Determination of the direct capture contribution forN13(p,γ)O

Abstract

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.

N13(d,n)Li1, Yan2, Liu3 et al. 2006Phys. Rev. C

“…7 shows the comparison of total S-factors from the present work, Refs. [18] and [17]. Our updated total S-factors are about 40% higher than the previous ones in Ref.…”

“…Since we do not measure the optical potential parameters and used six sets of potential parameters from the neighboring nuclei, the error bar of present work is a bit larger than that of Ref. [18]. According to the traditional direct capture model [15,16,25], the direct capture of the…”

“…The updated rates are listed in Table III, together with the previous ones from Ref. [18] and NACRE's compilation. The results from the three works agree with each other within a factor of 2 at low temperature of T < 0.2 GK and are almost identical at higher temperature of T > 0.7 GK.…”

“…Recently, Tang et al deduced constructive interference below the resonance using an R-matrix method [18]. Based on this interference pattern, the present total S-factor is then obtained.…”

“…[24]. The normalized angular distributions from the six sets of optical potential parameters are also presented in [18], and the present spectroscopic factor is larger than the previous one (0.9) extracted from the total cross section of 13 N(d, n) 14 O at lower energy [17]. The uncertainties of the nuclear ANC and the spectroscopic factor are mainly from the difference of the calculated angular distributions with different optical potentials, as well as the experimental errors.…”