Taprogge, J. et al, Gadea, A., & Montaner-Piza, A. (2015). beta decay of Cd-129 and excited states in In-129. Phys. Rev. C, 91(5), 054324–11pp.
Abstract: The beta decay of Cd-129, produced in the relativistic fission of a U-238 beam, was experimentally studied at the RIBF facility at the RIKEN Nishina Center. From the gamma radiation emitted after the beta decays, a level scheme of In-129 was established comprising 31 excited states and 69 gamma-ray transitions. The experimentally determined level energies are compared to state-of-the-art shell-model calculations. The half-lives of the two beta-decaying states in Cd-129 were deduced and the beta feeding to excited states in In-129 were analyzed. It is found that, as in most cases in the Z < 50, N <= 82 region, both decays are dominated by the nu 0g(7/2) -> pi 0g(9/2) Gamow-Teller transition, although the contribution of first-forbidden transitions cannot be neglected.
|
Davesne, D., Navarro, J., Becker, P., Jodon, R., Meyer, J., & Pastore, A. (2015). Extended Skyrme pseudopotential deduced from infinite nuclear matter properties. Phys. Rev. C, 91(6), 064303–6pp.
Abstract: We discuss the contributions to the equation of state for the NlLO Skyrme pseudopotential (l = 2,3). We show that by adding fourth- and sixth-order gradient terms, it is possible to fairly reproduce the spin/isospin decomposition of an equation of state obtained from ab initio methods. Moreover, by inspecting the partial-wave decomposition of the equation of state, we show for the first time a possible way to add explicit constraints on the sign of the tensor terms of the Skyrme interaction.
|
Fujita, Y. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2015). High-resolution study of Gamow-Teller excitations in the Ca-42(He-3,t)Sc-42 reaction and the observation of a “low-energy super-Gamow-Teller state”. Phys. Rev. C, 91(6), 064316–15pp.
Abstract: To study the Gamow-Teller (GT) transitions from the T-z = +1 nucleus Ca-42 to the T-z = 0 nucleus Sc-42, where T-z is the z component of isospin T, we performed a (p, n)-type (He-3, t) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0 degrees. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B(GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0 degrees and B(GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, J(pi) = 1(+) GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B(GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a “low-energy super-Gamow-Teller state.” It is expected that low-lying J(pi) = 1(+) GT states have T = 0 in the T-z = 0 nucleus Sc-42. However, T = 1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A = 42 isobars, analogous T = 1, 1(+) states are also expected in Ca-42. Comparing the Ca-42(He-3, t)Sc-42 and Ca-42(p, p') spectra measured at 0 degrees, candidates for T = 1 GT states could be found in the 10-12-MeV region of Sc-42. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed.
|
Pastore, A., Tarpanov, D., Davesne, D., & Navarro, J. (2015). Spurious finite-size instabilities in nuclear energy density functionals: Spin channel. Phys. Rev. C, 92(2), 024305–9pp.
Abstract: Background: It has been recently shown that some Skyrme functionals can lead to nonconverging results in the calculation of some properties of atomic nuclei. A previous study has pointed out a possible link between these convergence problems and the appearance of finite-size instabilities in symmetric nuclear matter (SNM) around saturation density. Purpose: We show that the finite-size instabilities not only affect the ground-state properties of atomic nuclei, but they can also influence the calculations of vibrational excited states in finite nuclei. Method: We perform systematic fully-self consistent random phase approximation (RPA) calculations in spherical doubly magic nuclei. We employ several Skyrme functionals and vary the isoscalar and isovector coupling constants of the time-odd term s . Delta s. We determine critical values of these coupling constants beyond which the RPA calculations do not converge because the RPA stability matrix becomes nonpositive. Results: By comparing the RPA calculations of atomic nuclei with those performed for SNM we establish a correspondence between the critical densities in the infinite system and the critical coupling constants for which the RPA calculations do not converge. Conclusions: We find a quantitative stability criterion to detect finite-size instabilities related to the spin s . Delta s term of a functional. This criterion could be easily implemented in the standard fitting protocols to fix the coupling constants of the Skyrme functional.
|
Pellegri, L. et al, & Gadea, A. (2015). Multitude of 2(+) discrete states in Sn-124 observed via the (O-17, O-17 'gamma) reaction: Evidence for pygmy quadrupole states. Phys. Rev. C, 92(1), 014330–7pp.
Abstract: A multitude of discrete 2(+) states in Sn-124 with energy up to 5 MeV were populated and identified with the (O-17, O-17'gamma) reaction at 340 MeV. Cross sections were compared with distorted wave Born approximation predictions and in general a good agreement was found. The measured energy and intensity distributions of the 2(+) states are very similar to the predictions based on self-consistent density functional theory and extended QRPA approach accounting for multiphonon degrees of freedom. This provides evidence of the excitation of the pygmy quadrupole resonance in skin nuclei.
|
