C12+C12Fusion Reactions near the Gamow Energy

Abstract

The fusion reactions 12C(12C,alpha)20Ne and 12C(12C,p)23Na have been studied from E=2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultralow hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E< or =3.0 MeV, in particular, a strong resonance at E=2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present nonresonant reaction rate of the alpha channel by a factor of 5 near T=8x10(8) K. Because of the resonance structure, extrapolation to the Gamow energy EG=1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full EG energy range.

Uncertainties and robustness of the ignition process in type Ia supernovae

“…In a recent study, Spillane et al (2007) present new reaction rates for the reactions 12 C( 12 C, α) 20 Ne and 12 C( 12 C, p) 23 Na, which are higher than previously assumed (Caughlan & Fowler 1988). Those authors suggest that the new measurements could affect the ignition and even the explosion theory of SNe Ia.…”

“…Nomoto 1982). An extrapolation at these temperatures rests upon the new evaluation of the non-resonant contribution to the reaction rate from Spillane et al (2007), plus general considerations on the unknown resonance structure below 2.0 MeV. Assuming that the observed resonance pattern of the reactions continues in a similar way at lower energies, Spillane et al (2007) state that their rates at lower temperature represent the nonresonant, lower limits to the true values at E 1.5 MeV.…”

“…The increase of the rate of C-burning in Spillane et al (2007), though not dramatic, has a relevant impact on the evolution of temperature perturbations due to the high power dependence on T in Eq. (2).…”

“…This is shown in Fig. 3, which refers to two simulations with the same bubble parameters but different references for the C-burning rate, namely Caughlan & Fowler (1988) and Spillane et al (2007). The WD background model is the same as in Iapichino et al (2006), and the bubble parameters are T = 7.7 × 10 8 K, D = 1 km and R = 100 km.…”

“…Model 3.1 was run with the rate of Spillane et al (2007) instead of the Caughlan & Fowler (1988) rate used for Model 3. The extrapolation of the rate at low temperature is about half the Caughlan & Fowler (1988) rate in the low temperature range between 10 8 K and 5 × 10 8 K (see Fig.…”