W. Knauer

The12C(2 1 + ) state as probe for transient magnetic fields in polarized iron

PAC measurements on the 4.43 MeV12C(2+) state on recoil in magnetized iron at velocitiesvion=2.1v0, 6.0v0, 7.4v0 yield integral precession angles of ϕ=+0.72(18), +0.94(16) and +0.71(18) mrad, respectively. The results supplementary to existing precession data are interpreted by a distribution of C5+ ions implying a K-shell polarization of ≃28% and an effective charge larger than measured after emergence from the solid. The low-velocity precession tends to disagree with the empirical law of linear relationship between transient field and ion velocity. The presence of molecular orbital effects is discussed.

Evidence for K-shell polarization of C-ions in ferromagnets via molecular-orbital promotion

Abstract Transient field precessions of the 12 C 4.43 MeV state in polarized Fe and Ni are found to scale with the polarized electron density of the hosts at υ ion = 4.1 υ 0 , but are comparable at υ ion = 2.1 υ 0 . The latter is attributed to direct K-shell polarization of carbon via molecular-orbital promotion.

Can projectiles traversing solids bind electrons at all velocities

Abstract PAC measurements on the 4.43 MeV 12 C(2 + ) state on recoil in magnetized iron at velocities υ ion = 0.058 c , 0.071 c yield integral nuclear precession angles of Φ = −0.18 (30), +0.17 (39) mrad respectively. Evidently, the high electron-spin-polarization transfer to the innermost carbon orbits implied by a previous measurement (υ ion = 0.03 c , Φ = +0.85 (14) mrad) is suppressed at higher ion velocities.

K-shell polarization of O ions in ferromagnets by spin dependent electron promotion via molecular orbitals

Abstract Transient field precessions of the 6.13 MeV 16 O(3 - ) state have been measured in polarized Fe and Ni in order to corroborate our earlier results on C ions. It is found that precessions in Fe and Ni scale with the polarized electron density of the host at v ion = 3.0 v 0 and are comparable at v ion = 1.5 v 0 . The latter is attributed to direct K-shell polarization of the ion by spin dependent electron promotion via molecular orbitals.

Hyperfine interaction and g-factor measurements in Er isotopes

Abstract Energy levels in 160 Er and 159 Er were excited in the reactions 28 Si( 136 Xe, 4n) 160 Er and 28 Si( 136 Xe, 5n) 159 Er, and the product nuclei, recoiling with a velocity v = 0.07 c were stopped in a plunger instrument after traversing a volume of hydrogen gas. The angular distribution of de-excitation γ-rays was studied as a function of flight time and gas pressure. Appreciable perturbations were detected in 160 Er at times as short as 2 ps and in an angular momentum region as high as 12ħ. No perturbation could be detected in the 21 2 + level of 159 Er even after 12 ps, signifying a low value for the g -factor of this level.

A curved plunger for time-differential PAC measurements on recoil into gas

Abstract For a time-differential study of the hyperfine interaction on nuclear high spin states in highly ionized atoms recoiling into gas, a target-plunger was constructed having a well-defined curvature under gas pressure. Its perfect operation in this geometry is demonstrated by remeasuring lifetimes of excited states in 160 Er which were populated in the reaction 28 Si( 136 Xe, 4n) 160 Er with 632 MeV Xe-projectiles.