Seeking the PurportedMagic Number N=32 with

High-Precision Mass Spectrometry

Susanne KreimNovember 4th 2011

skreim@cern.ch

OverviewPhysics Aims

Technical Novelties

Physics Interest

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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

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Sub-Shell Closure at N=32,34?

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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

skreim@cern.chJ. Menendez and A. Schwenk, private communication (2011)

N=28 shell closure

N=32, N=34 shell gaps

Current Performance of ISOLTRAP

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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

skreim@cern.chR. 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

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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

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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

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... 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

skreim@cern.chT. 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

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J. Menendez and A. Schwenk, private communication (2011)

N=28 shell closure

N=32, N=34 shell gaps