On discrepancies within the experimental and theoretical low energy3H(?, ?)7Li cross sections

Abstract

The two presently available measurements of the low-energy 3H(a, ~)TLi reaction differ from each other by roughly 30% in total magnitude as well as in their determination of the branching ratios for the transition into the two final 7Li bound states. Studying the 3H(e, 7)7Li reaction in the framework of the microscopic Resonating Group Method we were able to reproduce both experimental total cross sections using different effective nucleon-nucleon interactions. However, none of the effective forces yields branching ratios compatible with the data measured by the Toronto-M/inster-collaboration. PACS: 25.55. -e; 25.70.Jj; 21.60.GxThe 3H(e, 7)7Li reaction is a main source for the 7Li production during the big bang nucleosynthesis [1]. Measurements of this reaction rate in the energy range E= 150-600 keV performed by Griffith et al.[2] are consistent with the assumption of an energy independent astrophysical S-factor for the 3H(c~, 7)7Li reaction at stellar energies with a value of S(0)=0.064keV-b [3]. This energy-independent S(E)-factor has been adopted in standard hot big bang model studies [4,5].Recently several microscopic calculations of the 3H(e, 7)VLi reaction at low energies (E < 1 MeV) have been performed in the framework of the Resonating Group Method [6][7][8] or on the basis of a microscopic potential model [9]. While these studies reproduced the experimental data of [2], they do not support the assumption of an energy-independent 3H(e, 7)7Li S-factor at low energies. In agreement with each other these calculations predict the S-factor to increase noticeably with decreasing energy resulting in S(0)~0.10keV.b [6][7][8][9]. Consequently the microscopic studies recommend a higher thermally averaged 3H(c~, 7)7Li reaction rate at astrophysically important temperatures T< 109K than the rate given by Fowler et al. [-3] resulting in a production of 7Li during the big bang which is noticeably higher than currently believed.Motivated by the theoretical predictions a Mfinster-Toronto collaboration [10] has very recently measured the 3H(~, y)VLi cross sections in the energy range E = 80-500 keV. In fact the new experimental data show the predicted increase of the S-factor towards E =0, however, they exceed the data of [-2] by roughly 30% and are also noticeably larger than the microscopically calculated cross sections [6][7][8][9]. An extrapolation of the new experimental data resulted in S (0) ~ 0.14 + 0.02 keV. b [ 10]. Without knowledge of the data of [10] Kajino investigated the dependence of the microscopically calculated 3H(c~, 7)7Li cross sections and those of its analogue reaction 3He(e, 7)TBe on the effective nucleon-nucleon interaction used in these studies [11]. As a main result he observed that the various calculations predict different energy dependences of the Sfactor in the astrophysically important energy regime. In close relation to the study of Kajino [11] we will show in the following that the experimental data of [10] are compatible with the results of the microscopic calculations if other force...

Radiativeα-capture cross sections from realistic nucleon-nucleon interactions and variational Monte Carlo wave functions

“…8, along with the contributions of individual terms of Eq. (16). Total S-factors from five cluster-cluster potentials are shown along with the laboratory data in Fig.…”

“…The potential models now have a well-founded justification in the resonating-group work, in the form of the microscopic potential model [18,19]. Although the RGM models have apparently been very successful in describing these reactions (the calculation of Kajino [14] correctly predicted both energy dependence and normalization for the experiment of Brune et al [20]), it is not clear that this is the final word, because the agreement with the data seems to be spoiled when the model space is expanded [16,17].…”

Static and Dynamic Moments of the 7Li Nucleus

“…In recent years, measured values of the quadrupole moment (Q) of the iground state of 7U and the reduced E2 transition probability (B(E2)l) to the ~-first excited state have been used to test models describing the low-lying states of 7U and 7Be, or at least to select parameter values in the models (Mertelmeier and Hofmann 1986;Kajino 1986; Altmeyer et al 1988; Buck and Merchant 1988). Such models have been used in the calculation of astrophysical S-factors for radiative-capture reactions involving these nuclei.…”

Theoretical evidence for di-molecular rotational behaviour in the hypernuclei ? 8 Li and ? 8 Be

“…Note that with this parametrization the binding energies and rms-radii of the nuclear clusters are reasonably well reproduced [13]. Adjusting the Majorana exchange parameter in the central force to u = 0.9835 (the properties of the nuclear clusters are independent of u) our model reproduces the properties of the bound levels in 7Li and VBe very well [14]. The relative wave functions between the various clusters, g and G, have been determined by solving the manybody Schr6dinger equation for the microscopic Hamiltonian defined above in the model space spanned by the 3-cluster wave functions with fixed internal degrees of freedom (see for example [15]).…”