Seeking the Purported Magic Number N=32 with High-Precision Mass Spectrometry

1. Seeking the PurportedMagic Number N=32 withHigh-Precision Mass Spectrometry Susanne Kreim November 4th 2011 Overview Physics Aims Technical Novelties skreim@cern.ch

2. Physics Interest Z=20 N=32 M. Bissell, et al., `Spins, moments, and charge radii beyond 48Ca', INTC-P-313 (2011) G. Audi and M. Wang, private communication (2011) skreim@cern.ch

3. Structural Evolution • Evolution of shell strength • Disappearing of magic numbers, appearing of new shell or sub-shell closures • O. Sorlin, M.-G. Porquet, Porgr. Part. Nucl. Phys. 61, 602 (2008) • Island of inversion at N=20: „intruding“ pf orbitals had to be included in calculations • Ordering of shell occupation from binding energies • Low uncertainty needed because of small relative effect • R. B. Cakirli et al., PRL 102, 082501 (2009) • Exacting test for nuclear models skreim@cern.ch

4. Sub-Shell Closure at N=32,34? • Evidence for N=32 shell gap but not for N=34 • Behavior of E(21+) energies in n-rich Ca isotopes • H. L. Crawford et al., PRC 82, 014311 (2010) • Behavior of E(21+) energy of n-rich Ti isotopes • S. N. Liddicket al., PRC 70, 064303 (2004) • B. Fornal et al., PRC 70, 064304 (2004) • Behavior of E(21+) energy of n-rich Cr isotopes • J. I. Prisciandaro et al., Phys. Lett. B 510, 17 (2001) • Theoretical predictions • Shell gaps for N=32 and N=34 within shell-model calculations • M. Honma et al., PRC 65, 061301(R) (2002) • BMF calculations confirm N=32 but negate N=34 • T. Rodríguez et al., PRL 99, 062501 (2007) N=32 Isotones S. N. Liddicket al., PRC 70, 064303 (2004) skreim@cern.ch

5. Three-Body Forces • Pairing gaps reproduced • Include NN and 3N forces on the microscopic level • Example: n-rich Ca isotopes full calculation needed • Strong evidence for N=32 and N=34 shell gaps • Pairing gap accessible via mass measurements N=28 shell closure N=32, N=34 shell gaps J. Menendez and A. Schwenk, private communication (2011) skreim@cern.ch

6. Current Performance of ISOLTRAP • Accuracy ≈ 1·10-8 achievable via frequency measurement to extract wanted mass • Half-life ≈ 60ms • Production yield ≈ few 100 ions per second • Efficiency ≈ 1% • Resolving power for isobar separation ≈ 105 • Contamination ratio ≈ 104:1 plus ≈ 103:1 • Resolving power for isomer separation ≈ 107 • Time-of-flight detection via “Ramsey method” M. Mukherjee et al., Eur. Phys. J. D 22, 53 (2008) skreim@cern.ch

7. MR-ToF Measurement Mode • Advantages: • few 10ms vs. few 100ms measurement time → lower half-life • high repetition rate → lower yield • Disadvantage: • Separation limit ~200,000 • Less precise but well within limit of physic‘s case • Alternative: • Use in stacking mode → higher contamination ratio R. N. Wolf et al., Hyp. Int. 199, 115 (2011) skreim@cern.ch

8. Beam Time Requests • Half-lives between 50ms and 10s • 1 case only extrapolated • Mass uncertainty between 200-700 keV • 4 cases only extrapolated • Yield between 100 and 104 ions/µC • measured and extrapolated, already demonstrated at ISOLTRAP • MR-ToF mass separator calibration 0.3 shifts per A → 3 additional shifts • MR-ToF measurement mode → 4 additional shifts skreim@cern.ch

9. Outlook • Measurements on atomic Sc in 2012 ? • 52,55Sc not accessible via in-trap decay • 52Sc test case for ongoing UV break-up studies • 55Sc only accessible with direct MR-ToF measurement • Laser-ionization scheme could be enhanced • Measurements on Cr in 2014 ? • Feasible with laser-ionization scheme skreim@cern.ch

10. The ISOLTRAP Collaboration ... with support from our newly established collaboration with the theory group of Achim Schwenk: Thank you! skreim@cern.ch

11. Three-Body Forces • Current limitations for medium-mass nuclei • Theoretical approaches based on phenomenology • Extrapolations to n-rich nuclei suffer from large divergence • 3N forces not included • Chiral Effective Field Theory • low-energy approach to QCD • Include NN and 3N forces on the microscopic level • Test nuclear forces also for exotic nuclei: example O dripline • 3N forces for SM calculations • 2 valence, 1 core particle → (effective) TBME • 1 valence, 2 core particles → effective SPE T. Ostuka et al., PRL 105, 032501 (2010) skreim@cern.ch

12. N-Rich Ca Isotopes • Pairing gaps reproduced • 3rd order MBPT + 3N forces + pfg9/2 space • Strong evidence for N=32 and N=34 shell gaps • Pairing gap accessible via mass measurements N=28 shell closure N=32, N=34 shell gaps J. Menendez and A. Schwenk, private communication (2011) skreim@cern.ch