MSU RIKEN collaboration Production of very neutron rich isotopes: What should we know? Oleg B. Tarasov * National Superconducting Cyclotron Laboratory, Michigan State University Keywords of this experimental program New isotopes campaign (with 48 Ca, 76 Ge, 82 Se) @ MSU Projectile fragmentation as a tool to observe effects close to the neutron drip-line New light isotopes campaign @ RIKEN 33 F & 36 Ne 39 Na 60 Ca (new isotopes, secondary reactions study, new isomers & ) * On leave FLNR / JINR, Dubna, Moscow region, 141980, Russian Federation This work is supported in part by the US National Science Foundation under grants no. PHY-10-68217 and PHY-11-02511 1
Introduction: Keywords of this experimental program Search for new isotopes The limits of nuclear stability provide a key benchmark of nuclear models The context of astrophysics Production mechanism Understanding the r-process abundance patterns of elements Production cross sections, Momentum distributions, Reaction choice Secondary beam intensities. Planning new experiments, set-ups (FRIB, RIBF, FAIR) Nuclear structure Changes in the structure of neutron-rich nuclei Region around 32 Mg is now known as the island of inversion Deformation around neutron number N = 40 in Fe and Cr nuclei Shell closures at N=32 and N=34 Masses of exotic calcium isotopes pin down nuclear forces ( 53,54 Ca) F. Wienholtz et al., Nature 498 (2013) 346 Evidence for a new nuclear magic number from the level structure of 54 Ca D. Steppenbeck et al., Nature 502 (2013) 207 Projectile fragmentation as a tool to observe effects close to the neutron drip-line MSU 76 Ge & 82 Se experiments: see the next slides) OT@ISPUN.VN 9/25-30/2017 2
Z=8-14, 1970 2002 : one stage separation FLNR GANIL GANIL RIKEN RIKEN GANIL One-stage separation OT@ISPUN.VN 9/25-30/2017 3
1 MSU campaign OT@ISPUN.VN 9/25-30/2017 4
48 Ca (140MeV/u) + W (NSCL@MSU) Two-stage separation a) New isotope: 44 Si O.T. et al., Phys.Rev. C 75, 064613 (2007) New isotopes 40 Mg, 42 Al, 43 Al T.Baumann et al.,nature(london) 449, 1022 (2007) OT@ISPUN.VN 9/25-30/2017 5
Production cross sections Q g systematics 48 Ca(140MeV/u) + W,Be A simple systematic framework was found to describe the production cross sections based on thermal evaporation from excited prefragments that allows extrapolation to other weak reaction products. O.T. et al., Phys.Rev. C 75, 064613 (2007) Compilation with data from M. Mocko et al., Phys. Rev. C 74, 054612 (2006) OT@ISPUN.VN 9/25-30/2017 6
76 Ge (130 MeV/u) new isotopes, CS, momentum distributions, Calcium anomaly 50 Cl, 53 Ar, 55,56 K, 57,58 Ca, 59,60,61 Sc, 62,63 Ti, 65,66 V, 68 Cr, 70 Mn Calcium anomaly Enhanced cross sections might be the result of increased binding This region (around 62 Ti) was previously predicted to be a new island of inversion B. A. Brown Prog. Part. Nucl. Phys. 47 (2001) 517 Phys.Rev.Lett. 102, 142501 (2009) : New isotopes, Evidence for a Change in the Nuclear Mass Surface Phys.Rev.C. 80, 034609 (2009) : Set-up, cross sections, momentum distributions OT@ISPUN.VN 9/25-30/2017 NIM A 620, 578-584 (2010) : A new approach to measure momentum distributions 7
Confirmation of the Calcium anomaly Newly-developed 82 Se (139 MeV/u) Beam E (MeV/u) I (pna) N/Z 82 Se 139 35 1.412 76 Ge 130 20 1.375 DN / DZ=2 64 Ti, 67 V, 69 Cr, 72 Mn, 70 Cr, 75 Fe O.T. et al., Phys. Rev. C 87, 054612 (2013) Currently @ MSU the 82 Se experiment takes place to measure properties of nuclei around 58 Ca OT@ISPUN.VN 9/25-30/2017 8
Calcium anomaly as shell effects close to drip line The measured cross sections were best reproduced by using masses derived from the full pf shell-model space with the GXPF1B5 [1] effective interaction modified to a recent 54 Ca E x ( 2+ 1 ) measurement [2]. The Calcium anomaly can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. [1] M. Honma, T. Otsuka, B. A. Brown, and T. Mizusaki, Eur. Phys. J. A 25, Suppl. 1, 499 (2005) [2] D. Steppenbeck et al., Nature 502, 207 (2013) No such dip other theoretical models OT@ISPUN.VN 9/25-30/2017 9
1 33 F & 36 Ne @ RIKEN OT@ISPUN.VN 9/25-30/2017 10
Searched for the drip-line nuclei: 33 F, 36 Ne, 39 Na by using an intense 48 Ca beam (400-500 pna, 345 MeV/u) and exploiting advanced features of a new-generation RI beam facility. Investigated the existence/non-existence of these nuclei and also their neighboring nuclei to locate the neutron drip-line. Spokesperson: T.Kubo Conducted neutron drip-line search for higher Z nuclei at RIBF 44 Si 45 Al 42 Mg 36 Ne 39 Na KTUY05 33 F A=3Z+6 17 B 19 B Nuclear chart from T. Baumann et al.: Nature 449, 1022 (2007) OT@ISPUN.VN 9/25-30/2017 11
Results Courtesy of T.Kubo Observation of 39 Na was confirmed in April 2017. (see next slides) OT@ISPUN.VN 9/25-30/2017 12
Systematic measurement of production cross sections Courtesy of T.Kubo Evaluated the probability that unobserved 32,33 F and 35,36 Ne are unbound (1-P), using the zero-event probability (P) obtained from the expected yield and Poisson distribution. The obtained probability is very high as shown in this table. Concluded that these isotopes are unbound with high confidence level. OT@ISPUN.VN 9/25-30/2017 13
1 39 Na @ RIKEN OT@ISPUN.VN 9/25-30/2017 14
New isotope ( 39 Na) search using a 48 Ca beam Running time:46.1 hours (run130-run186) 48 Ca beam intensity : 747 pna Live time: 98.8% [Setting] Target: rot. Be-20mm, Brho01=9.155 Tm F1degrader :Al-15mm, F5degrader: Al-7mm F1slit: +/-120mm, F2slit: +/-8.3mm F5slit:+/-95.1mm, F7slit:+/-50mm 2017.3.31, 00:00 [ 39 Na] Preliminary 8 events Yield: 6.5e-8 pps/pna Cross section: 1.6e-13 mb (2014: 1.9e-13) [ 40 Mg] Yield:1.23-06 pps/pna Cross section: 8.3e-12 mb (2014: 2.9e-11) OT@ISPUN.VN 9/25-30/2017 15
1 60 Ca @ RIKEN OT@ISPUN.VN 9/25-30/2017 16
60 Ca: Experimental setup and particle identification at BigRIPS 70 Zn beam @ 345 MeV/u 250 pna (1.6e12pps) PID by TOF-Br-DE-TKE method: Z, A/q, Q New isotopes search Production cross section and momentum distribution measurement Secondary reactions yield measurement as target thickness New isomers search F0 Target: Be, W F1 Slit Wedge 1 BigRIPS 1 st stage F2 Slit Thick Fe collimator F3 PPAC x2 Plastic 2 nd stage F5 PPAC x2 Plastic Wedge 2 Br : Plastic, PPACs (position measurement) TOF(b) : Plastic, PPAC PPAC x2 Plastic Slit F7 DE : 6 x Si (1 mm) TKE : CsI Veto: plastic OT@ISPUN.VN 9/25-30/2017 17
Summary of the new isotope search settings settings Brho01 [Tm] Brho12 [Tm] Target F1deg (Al) F5deg (Al) F2slit [mm] F7slit [mm] Intensity [pna] Accumulation time [h] Run 54 Ar 8.0 7.814 rotbe10 3 mm 1 mm +/- 10 +/-15 200 11.2 74-88 57 K 8.0 7.792 rotbe10 3 mm 1 mm +/- 10 +/-15 193 17.0 101-119 53 Ar 7.8 7.611 W1.5 3 mm 1 mm +/- 10 +/-15 47.4 1.4 132-133 53 Cl 7.8 7.609 rotbe15 3 mm 1 mm +11/- 10 +/-15 179 23.5 140-164 60 Ca 7.35 7.1066 rotbe15 3 mm 3 mm +/- 10 24.5 178-201 +/-20 225.6 +/- 12 14.4 202-216 50 S 7.35 7.1410 rotbe20 3 mm 3 mm +/- 10 +/-20 220.0 8.9 220-233 Total Experiment : 7 days Total 100.9 h (4.2 days) OT@ISPUN.VN 9/25-30/2017 18
New Isotope Search Settings 60 Ca setting 62 Sc 59,60 Ca 57,59 K 54 Ar 57 K setting 59 Ca 57 K 54 Ar 52 Cl 49 S 54 Ar setting 54 Ar 52 Cl 49 S 47 P W 1.5 mm: 53 Ar setting 53 Cl setting 50 S setting 57 K 54 Ar 49 S 47 P 54 Ar 49 S 47 P OT@ISPUN.VN 9/25-30/2017 19
PID plots using PPAC and Sci positions OT@ISPUN.VN 9/25-30/2017 20
Observed events of the new isotopes (9) in each setting Settings 62 Sc (Z=21) (N=41) 59 Ca (Z=20) (N=39) 60 Ca (Z=20) (N=40) 57 K (Z=19) (N=38) 59 K (Z=19) (N=40) 54 Ar (Z=18) (N=36) 52 Cl (Z=17) (N=35) 49 S (Z=16) (N=33) 47 P (Z=15) (N=32) 54 Ar 0 1 0 1 0 1 1 3 3 57 K 0 1 0 1 0 4 1 1 0 53 Ar (W tgt) 0 0 0 0 0 0 0 0 0 53 Cl 0 0 0 0 0 2 0 1 6 60 Ca 2 6 2 6 1 4 0 0 0 50 S 0 1 0 0 0 2 0 0 3 SUM 2 9 2 8 1 13 2 5 12 OT@ISPUN.VN 9/25-30/2017 21
Final PID results 9 new isotopes including 60 Ca 62 Sc 59 K 49 S 50 S Green color : observed at the first time Red color : isotopes that surprised us OT@ISPUN.VN 9/25-30/2017 22
Confirmation of New Isotopes PID Three crosschecking PID and filtering analysis: 1. BigRIPS group using ROOT during and just after the experiment 2. OT (July-September) : using SpecTcl analysis additionally with TKE 3. D.S.Ahn using ROOT analysis (special visit in September to MSU) Double position (Sci, PPAC) @ F3, F5, F7, Double timing signals (Sci, PPAC) @ F3, F5, F7, Advanced techniques against pile-ups at PPACs & Sci, Six PIN diodes (6 cross checking Z-identification), TKE measurement (CsI),additional veto detector after CsI OT@ISPUN.VN 9/25-30/2017 23
Experimental production vs EPAX2 & FRACS EPAX2 & FRACS -- no physics, no mass models just reference lines. Waiting for Abrasion- Ablation results with reasonable mass models OT@ISPUN.VN 9/25-30/2017 24
Mass models (we need time )?? & LISE++ LDM1 OT@ISPUN.VN 9/25-30/2017 25
Target thickness scanning MSU data Target thickness scanning data from this RIKEN experiment under analysis!!! OT@ISPUN.VN 9/25-30/2017 26
Isomer run (center nuclide 54 Ca) Gated on 55Ca T g = 0.2 15 us 55 Ca Preliminary! All runs (run 242 252) OT@ISPUN.VN 9/25-30/2017 Runs 242 252 Average 70 Zn current: 238 pna Data accumulation time : 12.0 hours Isomer data from this RIKEN experiment under analysis!!! Br 01 = 7.250 Tm, Br 12 = 7.047Tm Be 10 mm (rot) F1 deg: Al 3 mm, F5 deg: Al 3 mm Slits: F1 60/70 mm, F2 mm, F5 +/-110 mm, F7 +/-20 mm F1 +/- 80 mm (from run 229) 27
Secondary reactions study Data of the Secondary reactions run from this RIKEN experiment under analysis!!! OT@ISPUN.VN 9/25-30/2017 28
Secondary reactions : results with use of low-energy data Analysis from 01/19/2015 + 38 Mg & 35 Na points from @ 10/16/2016 1. We did not have thin target in the 2014 experiment 2. Data from the RIPS experiment 48 Ca(64 MeV/u)+Ta were used with scale parameter (1./2.1) to compare with current data. 3. Fair agreement is observed in this comparison OT@ISPUN.VN 9/25-30/2017 29
Residue Cross Section of neutron-rich isotopes res dbe(z,n) dbe(z,n-1) (Z,N) = f [ dbe(z,n), S n (Z,N)] S n (Z,N) minimum separation energy 1. (Z,N) ~ [dbe(z,n)+a 1 )] a2 * S n (Z,N) If S n (Z,N) 0, Then (Z,N) = 0, whereas Q g or BE/A systematics show unbound nuclei dbe(z,n) difference between the maximum biding energy for isotopes (Z) and binding energy of the nucleus (Z,N) Or Using dbe(z,n-1) = dbe(z,n) + S n (Z,N), 2. (Z,N) ~ dbe(z,n-1) If S n (Z,N) 0 it becomes incorrect OT@ISPUN.VN 9/25-30/2017 30
d_besn Cross Section Systematic vs. 82 Se MSU Experiment CS ~ a * dbesn 9 No two slopes behavior Should be published ASAP!!! OT@ISPUN.VN 9/25-30/2017 31
dbe systematics for the 2014 data Straight lines should describe well experimental data if: 1. No significant secondary reactions contributions These deviations are probably due to secondary reactions. We can estimate secondary reaction coefficients 2. Mass model describes well experimental masses This point ( 40 Mg) indicates probable binding overestimation: should shifted to left OT@ISPUN.VN 9/25-30/2017 32
Summary of 2017 experimental results We have determined the neutron dripline of F and Ne isotopes to be 31 F and 36 Ne by the nonobservation of 32,33 F and 35,36 Ne isotopes and established the neutron dripline up to Ne (Z=10) for the first time in 20 years. We have observed the 39 Na isotope with a 48 Ca beam and concluded that it is bound, whereas 38 Na is unbound. We have observed 9 new isotopes ( 47 P, 49 S, 52 Cl, 54 Ar, 57 K, 59 K, 59 Ca, 60 Ca, 62 Sc) with a 70 Zn beam. Production cross sections, momentum distributions, secondary reaction contribution runs were performed. Data are under analysis. Gammas corresponding to the 55 Ca isomeric state in microsecond region have been registered. 47 P 49 S 52 Cl 54 Ar 59 Ca 60 Ca 57 K 59 K 62 Sc OT@ISPUN.VN 9/25-30/2017 33
Collaborators of the 33 F, 36 Ne, 39 Na experiments T. Kubo*, N. Inabe, N. Fukuda, H. Suzuki, D.S. Ahn, Y. Shimizu, H. Takeda, H. Sato, H.Ueno, K. Kusaka, Y. Yanagisawa, M. Ohtake, Y. Yoshida, H. Otsu, RIKEN Nishina Center, Japan *Present address: FRIB/NSCL, Michigan State University D. Murai Department of Physics, Rikkyo University, Japan N. Iwasa Department of Physics, Tohoku University, Japan T. Nakamura Department of Physics, Tokyo Institute of Technology, Japan O.B. Tarasov, B.M. Sherrill, D.J. Morrissey NSCL, Michigan State University, USA H. Geissel GSI, Helmholtzzentrum feur Schwerionenforschung, Germany OT@ISPUN.VN 9/25-30/2017 34
Collaborators of the 60 Ca experiment 2017.05.06 08:00 TARASOV, Oleg B. (BigRIPS Team) KUBO, Toshiyuki (Research Instruments Group) BAZIN, Daniel P. (BigRIPS Team) MORRISSEY, David J. (BigRIPS Team) PORTILLO, Mauricio (BigRIPS Team) SHERRILL, Bradley M. (BigRIPS Team) STOLZ, Andreas (RIBF Independent User) THOENNESSEN, Michael R. (RIBF Independent User) UENO Hideki, Research Instruments Group FUKUDA, Naoki (BigRIPS Team) INABE, Naohito (BigRIPS Team) TAKEDA, Hiroyuki (BigRIPS Team) SUZUKI, Hiroshi (BigRIPS Team) SHIMIZU, Yohei (BigRIPS Team) AHN, Deuk Soon (BigRIPS Team) MURAI, Daichi (Research Instruments Group) KUSAKA, Kensuke (BigRIPS Team) YANAGISAWA, Yoshiyuki (BigRIPS Team) OHTAKE, Masao (BigRIPS Team) YOSHIDA, Koichi (BigRIPS Team) SATO, Hiromi (Detector Team) OTSU, Hideaki (SAMURAI Team) BABA, Hidetada (Computing and Network Team) IWASA, Naohito (BigRIPS Team) SUMIKAMA, Toshiyuki (Radioactive Isotope Physics Laboratory) SAKURAI, Hiroyoshi (Radioactive Isotope Physics Laboratory) Acknowledgements to T.Kubo & D.S.Ahn for kindly presented slides OT@ISPUN.VN 9/25-30/2017 35