Electromagnetic moments of nuclei at high-spin

Choosing some of the current topics in the field of high-spin nuclear physics, I discuss what we learn from the study of electromagnetic moments of the high-spin states. Chosen topics are triaxial shape, superdeformed band, high-spin states with oblate shape, and g-factor before and after band-crossings.     

Neutron-nucleus spin-spin interaction studied with polarized neutrons and polarized 59Co nuclei

We measured the spin-spin cross section of polarized ⁵⁹Co for polarized neutrons of 0.39–2.88 MeV in the perpendicular geometry. Comparing our results with existing data we conclude that the spin-spin potential is of the spherical type.     

Characteristics of alpha projectile fragments emission in interaction of nuclei with emulsion

The properties of the relativistic alpha fragments produced in interactions of ⁸⁴Kr at around 1 A GeV in nuclear emulsion are investigated. The experimental results are compared with the similar results obtained from various projectiles with emulsion interactions at different energies. The total, partial nuclear cross-sections and production rates of alpha fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass number and initial energy of the incident projectile nucleus are investigated. The yields of multiple alpha fragments emitted from the interactions of projectile nuclei with the nuclei of light, medium and heavy target groups of emulsion-detector are discussed and they indicate that the projectile-breakup mechanism seems to be free from the target mass number. It is found that the multiplicity distributions of alpha fragments are well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The mean multiplicities of the freshly produced or newly created charged secondary particles, normally known as shower and secondary particles associated with target in the events where the emission of alpha fragments were accompanied by heavy projectile fragments having Z ≥ 3 seem to be constant as the alpha fragments multiplicity increases, and exhibit a behavior independent of the alpha fragments multiplicity.     

Vector polarization effect appearing in tensor polarized beams of nuclei under channeling conditions and during measurements of the quadrupole moments of unstable nuclei

General relations describing the spin dynamics of beams of nuclei with initial tensor and vector polarizations have been derived upon planar channeling in bent crystals. The performed analysis indicates that the vector polarization effect predicted by Baryshevsky and Sokolsky can be detected, occurring upon the planar channeling of a beam of nuclei with initial tensor polarization. The planar channeling of a beam of nuclei with initial tensor and vector polarizations can be used to determine the quadrupole moments of unstable nuclei with small lifetimes, up to 10⁻⁷ s. The quadrupole moments of nuclei with lifetimes of about 10⁻⁷ s cannot be measured via known methods, including optical methods.     

Development of atomic-beam resonance method to measure the nuclear moments of unstable nuclei

We have been working on the development of a new technique of atomic-beam resonance method to measure the nuclear moments of unstable nuclei. In the present study, an ion-guiding system to be used as an atomic-beam source have been developed.     

Azimuthal correlations of projectile and target fragments in collisions between gold nuclei of energy 10.6 GeV per nucleon and emulsion nuclei

Intra-and intergroup azimuthal correlations of projectile and target fragments are found in collisions between gold and emulsion nuclei. The statistical significance of these correlations is high. The methodological distortions associated with the measurement errors are investigated in detail and are taken into account.     

Neutron-rich nuclei studied with AMD

Antisymmetrized molecular dynamics (AMD) which is a newly constructed theory of quantum-mechanical microscopic simulation of heavy ion collisions is explained to present us with a very useful theoretical approach for the study of the structure-changes which occur when we go from ordinary nuclei to exotic neutron-rich nuclei. It is because of the flexible nature of the AMD wave function which can describe the formation and dissolution of clusters both in collision problems and in structure problems. After brief explanation of successful applications of AMD to heavy ion collisions and that of the frictional cooling technique for constructing minimum-energy wave functions, the results of the AMD analyses of Li, Be, and B isotopes are discussed. Very good reproduction of magnetic moments is obtained and is explained to be related with the structure-change between cluster structure and shell-model-like structure within each isotope. The superposition of AMD determinants is shown to reproduce neutron halo structure.     

The determination of nuclear moments from the angular distribution of radiation emitted by dynamically polarized nuclei

A method is suggested which allows the establishment both of the sign and magnitude of quadrupole interaction and the magnitude of magnetic moment of radioactive nuclei. The dynamic polarization of these nuclei is assumed (by means of the effet solide or the method of Jeffries) as well as the subsequent change of the degree of orientation (by means of saturation of some suitable nuclear transitions). The comparison of resonant frequencies for negative and positive initial polarization gives the values of the above-mentioned quantities. The angular distribution of the intensity of radiation emitted is used for the detection of changes in the degree of polarization.     

Electromagnetic properties of the transitional odd-A nuclei studied by projection method

In the framework of the angular momentum projection method, the amplitudes of quadrupole electric transitions and the quadrupole moments of odd-A nuclei are calculated. A microscopic method is presented to evaluate these quantities. The method is applied to ¹⁹³Ir and ^195,197Au.     

Extraction of thermalized projectile fragments from gas

The NSCL gas cell and quadrupole ion-guide system has been used to study the thermalization of fast nuclear reaction products in a buffer gas. The fraction of radioactive ions that can be extracted from the gas cell is dramatically suppressed by space charge created by the stopping ions. The results of a review of the ion yields from the NSCL and from other gas cells from the literature with different sizes and different incident particle energies shows an overall consistency with a dramatic decline in extraction efficiency at high ionization rates.     

Magnetic moments of mirror nuclei with tilted-foil polarization

We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions. The nuclei are polarized by the tilted foil technique and the resulting 0–180^○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in this program was the measurement of the βasymmetry and the NMR resonance for the ground state of ²³Mg (I=3/2, T_1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique is also contemplated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electromagnetic moments of the doubly closed shell ±1 nucleon nuclei and on-line nuclear polarization

Electromagnetic moments of doubly closed shell ±1 nucleon nuclei were studied. Recent technical developments of the β-NMR was shown that was applicable for the polarized β emitters. Also, the implication of those new moments were discussed especially on the nuclear interactions and non nucleonic degrees of freedom.     

Electric dipole moments of nuclei

Recent calculations by Sushkov, Flambaum and Khriplovich have suggested that the existence of the possibility of kaon exchange within nuclei allows nuclear electric dipole moments within the standard model to be enhanced substantially over those of nucleons. This suggestion is analysed carefully and it is found that the constraints of chiral symmetry, which were not correctly included in the earlier calculation, reduce this prediction substantially.     

Magnetic moments of Gd nuclei

Low temperature nuclear orientation experiments down to 2 mK on¹⁴⁷GdFe,¹⁴⁹GdFe,¹⁴⁹GdGd and¹⁵³GdGd have yielded the magnetic hyperfine interaction strength. Bhf as 31.0(1.6) _NT, 28.3(2.0) _NT, 33.8(4.7) _NT and 13.3(2.1) _NT respectively. From these values the respective ground state magnetic moments ¦¦ of¹⁴⁷Gd,¹⁴⁹Gd and¹⁵⁹Gd were deduced as 1.12(20) _N, 1.01(16) _N and 0.40(8) _N.     

Magnetic moments of light nuclei

Magnetic moments of the nuclei ¹⁵N, ¹⁵O, ¹⁷O, ¹⁷F and ¹⁹F are investigated. The importance ; of configuration mixing as well as meson-exchange currents is discussed in detail. Meson-exchange currents are treated in the one-boson exchange limit. Short-range N-N correlations are obtained from solutions of the Bethe-Goldstone equation for doubly closed shell nuclei by the use of realistic N-N potentials which ensure a correct treatment of tensor correlations.     

NMR of short-lived nuclei implanted in crystals and a new isol for projectile fragments in relativistic heavy-ion reaction

Hyperfine interactions of substitutional and interstitial impurities in crystals were studied by use of the asymmetric β decay and NMR detection, following recoil implantation. A new ISOL for the projectile fragments produced in relativistic heavy-ion reaction separated radioactive isotopes. Their high kinetic energies obtained in the reaction enabled us to created spin polarization artificially in the isotopes and to implant them deep in any material.     

The 51V(n, γ)52V reaction studied with polarized neutrons and polarized vanadium nuclei

Circular polarization of γ- radiation following capture of polarized thermal neutrons by unoriented nuclei and the angular distribution of such radiation, using polarized neutrons and polarized nuclei, made it possible to assign spins to 13 levels of ⁵²V. In addition the admixtures of spin-3 and spin-4 reaction channels could be derived for 20 primary γ-ray transitions. With this information interference phenomena in the ⁵¹V(n, γ) reaction were studied. The low-lying levels of ⁵²V are compared with shell-model calculations. The capture mechanism is discussed in terms of a doorway-state model.     

Rotation of fissioning nuclei in reactions with polarized neutrons

Advantages and disadvantages of taking into account rotation of polarized nuclei in classical trajectory calculations of ternary fission are considered. Expressions for polarization of the fissioning deformed compound nucleus which allow for the quantum number K in the fission channel are derived.     

Magnetic moments of odd-odd spherical nuclei

We analyze the time-like processes $ \gamma\gamma\rightarrow B\overline{B}$ and $ p\bar{p}\rightarrow\gamma M$ at large Mandelstam variables within the handbag approach, for which the process amplitudes factorize in hard partonic subprocesses and annihilation form factors. The latter represent moments of baryon-antibaryon generalized parton distributions (GPDs). Symmetry relations restrict the number of independent annihilation form factors for the ground state baryons drastically. We determine these form factors from the present BELLE data on $ \gamma\gamma\rightarrow B\overline{B}$ with the help of simplifying assumptions. The knowledge of these form factors allow for predictions of $ p\bar{p}\rightarrow\gamma M$ for various mesons which may be probed at FAIR.