R. M. Lieder

An analog-to-digital conversion based on a moving window deconvolution

A high-performance analog-to-digital conversion technique for nuclear spectroscopy applications with unconventional architecture is described. This technique is planned to be used in Phase III of the European /spl gamma/-ray facility project EUROBALL. The conversion is based on the Moving Window Deconvolution (MWD) method for signal processing in nuclear spectroscopy which has been introduced recently. This method allows the conversion to be represented as a sequence of measurements of the total charge of the event and consequently, by applying for example a simple oversampling scheme to achieve a high accuracy. The proposed MWD-type conversion exhibits very low differential and integral nonlinearities over a 14-bit resolution range with an effective conversion dead-time virtually zero. The last feature combined with an inherent pipeline conversion structure is of great importance for applications in large-scale multi-detector arrays like EUROBALL. The key parameters of the development have been theoretically estimated and measured with a prototype consisting of a free running A/D converter and a digital signal processor. >

Use of DCO ratios for spin determination in γ-γ coincidence measurements

Abstract The use of large detector arrays allows to measure γ-γ angular correlations and to determine spins and multipolarities, even of weak and unresolved transitions. The method utilizing directional correlations of γ-rays deexciting oriented states (DCO ratio method) has been described and applied to experimental data on 178 W taken with the γ-γ coincidence spectrometer OSIRIS. The spin of the 35 ns isomer in 178 W has been established to be 14.

The influence of anisotropic electron drift velocity on the signal shapes of closed-end HPGe detectors

Abstract This study is concerned with the anisotropy of the electron drift velocity in germanium crystals at high electric fields and low temperature, and its influence on the charge collection process in n-type, high-purity germanium (HPGe) detectors of closed-end, coaxial geometry. The electron trajectories inside HPGe detectors are simulated using a phenomenological model to calculate the dependence of the drift velocity on the angle between the electric field and the crystal orientation. The resulting induced currents and pulse shapes for a given detector geometry and preamplifier bandwidth are compared to experiment. Experimentally, the dependence of the pulse shapes on the conductivity anisotropy in closed-end HPGe detectors was observed. The experimental data on pulse shapes were obtained by sampling preamplifier signals of an encapsulated, hexaconical EUROBALL detector, which was irradiated by collimated 22 Na and 241 Am sources. The crystal orientation was measured by neutron reflection. Qualitative agreement between the simulated and experimental pulse shapes was found. A variation in the charge collection time of up to 50xa0ns was observed for different drift directions of the carriers relative to the crystal orientation. Furthermore, a deflection of the trajectories from a straight radial drift direction of about 20° was predicted by the simulations. These two main effects of charge carrier drift velocity anisotropy in coaxial Ge detectors are expected to play an important role in the development of γ-ray tracking detectors.

On the careful determination of gamma-ray angular distributions in (α, xnγ) reactions: Example of the 186W(α, 7nγ) 183Os reaction

Abstract Using the reaction 186 W(α, 7nγ) 183 Os as an example the measurement and analysis procedures of γ-ray angular distributions following ( α , x n) reactions are outlined and discussed. Special emphasis has been devoted to the factors influencing the accuracy that can be obtained in such γ-ray angular-distribution measurements.

On the careful determination of gamma-ray angular distributions in (

Abstract Using the reaction 186 W(α, 7nγ) 183 Os as an example the measurement and analysis procedures of γ-ray angular distributions following ( α , x n) reactions are outlined and discussed. Special emphasis has been devoted to the factors influencing the accuracy that can be obtained in such γ-ray angular-distribution measurements.

alpha

The level scheme of 189Au has been extended to high spins. Decoupled, strongly coupled as well as vibrational bands have been found indicating shape coexistence in this nucleus.

,xn

Excited states of the {sup 146}Tb nucleus have been studied using {gamma}-ray and electron spectroscopy in off-beam and in-beam modes following {sup 112}Sn({sup 40}Ar,3n3p) reaction with the use of the OSIRIS-II, HPGe detector array and the conversion electron spectrometer. The multipolarity of the 343 keV transition deexciting the (7{sup -}) level in {sup 146}Tb shows mainly an E2 nature and the first excited state above the 23 s isomer is assigned as a (5{sup -},6{sup -}) state. The log ft values have been deduced for 11 {beta}{sup +}/EC transitions populating excited states in {sup 146}Gd. The systematic behavior of spins and parities of the long-lived levels at 0+x keV and the first excited states above them in the N=81 isotones {sup 146}Tb, {sup 148}Ho, and {sup 150}Tm is discussed.

gamma

The excited states of {sup 148}Ho and {sup 149}Ho isotopes are studied using gamma-ray and electron spectroscopy in off-beam and in-beam modes following {sup 112,114}Sn({sup 40}Ar,xnyp) reactions. Experiments include measurements of single gamma-rays and conversion electron spectra as well as gamma-gamma, electron-gamma, gamma-t, and gamma-gamma-t coincidences with the use of the OSIRIS-II 12-HPGe array and conversion electron spectrometer. Based on the present results, the level schemes of {sup 148}Ho and {sup 149}Ho are revised and significantly extended, up to about 4 and 5 MeV of excitation energy, respectively. Spin and parity of 5{sup -} are assigned to the 9.59-s isomer in {sup 148}Ho based on conversion electron results. Previously unobserved gamma rays feeding the 10{sup +} isomer in {sup 148}Ho and the 27/2{sup -} isomer in {sup 149}Ho nuclei are proposed. Shell-model calculations are performed. Possible core-excited states in {sup 149}Ho are discussed.

) reactions: example of the

An investigation of γ‐ray fold distributions has been carried out for the 97Mo(51V,zαu2009ypu2009xn) reaction. For the α2n channel leading to 142Eu a double‐humped fold distribution was found. An explanation in terms of an incomplete‐fusion reaction mechanism is proposed.

sup 186

Very exotic shapes can be assumed for the nuclei at high angular momenta. Their study has become possible with the advent of the last generation high-resolution γ-ray spectrometers. In this talk results are presented on superdeformed nuclei of theA=140 mass region where a detailed spectroscopy in the second minimum is now possible. Hyperdeformed rotational bands, expected in the third minimum, lie at even higher spins where their observation is very difficult from the experimental point of view. We have up to now only weak signals of their presence. The status of the search for hyperdeformation in152Dy is reported.