K. H. Speidel

Heavy ion beam induced attenuations of transient magnetic fields

Abstract Measurements of transient magnetic fields for Coulomb-excited 28 Si(2 + ) and 62 Ni(2 + ) ions recoiling in Fe(Gd) host with high and low velocity, respectively, gave clear evidence that the field strengths are substantially reduced due to momentary loss in ferromagnetism when using Ni-beams for excitation. There are strong indications that many earlier measurements suffered from the same effect and must be therefore reviewed.

Targets with magnetic properties

Abstract Various multilayer targets with ferromagnetic matter as a middle layer for TF (transient magnetic field) measurements were prepared using rolling and vacuum evaporation-condensation techniques. The compatibility of different backing materials with the condensed ferromagnetic matter was investigated. The influence of the substrate temperature on the magnetic properties was analyzed as well. Ferromagnetic Fe layers consisting of separated segments of domain size were prepared by vacuum evaporation-condensation through suitable mesh masks. For NMR-ON (nuclear magnetic resonance on oriented nuclei) experiments and for studies of the circular magnetic X-ray dichroism rolled foils of highly diluted ferromagnetic alloys were needed. The preparation of such impurity systems by means of an electron beam source in high vacuum is described. The diluting process strongly depends on the relative vapor pressures of the two metals.

Applications of large barium fluoride scintillators to in-beam gamma-ray spectroscopy

Properties of large-volume BaF2 scintillators have been studied and first experiences of applications to in-beam γ-ray spectroscopy are reported. Energy resolutions of 9.1% at 662 keV and 6.3% at 1332 keV γ-ray energies were obtained. A time resolution of 375 ps FWHM was measured using a 60Co source. Gain variations of the phototubes from changes in count rate could be limited to a 2% level. Lifetimes have been measured for the first 2+ state of 152Sm using a 152Eu source and the 51− state of 40Ca at 4.49 MeV populated in the (α, α′) reaction.

New aspect in transient magnetic fields using heavy ion beams

Transient field precessions have been measured with the first excited 21+-state as probe for ions of28Si traversing Fe at vion−1v0 and 13v0(v0=c/137) and62Ni being stopped in Fe. The degree of polarization deduced for the Si ions, p1s=0.19(6), is consistent with low-velocity data. There is clear evidence that the field strength is attenuated by heavy ion beams. For the62Ni(21+) state at 1.173 MeV a g-factor value of g=0.34(7) was obtained in good agreement with a previous result.

Evidence for electron orbital dependence of ion-beam induced attenuations of transient magnetic fields

From measurements of transient magnetic fields (TF) on56Fe(21+) ions in Gd host there is evidence that beam induced attenuations of TF not only depend on the energy loss of the beam ions in the ferromagnet but also on the electron ns-orbitals of the probe ion contributing to the field. This has been demonstrated for 2s- and 3s-electron states of56Fe ions which are preferentially populated by setting the ion velocity to their respective orbital Bohr velocities.

New aspects of transient magnetic fields

Strong attenuations of transient magnetic fields are observed in Fe and Gd host for Coulomb excited2HSi(21+)- and24Mg(21+)-ions in their single-electron charge state as well as for multi-electron62Ni(21+) ions. These effects are shown to be induced by the heavy ion beams used. The perturbations are found to be dynamic in nature and are attributed to a momentary loss of ferromagnetism of the host. This feature is also present in many earlier measurements using heavy ion beams but was not identified. The magnitude of the attenuations seems to be correlated with the energy loss of the beam ions in the ferromagnet.

New determination of the magnetic moment of the54Fe(2 1 + ) state at 1.408 MeV

Relative to the wellknowng-factor of56Fe(21+) at 0.847 MeV, theg-factor of the54Fe(21+) state at 1.408 MeV has been remeasured employing the technique of transient magnetic fields (TF) with the ions slowed down in ferromagnetic Gd host at initial velocities of 2.5 ν0. Coulomb excitation on beams of54,56Fe was accomplished with a Si target. The value obtained,g=1.05(17), is in excellent agreement with two previous results but disagrees with the value from a TF measurement where the ions passed through ferromagnetic Fe.

Large electron polarization of H-like20Ne-ions traversing gd foils at very high velocities

It is shown that transient magnetic fields in Gd-host for20Ne ions at a mean velocity of 12.5v0(v0=c/137), considerably beyond the Bohr velocity of 1s electrons of Ne ions (v1s=10v0), are dominated by the Fermi contact field of these electrons. The first excited 2+-state of2Ne was used as probe. The derived value for the mean degree of polarization p1s=0.32(13), is surprisingly large, though still consistent with values obtained at lower velocities. Present calculations of spin exchange cross sections severely underestimate the observed polarization at this high velocity.

Spin exchange scattering as the most likely polarization mechanism in transient magnetic fields

Salient features of transient magnetic fields, like the degree of polarization, host dependence etc. emerging from studies of high velocity single-electron light ions,Z ≦ 16, are well described by spin exchange scattering as the polarization transfer mechanism. Inclusion of density enhancement effects of the electrons of the solid in the Coulomb field of the moving ion are necessary for a quantitative understanding of the observed large degrees of polarization of the ions.

Large transient magnetic fields for single electron O ions on a 10 fs time scale

Abstract Large transient magnetic fields have been observed for single-electron O ions for short interaction times of 10 fs and 100 fs passing through thin magnetized Gd layers. The derived value for the degree of polarization, p ¯ 1 s = 0.26 ( 1 ) , demonstrates that the polarization transfer cross sections are large enough to generate in very short times substantial polarization of 1s electrons in these ions.