Breakup of loosely bound nuclei as indirect method in nuclear astrophysics: 8B, 9C, 23Al

Abstract

Abstract. We discuss the use of one-nucleon breakup reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. These are peripheral processes, therefore we can extract asymptotic normalization coefficients (ANC) from which reaction rates of astrophysical interest can be inferred. To show the usefulness of the method, three different cases are discussed. In the first, existing experimental data for the breakup of 8 B at energies from 30 to 1000 MeV/u and of 9 C at 285 MeV/u on light through heavy targets are analyzed. Glauber model calculations in the eikonal approximation and in the optical limit using different effective interactions give consistent, though slightly different results, showing the limits of the precision of the method. The results lead to the astrophysical factor S17(0) = 18.7 ± 1.9 eV · b for the key reaction for solar neutrino production 7 Be(p, γ) 8 B. It is consistent with the values from other indirect methods and most direct measurements, but one. Breakup reactions can be measured with radioactive beams as weak as a few particles per second, and therefore can be used for cases where no direct measurements or other indirect methods for nuclear astrophysics can be applied. We discuss a proposed use of the breakup of the proton drip line nucleus 23 Al to obtain spectroscopic information and the stellar reaction rate for

β decay of proton-rich nucleusAl23and astrophysical consequences

“…Indeed, assuming such an inversion, we recalculate the astrophysical S factor (Fig. 1) and the stellar reaction rate for the 22 Mg(p,γ ) 23 Al reaction and find an increase of 30 to 50 times over the current estimate of the rate for the temperature range of ONe novae; viz.,T 9 = 0.1-0.5 (see also [22]). This is due to the larger proton penetration for an s-wave capture and the absence of a centrifugal barrier for the last proton in 23 Al, which allows the wave function of the barely bound proton in the final state to extend far beyond the nuclear interior, thus increasing its overlap with the wave function of the incoming proton.…”

“…γ rays from the decay of longlived isotopes like 26 Al (t 1/2 = 7.2 × 10 5 yr), 44 Ti (60.0 yr), 56 Ni (6.1 d), etc., have been detected. Among the expected γ -ray emitters is 22 Na (t 1/2 = 2.6 yr), thought to be produced in the thermonuclear runaway and in the high-temperature phase of so-called ONe novae (oxygen-neon novae) through the reaction chain 20 Ne(p,γ ) 21 Na(p,γ ) 22 Mg(βγ ) 22 Na-the NeNa cycle [1][2][3][4]. Measurements, however, have not detected the 1.275 MeV γ ray that follows the decay of 22 Na and have only been able to set an upper limit on its production, a limit which is below the theoretical predictions (see, for example, [5,6] and the references therein).…”

“…In particular, it has been proposed that 22 Na itself or its precursor 22 Mg could be depleted by the radiative proton capture reactions 22 Na(p,γ ) 23 Mg [7] and 22 Mg(p,γ ) 23 Al [8], both leading to a serious reduction of the residual 22 Na abundance. The former is the prime candidate for this depletion.…”

“…The reaction is dominated by direct capture to the ground state and by resonant capture through the first excited state in 23 Al. There is no direct measurement of the cross section at stellar energies because it is impossible to make a 22 Mg (t 1/2 = 3.86 s) target and difficult to obtain an intense 22 Mg beam for measurements in inverse kinematics.…”

“…Efforts have been made for a long time to determine the reaction rate for the proton capture reaction 22 Na(p,γ ) 23 Mg, the most credible candidate for depleting 22 Na out of the NeNa cycle. Data showed early on that resonance capture plays the overwhelming role.…”