H. Spehl

Nuclear deorientation for heavy ions recoiling in vacuum and low pressure gas

Time-differential perturbed gamma-ray angular correlations have been measured for148, 150Nd(21+) recoiling into vacuum and into helium (ν/c=1.3%) in the pressure region from 0.75 to 25 Torr. A model is presented of the perturbation mechanism for recoils travelling in vacuum, which allows for the hitherto hidden fact that a hard core of the attenuation exists. In addition, a higher order modification of the first order Abragam and Pound theory for random perturbations has to be taken into account at very low pressure.

Perturbed angular distribution of recoil implanted F19-nuclei in a nickel-environment

Magnetic hyperfine fields acting on F19 in a Nickel lattice have been investigated. Time-dependent spin rotation has been observed following the excitation and recoil implantation with a pulsed proton beam using the reaction F19(p,p′)F19⋆. Two hyperfine fields were detected at 290 °K:Hhf(1)=+17.6 ± 0.5 kGHhf(2)=+91 ± 3 kG.The variation of the effective fields with the external polarizing field was studied. The mean life of the 197 keV level has been remeasured as τ=128±2 nsec.

Search for a quadrupole component in the hyperfine interaction on recoil into vacuum

Abstract Time-differential perturbed γ-ray angular correlations have been measured with the plunger technique for fast Nd nuclei recoiling into vacuum. A clear trend of increasing quadrupole interaction with increasing nuclear quadrupole moment has been found. The hyperfine interaction on recoil into vacuum and recoil into gas is discussed in terms of stochastic models.

Hyperfine fields on recoil implanted nuclei 62≦Z≦74 in a polarized Fe-, Co- and Ni-environment

Hyperfine fields acting on Sm, Gd, Dy, Er, Yb, Hf and W nuclei in a polarized ferromagnetic environment of Fe, Co and Ni have been investigated. The nuclei have been implanted into the host lattice by the recoil associated with Coulomb excitation with 11 MeV C12-ions from a 5.5 MV Van de Graaff accelerator. The precession of theγ-ray angular distribution has been measured and substantial perturbations were found. It is shown that the perturbation, at least for the case of the strongly perturbed rare earth nuclei, cannot be explained by a combined static electric quadrupole and magnetic dipole interaction.

Time differential perturbed angular correlations of Gd160 implanted into ferromagnetic Gd and of Yb176 into Fe and Ni

Time differential perturbed angular correlation measurements of Gd160 in ferromagnetic Gd at various temperatures and of Yb176 in Fe and Ni have been performed following Coulomb excitation with a pulsed beam and recoil implantation. Using the theory of combined static magnetic and electric hyperfine interaction the measured time spectra are reasonably well reproduced, the magnetic fields and electric field gradients being in agreement with other works. A phase shift of the Larmor precession, however, points to anomalous hyperfine fields acting on the nuclei in a very short time interval after the beam pulse.

Asymptotic attenuation coefficients in random perturbations of Angular Correlations

The time-differential attenuation coefficients for randomly fluctuating interactions in isotropic systems are shown to be of the simple exponential type (well known from the first order treatment of Abragam and Pound) fort≫Τc, notwithstanding the strength of 〈Ω2〉1/2Τc. Explicit expressions for the relaxation constant are given which are strongly dependent on the strength of 〈Ω2〉1/2Τc and on the type of interaction but prove to be virtually independent of the stochastic model assumptions.

Die relativen Quadrupolmomente der ersten angeregten 2+-Zustände von Os188, Os190 und Os192

The angular distributions of the deexitationγ-rays following Coulomb-excitation of the first excited 2+-states in Os188, Os190 and Os192 were measured using a metallic Target of natural Osmium. The measured attenuation coefficients areG2(Os188)=0.798±0.013,G2(Os190)=0.917±0.030 andG2(Os192)=0.940±0.030. As a general test the angular distribution of the 330 keV-γ-rays of Pt194 was also measured. This distribution was found to be completely undisturbed. Assuming pure electric quadrupole interaction with the internal crystalline fields one obtains an interaction frequency ofΔvQ=eQ Vzz/h=278±32 MHz for the 155 keV-state of Os188. Because the electric field gradients acting on the decaying nucleus are the same for all isotopes, one can deduce the ratio of the quadrupole moments of the excited states. The result isQ(Os188)∶Q(Os190)=1.11−0.19+0.28 andQ(Os190)∶Q(Os192)=1.03±0.30. The effects of the uncertainties in the effective field gradients and their possible asymmetries on the integral attenuation factors are discussed. For 1≧G2≳0.75 these effects are found to be small.

Perturbed gamma-ray angular distribution from Yb nuclei recoiling in vacuum

Abstract The attenuation of they γ-ray angular distribution of Coulomb excited Yb nuclei recoiling in vacuum has been measured with a new time-differential technique. The perturbation mechanism due to the time-dependent hyperfine interaction in highly ionized and excited, free ions is discussed in terms of the Abragam and Pound and the Dillenburg and Maris theories.

Gamma-ray angular correlations perturbed by a stochastic Gaussian-Markov process

Perturbed angular correlation attenuation coefficients are given for randomly fluctuating extranuclear fields in the, what we call, “Fixed Orientation Gaussian Approximation” (FOGA). The fluctuating field is regarded as a stochastic Markov process with Gaussian probability distribution of the field strengths. The results are applicable to any correlation time.

Herstellung eines neutralen Wasserstoffatomstrahls im MeV-Bereich

An arrangement is described to produce a neutral hydrogen beam by splitting an accelerated H2+-Ion in a gas target. At 500 keV energy of the neutral H-atom, the ratio of H2+-ions to neutral H-atoms is measured to be about 12%. In the energy domain of 300 to 650 keV this ratio decreases only very little with increasing energy. The cross sections σ1, σ2 and σ3 for splitting inH++H°, 2H++e− and for electronloss of the neutral atom are given.