M. Palacz

Experimental approach towards shell structure at 100Sn and 78Ni

The status of experimental approach to Sn-100 and Ni-78 is reviewed. Revised single particle energies for neutrons are deduced for the N=Z=50 shell closure and evidence for low lying I-pi=2(+) and 3(-) states is presented. Moderate E2 polarization charges of 0.1 e and 0.6 e are found to reproduce the experimental data when core excitation of Sn-100 is properly accounted for in the shell model. For the neutron rich Ni region no conclusive evidence for an N=40 subshell is found, whereas firm evidence for the persistence of the N=50 shell at Ni-78 is inferred from the existence of seniority isomers. The disappearance of this isomerism in the mid nug(9/2) shell is discussed.

Cd-98(48)50: The two-proton-hole spectrum in Sn-100(50)50

Excited states in {sup 98}Cd, two proton holes from {sup 100}Sn, were identified and studied for the first time, using in-beam spectroscopy with highly selective ancillary detectors. The structure of the ({pi}g{sub 9/2}){sup {minus}2} two-proton-hole spectrum below a T{sub 1/2}=0.48(16) {mu}s isomer is deduced and compared to shell-model predictions. A tentative I{sup {pi}}=(8{sup +}) assignment, as suggested by systematics, yields a strongly reduced B(E2,8{sup +}{r_arrow}6{sup +})=0.44({sup +20}{sub {minus}10}) W.u., corresponding to an effective proton charge of e{sub {pi}}=0.85({sup +20}{sub {minus}10}) e , which is at variance with existing theoretical predictions. {copyright} {ital 1997} {ital The American Physical Society}Excited states in Cd-98, two proton holes from Sn-100, were identified and studied for the first time, using in-beam spectroscopy with highly selective ancillary detectors. The structure of the (pi g(9/2))(-2) two-proton-hole spectrum below a T-1/2 = 0.48(16) mu s isomer is deduced and compared to shell-model predictions. A tentative I-pi = (8(+)) assignment, as suggested by systematics, yields a strongly reduced B(E2,8(+) --> 6(+)) = 0.44((+20)(-10)) W.u., corresponding to an effective proton charge of e(pi) = 0.85((+20)(-10))e, which is at variance with existing theoretical predictions.

High-spin studies of the neutron deficient nuclei In-103, In-105, In-107, and In-109

High-spin states of the isotopes In-103,In-105,In-107,In-109 have been investigated using in-beam gamma-ray spectroscopic methods. Results from three different experiments are presented. Targets of Fe-54, Cr-50, and Mo-92 were bombarded by a 270 and 261 MeV Ni-58 beam and by a 95 MeV F-19 beam, respectively. Reaction channel separation was achieved with a charged-particle detector array and in the first two experiments also with a 1 pi neutron detector system. As a result of these experiments the level schemes of In-103,In-105,In-107,In-109 were significantly extended. Excited states of these odd-A indium isotopes are discussed within the framework of the nuclear shell model and the hole-core coupling scheme. The systematics of excited states of light odd-A indium isotopes is also discussed

In-beam gamma-ray spectroscopy of Cd-102

Neutron deficient nuclei close to 100Sn have been studied using the NORDBALL Ge-detector array together with ancillary particle detectors. Evaporation residues from the compound nucleus 108Te were identified with charged particle and neutron detectors. In this paper a considerable extension of the level scheme of the nucleus 102Cd is presented. The strongest cascade of the new level scheme reveals an irregular sequence of dipole transitions above Iπ = 10+ extending up to spin 17. A strongly populated rather regular side band consisting of four quadrupole transitions ranging from spin 9 to spin 17 was also discovered. This band was tentatively assigned negative parity. Shell model calculations were performed and a very good agreement with the experimental results was found. The excited states could successfully be interpreted as neutron particle and proton hole excitations with respect to the doubly closed core 50100Sn50.

The lifetime of the proton-decaying 8915 keV state in 58Cu

Energy correlations between gamma -ray transitions and the prompt proton decay line in Cu-58 were studied by means of the fusion-evaporation reaction Ca-40(Mg-24,1 alpha 1p1n) using the EUROBALL spectrometer coupled to ancillary detector devices. A lifetime of 0.06 < tau < 0.58 ps for the 8915 keV proton-decaying state in Cu-58 is deduced

Design and test of a high-speed flash ADC mezzanine card for high-resolution and timing performance in nuclear structure experiments

This work describes new electronics for the EXOGAM2 (HP-Ge detector array) and NEDA (BC501A-based neutron detector array). A new digitizing card with high resolution has been designed for gamma-ray and neutron spectroscopy experiments. The higher bandwidth requirement of the NEDA signals, together with the necessity for accuracy, require a high sampling rate in order to preserve the shape for real-time Pulse Shape Analysis (PSA). The PSA is of paramount importance for the NEDA to discriminate between neutrons and -ray signals. Both high resolution and high speed parameters are often difficult to achieve in a single electronic unit. These constraints, together with the need to build new digitizing electronics to improve performance and flexibility of signal analysis in nuclear physics experiments, led to the development a new FADC mezzanine card. In this work, the design and development are described, including the characterization procedure and the preliminary measurement results.

In-beam study of 102Sn

Excited states in 102Sn have been identified for the first time, in an in-beam γ-ray spectroscopic experiment. Two γ-ray transitions with energies 1472 and 497 keV following the decay of the seniority 6+ isomer with t1/2 = 1.0(5) μs were unambiguously assigned to 102Sn. Due to the very low cross section of about 2 μb for producing 102Sn in the reaction 50Cr(58Ni,1α2n), a highly selective detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High γ-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.

A new front-end high-resolution sampling board for the new-generation electronics of EXOGAM2 and NEDA detectors

This paper presents the final design and results of the FADC Mezzanine for the EXOGAM (EXOtic GAMma array spectrometer) and NEDA (Neutron Detector Array) detectors. The measurements performed include those of studying the effective number of bits, the energy resolution using HP-Ge detectors, as well as timing histograms and n/γ discrimination performance. Finally, the conclusion shows how a common digitizing device has been integrated in the experimental environment of two very different detectors which combine both low-noise acquisition and fast sampling rates. Not only the integration fulfilled the expected specifications on both systems, but it also showed how a study of synergy between detectors could lead to the reduction of resources and time by applying a common strategy.

A digital front-end electronics for the neutron detector NEDA

This paper presents the design of the NEDA front-end electronics, a first attempt to involve the use of digital electronics in large neutron detector arrays. Among the electronic modules taking part, we emphasize on the front-end analog processing, the digitalization, digital pre-processing, communications firmware, as well as the integration of the Global Trigger and Synchronization system. The NEDA array will be available for measurements in 2015.

Maximally aligned states in Ag-99

Abstract:Excited states of 99Ag were populated via the 50Cr + 58Ni (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. On the basis of the measured γγ-coincidence relations and angular distribution ratios a significantly extended level scheme has been constructed up to Ex ∼ 7.8 MeV and I = 35/2. The experimental results were described within the framework of the shell model. Candidates for states fully aligned in the πg9/2-3ν(d5/2, g7/2)2 valence configuration space were found at 4109 and 6265 keV.