H.A. Doubt

Large transient magnetic fields at high ion velocities in polarized iron

Nuclear spin precessions due to the transient magnetic field in polarized Fe have been measured as a function of the initial velocity of28Si ions in the first-excited nuclear state. The transient field was found to increase linearly with the ion velocityv in the regionv/c=0.006–0.049. This is in contrast to the Lindhard and Winther model, which requires an inverse proportionality with ion velocity. Reanalysis of an earlier measurement on30Si(21+) with the linear velocity dependence yields a reduced value for theg-factor ofg=0.37±0.12. Other available velocity-dependent data for22Ne,56Fe and196Pt are consistent with a linear velocity dependence and suggest in addition a linear dependence on the nuclear charge Z of the moving ion. The increase of the transient field with recoil velocity can be explained semi-quantitatively by the capture of polarized Fe electrons into 1s and 2s vacancies in the moving ion. The velocity-dependent data and other discrepancies from the Lindhard and Winther model for16N,18O and very recently, for12C are also discussed in terms of the proposed microscopic model.

Recoil-distance measurements of g-factors for 24Mg(21+) and 20Ne(21+)

Time-differential recoil-into-vacuum measurements have been performed with a plunger on the first-excited Iπ = 2+ states of 24Mg and 20Ne. The states were populated by the reactions 12C(16O, α)24Mg and 12C(12C, α)20Ne. The measured anisotropy of the α-γ angular correlation was greatly increased by means of a vertical slit on the annular particle detector. Values of ¦g¦= 0.51 ± 0.02 and 0.54 ± 0.04 have been deduced for the 24Mg and 20Ne g-factors, respectively. The mean lives of these states have been determined as τm = 2.09 ± 0.13 ps and 0.8 ± 0.2 ps, respectively. Various theoretical calculations are discussed and compared with the measured g-factors. The analysis of the measurement also yields values for the populations of electronic states contributing to the hyperfine interaction. For 20Ne the populations of the different electronic configurations are compared with the results of a separate time-integral measurement, in which the correlations were measured for each ionic state separately. Large fractions of two-electron excited states are found to contribute.

Anomalously large transient field through polarized electron capture

The measured precession for 28Si(21+) recoiling into magnetized Fe shows an anomalous increase with initial recoil velocity. This is explained quantitatively by capture of polarized Fe electrons into 2s vacancies in the moving ion.

Nuclear deorientation for heavy ions recoiling in vacuum and low pressure gas

Time-differential perturbed gamma-ray angular correlations have been measured for148, 150Nd(21+) recoiling into vacuum and into helium (ν/c=1.3%) in the pressure region from 0.75 to 25 Torr. A model is presented of the perturbation mechanism for recoils travelling in vacuum, which allows for the hitherto hidden fact that a hard core of the attenuation exists. In addition, a higher order modification of the first order Abragam and Pound theory for random perturbations has to be taken into account at very low pressure.

Recoil-distance measurements of the g-factor of 22Ne(21+)

Abstract Time-differential recoil-into-vacuum measurements with a plunger have been performed on the first-excited Iπ = 2+ state of 22Ne. The state was populated with the 4He(19F, p)22Ne reaction on 4He-implanted foils. The measurements lead to a g- factor of ¦g¦ = 0.326 ± 0.012 and to a mean life of τm = 5.2 ± 0.3 ps. The analysis also yields the population of excited two-electron ions and indicates that the population may depend on the thickness of the 12C contamination layer through which the ions recoil into vacuum.

A magnetic moment measurement of a very short-lived state (24Mg, 21+)

Abstract The magnetic dipole moment of the 1.37 MeV J π =2 + state (with τ m =1.75 ± 0.08 ps has been measured with the time-differential recoil-into-vacuum technique for single-electron ions. The value of the g -factor obtained, | g |=0.44 ± 0.04, is lower than theoretical predictions.