1. Study of neutron-rich nuclei 18-21 N and 25 F Zsolt Vajta ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012

2. 2 Introduction Study of exotic nuclei near the neutron dripline where subshell closures at N=14 and N=16 were remained. Flourine isotopes: 19 F – deformed ground state very low energy negative parity state 27 F – 2 bound excited state No bound states from USD shell model 17,19,21 F – 3 lowest lying levels observed 5/2+, 1/2-, 1/2+ 21 N and lighter nitrogen isotopes: 22 O – E(2+) = 4.2 MeV, B(E2) is low in ground state, subshell at N=14 closed 20 C – First excited state is low (1.6 MeV) and subshell gap at N=14 is narrow 21 N – Limited information, one γ spectroscopy investigation subshell gap at N=14 is ~3 MeV No deformation data from nuclear reaction

3. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 3 What is the goal? 25 F Does the subshell closure at N=16 remain here? Energy of the excited states? Level scheme? 18,19,20,21 N Energy of the excited states? Level scheme? Deformation of 21 N Quadrupole deformation parameter β comparison of 22 O and 20 C. Subshell closure at N=14?

4. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 4 Experimental methods Production of primary beam: Multistep acceleration(high intensity, low E) Electron stripping between accelerators High E and high intensity beam 36 S 16+ and 40 Ar (~70 MeV/nucleon, ~100 pnA) One-step fragmentation: stable beam target nuclear reactions & gamma detection beam identification Two-step fragmentation: stable beam Fragmentation on primary target Identification of secondary beam Nuclear reactions on secondary target beam identification

5. γ -spectroscopy with fragmentation reactions in GANIL ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 5 Primary beam: 36 S 16+ beam with 77.5 MeV*A Intensity ~1 pnA or ~100 pnA SISSI: Superconducting Intense Source for Secondary Ions (Carbon, 348 mg/cm 2 ) α-spectrometer: cocktail beam identification and optimization (Al wedge & Bρ magnetic rigidity) F, Na, Ne, Mg nuclei with E ~60 MeV*A Chateau de Crystal – BaF 2 : detection of γ-ray from 9 Be or active C-Plastic-C target Plastic scintillator: ToF, E loss Efficiency: ~30% at 1.3 MeV FWHM: ~12% at 1.3 MeV SPEG: identification of outgoing beam with ToF E loss, E total and position

6. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 6 Isotope separation - GANIL α-spectrometerSPEG 25 F One-step fragmentation: Only the SPEG is required due to the stable primary beam.

7. 25 F results from two-step fragmentation ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 7 Fitting process: GEANT4 simulated spectra + exponential backround FWHM & escape peaks handled FWHM in GEANT4: I fitted the spectrum 22 O to determine the fwhm at high energy. Multiplicity all

8. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 8 25 F results from the one-step fragmentation FWHM: I adjusted the energy-dependent FWHM basis of peaks of known nuclei. Fitting process: ● GEANT4 simulated spectra + exponential background ● FWHM & escape peaks handled Multiplicity 2 Multiplicity all The GEANT4 simulation: We can only handled the high energy bump, photo-peaks and escape-peaks with it. Thus, I could resolve the high energy bump with 4 gamma lines and I found 8 gamma transitions.

9. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 9 Level scheme of 25 F 25 F: some states near the neutron separation energy E(2+) ~ 4 MeV 24 O: E(2+) ~ 4.6 MeV Subshell closure at N=16 is closed.

10. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 10 γ -spectroscopy with fragmentation reactions in RIKEN RIP S Hodoscop e 40 Ar 63 MeV*A 700 pnA 181 Ta 2 mm Al 221 mg/cm 2 B ρ DALI2 160 NaI(Tl) Target: 208 Pb or liquid H Δ E, ToF, E total Nucleon knockout reaction is stronger on liquid H target so the identification of outgoing nuclei is very important.

11. Isotope separation - RIKEN ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 11 RIPS Hodoscope

12. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 12 Results – 18,19,20 N

13. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 13 Deformation of 21 N Quadrupole deformation parameters: 22 O: β 2 n = 0.24(7),β 2 p = 0.23(7) Subshell closure at N=14 is closed, E gap ~ 4.2 MeV 21 N: β 2 n = 0.29(5),β 2 p = 0.29(2) 20 C: β 2 n = 0.18(10),β 2 p = 0.48(4) Subshell closure at N=14 is missing here Conclusion: subshell closure at N=14 was remained Excitation cross section from Coulomb excitation and (p,p') reaction I calculated the proton and neutron deformation lengths by FRESCO. From δ p and δ n I could derive the proton and neutron quadrupole deformation parameters. σ(2350, H) σ(1140, H) σ(1140, Pb) δ p, δ n β p, β n

14. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 14 Summary Results to 25 F: ● The high energy bump observed in the spectrum of 25 F is resolved with 4 γ lines. ● This is the first time that the level scheme ● has been built. ● Subshell closure at N=16 is remained here. Results to 18,19,20,21 N: ● Based on mutiplicity spectra, γ transitions were identified for all analyzed isotopes. ● According the β, 21 N is like 22 O. ● Subshell closure at N=14 is remained in 21 N. 25 F and 21 N: Removal of π from 22 O and addition of π to 24 O do not cause drastic change in nuclear structure.

15. ZAKOPANE CONFERENCE ON NUCLEAR PHYSICS ● August 27 – September 2, 2012 15 Thank you for your attention! The work is supported by the TÁMOP-4.2.2/B-10/1-2010-0024 project. The project is co-financed by the European Union and the European Social Fund. Special thanks to collaborators: M. L. Achouri 2, T. Aiba 3, J. C. Angélique 2, N. Aoi 4, F. Azaiez 5, H. Baba 4, M. Belleguic 5, D. Bemmerer 6, C. Borcea 7, C. Bourgeois 5, J. M. Daugas 8, F. De Oliveira-Santos 8, Z. Dlouhy 9, Zs. Dombrádi 1, C. Donzaud 5, J. Duprat 5, Z. Elekes 1, T. Furumoto 10, Zs. Fülöp 1, S. Grévy 2, D. Guillemaud-Mueller 5, N. Iwasa 11, Á. Kiss 1, T. Kobayashi 11, Y. Kondo 12, S. Leenhardt 5, M. Lewitowicz 8, M. J. Lopez-Jimenez 8, S. M. Lukyanov 13, W. Mittig 8, T. Motobayashi 4, T. Nakabayashi 12, T. Nannichi 12, Yu.-E. Penionzhkevich 13, M. G. Porquet 14, F. Pougheon 5, P. Roussel-Chomaz 8, M. G. Saint-Laurent 8, Y. Sakuragi 4,10, H. Sakurai 4, H. Savajols 8, Y. Sobolev 13, D. Sohler 1, O. Sorlin 5, M. Stanoiu 5, C. Stodel 8, M. Takashina 15, S. Takeuchi 4, K. Tanaka 4, J. Timar 1, Y. Togano 16, K. Yamada 4, M. Yamaguchi 4, K. Yoneda 4 1 Institute of Nuclear Research, P.O. Box 51., Debrecen, H-4001, Hungary 2 Laboratoire de Physique Corpusculaire, 14000 Caen Cedex, France Caen, 14021 France 3 Niigata University, Niigata 950-2181, Japan 4 The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 5 Institut de Physique Nucléaire, IN2P3-CNRS, F-91406 Orsay Cedex, France 6 Forschungszentrum Dresden-Rossendorf, Bautzner Landstrasse 128, 01328 Dresden (Rossendorf), Germany 7 IFIN-HH, P.O. Box MG-6, 76900 Bucharest-Magurele, Romania 8 GANIL, B. P. 55027, F-14076 Caen Cedex 5, France 9 Nuclear Physics Institute, AS CR, CZ 25068, Rez, Czech Republic 10 Department of Physics, Osaka City University, Osaka 558-8585, Japan 11 Tohoku University, Sendai, Miyagi 980-8578, Japan 12 Tokyo Institute of Technology, 2-12-1 Oh-Okayama, Megro, Tokyo 152-8551, Japan 13 FLNR, JINR, 141980 Dubna, Moscow Region, Russia 14 CSNSM, IN2P3-CNRS and Université Paris-Sud, F-91405 Orsay Campus, France 15 Research Center for Nuclear Physics (RCNP), Osaka University, Osaka 567-0047, Japan 16 Rikkyo University, 3 Nishi-Ikebukoro, Toshima, Tokyo 171, Japan