Light nuclei as distinct probes for transient magnetic fields

Abstract

Salient features of transient magnetic fields are brought out from nuclear spin precession measurements on light ions penetrating polarized Fe-, Ni-and Gd-hosts. At low velocities ion fractions with single K-shell vacancies, at high velocities H-like charge state fractions, can account for the observed precessions. The data suggest a sharp reduction of the K-shell field at a velocity Vion~--0.5VO . Large degrees of K-shell polarization have been derived for C-and O-ions. Measurements in different ferromagnets show that the transient fields scale with the polarized electron density of the host.

Measurement of K-shell population of swift sulphur ions penetrating Fe and Ni foils using the probe layer technique

“…In addition, the ratio of the polarization acquired by the ion in Gd host to that in Fe host (see Table 1) shows nearly a constant value independent of Z of the ion. This ratio is consistent with the value of 1.16 which one would expect if the TF scale with the polarized electron density of the hosts [3].…”

“…Using this value for q~ and the measured TF at this velocity in Ni host [5] we obtain a value of 0.07(3) for ply. On comparison with the p~ value for Fe this value fits in with the expected scaling of the TF with the polarized electron density of the host [3].…”

“…The measured value at 8 vo was found to be nearly a factor of two higher than the estimated value [5]. Using this measured value of q is and the available TF data at this velocity [5] in Gd host the value of Pas is obtained to be 0.15 (3) which is substantially lower than the observed nearly constant value of 0.24 for other light ions with 6 _< Z < 14 [5]. In order to check whether this reduction in P~s for S ions also exists in other ferromagnetic hosts, we have measured qls at velocities between 7% and 14% for these ions penetrating Fe and Ni foils and used the existing TF data at a velocity of 8% [5] to decuce Pl, value.…”

“…This transient field (TF) in case of light ions arises predominantly from the polarization of the unpaired electron in its K-shell and is shown to be related directly to the number of single K-shell vacancies carried by them [2]. For the case of hydrogen like light ions it can be expressed as [3] BTF=Bls ql~Pls, (1) where BI~ is the hyperfine field due to l s electron of the ion, q~ the fraction of ions with single K-shell vacan~ cies and Pa~ their acquired degree of polarization. At ion velocities close to Zvo, where Z is the atomic number of the ion and v0 the Bohr velocity, the quantity qas approaches a value of 0.5 and hence pl ~ can be estimated quite reliably from a measurement of the TF using (1).…”

A stochastic model for transient magnetic fields as observed by perturbed angular distribution of gamma rays

“…This theory failed to explain very large TFs observed in 1975-76 [3]. Another approach considered the capture of electrons with a particular spin orientation from the outer orbitals of the host by the inner shells of the ion, to be the mechanism for producing TF [4], which again failed to explain TF data on light ions [5].…”