Elsevier

Nuclear Physics A

Volume 406, Issue 2, 19 September 1983, Pages 339-368
Nuclear Physics A

Large transient magnetic fields for rare-earth ions recoiling in gadolinium and g-factors of high-spin states in 156, 158, 160Gd

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Abstract

We have determined the transient magnetic field for Coulomb-excited rare-earth nuclei recoiling with velocities in the range between 0.7ν0 and 6ν0 into ferromagnetic gadolinium cooled to a temperature T = 80 K. Measured and calculated g-factors in 169Tm have been used as calibration standards. The transient field is found at first to increase with increasing recoil velocity, and then to level off, approaching a nearly constant value of 5.5 kT at ν = 6ν0. At the higher velocities (3ν0 < ν < 6ν0) the transient fields for 169Tm recoils in gadolinium are a factor of 1.42 ± 0.12 larger than those in iron, whereas the densities of polarized electrons are the same in both ferromagnets. This result demonstrates that an explanation of the transient field must take into account the atomic structure of the host (and probably also that of the recoil). The transient field is too large to be described only in a statistical picture in which inner-shell (ns) vancancies are filled by capture of polarized (4f) electrons. Possible mechanisms may involve either polarization transfer from the outer shells by spin-flip interactions, or direct vacancy polarization by diabatic molecular orbitals.

The transient field calibration has been corroborated making use of known g-factors of low-spin states in 156, 158, 160Gd populated by Coulomb excitation of thick Gd single crystals. For the high-spin states in these nuclei, the g-factors are found to decrease slightly, with the ratio g(10+)g(2+) reduced to 0.89±0.12, 0.83±0.11, and 0.93±0.13, respectively. Similar decreases have been observed previously for other N = 90−96 nuclei.

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