1. A Systematic Experimental Study of R-process Nuclei NIC12 (2012, Aug. 5-10) Shunji NISHIMURA RIKEN Nishina Center (RNC) C.Freiburghause et al. ApJ 516 (1999) ☆ Half-lives （Ｔ 1/2 )  abundance  process speed *38 half-lives are measured including 100 Kr, 103-105 Sr, 106-108 Y, 108-110 Zr, 111,112 Nb, 112-115 Mo, 116,117 Tc  1/2~ 1/3 Shorter half-lives for Zr & Nb * Impact to r-process around 凹  Faster r-matter flow  More suppression? or Filling in? Issue around mass A = 110 – 125

2. Radioactive Isotope Beam Facility (RIBF) at RIKEN 238 U … 345 MeV/u New Generation Radioactive Isotope Beam Facility Decay Exp.

3. Beam Production in BigRIPS/ZDS Beam STOP Detector ( Decay experiment ) Double-Sided Silicon Strip detector (DSSSD) - Charge stripper @ F5 - Degrader @ F11 238 U @ 345 MeV/u  Be target Charge stripper Decay Station - 9 DSSSD (50x50mm2) -16x16 strips  ~ 2000 virtual pixels -Beta detection efficiency 40 – 80%

4. Experimental Setup in 2009 β-ray γ-ray  ΔE-TOF-Bρ method using the focal plane detectors in BigRIPS  The implantation of an identified RI is associated with the following β-decay events that are detected in the same DSSSD pixel

5. R-process Abundance around 2 nd peak N Z - Shell quenching? 125 110 N Z B.Pfeiffer et al. Z. Phys. A357 (1997) - Shell quenching? 125 110 T.Ohnishi, JPSJ 79 (2010).. 45 new isotopes 38 38 half-lives of very neutron-rich nuclei were measured.

6. Beta-decay Half-life T 1/2 for Kr-Tc Part of data set (8 hours) Implantation rate ~ 8 cps Classical R-Process Path H.Schatz, ApJ 583 (2002) New !!! 110 Zr Decay Curves 0 – 5 sec

7. Decay curve and T 1/2 Likelihood method with 10ms bins (0 – 5 sec) Free parameters for fitting - Background … ~ 0.5 cps - Neutron emission Probability (Pn) - Detection efficiency (  ) … 40% - 80% Consistency check - Monte Carlo Simulation T 1/2 98 Rb decay daughter and granddaugter (  &  -n branches ) background

8. Neutron Number Dependence of T 1/2 improvement (18 Significant improvement of T 1/2 information (18 new half-lives )

9. Comparison with Theoretical Prediction T 1/2 Zr and Nb decay faster than expected by FRDM+QRPA ( T 1/2 : 1/2 ~ 1/3 )

10. Shorter half-lives for very neutron-rich Zr and Nb

11. Mass A dependence around A=110-117 T 1/2 (Theory) / T 1/2 (Exp.) Overestimation of T 1/2 by factor of 2~3 Better agreement for KTUY !  WHY ?! Mass A 100 105 110 115 Mass A FRDM+GT2KTUY+GT2

12. Better prediction with KTUY (H.Koura) ? FRDM may underestimate the Q value : ~ 1 MeV dQ ~ 1 MeV @ A ~ 110. FRDM may underestimate the Q value : ~ 1 MeV dQ ~ 1 MeV @ A ~ 110.

13. RIBF data  Impact to r-process abundance Nobuya Nishimura, T.Kajino, G.Mathew, SN, T.Suzuki, PRC 85 (2012) 38 Half-lives from RIBF 38 Half-lives + ΔQbeta from RIBF MHD supernova explosion model

14. RIBF data  Impact to r-process abundance r-matter flow Nobuya Nishimura, T.Kajino, G.Mathew, SN, T.Suzuki, PRC 85 (2012) Ratio : X / X FRDM Recovery x 2.5 The calculated r-process abundance is improved by factor of x 2.5. But, there is still issue remaining in mass A=110 – 125!

15. Evolution of shell structure around N = 70 Zr, Nb : N=70  82 s Structural Evolution in 106 106 Zr and 108 Zr T.Sumikama, et al., PRL 106 (2011)

16. Neutron Separation Energies ~ 110 Zr Location of r-process path depends on S n (2 – 3 MeV) (n,  )-( ,n) competition S.Wanajo, S.Goriely, M.Samyn, N.Itoh, Astro.J 606 (2004). HFB-2 FRDM

17. - Decay curve : T 1/2 - Excited states : E(2 + ),.. - Isomeric states - Q  - Neutron emission (P n ) High light : around 78 Ni,.. 110 Zr,.. 128 Pd, 136-138 Sn,.. 170 Dy EURICA Campaign: Survey of exotic nuclei EURICA Project at RIBF 2011 Nov.

18. Summary Systematic experimental study on r-process nuclei was performed around mass A=110 region. -38 half-lives were measured including 100 Kr, 103-105 Sr, 106-108 Y, 108-110 Zr, 111,112 Nb, 112-115 Mo, 116,117 Tc -Very neutron-rich Zr and Nb isotopes have shorter half-lives relative to theoretical prediction (FRDM+QRPA).  2 ~ 3 faster decay rate -Impact of new  -decay half-lives on r-process abundance was studied.  r-matter flow with shorter T 1/2 fills in the 凹 around A=110-125.  The abundance in the 凹 was recovered by factor of ~ 2.5. - Effect is, however, still not enough to explain discrepancy.  Further investigation is required. -Beta-decay half-lives of very neutron-rich nuclei beyond 110 Zr -Study on nuclear structure (Deformation and Magicity) -EURICA project has been started at RIBF in 2012-2013 ! -N = 50 78 Ni  110 Zr (N=70)  128 Pd (N=82)  170 Dy..

19. RIBF Decay Collaboration RIKEN Nishina Center –S. Nishimura, H. Watanabe, Z. Li, H. Baba, M. Nishimura, T. Isobe, H. Scheit, P. Doornenbal, D. Steppenbeck, H. Sakurai Tokyo University of Science –T. Sumikama, K. Yoshinaga, Y. Miyashita, T. Nakano, K. Sugimoto, S. Takano, J. Chiba Osaka University –K. Yamaguchi, A. Odahara, A. Takashima, Y. Ito, K. Tajiri, T. Shimoda, H.J. Ong Tokyo Institute of Technology –N. Kobayashi, Y. Kawada, Y. Kondo, T. Nakamura CNS –E. Ideguchi, S. Go, S. Ota, S. Kubono, H. Yamaguchi, T. Hashimoto, S. Hayakawa Japan Atomic Energy Agency Y. Wakabayashi Kyushu University –T. Teranishi Technishe Universit ä t M ü nchen –C. Hinke, K. Steiger, R. Kruecken Michigan State University G. Lorusso, Lawrence Berkeley National Laboratory –J.S. Berryman INFN –O. Wieland, N. Blasi Universit à di Milano –A. Bracco, F. Camera University of Surrey –Zs. Podoly á k, P.M. Walker Theoretical calc. : PRC 85, 048801 (2012) Nobuya Nishimura (Basel Univ./GSI) T.Kajino (NAOJ/U.Tokyo) G.J.Mathew (Notre Dame) T.Suzuki (Nihon Univ.) Special thanks to P.Moller, H.Koura, T.Tachibana

20. Thank you.

21. Collaboration Beta-Decay Experiment MHD simulation by theoretical Group

22. EURICA Project at RIBF RIKEN RIBF (Japan) Euroball Cluster detectors Support structure Readout electronics used for GSI-RISING 2011 Nov.

23. Decay Spectroscopy : 2 nd Phase U-beam intensity - 0.2 pnA  3-5 pnA … x 15 – 25 times Beam time … - 0.3 - 2.5 days  100 days … x 40 – 300 times Beta counting system - 16 x 16 pixels x 7 layers = 1792 pixels  40x60 pixels x 8 layers = 19200 pixels … x 4-10 times - Accept higher implantation rate for T 1/2 measurement  x 2 – 5 times Gamma-ray detector - 4 Clover detectors (Det. Effi. ~1.5% at 662 keV)  12 Cluster detectors (Det. Eff. ~ 15 % at 662keV) … x 10 times (  gamma-gamma coincidence … x 100 times )

24. Let’s enjoy and a lots of discoveries from RIBF & EURICA ! First EURICA Exp. Online spectra Xe-beam int. : 10 ~ 20 pnA 96 Pd isomer PreliminaryRIBF-083(P.Boutachkov)

25. Deformation of Zr, Nb, and Mo isotopes “Possible shape co-existence in 109Nb” H.Watanabe, et al., PLB 696 (2011) 186. “Axial symmetry in 110Mo” H.Watanabe, et al., PLB 704 (2011) 270.

27. R-Process Abundance (FRDM vs KUTY) F 20016012080 Mass number KUTY logN n =24.26 T 9 =1.5  =0.9 20016012080 Mass number FRDM logN n =23.89 T 9 =1.5  = 2.0 N r =N(Solar abund.)-N s-pro N r r-only nuclei Calculation by H.Koura, et al.  = 0.9 s  = 2.0 s FRDM+GT2KUTY+GT2

28. Evolution of shell structure N = 70-82 Fission?

29. EURICA System Each sub-system DAQ with time-stamp (lupo) Cluster detectors (GSI-Go4) Silicon detectors (RIKEN) Beam line detectors (RIKEN) are successfully combined. Beam (PID) DSSSD (RI/beta) Cluster detector (gamma) Beta-delayed gamma Beta-decay Isomer

30. Mass Measurements Hakala, et al., EPJA (2011) 47, 129 First systematic check by decay spectroscopy  Direct mass measurement by SlowRI / Mass Ring