Cross Sections for theLi7(n, γ)Li8Reaction

Abstract

1037the only negative ion which has been identified in HC1 by previous workers is Cl~. Charge transfer would not be expected to play a significant role if this were the ion in our experiment. The observed value of 0.71 ±0.02 cm 2 /v-sec is to be contrasted with that of 0.88 expected if Eq. (14) is applicable. This suggests that an orientation-dependent R~* interaction is important in this case, so that the mobility should vary as T 1/6 . If, however, these forces averaged out, so that only the INTRODUCTION R ADIATIVE capture of neutrons by Li 7 leads to an unstable isotope, Li 8 , which decays with about a 0.9 sec half-life by emitting electrons with a maximum energy of 13 Mev. 1 The residual nucleus, Be 8 , further decays into two alpha particles in about 10~1 5 second. Since the spin and parity of the ground state of Li 8 are 2, even, 2 and the spin and parity of the ground state of Li 7 are f, odd, the excited state of Li 8 formed by s-wave neutron capture in Li 7 will decay to the ground state by electric dipole emission. Calculations of the cross section for this process have been made by Thomas 3 and his results predict a cross section which decreases smoothly with increasing neutron energy. However, a maximum in the capture cross section might be expected near 250 kev because of a resonance in the total cross section of Li 7 at this energy. 4 The 2.28-Mev state in Li 8 , which is responsible for this resonance, has spin 3 and even parity and may decay to the ground state by 1 W. F. Hornyak and T.

Neutron capture nucleosynthesis in the universe

“…Of course there were old data which were consistent with the theoretical prediction: these [12] were 59G11.8 and 39.5G7.9 mb. In these circumstances, our result [3] was 39.8G6.0 mb: the puzzle was solved.…”

“…Finally, the capture cross sections of the objective nucleus were derived from the capture yields, the neutron data obtained with the 6 Li-glass detector, and the standard capture cross sections of 197 Au. 12 C, there were two experimental data previously: 200G400 mb at 30 keV by Gibbons et al [5] and an upper limit of 14 mb at 30 keV by Macklin [6]. On the other hand, an extrapolation with the 1/v law [7] and the capture cross section [8] at the thermal energy (0.025 eV) gave about 3 mb at 30 keV, where v is the velocity of incident neutron in the center of mass system.…”

Structure of8B from elastic and inelastic7Be+pscattering

“…energies (up to 1 MeV) [20][21][22][23]. Only the 3 + state at 2.25 MeV (0.22 MeV above the neutron decay threshold) has been observed.…”

Synthesis of the elements in stars: forty years of progress

“…Measurements by Wiescher et al (1989) had indicated that the cross section for this reaction was a factor of 2 smaller than reported by Imhof et al (1959), thereby reducing the rate of heavy element synthesis in any primordial r process. However, a number of more recent measurements (Blackmon et al, 1996, and references therein) are in good agreement with the Imhof (1959) results supporting the reaction rate used in the calculation of heavy element production by Malaney and Fowler (1987). It is perhaps interesting to note that the three-cluster generator coordinate method calculations of Descouvemont and Baye (1994), which are consistent with the Imhof/Blackmon 7 Li(n,␥) 8 Li results, predict S 17 (0)у24 eV b for the isospin mirror, 7 Be(p,␥) 8 B reaction.…”