PANIC’08 Eilat, November 13th, 2008 Teresa Kurtukian Nieto CEN Bordeaux-Gradignan Supernova remnant N49 Photo Credit: Hubble Heritage Team (STScI / AURA), Y. Chu (UIUC) et al., NASA

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th MSU 80 OSIRIS/TRISTAN 130 Great progress have been achieved during the last years using fragmentation and fission to produce and study nuclei in the r-process path r-process experimental inputs Experimental study of the r-process Production and separation nuclei far from stability  Nuclei around the waiting point A=195 are completely unexplored A general understanding of their nuclear properties remains to be obtained only through theoretical models

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 r-process around A=195 waiting point  Our present understanding of the r-process around A=195 is far from being complete: P. Stevenson et al., PRC 63 (2001) FK²L (Ap.J. 403 ; 1993) - nuclear deformation - shell quenching at N=126  Experimental data is required to answer these questions, but it has been a challenge over the years

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Production of heavy neutron-rich nuclei Production of heavy neutron-rich nuclei in cold-fragmentation reactions r-process nucleosynthesis - Mainly abrasion of protons - Low excitation energy  Cold-fragmentation channels:  Our goal: - investigate the production of heavy neutron-rich nuclei - measure its  -decay half-lives opens a region not accessible by fission. J. Benlliure et al.,Nucl. Phys. A 660 (1999) 87

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Production of heavy neutron-rich nuclei  Experiment: SIS18/FRS at Darmstadt, Germany 208 Pb(1 A GeV)+Be (10 7 ions/s)

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008  Experimental setup: One of the challenges of the experiment was the identification of charge states  Relativistic primary beam:  degrader energy loss method Energy loss (Degrader, Ionization chamber ) Production of heavy neutron-rich nuclei

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Production of heavy neutron-rich nuclei 25 new heavy neutron-rich nuclei “south” of lead have been produced for the first time Production and identification of more than 190 heavy neutron-rich nuclei

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Implantation technique 4 DSSD Micron W(DS)-1000 active stopper 4 double-side strip detectors: surface: 5x5 cm 2 thickness 1 mm 2x mm strips ionization chamber (reaction rejection in the stopper) 2 scintillator detectors (veto) Centered on 198 Ir Produced Implanted

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Implantation-decay correlations Time Implantation  like Spill length ~ 2 s Cycle 10 s

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Forward time Backward time Numerical analysis method  conventional analysis tools, based on analytical time-distribution functions could not be applied  A new analysis procedure has been developed to extract the β-decay half- lives by using a numerical function (T. Kurtukian-Nieto et al. NIMA 589, (2008) 472) Background evaluation (uncorrelated events): backward-time correlations Time

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Numerical analysis method  The numerical function is obtained from Monte Carlo simulations of time correlations between implantations and β-like events:  The time sequence of fragment implantation and  detection are simulated according to the experimental conditions observed in the FRS:  spill sequence  fragment implantation rate  background rate during spill and pause  leaving two free parameters: the lifetimes, and the efficiency  The code produces time-correlation spectra in forward- and backward-time direction.  The half-lives of the different nuclides under study were from two-dimensional fits of the measured and simulated ratios of time correlations in forward- and backward- time direction. This was achieved by applying the least-squares method in which the lifetime  and the β-detection efficiency ε were the two fitting parameters.

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Fitting procedure: example spill+pause only pause

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008  2 contour :  vs   Results for 195 Re : T 1/2 = s spill+pause only pause

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Dividing the number of true β decays by the magnitude of random fluctuations, a ‘figure of merit’ F can be defined, characterizing the statistical significance of the experimental conditions for the determination of the half-life of a specific nuclide: A value of F = 1 means that the decay-time spectrum of β-like events after the implantation can very likely be interpreted as a statistical fluctuation of the background. For larger values of F, this possibility becomes less and less probable: For F = 3 and F = 4, this probability reduces to 2×10 -5 and 1.5×10 -8, respectively. Applicability of the method

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Results: β-decay half-lives  half lives for 8 neutron-rich nuclei have been determined

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Previously measured value: A.Szalay et al., Radiochem. Radioanal. Letters 14 (1973) 136 T 1/2 ( 198 Ir) = s B.F.J.Schweden, N.Kaffrell BMBW- FBK-72-15, (1972) p.88 T 1/2 ( 198 Ir) = s This work:  T 1/2 ( 198 Ir) = s Results: β-decay half-lives  Results for 198 Ir (benchmarcking of the method): Good agreement between our measurement and the previous one

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 R-process implications The shorter half-lives predicted by Borzov and measured in the present work would imply a speeding up of the r-process nucleosynthesis in this region of the nuclear chart, and thus, an acceleration of the matter flow through the A=195 r-process `waiting-point‘, which implies that the flow in the r-process to heavier fissioning nuclei is faster than previously expected. More experiments including detailed spectroscopy will be need to clarify this  Short term:  -  coincidences using the germanium array

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 J. Benlliure et al.,Nucl. Phys. A 660 (1999) 87 r-process Beam intensity in this work 10 7 /s (nb) FAIR /s (10 pb) Long term perspectives

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 Summary  In the present work we were able to synthesise more than 190 heavy neutron- rich residues, 25 of which were produced for the first time.  The results shown in this pioneering work represent a first step towards the study of heavy neutron-rich nuclei approaching the r-process waiting point at A=195. It has been shown that the N=126 region far below the doubly magic 208 Pb has become accessible experimentally.  A new analysis procedure has been developed to extract the β-decay half-lives of the exotic nuclei under complex background conditions.  β half-lives were determined from position-time correlations between implanted ions and subsequent  decays using an active catcher  The shorter half-lives measured in the present work are shorter that previously expected and this would imply an acceleration of the matter flow through the A=195 waiting-point, which in turn could changes the overall picture regarding the r-process in this region  Future radioactive beam facilities will open the door to the study many nuclei involved in the r-process nucleosynthesis.

Teresa Kurtukian-Nieto CEN Bordeaux-GradignanPANIC’08 Nov 13th 2008 B. Blank, J.Giovinazzo, B. Jurado CEN Bourdeaux-Gradignan, France J. Benlliure, E. Casarejos, M. Fernandez-Ordoñez, J. Pereira Universidad de Santiago de Compostela, Spain K.-H. Schmidt, F.Becker, D. Henzlova, O. Yordanov I. Borzov, K. Langanke, G. Matinez-Pinedo, GSI, Darmstadt, Germany F. Rejmund GANIL, Caen, France L. Audouin Institut de Physique Nucleaire, Orsay, France Collaborators