Origin of the anomalous long lifetime of ¹4C.

We report the microscopic origins of the anomalously suppressed beta decay of ¹4C to ¹4N using the ab initio no-core shell model with the Hamiltonian from the chiral effective field theory including three-nucleon force terms. The three-nucleon force induces unexpectedly large cancellations within the p shell between contributions to beta decay, which reduce the traditionally large contributions from the nucleon-nucleon interactions by an order of magnitude, leading to the long lifetime of ¹4C.

Structure of A=10-13 nuclei with two- plus three-nucleon interactions from chiral effective field theory.

Properties of finite nuclei are evaluated with two-nucleon (NN) and three-nucleon (NNN) interactions derived within chiral effective field theory. The nuclear Hamiltonian is fixed by properties of the A=2 system, except for two low-energy constants (LECs) that parametrize the short range NNN interaction, which we constrain with the A=3 binding energies. We investigate the sensitivity of 4He, 6Li, 10,11B, and 12,13C properties to the variation of the constrained LECs. We identify observables that are sensitive to this variation and find preferred values that give the best overall description. We demonstrate that the NNN interaction terms significantly improve the binding energies and spectra of mid-p-shell nuclei not just with the preferred choice of the LECs but even within a wide range of the constrained LECs. We find that a very high quality description of these nuclei requires further improvements to the chiral Hamiltonian.

Six-nucleon spectroscopy from a realistic nonlocal Hamiltonian.

We apply the ab initio no-core nuclear shell model to solve the six-nucleon systems, (6)Li and (6)He, interacting by realistic nucleon-nucleon ( NN) potentials. In particular, we present the first results for A = 6 with the nonlocal CD-Bonn NN potential. The resulting (6)Li binding energy -29.3(6) MeV and the excitation spectra improve the agreement between the theory and experiment compared to results with local NN potentials, but the need for the inclusion of a real three-body interaction and/or further improvement of the NN forces remains. We predict properties of the (6)He dipole modes, a subject of current controversy.

Observation of (46)Cr and testing the isobaric multiplet mass equation at high spin.

The ground state band in (46)Cr and the isospin T = 1 band in (46)V have been delineated up to Ipi = 10(+) (tentatively 12(+)). These observations complete the highest spin T = 1 isospin triplet known. Following the isobaric multiplet mass equation, a combination of level energies in (46)Cr, (46)Ti, and (46)V are taken to highlight the angular momentum dependence of the isovector and isotensor parts of the interaction. The results are compared with full- fp-space shell model calculations. The influence of the one-body and two-body contributions to the isovector energy difference are investigated.