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Register a new userCross sections of solar neutrino capture by 127I nuclei and Gamow Teller resonances
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Solar neutrino capture cross-section by 127I nucleus has been studied with taking into account the influence of the resonance structure of the nuclear strength function S(E). Three types of isobaric resonances: giant Gamow-Teller, analog resonance and low-lying Gamow-Teller pigmy resonances has been investigated on the framework of self-consistent theory of finite Fermi systems. The calculations have been performed considering the resonance structure of the charge-exchange strength function S(E). We analyze the effect of each resonance on the energy dependence of the cross-section. It has been shown that all high-lying resonances should be considered. Neutron emission process for high energy nuclear excitation leads to formation 126Xe isotope. We evaluate contribution from various sources of solar neutrinos to the 126Xe/127Xe isotopes ratio formed by energetic neutrinos. 126Xe/127Xe isotope ratio could be an indicator of high-energy boron neutrinos in the solar spectrum. We also discuss the uncertainties in the often used Fermi-functions calculations.
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Alternative methods to calculate neutron capture cross sections on radioactive nuclei are reported using the theory of Inclusive Non-Elastic Breakup (INEB) developed by Hussein and McVoy [1]. The statistical coupled-channels theory proposed in Ref. [2] is further extended in the realm of random matrices. The case of reactions with the projectile and the target being two-cluster nuclei is also analyzed and applications are made for scattering from a deuteron target [3]. An extension of the theory to a three-cluster projectile incident on a two-cluster target is also discussed. The theoretical developments described here should open new possibilities to obtain information on the neutron capture cross sections of radioactive nuclei using indirect methods.
A systematic shell model description of the experimental Gamow-Teller transition strength distributions in $^{42}$Ti, $^{46}$Cr, $^{50}$Fe and $^{54}$Ni is presented. These transitions have been recently measured via $beta$ decay of these $T_z$=-1 nuclei, produced in fragmentation reactions at GSI and also with ($^3${He},$t$) charge-exchange (CE) reactions corresponding to $T_z = + 1$ to $T_z = 0$ carried out at RCNP-Osaka.The calculations are performed in the $pf$ model space, using the GXPF1a and KB3G effective interactions. Qualitative agreement is obtained for the individual transitions, while the calculated summed transition strengths closely reproduce the observed ones.
Gamow-Teller (GT) transitions from high-spin isomers are studied using the sum-rule approach and the shell model. The GT transition strengths from the high-spin isomeric states show a stronger collectivity than those from the ground states in two $N=Z$ nuclei, $^{52}$Fe and $^{94}$Ag. It is argued that the spin-up and spin-down Fermi spheres involved in the GT transitions from the high-spin isomeric states play important roles. These Fermi spheres are analogous to the isospin-up and isospin-down Fermi spheres for the GT transitions from the ground states in $N>Z$ nuclei and create a strong collectivity.
Gamow-Teller (GT) and spin-dipole (SD) strength distributions of four doubly magic nuclei $^{48}$Ca, $^{90}$Zr, $^{132}$Sn and $^{208}$Pb are studied by the self-consistent Hartree-Fock plus random phase approximation (RPA) method. The Skyrme forces SAMi and SAMi-T without/with tensor interactions are adopted in our calculations. The calculated strengths are compared with available experimental data. The RPA results of GT and SD strengths of all four nuclei show fine agreement with observed GT and SD resonances in energy. A small GT peak below the main GT resonance is better described by the Skyrme interaction SAMi-T with the tensor terms. The quenching factors for GT and SD are extracted from the comparisons between RPA results and experimental strengths. It is pointed out that the quenching effect on experimental SD peaks is somewhat modest compared with that on GT peaks in the four nuclei.
The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the textit{unit cross section} ($hat{sigma}_{GT}$) was studied as a function of target mass number for ($t$,$^{3}$He) and ($^{3}$He,$t$) reactions at 115 $A$MeV and 140 $A$MeV, respectively. Existing ($^{3}$He,$t$) and ($t$,$^{3}$He) data on targets with mass number $12leq Aleq 120$ were complemented with new and reevaluated ($t$,$^{3}$He) data on proton, deuteron, $^{6}$Li and $^{12}$C targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number $A$, for $Ageq 12$: $hat{sigma}_{GT}=109/A^{0.65}$. The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number $A$ were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite ($^{3}$He,$t$) and ($t$,$^{3}$He) probes.
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