seeking the purported magic number n=32 with high-precision mass spectrometry
DESCRIPTION
Seeking the Purported Magic Number N=32 with High-Precision Mass Spectrometry. Susanne Kreim November 4 th 2011. Overview Physics Aims Technical Novelties. Physics Interest. Z=20. N=32. M. Bissell, et al. , `Spins, moments, and charge radii beyond 48Ca', INTC-P-313 (2011). - PowerPoint PPT PresentationTRANSCRIPT
Seeking the PurportedMagic Number N=32 with
High-Precision Mass Spectrometry
Susanne KreimNovember 4th 2011
OverviewPhysics Aims
Technical Novelties
Physics Interest
M. Bissell, et al., `Spins, moments, and charge radii beyond 48Ca', INTC-P-313 (2011)
Z=20
N=32
G. Audi and M. Wang, private communication (2011)
Structural Evolution Evolution of shell strength
Disappearing of magic numbers, appearing of new shell or sub-shell closuresO. 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
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 isotopesS. N. Liddick et 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. Liddick et al., PRC 70, 064303 (2004)
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
Three-Body Forces
[email protected]. Menendez and A. Schwenk, private communication (2011)
N=28 shell closure
N=32, N=34 shell gaps
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)
MR-ToF Measurement Mode
[email protected]. N. Wolf et al., Hyp. Int. 199, 115 (2011)
Advantages: few 10ms vs. few 100ms measurement time → lower half-life high repetition rate → lower yield
Disadvantage:Separation limit ~200,000Less precise but well within limit of physic‘s case
Alternative:Use in stacking mode → higher contamination ratio
Beam Time Requests
Nuclei Shifts Target Ion Source52-54Ca 6 UCx RILIS52-55Sc 8 UCx RILIS58-60Cr 6 YO or UCx RILIS
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
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
The ISOLTRAP Collaboration
... with support from our newly established collaboration with the theory group of Achim Schwenk:
Thank you!
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
Three-Body Forces
[email protected]. Ostuka et al., PRL 105, 032501 (2010)
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-Rich Ca Isotopes
J. Menendez and A. Schwenk, private communication (2011)
N=28 shell closure
N=32, N=34 shell gaps