Penning-Trap Mass Measurements of the Neutron-Rich K and Ca Isotopes: Resurgence of the N = 28 Shell Strength

Abstract

We present Penning-trap mass measurements of neutron-rich 44,47-50K and 49,50Ca isotopes carried out at the TITAN facility at TRIUMF-ISAC. The 44K mass measurement was performed with a charge-bred 4+ ion utilizing the TITAN EBIT, and agrees with the literature. The mass excesses obtained for 47K and 49,50Ca are more precise and agree with the values published in the 2003 Atomic Mass Evaluation (AME'03). The 48,49,50K mass excesses are more precise than the AME'03 values by more than one order of magnitude. For 48,49K, we find deviations by 7 sigma and 10 sigma, respectively. The new 49K mass excess lowers significantly the two-neutron separation energy at the neutron number N=30 compared with the separation energy calculated from the AME'03 mass-excess values, and thus, increases the N=28 neutron-shell gap energy at Z=19 by approximately 1 MeV.

6 pages, 5 figures, accepted for PRC

References in corpus (8)

• Nuclear magic numbers: new features far from stability
• Collapse of the N=28 shell closure in ${}^{42}$Si
• First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
• Discovery of the shape coexisting 0+ state in 32Mg by a two neutron transfer reaction
• First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
• First Use of High Charge States for Mass Measurements of Short-lived Nuclides in a Penning Trap
• Evidence for a breakdown of the Isobaric Multiplet Mass Equation: A study of the A=35, T=3/2 isospin quartet
• Verifying the accuracy of the TITAN Penning-trap mass spectrometer

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• Efimov Physics around the neutron rich Calcium-60 isotope
• Spins and Magnetic Moments of ${}^{49}$K and ${}^{51}$K: establishing the 1/2${}^{+}$ and 3/2${}^{+}$ level ordering beyond $N$ = 28
• Penning-trap mass spectrometry of highly charged, neutron-rich Rb and Sr isotopes in the vicinity of $A\approx 100$
• Shell evolution and its indication on the isospin dependence of the spin-orbit splitting
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