J. Wolfgang Hammer

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.

Der Zerfall des84Rb und die Fluoreszenzausbeute von Krypton

The electron capture decay and the positron decay of84Rb were investigated using NaJ (Tl)-detectors and a Ge (Li)-detector. Measurements of all intensities and of some informative double and triple coincidences were performed.From coincidence measurements betweenK-X-radiation and the following γ-radiation we got theK-fluorescence yield of Krypton ΩitK=0.653 ± 0.004. Taking in consideration former measurements1 one concludes a continuous behaviour of ΩitK(Z) forZ=36, 37 and 38 within an uncertainty of 1%.For the branching ratios of the decay of84Rb we obtained The half-life of84Rb was determined to beT1/2=(34.5 ± 0.2) d.

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.

Scorpion, the Stuttgart scattering facility for fast polarized neutrons

Abstract The scattering facility SCORPION has been designed for simultaneous measurement of neutron differential cross sections and analyzing powers in the energy range of 4–16 MeV. This facility is constructed in close double shielded geometry and utilizes the high neutron fluxes produced with 0.5–1 mA currents of the 4 MV Dynamitron accelerator. Neutron spectroscopy is performed by pulse height analysis and by unfolding of the proton recoil spectra, using the new code FANTI, developed for this experiment. Results are given for the nucleus 12 C as an example. As measured simultaneously in the same setup, consistent evaluation of cross section and polarization data reveal new and accurate information on optical model parameters in particular for the spin orbit term.

Imaging with the coded aperture gamma-ray spectrometer SPI aboard INTEGRAL

ESAs INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) will be launched in October 2002. Its two main instruments are the imager IBIS and the spectrometer SPI. Both emply coded apertures to obtain directional information on the incoming radiation. SPIs detection plane consists of 19 hexagonal Ge detectors, its coded aperture has 63 tungsten-alloy elements of 30 mm thickness.

TheK-Fluorescence Yield of Germanium

TheK-Fluorescence Yield ωk of Germanium has been measured using the coincidence method and investigating the decay of74As. The branching ratios of this decay had to be measured and all relevant determining values, as detection efficiencies, absorption coefficients etc. The experimental results arePK ωK = 0.494±0.012 andωK= 0.561±0.015 usingPK= 0.881±0.003. For the branching ratios of the decay of74As we obtainedEC2 (1.204) 0.88±0.06%EC1 (0.596) 32.8±0.8 %Β1+ (0.596) 24.7±0.8 %EC1Β1+=1.332±0.046.Additionally the half-lifeT1/2=(17.76±0.03) d has been measured.

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.

DieK-ElektroneneinfangwahrscheinlichkeitPK beim Zerfall von139Ce

TheK-Shell Electron-Capture ProbabilityPK for the Electron Capture of139Ce has been measured using the coincidence method. The detectors used have been a NaJ(Tl)-detector with Be-window for the Lanthan-X-ray, a Ge(Li)- and a 76.2 mm Ø×76.2 mm-NaJ(Tl)-detector for the 166 keV-γ-ray. The escape-effect of the Lanthan-X-ray in the NaJ(Tl)-detector was investigated. The experimental results arePKΩK= 0.726±0.010 andPK=0.801±0.034 using ΩK=0.906±0.026.

Die K -Elektroneneinfangwahrscheinlichkeit P K beim Zerfall von 139 Ce

TheK-Shell Electron-Capture ProbabilityPK for the Electron Capture of139Ce has been measured using the coincidence method. The detectors used have been a NaJ(Tl)-detector with Be-window for the Lanthan-X-ray, a Ge(Li)- and a 76.2 mm Ø×76.2 mm-NaJ(Tl)-detector for the 166 keV-γ-ray. The escape-effect of the Lanthan-X-ray in the NaJ(Tl)-detector was investigated. The experimental results arePKΩK= 0.726±0.010 andPK=0.801±0.034 using ΩK=0.906±0.026.

Optical potentials from polarized neutron scattering

A research program on optical potentials has been performed for a broad range of nuclei. The data were deduced from the simultaneous measurement of the angular distributions of analyzing power and differential cross section in a polarized neutron scattering experiment. For these experiments the facility Scorpion has been used, and it is briefly characterized. Some typical results are shown in this overview.