Monday, March 11, 2002 - DPG-Tagungen

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Nuclear Physics Tuesday A complete spectrometer also requires ancillary detectors and although the simplest method is to use the same digital electronics for the ancillary detectors, this may be an expensive option if traditional electronics is already available. To circumvent this problem, we have conceived a method to use a single DGF card together with traditional analogue electronics, where the DGF card provides a timestamp for the analogue data which is read out in the conventional way. Funded by BMBF under contract no. 060K958. HK 10.7 Tue 10:30 Foyer Chemie Picosecond lifetime determination in the mirror nuclei 47Cr and 47V — •Dimitar Tonev 1 , Pavel Petkov 1,2 , Alfred Dewald 1 , Silvia Lenzi 3 , Daniel R. Napoli 4 , Ventseslav Andrejtscheff 2 , and Peter von Brentano 1 — 1 Institut fuer Kernphysik, der Universitaet zu Koeln, Zuelpicherstr 77, 50937 Koeln, Deutschland — 2 Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria — 3 Dipartimento di Fisica and INFN, Sezione di Padova, Padova, Italy — 4 INFN, Laboratory Nazionali di Legnaro, Legnaro, Italy Lifetime measurements in the mirror nuclei 47Cr and 47V are performed by means of the Doppler-shift attenuation method using the multidetector array EUROBALL. The determined transition strengths in the yrast cascades are well described by full pf-Shell model calculations and the behaviour of the transition quadrupole moments with increasing spin confirms the nuclear structure and shape changes inferred in earlier works investigating Coulomb energy differences (CED). HK 10.8 Tue 10:30 Foyer Chemie Transition Matrix Elements in Neutron-rich Fission Fragments — •C. Hutter 1,2 , R. Krücken 1 , J.R. Cooper 1,3 , C.J. Barton 1 , C.W. Beausang 1 , M. Caprio 1 , R.F. Casten 1 , W.-T. Chou 1 , A.A. Hecht 1 , N. Pietralla 1,4 , N.V. Zamfir 1 , A. Aprahamian 5 , M. Shawcross 5 , D. Cline 6 , C.Y. Wu 6 , K.E. Gregorich 7 , R.M. Clark 7 , A.O. Macchiavelli 7 , M. Stoyer 3 , and A. Zilges 2 — 1 WNSL-Yale University — 2 Institut für Kernphysik, Technische Universität Darmstadt — 3 Lawrence Livermore National Laboratory — 4 Institut für Kernphysik, Universität zu Köln — 5 Notre Dame University — 6 University of Rochester — 7 Lawrence Berkeley National Laboratory In view of the prospects of studying neutron-rich nuclei far from stability using RIBs it is important to get structural information on those nuclei already accessible today by means of spectroscopy following fission. The systematic knowledge of transition matrix elements in these nuclei is key to observe modifications off the shell structure of nuclei far from stability. In this contribution we report on a recoil distance Doppler shift experiment using Gammasphere and the New Yale Plunger Device to measure lifetimes of excited states in neutron rich nuclei produced in the fission of 252 Cf. Fission fragments emitted in a cone of ± 20 ◦ from a thin 50 µCi 252 Cf source were detected by a set of photo cells. Complementary fragments were stopped in a gold stopper after traveling a variable distance. Gamma rays in coincidence with fission fragments were detected by the Gammasphere array. First results for A≈ 100 and 140 nuclei will be presented. Supported by the U.S. DOE (DE-FG02-91ER-40609) and NSF, and the German DFG under contract No.Pi 393/1. HK 10.9 Tue 10:30 Foyer Chemie New g factor measurement of the 44 Ca(2 + 1 ) state + — •S. Schielke 1 , K.-H. Speidel 1 , O. Kenn 1 , J. Leske 1 , G. Müller 1 , and J. Gerber 2 — 1 Institut für Strahlen- und Kernphysik, Univ. Bonn, D-53115 Bonn — 2 Institut de Recherches Subatomiques, F-67037 Strasbourg, France In view of the precise g(2 + 1 ) values obtained for Ti and Cr isotopes [1] suggesting considerable excitations of protons and neutrons of the 40 Ca core to fp shell orbits the first 2 + states of Ca isotopes should show a similar behaviour. However, from an early measurement on 44 Ca [2] the g(2 + 1 ) value was found to be negative indicating a dominant f7/2 neutron component in the wave function. We have remeasured this g factor by employing projectile Coulomb excitation in inverse kinematics combined with the transient field technique. A 44 Ca beam provided by the Cologne tandem accelerator was Coulomb excited by scattering from a carbon target. The g factor was derived from spin precessions in ferromagnetic Gd. Contrary to [2] the newly determined g factor is definitely positive indicating collective admixtures due to core excitation. + supported by DFG [1] R. Ernst et al., Phys. Rev. Lett. 84 (2000) 416 [2] Y. Niv et al., Phys. Rev. Lett. 43 (1979) 326 HK 10.10 Tue 10:30 Foyer Chemie Search for hyperdeformation in the A ≈ 125 region∗ — •J. Domscheit1 , H. Amro2 , R. Clark3 , M. Cromaz3 , P. Fallon3 , A. Görgen3 , G.B. Hagemann4 , B. Herskind4 , H. Hübel1 , D.R. Jensen4 , I.Y. Lee3 , W.C. Ma2 , A.O. Macchiavelli3 , D. Ward 3 , and J.N. Wilson4 — 1ISKP Univ. Bonn, Germany — 2 3 4 Mississippi State Univ., USA — LBNL, Berkeley, USA — NBI, Copenhagen, Denmark The compound nucleus 128Ba was produced in the symmetric reaction 64Ni + 64Ni at a bombarding energy of 265 MeV at the 88-Inch cyclotron in Berkeley. This reaction was chosen in order to populate high-spin states with large deformation at relatively low excitation energy. Gamma-ray coincidences were measured with the Gammasphere spectrometer. The strongest exit channels and their relative intensities were: 122Xe (100), 124Ba (98), 125Ba (62), 125Cs (24) and 123Ba (7). A search was peformed for regular sequences of discrete transitions using different approaches, but up to date no hyperdeformed bands (axis ratio ≈ 3:1) could be established. Two different search routines are presented and the limits for the detection of regular sequences are discussed. The data were also used to extend and correct the previously known level scheme of 125Cs [1,2]. [1] J.R. Hughes et al., Phys. Rev. C 44 (1991) 2390 [2] D. Ward, AIP Conf. Proc. 259 (1992) 358 ∗Work supported by BMBF, Germany (contract no 06 BN 907) HK 10.11 Tue 10:30 Foyer Chemie High-spin spectroscopy in 161,162 Lu ∗ — •P. Bringel 1 , J. Domscheit 1 , H. Hübel 1 , A. Neusser 1 , G. Schönwasser 1 , A.K. Singh 1 , G.B. Hagemann 2 , D.R. Jensen 2 , D. Bazzacco 3 , S. Lunardi 3 , M. Axiotis 4 , Th. Kröll 4 , D.R. Napoli 4 , C. Ur 4 , H. Amro 5 , S.C. Pancholi 6 , R. Bhowmik 7 , S. Bhattacharya 8 ,andC. Petrache 9 — 1 ISKP, Univ. Bonn, Germany — 2 NBI, Copenhage, Denmark — 3 INFN e Dipart. di Fisica, Padova, Italy — 4 INFN,LNL,Legnaro,Italy — 5 Dep. of Physics, Mississippi State University, USA — 6 Dep. of Physics & Astronomy, Dehli University, Dehli, India — 7 Nuclear Science Centre, New Dehli, India — 8 SINP, Calcutta, India — 9 Univ. di Camerino, Italy Triaxial superdeformation (TSD) has recently been established in Lu and Hf isotopes in the mass 165 region. The aim of this work is to search for the predicted TSD in 161 Lu and 162 Lu. High-spin states in these nuclei have been populated in the r eaction 100 Mo( 65 Cu,xn) at 260 MeV beam energy at the Legnaro Tandem accelerator. Gamma-ray coincidences have been measured with the GASP array. The data permit an extension of all the known normal-deformed (ND) bands in 161,162 Lu. The searc h for TSD is in progress. ∗ Work supported by BMBF (Contract no. 06 BN 907) and by DFG (Contract no. Hu 325/10) HK 10.12 Tue 10:30 Foyer Chemie Photon scattering on 98Mo ⋆ — •G. Rusev1,2 , R. Schwengner1 , F. Dönau1 , L. Käubler1 , S. Mallion1 , K.D. Schilling1 , A. Wagner1 , H. von Garrel3 , U. Kneißl3 , C. Kohstall3 , M. Kreutz3 , H.H. Pitz3 , M. Scheck3 , and F. Stedile3 — 1Inst. für Kern- und Hadronenphysik, FZ Rossendorf — 2INRNE Sofia — 3IfS, Universität Stuttgart We present results of the first photon-scattering experiment on the nuclide 98Mo. This experiment was carried out at the bremsstrahlung facility of the Stuttgart Dynamitron accelerator at an electron energy of 3.8 MeV. Photons scattered from a 98Mo target with a mass of 1998 mg, enriched to 98.55%, were measured with three HPGe detectors placed at 90◦ , 127◦ and 150◦ , respectively, to the incident photon beam. We identified five states with J = 1 in the energy range from 2.8 to 3.6 MeV. A state at about 2.8 MeV is a candidate for the [2 + ⊗ 3− ] 1− two-phonon excitation while states with 3.2 to 3.6 MeV may be considered as J π =1 + states. An analogous experiment was carried out for the nuclide 100Mo and is also being analysed. ⋆ Supported by the DFG under contract no. Do 466/1-1. HK 10.13 Tue 10:30 Foyer Chemie Structure studies in odd-A iodine nuclei — •Hariprakash Sharma 1,2 and P. Banerjee 3 — 1 University of Kalyani, Kalyani-741 235, India — 2 Forschungszentrum Rossendorf, PF 510119, 01314 Dresden, Germany — 3 Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar,Calcutta-700 064, India
Nuclear Physics Tuesday Recent experimental data on odd-mass iodine isotopes (A=119-125) have revealed several interesting structural features. These include the observation of coexistence of prolate and oblate bands with similar proton configurations, three quasi-particle bands, signature inversion in yrast positive-parity bands, shape coexistence. Presently particle rotor model calculations have been performed for the πh11/2, πg9/2 and πg7/2 bands in 121,123,125 I using an axially symmetric deformed Nilsson potential. The calculations reproduced the experimental results well and predict a moderate quadrupole deformation ∼0.2 for these bands. Work supported by BRNS-DAE under project number 99/37/30 and BRNS/822. HK 10.14 Tue 10:30 Foyer Chemie γ-spectroscopic study of spin-isospin giant resonances in 208Bi — •A. Krasznahorkay1,2 , A.M. van den Berg2 , S. Brandenburg2 , M. Csatlós1 , M. Fujiwara3,4 , V. Hannen2 , M. N. Harakeh2 , J. Gulyás1 , F. Ihara4 , Z. Máté1 ,andR. Zegers2 — 1Institute of Nuclear Research (ATOMKI) Debrecen, Hungary — 2KVI, Groningen, The Netherlands — 3RCNP, Osaka, Japan — 4JAERI, Tokai, Japan Spin-isospin giant resonances have been excited in 208Bi using the 208 3 Pb( He,t) reaction and the γ-decay of the states has been investigated in order to get a deeper insight into the microscopic structure of the spin-dipole (SD) and Gamow-Teller (GT) excitations and Isobaric Analogue States (IAS). The experiments were carried out at the KVI using 177 MeV 3He beams from the AGOR superconducting cyclotron. The energy of the tritium ejectiles was analyzed by the BBSmagnetic specrometer, which was set at zero degree with respect to the beam direction, while the energy of the γ-rays was measured with a large NaI detector equipped with anticoincidence shield. We could observe transitions for the first time both from the SD and GT resonances to low-lying states with well defined particle-hole configurations. HK 10.15 Tue 10:30 Foyer Chemie Investigation of the 1S0 n-n FSI using the d(d, 2He) 2nreaction-a technique to measure the n-n scattering length — •C. Bäumer1 , A.M. van den Berg2 , N. Blasi3 , B. Davids2 , D. Frekers1 , D. De Frenne4 , E. Grewe1 , M. Hunyadi2 , M.A. de Huu2 , E. Jacobs4 , B. Junk1 , A. Negret4 , S.Rakers1 , R. Schmidt1 ,andH.J. Wörtche2 — 1Westfälische Wilhelms-Universität Münster, Germany — 2 3 Kernfysisch Versneller Instituut, Groningen, The Netherlands — INFN Milano, Italy — 4Universiteit Gent, Belgium The cross section for the d(d, 2He) 2n reaction at Ed=170 MeV and small momentum transfer has been measured. The experiment was carried out at the AGOR facility of the KVI (Groningen/NL). The two correlated protons of the 2He were momentum analyzed with the BBS magnetic spectrometer and detected in coincidence by the ESN-detector. An energy resolution of 140 keV was achieved. The (d, 2He) reaction is used to map out the 2nsystemwithhighpreci sion. In the region of lowest momentum transfer the reaction is mediated by the Gamow-Teller transition operator which excites the di-neutron system predominantly into the 1S0 state. In the region of low internal momentum of the 2n system the shape of the 1S0 final-state interaction gives quantitative information about the neutron-neutron scattering length ann. In this talk preliminary results are presented and the advantages of the d(d, 2He) 2n reaction over similiar approaches to extract ann are discussed. HK 10.16 Tue 10:30 Foyer Chemie Measurement of the M1 and M2 spin-flip strength distribution in 48 Ca — •N. Blasi 1 , C. Bäumer 2 , A.M. van den Berg 3 , R. Bieber 3 , D. Frekers 2 , M. Hagemann 4 , V.M. Hannen 3 , M.N. Harakeh 3 , J. Heyse 4 , F. Hofmann 5 , M.A. de Huu 3 , E. Jacobs 4 , Y. Kalmykov 5 , B.A.M. Krüsemann 3 , P. von Neumann-Cosel 5 , S.Rakers 2 , B. Reitz 5 , A. Richter 5 , R. Schmidt 2 , K. Schweda 5 , A. Shevchenko 5 ,andH.J. Wörtche 3 — 1 INFN, Milano (It) — 2 IKP, Münster (De) — 3 KVI, Groningen (Nl) — 4 Universiteit Gent (B) — 5 IKP, Darmstadt (De) Polarization transfer observables in intermediate energy proton-nucleus scattering carry important information about details of the nuclear structure, which in many cases are difficult to extract otherwise. We have started to measure the transverse spin-flip probability Snn with highest precision and statistics in 48 Ca scattering in order to disentangle the isovector spin-M1 and spin-M2 resonances. Of course, for further elucidation of the dynamics of spin magnetization, (e,e ′ )-measurements are also required to provide additional clues for a consistent interpretation. Our first measurements were done on 48 Ca at the focal-plane polarimeter set-up of the AGOR BBSmagnetic spectrometer at the KVI using polarized protons at 174 MeV. Spectral resolution of order 100 keV was achieved, and Snn spectral functions of 250 keV bin size allow a first insight into details of the nuclear response. The poster will describe the novel techniques of the measurement and present various results. It will also describe some of the potentials for future measurements of spin observables at intermediate energies using the present facility. HK 10.17 Tue 10:30 Foyer Chemie Side-feeding pattern investigation in the 114Cd( 36S,xn) and 100 48 1,2 1 Mo( Ti,xn) reactions — •A.A. Pasternak , W. Gast , H.M. Jäger1 , L. Mihailescu1 , R.M. Lieder1 , E.O. Podsvirova1,2 , D. Bazzacco3 , R. Menegazzo3 , S. Lunardi3 , C. Rossi Alvarez3 , G. de Angelis4 , E. Farnea4 , A. Gadea4 , D.R. Napoli4 , T. Rza¸ca-Urban5 ,andW. Urban5 — 1IKP, FZ Jülich, D-52425 Jülich — 2A.F. Joffe PTI, RU-194021 St. Petersburg — 3INFN, Sezione di Padova, I-35131 Padova — 4INFN, LNL, I-35020 Legnaro — 5IEP, Univ. Warsaw, PL-00-681 Warsaw A new approach for the investigation of continuum γ-ray cascades has been developed based on Monte-Carlo simulations of entry-state population distributions and the deexcitation of the entry states. The aim is to fit simultaneously different types of experimental data, viz. statistical distributions of γ-ray cascades like γ-multiplicity distributions and DSA γ-ray lineshapes, being sensitive to the time-distribution of the sidefeeding cascades. In the deexcitation process stretched E2 bands (including rotational damping) and statistical E1, M1 and E2 transitions have been considered. For the near-magic nuclei 142−146Gd also superdeformed bands (SDB) and magnetic rotational bands have been taken into account. Fold distributions for the 114Cd( 36S,xn) 144,145,146Gd (E=182MeV) and 100Mo( 48Ti,xn) 143,144,145Gd (E=215 MeV) reactions measured with GASP have been fitted. For the case of 114Cd( 36S,6n) 144Gd side-feeding time distributions have been calculated with the same fit parameters. Experimental DSA lineshapes can be reproduced assuming a considerable number of SDB in the continuum. HK 10.18 Tue 10:30 Foyer Chemie Fusion to superheavy nuclei and quasifission in the dinuclear model — •T.M. Shneidman1,2 , G.G. Adamian1,2,3 , N.V. Antonenko1,2 , and W. Scheid1 — 1Institut für Theoretische Physik der Justus-Liebig-Universität, D-35392 Giessen, Germany — 2Joint Institute for Nuclear Research, 141980 Dubna, Russia — 3Institute of Nucear Physics, Tashkent 702132, Uzbekistan The dinuclear system concept is used to describe the evaporation residue cross sections for the production of superheavy nuclei and charge and mass distributions from quasifission in the same reactions. Th dinuclear system evolves to fusion by the transfer of nucleons between the clusters and decays with some probability into fragments with a given mass and charge asymmetry which is the quasifission. Calculated evaporation residue cross sections and mass and charge distributions from quasifission are compared with available data from experiments at JINR in Dubna and at GSI in Darmstaft. Supported by BMBF and Volkswagen Stiftung. HK 10.19 Tue 10:30 Foyer Chemie Fusion to superheavy nuclei and quasifission in the dinuclear model — •T.M. Shneidman 1,2 , G.G. Adamian 1,2,3 , N.V. Antonenko 1,2 , and W. Scheid 1 — 1 Institut für Theoretische Physik der Justus-Liebig-Universität, D-35392 Giessen, Germany — 2 Joint Institute for Nuclear Research, 141980 Dubna, Russia — 3 Institute of Nucear Physics, Tashkent 702132, Uzbekistan The dinuclear system concept is used to describe the evaporation residue cross sections for the production of superheavy nuclei and charge and mass distributions from quasifission in the same reactions. The dinuclear system evolves to fusion by the transfer of nucleons between the clusters and decays with some probability into fragments with a given mass and charge asymmetry which is the quasifission. Calculated evaporation residue cross sections and mass and charge distributions from quasifission are compared with available data from experiments at JINR in Dubna and at GSI in Darmstadt. Supported by BMBF and Volkswagen-Stiftung.
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Friese, J. . HK 14.1, HK 14.3, HK 4
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Rusev, G. ..................HK 10.1
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Monday, March 11, 2002 - DPG-Tagungen

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