Measurement of quadrupole moments of unstable nuclei during channeling and the possibility of revealing the effect of vector polarization of tensor-polarized beams of nuclei

General relations are deduced which describe the spin dynamics of beams of nuclei with the initial tensor and vector polarizations upon planar channeling in bent crystals. Our analysis demonstrates the possibility of revealing the effect of vector polarization, as predicted by Baryshevsky and Sokolsky, which occurs upon the planar channeling of a beam of nuclei with initial tensor polarization. The planar channeling of a beam of nuclei with the initial tensor and vector polarizations may be used to determine the quadrupole moments of unstable nuclei with a small lifetime of up to the order of 10^?7 s. The quadrupole moments of nuclei with a lifetime on the order of 10^?7 s cannot be measured by known techniques, including optical methods.     

Transition strengths and shapes of 2-qp bands in 74Se and 76Kr

The lifetimes of the states of −ve parity 2-qp bands of N=40 nuclei ⁷⁴Se and ⁷⁶Kr were measured. The transition strengths and quadrupole moments, obtained from the lifetimes, show a large collectivity of such bands in both the nuclei. The alignment frequencies were calculated from Woods-Saxon cranking model. Previously suggested quasi proton nature of band 5 and 6 of ⁷¹Se were argued to be based on quasi neutron excitations. The total Routhian surface calculations suggest triaxial shapes with large +ve and −ve values of triaxiality parameter γ after proton and neutron alignments in these bands respectively.     

Tensor polarization of 12C(2+), 24Mg(2+), and 28Si(2+) oriented nuclei

Measured and calculated angular dependences of components of the polarization tensor of a ¹²C nucleus in the 2⁺ state at 4.44 MeV formed in various reactions involving light particles, as well as ²⁴Mg(2⁺, 1.369 MeV) and ²⁸Si(2⁺, 1.78 MeV) nuclei formed in inelastic alpha-particle scattering, are presented. The experimental tensor polarization in question was reconstructed on the basis of the densitymatrix spin-tensors found previously for these nuclei. The parameters of the quadrupole and hexadecapole orientation of the nuclei under study were obtained. The experimental polarization features were compared with the results of calculations based on the coupled-channel method. Special features of the behavior of tensor polarizations in various reactions were discussed. The similarity of the experimental angular dependences of the components of tensor polarizations in inelastic deuteron and ³He scattering on ¹²C nuclei, as well as in inelastic alpha-particle scattering on ²⁴Mg and ²⁸Si nuclei, was demonstrated.     

Polarization of quadrupolar nuclei

A method of obtaining high polarization and pure spin states of impurity nuclei with a moderately strong quadrupole interaction in solid diamagnetic hosts whose nuclei have spin 1/2, a large g factor (like ¹H and ¹⁹F), and a high degree of polarization is proposed. The method employs cross-relaxation transitions of the impurity nuclei with the host spins (with adiabatic variation of the external magnetic field) and simple radio-frequency pulses that invert the host nuclei or give rise to two-spin resonance of the host and impurity nuclei. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 539–543 (10 October 1998)     

Polarization of leading Λ hyperons produced by neutrons on target nuclei

The polarization of the leading Λ hyperons produced on carbon and lead target nuclei by 4–10 GeV neutrons in the angle range Θ<8.5° with respect to the beam and with only neutral-particle accompaniment is measured: 〈Π〉=−0.096±0.018 for C and 〈Π〉=− 0.128±0.047 for Pb. The dependence of the polarization on the transverse momentum and the Feynman variable is measured. The normalized invariant cross section as a function of p _⊥ ² is found to be approximated by the function A exp(−Bp _⊥ ² ), where the parameter B is independent of the kind of nucleus (B=8.71±0.09 (GeV/c)⁻² for carbon and B=8.83±0.18 (GeV/c)⁻² for lead). Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 237–240 (25 August 1996)     

Time reversal tests with polarized nuclei—A review

The concepts of time reversal tests with polarized nuclei and the present status of the data are reviewed. Terms odd inT orPT can be explored by studying the symmetry of the spatial correlations between the nuclear polarization vector, the momentum vectors of the electrons, neutrinos, or gamma rays, together with the polarization vectors of the electrons or gamma rays. At the present time, upper limits of about 10⁻³ for the amplitudes of these terms have been established.     

Nuclear spin echo in magnetics with inhomogeneous hyperfine and quadrupole interaction

Additional spin-ocho signale from quadrupole nuclei with I=7/2 (Co⁵⁹ nuclei in Co and Fe−Co thin films) were investigated. It has been shown, that the time dependence of the additional ocho signals, arising at the time moments 2nς reflect quadrupole interaction inhomogenety.     

Fission lifetimes of Th nuclei measured by crystal blocking

Crystal blocking lifetime measurements have been made for highly excited Th nuclei with neutron number well removed from the stability line. Thin W crystals were bombarded with ³²S ions in the energy range 170-180 MeV and the yield of fission fragments was measured for emission close to a 〈111〉 axis. The fission blocking dips are compared to the appropriately scaled ones for elastic scattering of the ³²S beam ions and no significant difference is seen between the dips. This implies that the fraction of nuclei fissioning with lifetimes longer than 10 as is less than 2%. Fission lifetimes are increased by viscosity in the nuclear mass flow and comparison with a statistical model calculation indicates that the viscosity parameter, η, must be lower than for Th and U nuclei near β-stability. The effect of the N = 126 magic number is discussed. Received: 2 October 2002 / Accepted: 16 January 2003 / Published online: 29 April 2003     

The challenge of polarizations in hadronic hyperon production

The large amount of data on hyperon polarizations in inclusive production by hadrons at high energies has recently been extended to Λ and Ξ ⁻ production by Σ ⁻ beams. The sign of the Ξ ⁻ polarization is negative and the same as in Λ and Ξ ⁻ production by protons. The sign of the Λ polarization, however, is positive, in contrast to the negative sign expected by analogy to the proton beam data for Λ and Ξ ⁻ polarization. Theoretical expectations, for instance from a recombination model, also favoured negative polarization of Λ produced by Σ ⁻. Moreover, while the Λ polarization increases with p _t at values below ≈1 GeV/c as observed for other hyperon polarizations, it vanishes above p _t ≈ 1.2 GeV/c. Such a breakdown at large pt has not been observed in any other beam/hyperon combination.     

Decoupling and coherence in E1 and E2 moments in drip line nuclei

I discuss first the effect of decoupling of extended wave functions and the coherence in the low-energy E1 strength in drip line nuclei ¹²Be and ¹³O, which are studied by large-scale shell model calculations including 3 ?ω configuration space. The calculated results are compared to recent experimental data of Coulomb excitations. The quenching of the core polarization charges in drip line nuclei is also discussed in relation to recent observations of quadrupole moments in B-isotopes. Received: 1 May 2001 / Accepted: 4 December 2001     

Polarized recoil nuclei from nuclear reactions induced by polarized lithium ions

The production of vector polarized recoil nuclei was investigated for nuclear reactions initiated by vector polarized⁶Li and⁷Li beams of energies up to 20 MeV. The vector polarization was detected by theβ-asymmetry of the decaying recoil nuclei implanted into various stopper materials. Considerable polarization values were observed for⁸Li produced in the systems⁷Li+⁹Be,⁷Li+⁷Li and⁶Li+⁷Li, and for¹²B in the systems⁷Li+⁷Li and⁶Li+¹¹B. However, no polarization has been observed for heavier nuclei with unknown nuclear moments. The relaxation of the vector polarization of⁸Li implanted into various stopper materials at room temperature was investigated in detail. For a gold stopper it was found to be much larger when compared to earlier results.     

Studies of weak electric quadrupole interaction in57,60CoFe using modulated adiabatic passage on oriented nuclei

The electric quadrupole interactions at⁵⁷Co and⁶⁰Co in co-diffused^57,60CoFe single crystal have been measured using Modulated Adiabatic Passage on Oriented Nuclei (MAPON). The quadrupole splittings Δν_Q<100> are + 18(2) kHz for⁵⁷Co and +9(2) kHz for⁶⁰Co, corresponding to a principal electric field gradient (efg) tensorV _zz =2.0(5)×10¹⁹ Vm⁻² and 2.5(6)×10¹⁹ Vm⁻², respectively, in broad agreement with previous MAPON results for CoFe. The distributions of the efg’s are very similar for the two isotopes, verifying that previously reported differences in⁵⁸CoFe and⁶⁰CoFe could be attributed to different host preparations. The measurement of such weak efg’s which are not spectroscopically resolved, allows determination of new nuclear electric quadrupole moments, not accessible by other techniques. Applications to other systems are discussed.     

Proton polarization in the p(e,e′p)π0 reaction and the measurement of quadrupole components in the N to Δ transition

The recoil proton polarization in the π⁰ production off the proton with longitudinally polarized electron beam has been studied as a means to measure quadrupole components in the N to Δ transition. On top of the Δ resonance a high sensitivity to a possible Coulomb quadrupole excitation is found in parallel kinematics. The ratio of S ₁₊/M ₁₊ multipole amplitudes can be determined from the ratio of the two in-scattering-plane recoil proton polarization components. Avoiding the absolute measurement of the polarizations, such a ratio allows small experimental uncertainties. Furthermore, the electron helicity independent proton polarization component enables the characterization of resonant and non-resonant pieces. Received: 3 November 1997     

Effect of the Pauli exclusion principle and the polarization of nuclei on the potential of their interaction for the example of the 16O+16O system

On the basis of the energy-density method, the effect of simultaneously taking into account the Pauli exclusion principle and the monopole and quadrupole polarizations of interacting nuclei on their interaction potential is considered for the example of the ¹⁶O + ¹⁶O system by using the wave function for the two-center shell model. The calculations performed in the adiabatic approximation reveal that the inclusion of the Pauli exclusion principle and the polarization of interacting nuclei, especially their quadrupole polarization, has a substantial effect on the potential of the nucleus-nucleus interaction.     

Polarization of Luminescence in the Nanostructure Si/CaF<Subscript>2</Subscript> Upon Polarization of the Nuclear Spins of Fluorine

The laws governing polarization of luminescence in the nanostructure Si/CaF₂ upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically. The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅10⁷ to 3⋅ 10⁸ sec⁻¹ with the CaF₂ layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 524–529, July–August, 2005.     

Quadrupole strength function and core polarization in drip line nuclei

Using the self-consistent Hartree-Fock calculation plus RPA with Skyrme interactions, the RPA quadrupole strength function is estimated in the coordinate space, including simulataneously both the isoscalar and the isovector correlation. We discuss the result of the isoscalar, the isovector and the electric quadrupole polarization of the Ca-isotopes from the proton drip line towards the neutron drip line. We study also the comparison of the polarizations in the A = 48 mirror nuclei, ₂₈⁴⁸Ni₂₀ and ₂₀⁴⁸Ca₂₈, and the dependence of the polarizations of ₈²⁸O₂₀ on various Skyrme interactions.     

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.     

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.     

A transmission γ-ray polarimeter for sign measurements of magnetic moments of radioactive nuclei

A transmission γ-ray circular polarimeter has been developed for the measurement of the sign of magnetic moments of radioactive nuclei with low-temperature nuclear orientation. The signs of the magnetic moments were determined for 30h¹⁹³Os (+), 4.9s^191mIr (+), 74 d¹⁹²Ir (+), 19h¹⁹⁴Ir (+) and 4.0 d^195mPt (−).     

Measurement of the Electric Quadrupole Moment of the 9/2− and 21/2− Isomers in 173Ta

The electric quadrupole moments of the 9/2⁻ and 21/2⁻ isomeric states of ¹⁷³Ta at 165.8 keV and 1713.2 keV, respectively, were measured as Q(9/2⁻)=2.92(15) b and Q(21/2⁻)=6.23(18) b for the first time using the TDPAD technique. A 66 MeV pulsed ¹²C ion beam from the 15UD pelletron accelerator facility of the Nuclear Science Centre at New Delhi was used in the reaction ¹⁶⁵Ho(¹²C, 4nγ)¹⁷³Ta. The experimental values of equilibrium deformations β₂(9/2⁻)=0.251(7) and β₂(21/2⁻)=0.391(7) were extracted. This revised version was published online in July 2006 with corrections to the Cover Date.