We present precision Penning trap mass measurements of neutron-rich calcium and potassium isotopes in the vicinity of neutron number N=32. Using the TITAN system, the mass of ⁵¹K was measured for the first time, and the precision of the ^51,52Ca mass values were improved significantly. The new mass values show a dramatic increase of the binding energy compared to those reported in the atomic mass evaluation. In particular, ⁵²Ca is more bound by 1.74 MeV, and the behavior with neutron number deviates substantially from the tabulated values. An increased binding was predicted recently based on calculations that include three-nucleon (3N) forces. We present a comparison to improved calculations, which agree remarkably with the evolution of masses with neutron number, making neutron-rich calcium isotopes an exciting region to probe 3N force

A 71 Ga(3 He, t) 71 Ge charge-exchange experiment was performed to extract with high precision the Gamow-Teller (GT) transition strengths to the three lowest-lying states in 71 Ge, i.e., the ground state (1/2 −), the 175 keV (5/2 −) and the 500 keV (3/2 −) excited states. These are the relevant states, which are populated via a charged-current reaction induced by neutrinos from reactor-produced 51 Cr and 37 Ar sources. A precise measurement of the GT transition strengths is an important input into the calibration of the SAGE and GALLEX solar neutrino detectors and addresses a long-standing discrepancy between the measured and evaluated capture rates from the 51 Cr and 37 Ar neutrino calibration sources, which has recently spawned new ideas about unconventional neutrino properties.

A 76 Ge( 3 He,t) 76 As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT − strength distribution in 76 As, which is the intermediate nucleus in the double-beta (ββ) decay of 76 Ge, has been extracted. An unusually strong fragmentation of the GT − strength is observed even at low excitation energies of E x 5 MeV. By combining the data with those for GT + transitions from a recent 76 Se(d, 2 He) 76 As measurement, the nuclear matrix element for the 76 Ge 2νββ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the 76 Ge 2νββ decay nuclear matrix element is discussed. PHYSICAL REVIEW C 86, 014304 (2012) 76 Ge 76 As 76 Se 2 − 1 + 1 + 1 + 0 + 0 + β − β − 44.425(1) keV 86.787(1) keV 120.258(1) keV Q β − β − = 2039.00(5) keV Q β − = 2962 keV Q EC = 923 keV J π =1 +