Heinz W. Drotleff

The third continuum of the rare gases emitted by heavy ion beam induced plasmas

Rare gases have been excited by dc ion beams of He+, Ne+ and Ar+ in the energy range 0.5–3.9 MeV using the Stuttgart DYNAMITRON accelerator and the gas target system RHINOCEROS. The VUV emission of the first, second and third continua was observed in the wavelength range between 50 and 300 nm. Especially the third continuum of neon could be observed at 99 nm for the first time in this way. The relative intensities of the continua depend strongly on the mass of the exciting ion and on the presence of contaminations. The observations support strongly the assignment of the third continuum to the radiative decay of Rg2+2 ionic excimers.

New22Ne(α,n)25Mg-resonances at very low energies relevant for the astrophysical s-process

The22Ne(α,n)25Mgreaction is thought to be one of the main neutron sources for the astrophysical s-process. Thus cross section data for this reaction have been obtained from near the threshold (Eα≈570keV) up toEα=2100 keV using the 4 MV DYNAMITRON accelerator at Stuttgart, the windowless gastarget system RHINOCEROS and a 4π neutron detector. Two new resonances have been observed atEα=623 ± 6 and 838 ± 6 kev, which dominate the reaction rate at T9<0.3.Possible background reactions are discussed.

Physical properties of a heavy-ion-beam-excited supersonic jet gas target

The profile, density, and temperature of a supersonic rare‐gas jet was determined applying methods of nuclear physics and optical spectroscopy. The jet was produced in the windowless gas target facility RHINOCEROS and the heavy‐ion particle beams were provided by the Stuttgart DYNAMITRON accelerator. Maximum densities in the range of 1017 to some 1018 particles/cm3 could be achieved in a gas jet of about 2.6 mm diam (FWHM). In a supersonic helium jet a cooling of the gas down to 45 K was observed. These results were compared with theoretical calculations.

Neutron sources in nuclear astrophysics

The excitations functions of the reactions 9Be((alpha) ,n)12C, 13C((alpha) ,n)16O, 17O((alpha) ,n)20Ne, 18O((alpha) ,n)21Ne, 21Ne((alpha) ,n)24Mg, 22Ne((alpha) ,n)25Mg, 25Mg((alpha) ,n)28Si and 26Mg((alpha) ,n)29Si have been measured at the 4 MV dynamitron accelerator in Stuttgart, Germany in the energy range of astrophysical interest, and from these S-factor- curves have been determined. Advanced techniques, especially with the windowless gastarget facility Rhinoceros have been applied. For neutron detection NE213 scintillation counters and a long counter like 4(pi) -detector have been used. A sensitivity limit in the range of 10-10b to 10-\11b was reached with these experiments. Using our new experimental results astrophysical reaction rates have been calculated for all reactions except the Mg-reactions. Analytic expressions have been fitted to all reaction rates.