Dynamical polarization of radioactive nuclei

In order to polarize radioactive nuclei implanted in a highly polarized protonic target, it is proposed to use methods for the dynamical orientation of nuclei. The angular distribution of photons that originate from the cascade beta-gamma decay of the ²²Na(3⁺) state in a strong magnetic field is calculated. It is shown that, if the populations of Zeeman magnetic sublevels obey the Boltzmann distribution, the angular distribution of emitted photons is independent of the sign of spin temperature; at the same time, the tensor polarization of quadrupole nuclei occurring in the intrinsic field of a crystal causes a strong dependence of the anisotropy on the sign of spin temperature. A rich potential of a dynamical orientation for studying the magnetic structure of rare nuclei and the dynamics of their spin-spin interactions in dielectric host materials is demonstrated. Physical and technological advantages and disadvantages of the method in the on-line regime of the implantation of heavy nuclei are discussed.     

Tilted foil technique applied to beta-NMR studies

In this article, applications of the tilted foil technique to beta-NMR studies using polarized beta-emitters by the Osaka group are reviewed. Many efforts have been made to expand the applicability of the tilted foil technique to a much wider variety of nuclei. Various aspects of experimental studies have been carried out to disclose fundamental polarization mechanisms utilized in the tilted foil technique.     

Tilted rotation of triaxial nuclei

The Tilted Axis Cranking theory is applied to the model of two particles coupled to a triaxial rotor. Comparing with the exact quantal solutions, the interpretation and quality of the mean field approximation is studied. Conditions are discussed when the axis of rotation lies inside or outside the principal planes of the triaxial density distribution. The planar solutions represent ΔI = 1 bands, whereas the aplanar solutions represent pairs of identical ΔI = 1 bands with the same parity. The two bands differ by the chirality of the principal axes with respect to the angular momentum vector. The transition from planar to chiral solutions is evident in both the quantal and the mean field calculations. Its physical origin is discussed.     

Tilted rotation of weakly deformed and triaxial nuclei

The Tilted Axis Cranking theory is reviewed. It is used to describe the appearance of magnetic rotation in weakly deformed nuclei. The possibility of aplanar solutions and their experimental signature are discussed.     

Search for radioactive superdense nuclei

The results of an experimental search for new long-lived particles performed at Serpukhov discussed in terms of the possible existence of superdense nuclei. The upper limits of cross sections for the production of radiactive superdense nuclei in collisions of high energy protons with normal nuclei are presented.     

Physics with beams of radioactive nuclei

A survey of the latest results from experiments devoted to studying the structure of nuclei and nuclear-reaction mechanisms by means of accelerated radioactive beams is given. Results obtained in Dubna with the aid of the DRIBs accelerator complex and at other radioactive-beam factories are presented.     

Spectroscopic factors for two-proton radioactive nuclei

Spectroscopic factors for two-proton emitting nuclei are discussed in the framework of the BCS (Bardeen-Cooper-Schriefer) model. Calculations carried out for the two-proton unstable⁴⁵Fe,⁴⁸Ni and⁵⁴Zn nuclei are presented.     

Production of nuclear polarization of unstable nuclei via polarization transfer reactions

To determine experimental conditions suitable for isotope analysis, we studied the plume dynamics of uranium. A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm². The temporal evolution of the ablation plume was investigated in 800 Pa helium environment. It was found that the observation at 3–5 μs after the ablation at the height of about 2.5 mm are most suited for obtaining higher sensitivity. Using the established conditions, we obtained the limit of detection of the isotope ratio (²³⁵U/²³⁸U) to be 0.01 %. In addition, the limit of detection of elemental abundance of uranium in uranium glass was also evaluated.     

Precision mass measurements of radioactive nuclei at JYFLTRAP

The Penning trap mass spectrometer JYFLTRAP was used to measure the atomic masses of radioactive nuclei with an uncertainty better than 10 keV. The atomic masses of the neutron-deficient nuclei around the line were measured to improve the understanding of the rp-process path and the SbSnTe cycle. Furthermore, the masses of the neutron-rich gallium ( ) to palladium ( ) nuclei have been measured. The physics impacts on the nuclear structure and the r-process paths are reviewed. A better understanding of the nuclear deformation is presented by studying the pairing energy around .     

Reactions with fast radioactive beams of neutron-rich nuclei

The neutron dripline has presently been reached only for the lightest nuclei up to the element oxygen. In this region of light neutron-rich nuclei, scattering experiments are feasible even for dripline nuclei by utilizing high-energy secondary beams produced by fragmentation. In the present article, reactions of high-energy radioactive beams will be exemplified using recent experimental results mainly derived from measurements of breakup reactions performed at the LAND and FRS facilities at GSI and at the S800 spectrometer at the NSCL. Nuclear and electromagnetically induced reactions allow probing different aspects of nuclear structure at the limits of stability related to the neutron-proton asymmetry and the weak binding close to the dripline. Properties of the valence-neutron wave functions are studied in the one-neutron knockout reaction, revealing the changes of shell structure when going from the beta-stability line to more asymmetric loosely bound neutron-rich systems. The vanishing of the N = 8 shell gap for neutron-rich systems like ¹¹Li and ¹²Be, or the new closed N = 14, 16 shells for the oxygen isotopes are examples. The continuum of weakly bound nuclei and halo states can be studied by inelastic scattering. The dipole response, for instance, is found to change dramatically when going away from the valley of stability. A redistribution of the dipole strength towards lower excitation energies is observed for neutron-rich nuclei, which partly might be due to a new collective excitation mode related to the neutron-proton asymmetry. Halo nuclei, in particular, show strong dipole transitions to the continuum at the threshold, being directly related to the ground-state properties of the projectile. Finally, an outlook on future experimental prospects is given.     

Symmetry properties of radioactive N=Z nuclei

Recent mass measurements of proton-rich nuclei close to the N=Z line were used for the calculation of the interaction strength δV _pn between valence protons and neutrons. When compared with δV _pn values calculated from mass values of the AME’95 mass tables, the breaking down of the SU(4) symmetry is verified at Z=32,33,34.     

放射性核束物理研究中的一些热点问题

文章介绍了放射性核束物理的现状和进展,给出了一些目前热点的研究问题和方向,比如垒下融合反应、费米能区和高能区直接核反应、滴线核性质、非稳定核区的新幻数和新的集体运动模式等.     

Alignment effects in heavy ionized beam foil excited atoms

We have measured the polarization of light emitted in optical transitions in P V, O VII and O VIII, produced by beam foil excitation, using a 400 keV phosphorus beam from a heavy ion accelerator and a 36 MeV oxygen beam from a Tandem Van de Graaff generator.     

Gamma-ray linear polarization measurement on oriented nuclei

Measurement of linear polarization of gamma-rays from nuclei oriented by hyperfine interaction at low temperatures using the³He/⁴He dilution refrigerator at the SERC Daresbury Laboratory is reported. Three different types of a Compton polarimeter were assembled using coaxial Ge(Li) detectors. The method was applied to¹⁹²IrFe and⁶⁰CoFe and a polarization detection efficiency curve and a figure of merit for each polarimeter were produced. As a result of combined directional distribution and linear polarization measurements multipole mixing ratios of several transitions in¹⁹²Pt have been obtained and are compared with theoretical predictions.     

Theory of chemical polarization of nuclei. II

A specific example is considered of a radical reaction on the basis of equations obtained in Pt. 1 which describe time-changes in magnetization of nuclei polarized in a reaction process. An explicit expression is found for the dynamic polarization coefficient of the nuclei and the contribution to this coefficient of two different processes is analyzed: spin polarization in the process of chemical reaction (when the activized complex is disintegrating) and the transfer of polarization which has occurred in the original particles due to the Overhouser intermolecular effect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 113–118, September, 1972.