W. Wölfli

A digitally controlled scanning microprobe for protons and heavy ions

Abstract A microprobe facility has been installed at the ETH-EN Tandem accelerator which is capable to focus protons and heavy ions with a mass-energy product P ≤70 amu·MeV/Z 2 to a spot size of 10–30 μ m 2 . By means of a digitally controlled electrostatic scanning system a proton beam of 3 MeV can be deflected in computer controlled patterns over a target area of 1.5 × 1.5 mm 2 . The system can be used either for highly sensitive trace element analysis or for the deep implantation of heavy ions.

Bremsstrahlung in α-α scattering

Abstract The bremsstrahlung cross section in α - α scattering has been determined for incident laboratory energies between 12.5 and 19.0 MeV. The experimental cross sections are compared with the theoretical calculations for external emission only.

Branching ratios between correlated and uncorrelated two electron transitions into the K-shell of Al, Ca, Fe and Ni ions

Abstract The branching ratios between the radiative single and double electron transitions into the doubly ionized K-shell were measured as a function of the atomic number. The results are compared with various theoretical predictions.

Impact parameter dependence ofL- andK-shell excitation in I-Ag collisions

The impact parameter dependence of theL- andK-vacancy production of target and projectile was measured in I-Ag collisions at 40 MeV and 63 MeV in a X-ray particle coincidence experiment. A largeL-vacancy production is found for impact parametersb smaller than theL-shell radius with a pronounced increase forb<250fm. TheL-shell excitation is discussed in terms of 4fσ excitation and vacancy transfer in the 3pσ, 3dπ, 3dσ molecular orbitals through 3pπ-3pσ and 3dδ-3dπ-3dσ rotational-couplings. The 2pσ excitation probability is obtained from the summedK-vacancy production probability, and compared with the prediction of 2pσ excitation in a multiple collision process. The latter is determined by folding the measured IL-shell excitation probability with the impact parameter dependence of the 2pπ-2pσ rotational coupling. The discrepancy observed at small impact parameters suggests an enhanced 2pπ and 2pσ excitation at small impact parameters in a one-collision process. TheL- andK-vacancy sharing probabilities are found to be impact parameter independent over a large impact parameter range.

An accurate measurement of the 10B(n,p)10Be cross section at thermal energies

Abstract Considering the varied geophysical applications of 10Be, we have made an accurate measurement of the thermal neutron cross section for the reaction 10B(n, p)10Be. In the literature, only upper and lower limit values have been reported for this cross section. Using the accelerator mass-spectrometric technique for the detection of 10Be, we obtained a value of 6.8 ± 0.5 mb. This value is one order of magnitude lower than the cross section for the tritium channel in 11B compound nucleus.

Azimuthal angle dependence of molecular orbital K X-rays in heavy ion collisions

The dependence of molecular X-ray emission on the azimuthal angle in heavy ion collisions has been measured as a function of the impact parameter in the collision systems F-Al and Cl-Cl at projectile energies of 20 and 48 MeV respectively. The values of the observed azimuthal anisotropies agree with dynamical calculations of molecular orbital X-ray emission, but they are at variance with predictions of the kinematic dipole model.

Particle accelerator measurements of10Be in marine accumulations: Intercomparison with beta counting method

Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to ∼6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at10Be levels of 109–1010 atoms/g agree within the absolute errors of the two methods. The detection limit for10Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.

Threshold behaviour of the MO x-ray anisotropy spectra observed in heavy ions collisions

Abstract The anisotropy of the MO-radiation between the characteristic L and K lines observed in Au-Au collisions has been measured as a function of the projectile energy between 8 and 60 MeV. The observed anisotropy peaks show a threshold behaviour. This behaviour results from transitions into well defined MO-minima formed at different internuclear distances.

The anisotropy of the MO-2pσ-radiation observed in symmetric heavy ion collisions

The anisotropies of the MO-2pσ-radiation have been measured for five symmetric systems with a united atom numberZu between 52 and 94 at beam energies in the range from 7 up to 66 MeV. A comparison with the available theoretical data suggests that the anisotropic part of the 2pσ-radiation is mainly due to transitions from near continuum initial states into the minimum of the molecular 2pσ-orbital.

Proton-proton bremsstrahlung at 11 and 13 MeV

Abstract The p-p bremsstrahlung cross sections were measured at two energies using the equal angle Harvard geometry with ϑ lab = 30°. The results corrected for noncoplanarity are 0.43 ± 0.03 μb/sr 2 at 11 MeV and 0.44 ± 0.05 μb/sr 2 at 13 MeV.