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).

Fusion data for 13 C+ 13 C, 12 C+ 13 C and 12 C+ 12 C are analyzed by coupled-channels calculations that are based on the M3Y+repulsion, double-folding potential. The fusion is determined by ingoingwave-boundary conditions (IWBC) that are imposed at the minimum of the pocket in the entrance channel potential. Quadrupole and octupole transitions to low-lying states in projectile and target are included in the calculations, as well as mutual excitations of these states. The effect of oneneutron transfer is also considered but the effect is small in the measured energy regime. It is shown that mutual excitations to high-lying states play a very important role in developing a comprehensive and consistent description of the measurements. Thus the shapes of the calculated cross sections for 12 C+ 13 C and 13 C+ 13 C are in good agreement with the data. The fusion cross sections for 12 C+ 12 C determined by the IWBC are generally larger than the measured cross sections but they are consistent with the maxima of some of the observed peak cross sections. They are therefore expected to provide an upper limit for the extrapolation into the low-energy regime of interest to astrophysics.

13N͑p , ␥͒ 14 O is one of the key reactions which trigger the onset of the hot CNO cycle. This transition occurs when the proton capture rate on 13 N is faster, due to increasing stellar temperature ͑ജ10 8 K͒, than the 13 N ␤-decay rate. The rate of this reaction is dominated by the resonant capture through the first excited state of 14 O ͑E r = 0.528 MeV͒. However, through constructive interference, direct capture below the resonance makes a non-negligible contribution to the reaction rate. We have determined this direct contribution by measuring the asymptotic normalization coefficient for 14 O → 13 N+ p. In our experiment, an 11.8 MeV/ nucleon 13 N radioactive beam was used to study the 14 N͑ 13 N, 14 O͒ 13 C peripheral transfer reaction, and the asymptotic normalization coefficient, ͑C p 1/2 14 O ͒ 2 = 29.0± 4.3 fm −1 , was extracted from the measured cross section. The radiative capture cross section was estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest resonance parameters. We find the S factor for 13 N͑p , ␥͒ 14 O to be larger than previous estimates. Consequently, the transition from the cold to hot CNO cycle for novae would be controlled by the slowest proton capture reaction 14 N͑p , ␥͒ 15 O.