revised version was published online in September 2006 with corrections to the Cover Date.