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

Sm (25). We prepared spectroscopic alpha sources (20-100 μg) from the three activations and counted them during several months using a silicon surface-barrier detector at Kanazawa University (Fig. 1, 25 Galactic-disk enrichment in low-metallicity gas (Fig. 3). This reduces the age of late events (≥ 50 Ma) (age is measured in this work relative to the birth of the solar system) but has a minor effect on earlier events (Table 1). Samarium-146 observations in terrestrial samples can be divided into two groups: (i) most terrestrial rocks display a 142 Nd/ 144 Nd ratio higher by ~18 parts per million (ppm) than CHUR (9) and (ii) anomalies in the 142 Nd/ 144 Nd ratio relative to the terrestrial standard, both positive, in rocks from Greenland and Australia (2,10), and negative, in rocks from Northern Quebec (2,11).

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