M.B. Goldberg

Hyperfine interaction studies of heavy nuclei in highly ionized atoms

Abstract A detailed and extensive study of the hyperfine interaction of nuclei with highly ionized atoms in gas is reported. Some new and unexpected features of the interaction are discussed. These relate to the pressure dependence of the perturbation, its variation with Z and dependence on recoil velocity; g -factors of 2 + levels were determined for nuclei in the mass range: 148 ≦ A ≦ 190.

Precession measurements following Coulomb excitation with oxygen ions (VI). Hyperfine interactions of nuclei in highly ionized atoms

Abstract Measurements are reported of angular distributions of gamma rays from excited 2 + states of various nuclei recoiling into vacuum or gas. The angular distributions are found to be perturbed by strong hyperfine fields generated by the highly ionized atoms. Both in vacuum and in gas, the interaction is found to be predominantly magnetic dipole and of a rapidly fluctuating character. In gas, the fluctuations in the field direction are due to collisions (at the rate of about 2 × 10 13 sec −1 at atmospheric pressure), and in vacuum they are brought about by optical transitions (at a rate of about 3 × 10 11 sec −1 ). The average hyperfine field of Nd or Sm emerging from a solid target with 10 MeV kinetic energy is found to be 25.5 ± 2.5 MG. Measurements of g -factors of 2 + excited states have been carried out, and the values of g -factors (relative to g( 152 Sm )) are reported for 150 Sm, 154 Sm, 148 Nd and 150 Nd.

Hyperfine interactions of the 6.13 MeV, 3− state of 16O in ions of low charge state

Abstract The hyperfine interactions of the 6.13 MeV, 3 − state of 16 O in ions recoiling into vacuum with velocity v / c = 1.06% have been studied using perturbed angular correlations. Time-differential and external magnetic field de-coupling experiments have been carried out. The de-coupling curve and the time dependence of the perturbation have been interpreted in terms of a microscopic calculation yielding values of ¦g¦ = 0.57 ± 0.05 and 0.54 ± 0.05 respectively, for the g -factor of the 3 − state. A value of 26.6 ± 0.7 ps for the lifetime of this level was also obtained as a by-product of the investigation.

The g-factor of the 8+ yrast level in 84Sr via a tilted multi-foil experiment☆

Abstract The g-factor of the 8+ yrast level of 84Sr has been measured using the polarized hyperfine fields of a tilted multi-foil target. The sign of the g-factor has been determined to be negative to better than six standard deviations. Calibration using similar measurements on levels in 77Se and 80Se ions yields the value of g=−0.15 (7), indicating a ν g 9 2 −4 configuration for this level.

Lifetime measurements following coulomb excitation

Abstract The lifetimes of 2 + states in 158 Gd, 160 Gd, 164 Dy, 170 Er were measured by charged particle gamma delayed coincidence following Coulomb excitation. The values obtained (in nsec) are 3.74±0.17, 3.88±0.08, 3.46±0.11, 2.81±0.11, respectively.

Magnetic moments at backbending and spectroscopy of 134Ce

Abstract Employing the static hyperfine fields at cerium nuclei in magnetized Fe and Gd hosts, the g -factor of the 134 Ce(10 + ) state at backbending ( E x = 3719.3 keV ) has been determined as g = − 0.30 (25). The coexistence of this neutron-dominated state with the ( v h 11 2 ) n 10 + isomer ( E x = 3208.5 keV, g = −0.19(1)) is unexpected. A comprehensive spectroscopic study following the 122 Sn( 16 O, 4n) reaction, including γ-angular distributions, prompt and delayed γ coincidence and recoil-distance measurements has yielded new information on quasi-collective bands of both parities. The properties of the low-lying positive-parity states are well described by the interacting boson model.

Spin precession of the12C(2 1 + ) state on recoil in polarized iron

A PAC measurement on the 4.43 MeV12C(2+) state on recoil in magnetized iron has yielded an integral precession angle of ϕ=+0.85(14) mrad, which exceeds the Lindhard-Winther prediction by about two orders of magnitude. Evidently, large magnetic fields act at nuclei traversing solids at high velocities (vrec/c = 0.03 in the present case), thereby holding out the prospect ofg-factor measurements for nuclear states in this lifetime range (τ2+ = 6.5 × 10−14 s).

Angular correlation measurements on 191,193Ir following coulomb excitation

Abstract Magnetic dipole matrix elements for low-lying positive parity states in 191 Ir, 193 Ir, have been measured by angular correlations following Coulomb excitation. The results are compared to previous measurements and discussed in the light of the core excitation model.

Hyperfine interaction studies of light nuclei in highly ionized atoms recoiling in vacuum

Abstract The hyperfine interaction in highly ionized atoms recoiling in vacuum has been studied using perturbed angular correlations following nuclear reactions. Nuclei in the A = 12–24 mass range were investigated. The lifetimes of the nuclear states varied from 10 −14 to 10 −7 sec. The interaction was found to be static over the measured range of recoil velocities. For short nuclear lifetimes the interaction is due mainly to the unpaired 1s electron. With increasing lifetime, 2s and higher electronic configurations were found to play a prominent role.

The sign of the magnetic moment of the first 2+ state in 18O

Abstract The measured precession of the 18 O(2 1 + ) spin in the transient magnetic field experienced on recoil in polarized iron implies a negative g -factor.