Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.Quantum-mechanical shell effects play a crucial role in determining the structure and the properties of matter. The electronic shell structure defines the architecture of the periodic table. An analogous effect leads to the so-called "magic nuclei," closed nucleon shells that lead to an enhanced binding of the atomic nucleus, that opposes Coulomb repulsion of protons and governs the landscape of the nuclear chart. The heaviest stable doubly magic nucleus is 208 Pb with Z = 82, N = 126. The quest for the end of the periodic table and the northeast limit of the nuclear chart (Fig. 1) drives the search for even heavier magic nuclei.In these superheavy elements (SHEs), nuclear shell effects are decisive for their mere existence. Without them, their nuclei would instantaneously disintegrate by spontaneous fission through Coulomb repulsion. A manifestation of these nuclear shell effects is an increase of the
We report a direct measurement of the Q ββ -value of the neutrinoless double-β-decay candidate 48 Ca at the TITAN Penning-trap mass spectrometer, with the result that Q ββ = 4267.98(32) keV. We measured the masses of both the mother and daughter nuclides, and in the latter case found a 1 keV deviation from the literature value. In addition to the Q ββ -value, we also present results of a new calculation of the neutrinoless double-β-decay nuclear matrix element of 48 Ca. Using diagrammatic many-body perturbation theory to second order to account for physics outside the valence space, we constructed an effective shell-model double-β-decay operator, which increased the nuclear matrix element by about 75% compared with that produced by the bare operator. The new Q ββ -value and matrix element strengthen the case for a 48 Ca double-β-decay experiment.The discovery of neutrino oscillations represents the first evidence for new physics beyond the Standard Model [1,2]. The oscillations conclusively demonstrate that neutrinos have mass, that flavor eigenstates are mixtures of mass eigenstates, and that neutrino physics is more complicated than we had thought. The observation of neutrinoless double-β (0νββ) decay, extremely rare if it exists, would at once fill multiple gaps in our understanding of the neutrino's nature and would represent a major breakthrough for particle physics. Since this lepton-number-violating process can occur only if the neutrino is its own antiparticle, its discovery would unambiguously confirm the neutrino as a Majorana particle, while a measured lifetime would provide a value for the neutrino mass scale [3]. In order to extract that value from the 0νββ-decay half-life, however, two quantities must be accurately determined: a phase-space factor, which depends on the Q ββ -value of the decay, and a nuclear matrix element, which is not observable and therefore must be obtained from nuclear structure theory.The twelve nuclides that have been observed to undergo two-neutrino double-β (2νββ) decay [4,5] are the basis for a number of large-scale experimental 0νββdecay searches currently underway. Of these nuclides, 48 Ca possesses the largest Q ββ -value of 4.3 MeV [6], giv-ing it several distinct experimental advantages. Because the Q ββ -value lies well above the energy of naturally occurring background, a good signal-to-noise ratio is ensured, while the large phase-space factor enhances the 0νββ-decay rate. The low isotopic abundance of 48 Ca, however, requires enrichment. 48 Ca is currently being measured at NEMO-III [7] and studied at CANDLES [8] and CARVEL [9]. The Q ββ -value provides vital input for the simulation of signal and background, the analysis of current data, and the design of future detectors. In order for the uncertainty of the Q ββ -value to be negligible in these studies, the required precision has to be better than the intrinsic resolution of the detector.The deep implications of massive neutrinos have led to a concentrated effort to calculate the nuclear matrix element for 0νββ-...
Determination of the direct double-β decay Q value of 96 Zr and atomic masses of [90][91][92]94,96 Experimental searches for the neutrinoless double-β decay offer one of the best opportunities to look for physics beyond the Standard Model. Detecting this decay would confirm the Majorana nature of the neutrino, and a measurement of its half-life can be used to determine the absolute neutrino mass scale. Important to both tasks is an accurate knowledge of the Q value of the double-β decay. The LEBIT Penning trap mass spectrometer was used for the first direct experimental determination of the 96 Zr double-β decay Q value: Q ββ = 3355.85 (15) keV. This value is nearly 7 keV larger than the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)
A laser ablation ion source has been developed and implemented at the Low-Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory. This offline ion source enhances the capabilities of LEBIT by providing increased access to ions used for calibration measurements and checks of systematic effects as well as stable and long-lived ions of scientific interest. The design of the laser ablation ion source and a demonstration of its successful operation are presented.
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