annual report RIJKSUNIVERSITEIT GRONINGEN KERNFYSISCH VERSNELLER INSTITUUT GRONINGEN THE NETHERLANDS

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1 annual report RIJKSUNIVERSITEIT GRONINGEN 2003 KERNFYSISCH VERSNELLER INSTITUUT GRONINGEN THE NETHERLANDS

2 KVI annual report 2003 KERNFYSISCH VERSNELLER INSTITUUT Zernikelaan AA Groningen - The Netherlands

3 Front cover Upper: The Al 41 Catraz experiment, which uses a magneto-optical trap as an extremely sensitive detector for very rare isotopes. The goal of the experiment is to separate and detect 41 Ca. This isotope, which has a half-life of years, has a natural abundance of in for example the calcium in our bones. Important applications in medical research such as the study of osteoporosis, and the possibility to date old bones (complementary to the well-known 14 C dating method) are important motivations for this research. See section 5.2. Bottom left: The TRIµP magnetic separator close to being fully installed. See section 3.2. Bottom right: The PANDORA detector mounted on a two-layer asphalt paving machine. See sections 7.1 and 7.2. Editors Editorial assistance Printing Peter Dendooven Thomas Schlathölter Amarins Petitiaux Grafisch Centrum, Facilitair Bedrijf, RuG

4 Preface In this annual report the scientific and related activities that took place in 2003 are presented. Only a few of the highlights and important events are reviewed in this preface. During 2003 three prolonged shutdown periods were used for rebuilding the experimental halls, to make room for the magnetic separator of TRIµP, for maintenance of AGOR, for installing the Plastic Ball at the BBS, for assembling BINA and for starting the installation of the TRIµP magnetic separator later in the year. The last operation will be finished around the end of April During the maintenance of AGOR special attention was given to vacuum problems. Leaks were localised and repaired and cryopumps were installed. Together with modifications on the high-energy beam line these improvements on the vacuum of AGOR are needed for future intense heavy-ion beams for TRIµP. One of the interesting developments with respect to AGOR is the quality improvement of high-energy proton and deuteron beams. Since the installation of AGOR at KVI in 1996, there were problems with internal loss of high-energy proton and deuteron beams. It was concluded from measurements and calculations that this may have to do with a deviation from mirror symmetry with respect to the median plane of AGOR. A vertical displacement of the superconducting coils resulted in improvement by a factor of two of the extraction efficiency of the high-energy proton beams. Because of the prolonged shutdowns in 2003 only 300 shifts were used by 11 experiments which were all successfully executed. Although the number of shifts is around 120 shifts less than what was delivered in 2002, the reliability of AGOR was very good with more than 90% availability of AGOR during the running periods. The Atomic Physics Group was successful in November 2003 in measuring fluorescence from one calcium atom trapped in the Magneto-Optical Trap (MOT) of the AlCatraz experiment. This is essential for the experimental plan to count 41 Ca atoms in natural samples and the application of that in dating and medical studies. The project application of Peter Dendooven in the FOM projectruimte to study the use of superfluid helium to stop high-energy radioactive ions and extract them as a low-energy ion beam was approved. A budget of around 250 keuro for this project RIASH (Radioactive Ions and Atoms in Superfluid Helium) was granted. In 2003, the Board of Governors of the University of Groningen (RuG) and the FOM Executive Board decided to grant our request for Storage Area Network. The requested budget of 308 keuro was approved and shared equally by both mother organisations. Furthermore, the FOM Executive Board approved the application for financial support of the KVI high-school project for cosmic radiation, a project set up in collaboration with a number of Dutch universities and NIKHEF (HISPARC). This project aiming to measure cosmic radiation will be set up with high schools thus involving their students in scientific research at an early stage. In December 2003, the FOM Executive Board approved our application for middle-large investment (NWO-middelgroot) for the FOM-programme Interacting hadrons and the RIASH project and granted a total amount of 315 keuro. The Interacting hadrons programme had its mid-term evaluation several months earlier, which was very positive. The KVI joined two applications in the framework of Integrated Infrastructure Initiatives (I3) of the EU 6 th Framework Programme: EURONS (EUROpean Nuclear Structure) and I3HP (I3 Hadron Physics). At the end of July, we were informed that out of the 158 I3 applications 24 were approved. I3HP was among them, but unfortunately EURONS ranked 25 and therefore came on the top of the 1

5 reserve list, which means it will be financially supported if money becomes available. A final decision on this will be taken in The KVI Nuclear Geophysics Division (NGD) demonstrated successfully in 2003 that it is possible to measure the layer thickness of road asphalt using nuclear detection techniques with a precision of less 1 mm. One of the large Dutch road-construction contractors, Heijmans, is interested in this non-invasive radiometric method because it is simple, fast, non-destructive and economically cheaper to apply. The KVI organised several meetings and workshops in A workshop was organised in the framework of the new GSI project with the topic Inelastic scattering with radioactive nuclei and held at KVI on February. Another workshop was organised by the European HINDAS Collaboration and held in Groningen on February to discuss the achieved results of this project in the EU 5 th framework programme and its possible continuation in the 6 th framework programme. A workshop with the title Advanced electromagnetic calorimetry and its applications was held on March in Jülich. This was organised by KVI and COSY Jülich in the framework of the European FINUPHY network. The third FANTOM Symposium was held on 8-9 May in Groningen. The staff of the various FAN- TOM partner institutes presented and discussed their present research programmes and future plans. FANTOM aims with these meetings to strengthen existing collaborations between partner institutes in FANTOM and stimulate new ones evolving around new research programmes. The KVI opened its doors to many visiting groups this year, and organised an open day on Sunday, 19 October in the framework of the National Science Week with the theme of this year Quality of Life (Kwaliteit van leven). It was a very successful open day with the total number of visitors exceeding 500, including many enthusiastic young visitors. We have had a number of mutations in the personnel sphere in The appointment of Rob Timmermans as Professor in theoretical nuclear physics at KVI was approved by the RuG Board of Governors. He started officially in this position and as head of the Theory Group on 1 June Johan Messchendorp started on 1 February 2003 in his new position as universitair docent (equivalent: assistant professor) at KVI with the immediate task to strengthen spin-physics within the experimental nuclear physics programmes at KVI. The search committee for the open staff position (universitair docent) in the Accelerator Group selected Mariët Hofstee, an ex-graduate student of the KVI, to fill this position. She started officially on 1 September A highlight in the personnel sphere is the success of Gerco Onderwater s application in the framework of the NWO Vernieuwingsimpuls programme (Vidi category). Gerco will receive from NWO (plus matching from the RuG) 600 keuro to cover his salary for five years and that of a graduate student plus some additional money for equipment and travel. Gerco started as a universitair docent at KVI in December 2003 with the task to develop plans for measuring the electric dipole moment of the deuteron. Since Reinhard Morgenstern became member of the Board of the Faculty of Mathematics and Sciences in November 2002, he resigned as KVI Scientific Deputy Director and Director of the research school FANTOM. Klaus Jungmann was appointed in his position as Scientific Deputy 2

6 Director, and Herbert Löhner in his position as Director of FANTOM. Rob Timmermans was appointed member of the FANTOM Board instead of Herbert Löhner. Also, the position of Technical Deputy Director was evaluated and following the changes in the management structure Ad van den Berg accepted to continue in this position till the middle of Six graduate-student positions in the various KVI groups were filled in Furthermore, six positions have been filled in the different technical departments at KVI. We had five Ph.D. graduations in 2003: Patrick Hendriks, Karsten Ermisch, Eric van Dalen, Peter van Luijk and David Heesbeen. David, a graduate student of Gerard van der Steenhoven, did his Ph.D. research in the framework of the HERMES collaboration at DESY in Hamburg. All got positions, some even before graduation, in academic research and in industry. Steven Knoop, now a Ph.D. student in the Atomic Physics Group, received for his master s thesis research in the same group, the Kamerlingh Onnes prize. He was invited to give the general Faculty colloquium with the title Serving cold atoms to hungry ions on 3 April where the prize was given to him in an open ceremony. In 2003, FANTOM organised two study-weeks. The first of these general study-weeks was organised in the week 2-6 June in Leuven, Belgium with the title: Trapping and manipulating atomic and subatomic particles. This was organised together with a number of European networks in the field of traps, and therefore the number of participants (around 50) was larger than usual. The second studyweek on the topic: Interplay between theory and experiment was held in Amsterdam, in the week 3-7 November. During the first study-week in Leuven an international committee visited FANTOM to evaluate its educational activities in the framework of its application for renewed recognition by the Royal Dutch Academy of Sciences (KNAW) as an international research school. This evaluation was positive. The application was submitted at the end of 2003 and a decision by KNAW is expected in the middle of The Programme Advisory Committee (PAC) of KVI met on November 21, The members of the PAC are: J. Äystö (University of Jyväskylä), Ph. Chomaz (GANIL, Caen), Sydney Galès (IPN, Orsay), L. Nilsson (TSL, Uppsala; chairman), M. Pignanelli (INFN, Milan), H. Sakai (University of Tokyo) and H. Ströher (FZ, Jülich). The PAC reviewed the status of the facility and considered the 8 proposals that were submitted. The proposals were approved but the requested shifts of some were cut substantially because of the pressure on the beam time. The PAC was satisfied with the progress with TRIµP and noted that the short stay of TAPS at KVI in 2005 should not hinder the completion of the envisaged scientific programme. The Beleidscollege (BC) (policy-advisory board) of KVI, which advises directly the Board of Governors of the University of Groningen (RuG) and the Executive Board of the funding agency FOM, consisted in 2003 of K. Bulthuis (FOM), D. Guerreau (IN2P3), M.A. Kooyman (RuG; chairman), G. Luijcks (NIKHEF), P.J.G. Mulders (VUA), W.J. van der Zande (AMOLF) and S. Daan (RuG). G.A. Mulder (RuG) and E.E.W. Bruins (FOM) served as first and second executive secretaries of the BC. The BC met on 25 June 2003 and was informed about developments in the personnel and financial sectors and over progress in the TRIµP project and programme. The BC was positive over the developments and was satisfied with the financial situation over 2002 and the way it seemed to develop in 2003 and further. This, however, was before the disclosure in early September of the increase in personnel costs, which influenced the KVI budget negatively. This required the implementation of a number of measures to keep the budget within the bounds set by RuG and FOM. The most painful of these was cutting the structural number of graduate student positions, blocking all opening vacancies and cutting the material budgets of all groups by about 10%. This was later compounded by 3

7 the announcement of FOM that cuts are needed within the Subatomic Physics (SAF) programmes, including those of the KVI, to keep the budget within the financial ceiling foreseen for this subfield in the strategic plans of FOM. The worsening financial situation in the Netherlands and the political push to move away from curiosity-driven fundamental research to strategic technical research with short-term horizon to benefit the industry, and thereby the economy, may have severe financial impact in the coming years. We have had many visitors for longer or shorter periods in 2003, who contributed to the scientific programmes of the KVI. A number of them received scholarships from NWO (The Dutch Organisation for Scientific Research) and stayed at KVI for long periods. I would like to mention in particular Professors Alex Korchin (Kharkov, Ukraine), Michael Urin (Moscow, Russia) and Czaba Korpa (Pecs, Hungary) who stayed at KVI for several months. Furthermore, I would like to acknowledge NWO also for the financial contributions to stimulate exchange programmes with France and Hungary. Last but not least, I thank the KVI scientific and technical staff, the colleagues from the various collaborations and institutes and the many guests for their valued contributions to the scientific activities of KVI in Groningen, March 2004 Muhsin N. Harakeh 4

8 Contents 1 Nuclear Structure Spectroscopy of the halo-nucleus 6 He The structure of 7 He and the strength of the spin-orbit force Experimental determination of the J π components of the spin-dipole resonance in 12 B Gamow-Teller strength in 14 C through the 14 N(d, 2 He) 14 C reaction Resonance states in 26 Si and reaction rates in the rp-process Suppression of Gamow-Teller transitions in deformed mirror nuclei 25 Mg and 25 Al Multipole-decomposition analysis of IVGR s strengths in 58 Co and 48 K Study of Gamow-Teller strength distributions in fp-shell nuclei through the 64 Ni(d, 2 He) 64 Co reaction Proton decay of the isoscalar Giant-Dipole Resonance in 208 Pb Optical-model analysis of deuteron scattering off 90 Zr and 116 Sn at 183 MeV GT + strength distribution in 48 Sc relevant for the 48 Ca double-beta decay GT + strength distribution in 116 In relevant for the 116 Cd double-beta decay Gamow-Teller transitions in the odd-n nuclei 57 Fe and 61 Ni studied through the (d, 2 He) reaction Feasibility of p-γ coincidence measurements in (p, p γ) reactions Hadronic Physics Few-body physics activities at KVI; an overview Proton-proton real bremsstrahlung measurement at 190 MeV Proton-proton virtual bremsstrahlung at 190 MeV Proton-deuteron capture measurements with BBS and the Plastic-Ball First results from p+d radiative-capture measurements Quantitative comparison of the experimental and theoretical cross sections of the 1 H( d,pp)n reaction at 130 MeV Effective analyzing powers of graphite sheets vs. energy Status of BINA Nucleon-resonance decay through the K 0 Σ + channel Proton response and radiation damage in detector crystals TRIµP Status of the TRIµP facility Current status of the TRIµP magnet separator Status of the TRIµP ion catcher project Radio Frequency Quadrupole for the TRIµP Facility Trapping of heavy alkaline earth elements Development of a polarimeter for the search of a permanent electric dipole moment of the deuteron

9 4 Theory The analysis of B d (η, η )l + l decays in the Standard Model Meson baryon couplings from QCD sum rules Coupled channels calculations for photo-induced K-Λ and K-Σ production The electric amplitude in strangeness photoproduction Overtones of isoscalar giant resonances in medium-heavy and heavy nuclei On the collapse dependence of the 2νββ-decay amplitude within the QRPA On direct proton decay of the isovector spin-flip giant monopole resonance Atomic Physics Ion interactions in cometary, planetary and fusion environments The needle in ten thousand haystacks Inner-shell capture in slow proton Na collisions Biomolecules in ultrastrong fields Probing surface magnetism by spin-polarized electron capture Miscellaneous Projects The Atomic Clock method for fission lifetime measurements Entanglement in nuclear physics Results for the HINDAS project Determination of neutron energy spectra and angular distributions for 90 MeV protons on a thick 13 C target The high-school project Cosmic Radiation Nuclear Geophysics Radiometric asphalt layer thickness determination In situ radiometry during road construction Gamma radiometry at a layered salt marsh Distinguishing between gravel and clay on ocean floors Radiometric assessment of terroir Optimisation of a landmine detector Simulation of gamma-ray standard spectra for PELAN Properties of the PNDT detector section Laboratory testing of NuPulse prototype Monte Carlo determination of peak efficiency of germanium detector to low-energy gamma-rays Mapping radiogenic heat sources in the Earth by antineutrinos Sources of the background for PHAROS detectors: Cosmic-ray contribution Radiometric forensics: dating archaeological artifacts Radiobiology Dose-volume effects in the rat parotid gland The heart and the lung: A highly sensitive couple Dose-volume effects in the rat lung D radiation detection with a scintillating GEM for proton therapy

10 9 AGOR, Ion Sources and Radiation Safety AGOR status report Survey of beam time used for experiments with AGOR in Beam phase measurement in the AGOR cyclotron Phase acceptance and bunch width in the AGOR cyclotron Vertical beam dynamics in AGOR revisited Improvement of the AGOR vacuum Adiabatic spin transitions revisited Status of POLIS and measurements with the LSP polarimeter Status of the ECR ion sources Improving an ECR Ion Source by means of a positively biased cylinder Radiation shielding calculations for the TRIµP facility Response functions for the on-site neutron monitoring system Technical Support Activities of the research technicians Activities of the mechanical department Activities of the electronics & electrotechnical department IT facilities Publications and Scientific Presentations Publications Ph.D. Theses Books Contributions to conferences, workshops, etc Internal reports Seminars at KVI Seminars and colloquia given outside KVI Personnel Scientific staff Technical and administrative staff

11 8

12 Chapter 1 Nuclear Structure 9

13 1.1 Spectroscopy of the halo-nucleus 6 He P. Haefner a), C. Bäumer a), A.M. van den Berg, D. Frekers a), D. De Frenne b), E.-W. Grewe a), M.N. Harakeh, M. Hunyadi, E. Jacobs b), H. Johansson d), B.C. Junk a), A. Korff a), A. Negret b), P. von Neumann-Cosel c), L. Popescu b), S. Rakers a), A. Richter c), N. Ryezayeva c), A. Shevchenko c), H.J. Wörtche Measurements of the (d, 2 He) chargeexchange reaction were performed on 6 Li at an incident energy of 85 MeV/A to investigate the structure of 6 He. A laboratory-angle range from 0 to 15 was covered, corresponding to a centre-of-mass angle of up to 22. ds/dw (mb/sr) H(d, 2 He)n 1 H(d, 2 He)n q c.m. = 0-3 q c.m. = 3-6 q c.m. = 6-9 q c.m. = 9-12 q c.m. = E x (MeV) Figure 1: : Excitation energy spectrum of 6 He obtained by the 6 Li(d, 2 He) 6 He reaction. The groundstate transition peak is scaled to enhance the view of the 2 + -excited state at MeV and the resonances above the two-neutron threshold (S 2n = MeV). The energy resolution was 100 kev (FWHM). The experiment was carried out using the ESN-BBS setup. Two self-supporting Li foils (95% enriched) with 10 mg/cm 2 and 5 mg/cm 2, respectively, were used as targets. Preliminary cross-section spectra are depicted in Fig. 1. The weakly bound nucleus 6 He is interesting, because of its pronounced halo structure. Furthermore, 6 He serves as a prototype for a Borromean system (α + n + n). We analysed angular distributions of the ground state transition, the first excited 2 + -state at MeV and broad resonances up to 25 MeV. The resonances seen in our experiment will be compared with theoretical predictions of threebody-models. Of particular interest is the possible existence of a soft dipole resonance at low excitation energies between 2 and 4 MeV as a result of the weak binding in 6 He. The position, width and nature of this resonance are still subject of theoretical [3-5] and experimental [6, 7] investigations. Such a resonance has already been found in the Borromean halo nucleus 11 Li. In both nuclei 6 He and 11 Li an enhanced cross section of electro-magnetic dissociation has been measured indicating a dipole resonance. We have some evidence for a soft dipole resonance around 3 MeV. Angular distributions and DWBA calculations are in preparation. a) Inst. f. Kernphysik, Universität Münster b) Universiteit Gent c) Inst. f. Kernphysik, TU Darmstadt d) GSI Darmstadt [1] S. Rakers et al., Nucl. Inst. Meth. A 481, 253 (2002). [2] J. Rapaport et al., Phys. Rev. C 41, 1920 (1990). [3] Y. Suzuki, Nucl. Phys. A 528, 395 (1991). [4] S. Funada et al., Nucl. Phys. A 575, 93 (1994). [5] B.V. Danilin et al., Nucl. Phys. A 632, 383 (1998). [6] S.B. Sakuta et al., Europhys. Lett. 22, 511 (1993). [7] S. Nakayama et al., Phys. Rev. Lett. 85, 262 (2000). 10

14 1.2 The structure of 7 He and the strength of the spin-orbit force N. Ryezayeva a), C. Bäumer b), A.M. van den Berg, D. Frekers b), D. De Frenne c), P. Haefner b), E. Jacobs c), H. Johansson d), B. Jonson e), Y. Kalmykov a), A. Negret c), P. von Neumann-Cosel a), L. Popescu c), S. Rakers b), A. Richter a), G. Schrieder a), A. Shevchenko a), H. Simon d), H.J. Wörtche We have investigated the structure of the halo nucleus 7 He by means of the (d, 2 He) charge-exchange reaction. The ground-state (g.s.) of 7 He is unbound against n-decay by 430 kev and yields a decay width of 160 kev [1]. Our objective was to measure the 7 He level scheme through 7 Li(d, 2 He) 7 He. A recent GSI measurement indicates a low-lying state at 570 kev assumed to be the 1/2 spinorbit partner of the 7 He g.s. (for details we refer to Ref. [2].) Such a low value for the spin-orbit splitting is in contrast with typical values of 5-6 MeV observed in heavier nuclei like 15 O, 17 O, or 39 Ca. For the equally unbound 5 He, the spin-orbit splitting is believed to be of order 4 MeV. For halo nuclei, little is known about the spin-orbit splitting, except that one could argue, that the large radial extent would significantly reduce the spin-orbit interaction. As the spin-orbit force is not deduced from first principles, important information may be gained. So far only the existence of an excited state in 7 He at about 3 MeV has been reported, which was believed to be the spin-orbit partner of the g.s.. In Refs. [3,4], however, it was reported that this state decays mainly via 4 He+3n and not via 6 He+n. This would indicate a core excited 6 He +n configuration. Shell-model calculations [5-8] predict a spin-orbit splitting of order 2-3 MeV. We have measured 7 Li(d, 2 He) with a resolution 130 kev (i.e. better than the line width of the 7 He g.s.). The spectrum, which covers a scattering-angle bin between 0 and 4 is shown up to 25 MeV excitation in Fig. 1. There is little GT strength located in the g.s. of 7 He. This can be understood assuming that 7 Li is composed of an α-particle and a triton. Broad continuum resonances are found at 2.9 MeV, 5.3 MeV, 8.0 MeV and 18.0 MeV above a quasi-free background, which is described by a smooth line. The p 1/2 spin-orbit partner of the g.s. should be excited equally strong by the GT transition operator and therefore be clearly visible if located at 570 kev. In the lower part of Fig. 1 the low excitation region is separately displayed showing no indication for a state at this energy. A full analysis which will include angular distributions for the spin structure of the continuum states is presently ongoing. yield / 50 kev (accpt. corr.) g.s. 2.9 MeV 5.3 MeV 8.0 MeV quasi-free 18.0 MeV Ex (MeV) E lab = 171 MeV qc.m. = 0-4 Figure 1: Excitation energy spectrum of 7 He obtained by the 7 Li(d, 2 He) 7 He reaction. To obtain better statistics the binning from 2 MeV on is 150 kev. a) Inst. f. Kernphysik, TU Darmstadt b) Inst. f. Kernphysik, Universität Münster c) Universiteit Gent d) GSI Darmstadt e) Chalmers U. of Technology, Göteborg [1] R.H. Stokes, P.G. Young, Phys. Rev. 178, 2024 (1969). [2] M. Meister et al., Phys. Rev. Lett. 88, (2002). [3] A.A. Korshenninikov et al., Phys. Rev. Lett. 82, 3581 (1999). [4] H.G. Bohlen et al., Phys. Rev. C 64, (2001). [5] P. Navratil, B.R. Barret, Phys. Rev. C 57, 3119 (1998). [6] N.A.F.M. Poppelier et al., Z. Phys. A 346, 11 (1993). [7] J. Wurzer, H.M. Hofmann, Phys. Rev. C 55, 688 (1997). [8] R.B. Wiringa, Nucl. Phys. A 631, 70c (1998) and references therein. 11

15 1.3 Experimental determination of the J π components of the spindipole resonance in 12 B M.A. de Huu, A.M. van den Berg, N.Blasi a), M. Hagemann b), M.N. Harakeh, J. Heyse b), M. Hunyadi, R. de Leo c), S. Micheletti a), H. Okamura d), H.J. Wörtche In November 2001, we performed an experiment to decompose the spin-dipole resonance (SDR) in 12 B into the J π components (for details, we refer to Ref. [1]). Taking advantage of a purely tensor polarized beam, we measured the ( d, 2 He) reaction for a natural carbon target. The experiments were performed at the Big-Bite Spectrometer (BBS) running in conjunction with the EuroSuperNova (ESN) detector system. In addition, we measured in coincidence decay neutrons by means of the EDEN detector system. Differential cross sections and tensoranalysing powers of states up to 5 MeV excitation energy have been extracted and compared to semi-microscopic DWBA calculations to verify predictions based on symmetry arguments for natural-parity states. The results are shown in Fig d /d ( b/sr) A yy A zz 5 J = 1 +, E x = 0.0 MeV x J = 2 +, E x = 0.96 MeV x 1.6 J = 1 +, E x = 5.0 MeV x c.m. (deg) c.m. (deg) c.m. (deg) C+T+EX C EX T C+EX Figure 1: Measured and calculated cross sections and tensor-analysing powers for the 12 C( d, 2 He) 12 B reaction at 171 MeV. The different contributions from the central (C), tensor (T) and exchange (EX) parts of the NN effective interaction are also shown The coincident measurement of decay neutrons proved to be very useful to determine the background in the continuum, supposed to originate from quasi-free processes. The information obtained from the polarisation observables and from the coincidence measurement allowed us to separate the SDR into the J π components. The results confirmed a previous J π = 0 assignment of a state at E x = 9.3 MeV [2] and yielded evidence for additional J π = 0 strength around E x = 4.0 MeV. Moreover, an existing controversy about the J π assignement of a bump at E x = 7.5 MeV could eventually be settled. Figure 2 shows the tensor-analysing power A zz extracted in bins of 100 kev, where large negative values of A zz around E x = 4.0 and 9.3 MeV indicate J π = 0 strength, while positive values of A zz at E x = 7.5 MeV indicate positive-parity states. A zz C ( d fi, 2 He) 12 B Q lab = deg E x in 12 B (MeV) Figure 2: Tensor-analysing power A zz spectra of 12 B. The binning is 100 kev. a) INFN, Milano, Italy b) Vakgroep Subatomaire en Stralingsfysica, Universiteit Gent, Belgium c) INFN, Bari, Italy d) Saitama University, Saitama, Japan [1] M.A. de Huu, Ph.D. thesis, Rijksuniversiteit Groningen (2004). [2] H. Okamura et al., Phys. Rev. C 66, (2002). 12

16 1.4 Gamow-Teller strength in 14 C through the 14 N(d, 2 He) 14 C reaction A. Negret a), T. Adachi b), C. Bäumer c) A. M. van den Berg, D. De Frenne a), D. Frekers c) Y. Fujita b), P. Haefner c), M. Hunyadi, M.A de Huu, E. Jacobs a), H. Johansson d), A. Korff c), P. von Neumann- Cosel e), L. Popescu a), S. Rakers c), N. Ryezayeva e), A. Richter e), A. Shevchenko e), H.J. Wörtche Although all the quantum numbers involved in the beta decay of 14 C and 14 O to the ground state of 14 N (1 +, T=0) suggest a Gamow-Teller (GT) character, the transitions are strongly hindered. Theoretically [1], the structure of the ground state of 14 N seems to favor the transition to a 2 + state rather than to 0 + or 1 + excited states in the final nuclei. (Fig. 1), however, remains an open question for the theory. The angular distribution for the strongly excited 2 + states (Fig. 2 depicts an example) proves the GT character of these transitions. 2 H(d, He)n d s /d W [arbitrary units] Counts C(d, He) B E x in C Figure 1: Excitation-energy spectrum of 14 C obtained in the 14 N(d, 2 He) experiment. The large peaks around 0.5 MeV and 13 MeV are due to the 1 H and 12 C chemical components of the melamine (C 3H 6N 6) target. A 14 N(d, 2 He) 14 C experiment has been performed at E d = 170 MeV using the AGOR cyclotron, the Big-Bite Spectrometer (BBS) and the EuroSuperNova (ESN) detector system, in order to address the issue of the GT strength distribution to the excited states of 14 C starting from the ground state (g.s.) of 14 N. Measurements were performed at four BBS angular settings θ BBS = 0, 3, 5 and 7.8. We found that, indeed, the g.s.-g.s. transition is strongly hindered, while the strength is going mainly to 2 + excited states. The fragmentation of the GT strengh over three 2 + excited states q CM Figure 2: The preliminary angular distribution for the 7.01 MeV 2 + level. The thin line represents the experimental distribution while the thick line represents a DWBA calculation for L=0. A mirror 14 N( 3 He,t) 14 O experiment has been performed at RCNP. The striking similarities of the 14 O and 14 C spectra, position of the levels, as well as the GT strength going to each individual level, illustrate the isospin symmetry. a) Vakgroep Subatomaire en Stralingsfysica, Universiteit Gent, Belgium b) RCNP, Osaka University, Japan c) Institut für Kernphysik, Universität Münster, Germany d) Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany e) Institut für Kernphysik, TU Darmstadt, Germany [1] S. Aroua et al., Nucl. Phys. A 720, 71 (2003) * Permanent address: NIPNE, Bucharest, Romania 13

17 1.5 Resonance states in 26 Si and reaction rates in the rp-process G.P.A. Berg, K. Hatanaka a), M.Wiescher b), H. Schatz c), T. Adachi d), Y. Fujita d), H. Fujita a), K. Fujita a), J. Görres b), J.P. Greene e), J. Kamiya a), Y. Sakemi a), Y. Shimbara d), Y. Shimizu a), T. Wakasa f), H.P. Yoshida a) and M. Yosoi g) In order to better understand the astrophysical rp-process and to determine spectroscopic information for stellar rate calculations of relevant (p,γ) and (α,p) reactions on proton rich target nuclei, it is necessary to measure resonance levels just above the proton and α-thresholds. For this purpose we have developed a method to measure α- beam induced 2- and 4-neutron pick-up reactions with the Grand-Raiden Spectrometer and the fully dispersion matched WS beam line [1] at the RCNP Ring cyclotron. A previous measurement [2] of the 24 Mg( 4 He, 6 He) 22 Mg at 206 MeV and 0 identified isolated resonance states. These states are relevant for rate calculations of the proton capture reaction 21 Na(p,γ) 22 Mg and the 18 Ne(α,p) 21 Na reaction that controls the break-out of the hot CNO cycles at X-ray burst conditions. We have extended the program to a similar measurement of resonant levels in 26 Si above the proton and α-thresholds at 5.5 MeV and 9.2 MeV, respectively. The former identifies resonances in the 25 Al(p,γ) 26 Si reaction which are important for the production of 26 Al in Novae which is a galactic γ-emitter. Fig. 1 shows parts of the measured spectra near these thresholds. From the lower panel of the figure we see that above the α-threshold only a few isolated states are seen in the ( 4 He, 6 He) reaction. These levels are important to improve the rate calculations that are presently performed under the Hauser-Feshbach level density assumption. The most sensitive parameter in the rate calculations is the excitation energy. It is, however also possible to extract the angular distribution from the data owing to the angular dispersion matching. This allows to distinguish between angular momentum L=0 and larger. Figure 1: Measured spectra of the 28 Si( 4 He, 6 He) 26 Si reaction at 206 MeV with a resolution of 60 kev. The proton and α-thresholds are shown as dotted lines in the upper and lower panels, respectively. The measured carbon and oxygen impurities are subtracted. a) RCNP, Osaka University, Osaka, Japan b) Univ. of Notre Dame, Notre Dame, USA c) NSCL, MSU, East Lansing, USA d) Dept. of Physics, Osaka Univ., Japan e) ANL, Argonne, Illinois USA f) Dept. of Phys., Kyushu Univ., Japan g) Dept. of Phys., Kyoto Univ., Japan [1] T. Wakasa, K. Hatanaka, Y. Fujita, G.P.A. Berg, et al., Nucl. Instr. Meth. Phys. Res. A 482, 79 (2002). [2] G.P.A. Berg, K. Hatanaka, M.Wiescher, H. Schatz, et al., Nucl. Phys. A 718, 608c (2003). 14

18 1.6 Suppression of Gamow-Teller transitions in deformed mirror nuclei 25 Mg and 25 Al Y. Shimbara a), Y. Fujita a), T. Adachi a), G.P.A. Berg, H. Fujita b), K. Fujita b), I. Hamamoto c), K. Hatanaka b), J. Kamiya b), K. Nakanishi b), Y. Sakemi b), Y.Shimizu b), M. Uchida d), T. Wakasa b), K. Yamasaki e), and M. Yosoi d) With the realization of complete dispersion matching [1,2] for the Grand Raiden spectrometer at the RCNP Ring Cyclotron it is now possible to study GT transitions at 0 via the ( 3 He,t) reaction at energies up to 140 MeV/u with a resolution of < 35 kev. We have performed such measurements and compared the GT transitions of two deformed nuclei in the middle of the sd shell via the 23 Mg( 3 He,t) 23 Na and the 25 Mg( 3 He,t) 25 Al reactions. Spectra of both reactions for the scattering angle range Θ < 0.8 are shown in Fig.1. The levels of the rotational bands (see Fig. 2) are identified by their excitation energies in MeV and the asymptotic quantum numbers of the Nilsson orbit K π [Nn z Λ]. The spectra a) and b) are scaled so that GT transitions with the same B(GT) values have the same peak heights. Counts Counts Counts a) g.s., 3/2 + b) g.s., 5/2 + 5/2 + [202] c) 3/2 + [211] 23 Na( 3 He,t) 23 Mg 0.451, 5/2 + 3/2 + [211] 13 N, , 1/2 + 1/2 + [211] 2.906, 3/ E in 23 Mg (MeV) x 25 Mg( 3 He,t) 25 Al 0.451, 1/2 + 1/2 + [211] 26 Al: 1.058, , 3/2 + 1/2 + [211] 1.613, 7/2 + 5/2 + [202] 1.790, 5/2 + 1/2 + [211] 2.485, 1/2 + 1/2 + [200] 2.674, 3/2 + 1/2 + [200]? 2.720, 7/2 + 1/2 + [211] 3.860, 5/2 + 1/2 + [220] 4.357, 1/ , 5/ , 5/2 + 5/2 + [202] E x in 25 Al (MeV) , 9/2 + 5/2 + [202] 3.859, 5/2 + 1/2 + [200] 4.196, 3/ , 9/2 + 1/2 + [211] 4.583, 5/2 + v. scl. x10 Figure 1: Measured spectra of the ( 3 He,t) E in 25 Al reaction (MeV) x at 140 MeV/u on 23 Na and 25 Mg targets showing the strong suppression of several GT transitions in 25 Al. The panel c) shows the same as panel b) scaled by a factor of , 7/2 + 1/2 + [200] 5.808, 5/ , 3/2 + Below E x = 6 MeV all GT excitations in 25 Al are strongly suppressed except for the 5/2 + ground and the 7/2 +, MeV states, while under στ-type GT spin-isospin selection rules all J π = 3/2 +, 5/2 +, 7/2 + states should be excited. This can be explained by the K selection rule of the GT operator, allowing intraor inter-band transitions with K K ± 1. The GT transitions from the g.s. of 25 Mg to the ground and MeV states in 25 Al are intra-band transitions with K = 0. The other weak transitions are inter-band transitions with K = 2. The suppression of the J π allowed transitions is well described by the K selection rules for the GT operator Ex (MeV) 4 Counts 23naspc0-08.KG 2 E=140 MeV/nucleon, q=0 o 25m g00_08.kg 0 Counts 1/2+[2 1 1] 5/2+[2 0 2] E=140 Figure MeV/u, 2: q=0 o Proposed band structure for the low-lying positive-parity states of 25 Al based on the Nilsson-orbit classification. Each state is denoted by the excitation energy (in MeV) and J π values. 25m g00_08.kg Counts 25 Mg( 3 He,t) 25 Al E=140 MeV/u, q=0 o 9/ /2+ 5/ / / / / / /2+ 5/2+ 3/2+ 1/2+ 1/2+[2 0 0] a) Dept. of Physics, Osaka University, Japan b) RCNP, Osaka University, Osaka, Japan c) Div. of Math. Phys., Univ. Lund, Sweden d) Dept. of Phys., Kyoto Univ., Japan e) Dept. of Phys., Konan Univ., Japan [1] Y. Fujita, K.Hatanaka, G.P.A. Berg, et al., Nucl. Instr. Meth. B 126, 274 (1997). [2] T. Wakasa, K. Hatanaka, Y. Fujita, G.P.A. Berg et al., Nucl. Instr. Meth. A 482, 79 (2002). 15

19 1.7 Multipole-decomposition analysis of IVGR s strengths in 58 Co and 48 K J. Guillot a), C. Bäumer b), D. Beaumel a), A.M. van den Berg, S. Brandenburg, B. Davids, S. Fortier a), D. Frekers b), E.-W. Grewe b), M. Fujiwara c)d), S. Galés a), P. Haefner b), M.N. Harakeh, M. Hunyadi, M. de Huu, B.C. Junk b), E. Rich a), H.J.Wörtche After a first (t, 3 He) experiment at 43 MeV/u in 2002 on 58 Ni and 48 Ca targets [1], we have measured in 2003, with the same BBS experimental setup and with a triton-beam intensity of pps, the (t, 3 He) residual energy spectra of 12 B and 90 Y nuclei between 0 and 5 lab angles. The standard ray-tracing procedure has allowed to obtain excitation-energy spectra up to 30 MeV for each target and for six angular bins. The data analysis is presently underway. We have made in parallel a mutipoledecomposition analysis (MDA) of Isovector Giant Resonance (IVGR) strengths in 58 Co and 48 K using normal mode (NM) wave functions and Raynal s DWBA98 code. The results of this analysis were presented at the last COMEX conference [2] and are illustrated in Fig. 1. One can observe a very good agreement for the strength distribution of L=1 transitions between the MDA and RPA calculations [3]. The L=0 strength distribution appears in both experimental and theoretical cases fragmented over a wide excitation energy range. The notenergy-weighted sum rule (NEWSR) deduced with V τ = - V στ = - V T τ = 5 MeV for 2 hω L=0 and 1 hω L=1 between 7 and 30 MeV is and 0.161, respectively. In order to have a better estimate of the experimental monopole-strength distributions, we want to directly introduce the RPA excited states in the DWBA calculations [4]. The strong correlation between the excitation energy and the collectivity of the final states is indeed absent in the NM standard analysis. This correlation affects the form factors and consequently the shape and the amplitude of the deduced cross section angular distributions. The strength of the V στ and V T τ terms of the effective 3 He-n interaction used in the analysis of the (t, 3 He) reaction at our incident energy can be deduced empirically from the analysis of the first low-lying 1 + and 2 states in 12 B. rel. strength (arb. units) rel. strength (arb. units) GT 1.87 MeV Exp. L=0 (S=0+S=1) Ex (MeV) Exp. L=1 (S=0+S=1) Ex (MeV) Figure 1: Comparison between the MDA results (histograms) and the RPA strength distributions for the 58 Co nucleus. For L=0 the solid curve and the dashed curve represent the IVSGMR and the IVGMR respectively. For L=1 the curve represents the GDR. The small black histogram gives the χ 2 of the MDA fits. a) Institut de Physique Nucléaire, IN2P3-CNRS, Orsay, France b) Institut für Kernphysik, Universität Münster, Germany c) Research Center for Nuclear Physics, Osaka University, Japan d) Advanced Science Research Center, Japan Atomic Energy Institute, Tokai, Japan [1] J. Guillot et al., KVI Annual Report 2002, p. 17. [2] Proceedings to be published in Nucl. Phys. A (February 2004). [3] G. Coló, Private communication. [4] Collaboration with S.Y. van der Werf and G. Coló. 16

20 1.8 Study of Gamow-Teller strength distributions in fp-shell nuclei through the 64 Ni(d, 2 He) 64 Co reaction L. Popescu a), C. Bäumer b), A.M. van den Berg, D. Frekers b), D. De Frenne a), Y. Fujita c), P. Haefner b), M. Hunyadi, M.A de Huu, E. Jacobs a), H. Johansson d), A. Korff b), A. Negret a), P. von Neumann-Cosel e), S. Rakers b), N. Ryezayeva e), A. Sevchenko e), H. Simon d), H.J. Wörtche A 64 Ni(d, 2 He) 64 Co experiment at E d = 170 MeV was performed at three angle settings of the Big-Bite Spectrometer (BBS) θ BBS = 0, 3 and 5. The target was a self supporting 64 Ni foil with a thickness of 5.25 mg/cm 2 and an enrichment of 96.48%. Focal-plane detection of correlated protons was performed by means of the ESN detector system. An energy resolution of 110 kev was achieved. are indicated in the figure. In addition to the ground-state (g.s.) with J π = 1 +, several other GT states could be identified, but almost all the strength is exhausted by the g.s., in good agreement with the Large-Scale Shell-Model calculations of Caurier et al. [1] (see Fig. 2). Figure 2: GT + strengths determined in Large-Scale Shell-Model calculations [1]. Figure 1: Background subtracted excitation spectra of 64 Co measured at θ BBS = 0 and at 5, respectively. In Fig. 1 excitation-energy spectra of 64 Co are shown for two scattering angles. In the first spectrum a cut on the scattering angle between 0 and 1 was used, while in the second spectrum the 2 He emission angle was limited to Levels known from literature a) Vakgroep Subatomaire en Stralingsfysica, Universiteit Gent, Belgium b) Institut für Kernphysik, Universität Münster,Germany c) Department of Physics, Osaka University, Japan d) Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany e) Institut für Kernphysik, TU Darmstadt, Germany [1] E. Caurier et al., Nucl. Phys. A 653, 439 (1999). 17

21 1.9 Proton decay of the isoscalar Giant-Dipole Resonance in 208 Pb M. Hunyadi, A.M. van den Berg, N. Blasi a), C. Bäumer b), M. Csatlós c), L. Csige c), B. Davids, U. Garg d), J. Gulyás c), M.N. Harakeh, M.A. de Huu, B.C. Junk b), A. Krasznahorkay c), S. Rakers b), D. Sohler c), H.J. Wörtche The direct proton decay channels of the 3 hω isoscalar giant-dipole resonance (ISGDR) have been studied in 208 Pb and published recently in [1]. The double-differential cross sections and partial-branching ratios of the IS- GDR were determined for various direct decay channels populating low-lying proton-hole states in 207 Tl. The final state spectrum generated by gating on the ISGDR region in 208 Pb is shown in Fig. 1. The four lowest hole-states were observed in two structures (group A and B) due to the moderate resolution of 600 kev. One group is centered at 0.3 MeV and the other at 1.6 MeV, related to states at E x =0, 0.35, 1.35 and 1.68 MeV in 207 Tl. The obtained partial-branching ratios were used to test the most recent continuum-rpa calculations [2]. Counts/150 kev s 1/2 2d 3/2 group A 1h 11/2 2d 5/2 group B final-state energy (MeV) decay from the ISGDR-region 1.5 o <Q a <3.0 o 1g 7/ Figure 1: Final state energy spectrum of the low-lying proton-hole states in 207 Tl generated by gating on the ISGDR region. The experiment was carried out at KVI in the fall of 2002 using inelastic α-scattering at E α =200 MeV on a 208 Pb target. The scattered α-particles were analyzed with the Big-Bite Spectrometer (BBS) in conjunction with the EuroSuperNova detector system. The BBS was set at Θ lab =2.8, covering a range of Θ c.m. = The decay-protons were detected by a detector-ball of 16 Si(Li) detectors placed in the backward hemisphere of the scattering chamber at a distance of 10 cm from the target. Further details of the experiment setup can be found in Ref. [1]. DS p fi The ISGDR strength was identified in the excitation energy region of E x =20-25 MeV by analyzing the angular distributions of the ejectiles. In Fig. 2, the spectra of the doubledifferential cross sections as a function of the excitation energy in 208 Pb are presented, which show a considerable direct population of holestates from the ISGDR strength and an additional structure at higher excitation energy (high-lying bump - HLB). The angular distribution analysis of the HLB indicated a quadrupole character, which in case of confirmation of further experimental evidences would correspond to the first observation of the overtone of the ISGQR, the third compression mode next to the ISGMR and ISGDR. d 2 sdw -1 de -1 (mb sr -1 MeV -1 ) a) b) HEOR HEOR ISGDR ISGDR E x (MeV) 208 Pb(a,a'p) 1.5 o < Q a' <3.0 o group A HLB 208 Pb(a,a'p) 1.5 o < Q a' <3.0 o group B HLB Figure 2: Double-differential cross sections as a function of excitation energy in 208 Pb gated on the finalstate groups A and B defined in Fig. 1. a) INFN, Milano, Italy b) Inst. für Kernphysik, Univ. Münster, Germany c) Inst. of Nucl. Res., Debrecen, Hungary d) Univ. of Notre Dame, Notre Dame, USA [1] M. Hunyadi et al., Phys. Lett. B 576, 253 (2003). [2] M.L. Gorelik et al., Phys. Rev. C 62, (2000); M.L. Gorelik and M.H. Urin, Phys. Rev. C 64, (2001). 18

22 1.10 Optical-model analysis of deuteron scattering off 90 Zr and 116 Sn at 183 MeV A. Korff a), C. Bäumer a), A.M. van den Berg, B. Davids, D. Frekers a), D. De Frenne b), E.-W. Grewe a), P. Haefner a), E. Jacobs b), A. Negret b), L. Popescu b), S. Rakers a), H.J. Wörtche In 2003 we measured elastic and inelastic deuteron scattering off 90 Zr and 116 Sn using the BBS-ESN setup at an incident energy of 183 MeV. These experiments allow the extraction of optical model parameters. The optical model is used in DWBA calculations to describe the distortion of the deuteron wavefunction in the entrance channel of the (d, 2 He) reaction. The 116 Sn(d, 2 He) reaction is of special interest for the study of the double-beta decay of 116 Cd, while 90 Zr was chosen to have a data point between existing data at A=72 and A=116. Data was taken at spectrometer angles ranging from Θ BBS =15-36 in steps of 3 and at 5 and 8. Excitation-energy spectra have been obtained with an energy resolution of about 110 kev (FWHM) for both nuclei. Examples are shown in Fig. 1 for a laboratory angle of 21. counts / 40 kev g.s. 1 * kev FWHM g.s. 1 * kev FWHM 2 +, , , , , , , , Zr(d,d') BBS = 21 E d = 183 MeV 116 Sn(d,d') BBS = 21 E d = 183 MeV Excitation energy [MeV] Figure 1: Excitation-energy spectra of 90 Zr and 116 Sn at Θ BBS = 21. The elastic lines are suppressed by a factor of 10. Angular distributions of the differential cross section of elastic scattering and inelastic scattering to the first 2 + excited states have been extracted from the data. These distributions were analyzed in terms of the optical model employing the coupled channels code ECIS97 [1]. Figure 2 shows the results of these calculations along with the experimental distributions [2]. d /d [mb/sr] Zr g.s. [x10 2 ] 116 Sn g.s. [x10 4 ] 90 Zr 2 +, 2.19 MeV [x10-2 ] 116 Sn 2 +, 1.29 MeV c.m. [deg.] Figure 2: Angular distributions of the differential cross section for elastic and inelastic deuteron scattering from 90 Zr and 116 Sn. a) Institut für Kernphysik, Universität Münster, Germany b) Vakgroep Subatomaire en Stralingsfysica, Universiteit Gent, Belgium [1] Program Ecis97, J. Raynal, unpublished. [2] A. Korff, Diploma thesis, Universität Münster (2004). 19