M. Knopp

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.

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.

Transient field precessions and electron polarizations for sulphur ions at high velocity

Effective transient magnetic fields have been measured for S ions traversing thin ferromagnetic foils of Fe, Ni and Gd at mean velocities of 8.0v0 (v0 =c/137). The deduced polarizations attached to 1s electrons are discussed together with all data available for light ions considering spin exchange scattering as polarization mechanism.

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.

TransientK-shell hyperfine fields and deduced polarizations for single-electron C and O ions in different ferromagnets

Effective transient magnetic fields have been measured for single-electron carbon and oxygen ions traversing ferromagnetic Ni and Gd hosts, respectively. The deduced values ofK-shell polarization are well explained considering spin exchange scattering as a dominant mode of polarization.

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.

Large dynamic perturbations of transient magnetic fields induced by heavy ion beams

Measurements of transient magnetic fields in Fe for Coulomb-excited24Mg(2↓)-ions at high velocity confirm strong attenuations as observed earller for single-electron28Si ions. In a measurement in which the beam was stopped in a non-magnetic buffer layer sandwiched between the target and the Fe layer the perturbation was shown to result from the interaction of the heavy Ni beam with the ferromagnet. The attenuations seem to be correlated with the dE/dx of the beam-ions in the ferromagnet.

The effect of helium layers implanted into thin iron foils on transient magnetic fields

Abstract Spin precessions in transient magnetic fields (TF) have been measured with the 16 O(3 − ) state as probe for oxygen ions recoiling through localized helium layers implanted into thin iron foils. Precession angles are determined to high precision for different foil thicknesses. The data can be understood only if one assumes that the TF is not operative over the helium implanted region of the ferromagnetic foil. This behaviour indicates that the iron lattice is severely damaged and loses magnetic properties by the implantation process.

Measurements of transient magnetic fields on single-electron Ni-ions

Measurements were performed to determine the transient magnetic field assoclated with polarized is electrons of highly-stripped Ni ions traversing a ferromagnetic Fe layer. Partiele γ angular correlations and spin precessions have been measured with the first excited 2↓-state in62Ni. The observed precession indicates that the transient field is considerabls weaker than expected.

Transient magnetic fields for highly stripped ions traversing ferromagnetic solids

Transient magnetic fields experienced by nuclei of single-electron ions in ferromagnetic solids have been analyzed in terms of the polarization of 1s electrons. Values obtained are well explained with spin-exchange scattering.In measurements for Si and Ni ions in Fe and Gd host at high and low velocity, respectively, it is demonstrated that the field strength also depends on the ion beam used for excitation of the nucleus. This new feature has direct relevance in the understanding of previous data.