Photodisintegration of heavy nuclei in the energy region above the giant dipole resonance

Experimental data on yields of multiparticle photonuclear reactions (involving the emission of up to seven neutrons from the nucleus involved) on ¹⁹⁷Au, ^203,205Tl, and ²⁰⁹Bi nuclei in the region extending from the giant dipole resonance to an energy of 67.7 MeV are presented. These data are compared with the results of modern theoretical calculations that take into account both the excitation of a giant dipole resonance (GDR) in a nucleus and the photodisintegration of quasideutrons (QD) in it. By and large, experimental data confirm the results of theoretical calculations—that is, only upon taking simultaneously into account both alternative photodisintegration mechanisms (GDR excitation and QD photodisintegration) can one describe these experimental data. The contribution of QD photodisintegration grows with increasing photon energy and neutron multiplicity and becomes dominant for reactions involving the emission of not less than five neutrons from the nucleus being considered. The integrated cross sections for the processes in question were estimated on the basis of simultaneously employing experimental yields of multinucleon photonuclear reactions and the respective cross-section shapes calculated theoretically.     

Soft dipole mode in the 11Li nucleus within the asymptotic-potential approximation

A soft dipole mode in the ¹¹Li nucleus treated within the microscopic three-cluster model is studied in the asymptotic-potential approximation. The model faithfully reproduces the energy and the root-means-quare radius of the ground state and the behavior of the effective photodisintegration cross section at low energies above the threshold for ¹¹Li breakup, suggesting the existence of two resonance states in this region.     

Cross sections for photodisintegration of 32S to excited residual states

Cross sections and integrated cross sections for photodisintegration of ³²S to specific residual states in ³¹P and ³¹S have been measured. Comparison with spectroscopic factors for nucleon pickup reactions on ³²S leading to the same residual states are made. It is concluded that the creation and decay of the dipole state in ³²S is predominantly a single-nucleon interaction.     

Translationally invariant description of particle-hole states

A translationally invariant model is proposed which allows to calculate one-particle excitations and dipole transition probabilities of closed-shell nuclei with inclusion of the continuum. The connection of this model with the nuclear shell model is shown, and it is applied to the calculation of the photodisintegration cross section of⁴He.     

Nuclear photodisintegration without effective charges

It is explicitly shown that the Thomas-Reiche-Kuhn electric dipole sum rule, for he case of nuclear photodisintegration, separates into a contribution due to dipole absorption by the nucleus as a whole, and a contribution representing excitation of the internal degrees of freedom (Bethe-Levinger sum rule). The concept of the “effective charge”, often employed in this connection, is not utilized in our derivation, and is seen to be not essential.     

Isovector giant E2 resonance and overtone of the isovector giant E1 resonance in photonucleon reactions

The effect of the isovector giant quadrupole resonance and an overtone of the isovector giant dipole resonance on the photodisintegration of medium-mass and heavy nuclei in the energy range of 20–40 MeV is studied on the basis of a combined model of photonucleon reactions. Basic features of these resonances are evaluated within a semimicroscopic approach. Their deformation spitting is described on the basis of the model of polarization vibrations of a two-component nuclear liquid.     

Simulation of photodisintegration of heavy nuclei

A comparative study of the results of the simulations of the photodisintegration of heavy nuclei in the energy range corresponding to the giant dipole resonance by the TALYS software package and by a combined model of is carried out. The cross sections of photoabsorption, photoneutron, and photoproton reactions and of the excitation of isomeric states for Hg and ²⁰⁸Pb isotopes are calculated. The results of the calculations are compared with the known experimental data.     

Analytic solutions to Maxwell–London equations and levitation force for a general magnetic source in the presence of a long type-II superconducting cylinder

The interaction between a general magnetic source and a long type-II superconducting cylinder in the Meissner or mixed state is studied within the London theory. We first study the Meissner state and solve the Maxwell–London equations when the source is a magnetic monopole located at an arbitrary position. Then the field and supercurrent for a more complicated magnetic charge distribution can be obtained by superposition. A magnetic point dipole with arbitrary direction is studied in detail. It turns out that the levitation force on the dipole contains in general an angular as well as a radial component. By integration we obtain the field and supercurrent when the source is a two-dimensional monopole (a magnetically charged long thread along the axial direction), from which the results for a two-dimensional point dipole easily follow. In the latter case the levitation force points in the radial direction regardless of the orientation of the dipole. The case for a current carrying long straight wire parallel to the cylindrical axis is solved separately. The limit of ideal Meissner state is discussed in most cases. The case of mixed state is discussed briefly. It turns out that vortex lines along the axial direction and vortex rings concentric with the cylinder have no effect outside the cylinder and the levitation forces remain the same as in the case of the Meissner state.     

Photodisintegration of 28Si to excited residual states

Integrated cross sections up to 28 MeV have been measured to excited residual states in ²¹Si, ²⁷Al and ²⁴Mg, following the photodisintegration of ²⁸Si. From comparisons with spectroscopic factors of nucleon pickup reactions on ²⁸Si, leading to the same residual states, it is concluded that the photonucleon emission process is predominantly single particle in nature. Estimates of isospin mixing in the ²⁸Si giant dipole resonance are also given.     

Cross sections for the photodisintegration of a deuteron and neutron capture by a proton calculated for the case of nonlocal potential

The processes of deuteron photodisintegration by a gamma-quantum and the radiative capture of a neutron by a proton with the emission of a gamma-quantum are considered. Interaction between nucleons is described by a nonlocal potential of the Yamaguchi type but allowing for repulsion due to the nucleon cores. In contrast to other potentials, the Schroedinger equation is solved exactly for the proposed potential. The potential is more exactly defined in comparison with the previously obtained values for the parameters; information on this potential is important in solving certain fundamental problems in nuclear theory. The effective cross sections for photodisintegration of a deuteron and for radiative capture are computed. Calculations show that the proposed potential makes it possible to describe the photodisintegration processes quite accurately for intermediate (up to 20 MeV) energies. The cross section computed for radiative capture is in somewhat better agreement with experiment than is the same cross section determined for other potentials.     

Magnetic structure of ground state of the KDy(WO4)2 single crystal

The data of low-temperature magnetic measurements of the monoclinic KDy(WO₄)₂ crystal are used to calculate the exchange and dipole–dipole interactions energy. The last are used for the determination of the magnetic structure of the ground state.     

Photodisintegration of Light Nuclei

Recent results of photodisintegration of deuteron and ³He measured with the CEBAF Large Acceptance Spectrometer at Jefferson Lab are reported. The onset of dimensional scaling is investigated in the two-body photodisintegration of ³He, with the results indicating a scaling onset at remarkably low energy and momentum transfer. Results on the azimuthal asymmetry of deuteron photodisintegration are expected to aid in understanding the dominant mechanisms of deuteron photodisintegration and the underlying dynamics in the medium-energy region. In this region, neither effective field theories nor perturbative QCD can be used to describe the reaction, and understanding the underlying dynamics is based on phenomenological quark models.     

Is MFM really useful?

The ill-posed linear inverse problems, characterised by Fredholm integral equations of the first kind, are encountered in many areas of science and technology. This type of problems present some loss of information under the inversion process. The loss of information often makes the inversion process very difficult. Magnetic force microscopy (MFM) is a technique where problems related to loss of information occur. Work is presented here to understand what can be measured by the magnetic force microscope. A simple model is constructed, where the magnetic tip is approximated by a point dipole. Given the force F() acting on the dipole tip, we attempt to determine the magnetization distributlon in a thin ferromagnetic film, M(). This calculation should be interesting due to the rapidiy growing interest in magnetic thin films and magnetic multilayers. Received 3 December 2001 and Received in final form 11 March 2002     

钫原子磁偶极超精细结构常数及其同位素的磁偶极矩的理论计算

应用基于B样条基组的相对论耦合簇理论方法,计算了~(212)Fr原子的n S (n=7—12), n P (n=7—12)和n D (n=6—11)态的磁偶极超精细结构常数.与精确实验值的比较说明这套理论方法能精确计算出磁偶极超精细结构常数,其中7P态的磁偶极超精细常数的理论值与实验值之间的差异小于1%.在忽略场移效应对Fr原子7P态超精细结构常数的影响下,通过结合实验值进一步定出了~(207-213,220-228)Fr核磁偶极矩μ,这些值与已有的测量值具有非常好的一致性.本文报道了12S, n P (n=9—12)和n D (n=10—11)态的磁偶极超精细结构常数.     

Measurement of nuclear moments and radii by collinear laser spectroscopy and by β-NMR spectroscopy

Experiments using laser spectroscopy and nuclear magnetic resonance techniques have been performed at ISOLDE on the unstable isotopes of several light elements. The results include nuclear ground state spins, magnetic dipole and electric quadrupole moments, and the behaviour of mean square nuclear charge radii within isotopic strings. These give important information about the nuclear structure at shell closures and close to the drip lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

磁记忆检测的力磁耦合型磁偶极子理论及解析解

磁偶极子理论在缺陷漏磁场解释中被成功广泛使用.由于磁荷密度等参数不易定量,磁偶极子理论在应用中常常进行归一化处理,被认为不适用于对应力相关的磁记忆信号做量化分析.本文通过建立力磁耦合型磁偶极子理论模型,以适用于分析磁记忆检测中应力对磁信号的影响.基于铁磁学理论确定应力和磁场联合作用下的等效场强度,基于弱磁化状态的一阶近似,获得了各向同性铁磁材料微弱环境磁场下的应力磁化解析解.结合磁信号二维问题中矩形和V形磁荷分布假定,建立了光滑与破坏试件表面磁信号、矩形和V形表面缺陷所诱导磁信号的力磁耦合型磁偶极子理论分析模型,并获得其解析解.基于力磁耦合型磁偶极子理论的解析解,对拉伸实验中试件破坏前后的信号差异、矩形和V形表面缺陷诱导磁信号,以及磁信号的影响因素和规律等进行了详细分析.理论研究表明,基于本文理论模型的解析解可实现对磁记忆检测中的一些基本实验现象和规律的解释.     

Zero field muon spin relaxation rate in the superconducting state of Nb3Al

It was shown that at T=12 k the dipole relaxation of a positive muon in Nb₃Al in the zero external magnetic field is well described by the Kubo-Toyabe function for the static distrubution of the dipole magnetic fields in the absence of muon diffusion. The superconducting state of Nb₃Al was used for eliminating the background from muons stopped in the cryostat walls.     

Determination of Deuteron Dipole Moment in Nuclear Quark-Like Model

Using the quark-like model, we have improved the existing deviation between theoretical and experimental values of magnetic dipole moment of deuteron. Based upon Pauli Exclusion Principle, the constituent quarks form a ground state for l = 0. The expectation value of the deuteron magnetic dipole moment operator is determined to be equal to 0.861 597 8μ N in better agreement with the measured value of 0.857 437 6μ N as compared to the shell model calculations.