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We implemented a variation after projection (VAP) algorithm based on a triaxially deformed Hartree-Fock- Bogoliubov vacuum state. This is the first projected mean field study that includes all the quantum numbers (except parity), i.e., spin (J), isospin (T), and mass number (A). Systematic VAP calculations with JTA projection have been performed for the even-even¿/-shell nuclei with the USDB Hamiltonian. All the VAP ground state energies are within 500 keV above the exact shell model values. Our VAP calculations show that the spin projection has two important effects: (1) the spin projection is crucial in achieving good approximation of the full shell model calculation; (2) the intrinsic shapes of the VAP wave functions with spin projection are always triaxial, while the Hartree-Fock-Bogoliubov methods likely provide axial intrinsic shapes. Finally, our analysis suggests that one may not be possible to associate an intrinsic shape to an exact shell model wave function. [ABSTRACT FROM AUTHOR]

The backbending phenomenon in 48Cr has been investigated using the recently developed projected configuration interaction (PCI) method, in which the deformed intrinsic states are directly associated with shell model wave functions. Two previous explanations, (i) K=0 band crossing and (ii) K=2 band crossing, have been reinvestigated using PCI, and it was found that both explanations can successfully reproduce the experimental backbending. The PCI wave functions in the pictures of K=0 band crossing and K=2 band crossing are highly overlapped. We conclude that there are no unique intrinsic states associated with the yrast states after backbending in 48Cr. [ABSTRACT FROM AUTHOR]

In the standard Big-Bang nucleosynthesis (BBN) model, the primordial 7Li abundance is overestimated by about a factor of 2 to 3 compared to astronomical observations; this is the so-called pending cosmological lithium problem. The 7Be(n,α)4He reaction was regarded as the secondary important reaction in affecting the 7Li abundance by destructing the 7Be nucleus in BBN. However, the reaction rate of 7Be(n,α)4He has not been well studied so far. This reaction rate was first estimated by Wagoner in 1969, which has been primarily adopted in the current BBN simulations. This simple estimate involved only a direct reaction contribution, but the resonant component should also be considered according to the later experimental results. In the present work, we revised this rate based on the indirect cross-section data available for the 4He(α,n)7Be and 4He(α,p)7Li reactions by applying the charge symmetry and the principle of detailed balance. Our new result shows that the previous rate (acting as an upper limit) is overestimated by about a factor of ten. The BBN simulation shows that the present rate leads to a 1.2% increase in the final 7Li abundance compared with the result using the Wagoner rate and, hence, the present rate even worsens the 7Li problem. By the present estimation, the role of 7Be(n,α)4He in destroying 7Be is weakened from the second most importance to the third and, in turn, the 7Be(d,p)24He reaction becomes of secondary importance in destroying 7Be. [ABSTRACT FROM AUTHOR]

The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The 12N(p, γ)130 reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3a process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the 2H(12N, 130)n proton transfer reaction at Ec.m. = 8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of 13Og s. --> 12N 4- p was extracted to be 3.92 ± 1.47 fm-' from the measured angular distribution and utilized to compute the direct component in the 12N(p, γ)130 reaction. The direct astrophysical S factor at zero energy was then found to be 0.39 ±0.15 keV b. By considering the direct capture into the ground state of 130, the resonant capture via the first excited state of 130 and their interference, we determined the total astrophysical S factors and rates of the 12N(p, γ130 reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that 12N(p, γ)130 will only compete successfully with the ß+ decay of 12N at higher (~2 orders of magnitude) densities than initially predicted. [ABSTRACT FROM AUTHOR]

High-spin states in 126I have been investigated by using in-beam γ-ray spectroscopy with the 124Sn(7Li, 5n)126I reaction at a beam energy of 48 MeV. The level scheme of 126I has been extended and modified considerably by adding about 80 new γ rays and establishing five new bands. The configurations have been tentatively assigned for the yrast, yrare, and other excited bands with the help of triaxial projected shell-model (TPSM) and cranked shell-model calculations. The first band crossing in the yrast band is found due to alignments of a pair of (h11/2)² neutrons. The first and the second band crossings in the yrare band are caused by the alignments of a pair of (d5/2)² protons and a pair of (h11/2)² neutrons, respectively. Due to the successive excitations of two, four, and six quasiparticles, the alignments in the yrare band present a gigantic rising feature. The yrast band exhibits a signature inversion at low spins and becomes normal after a reversion spin of lrev = 14. The yrare band exhibits an abnormal signature inversion in which the signature inversion phase persists up to the highest spin. The signature inversions in 126I are well reproduced and successfully interpreted by the TPSM calculations. Some features of chirality are found for the four-quasiparticle (4qp) part of the yrast band and the 4qp excited band 2. [ABSTRACT FROM AUTHOR]

The article discusses the experimental developments in nuclear physics. It presents the study which investigated the high-spin states in 126iodine (I) through the use of in-beam ϒ-ray spectroscopy with the 124tin (Sn)(7lithium (Li), 5n)126I reaction at a beam energy of 48 megaelectron volts (MeV). The triaxial projected shell-model (TPSM) and cranked shell-model calculations were also used.

High-spin excited states in the very neutron-rich nucleus 114Rh have been studied by examining the prompt γ rays emitted in the spontaneous fission of 252Cf with the Gammasphere detector array. A high-spin level scheme of 114Rh has been established for the first time with 13 new levels. The level scheme is proposed to be built on a 7- state. The existence of a relatively large signature splitting and an yrare band show features which may indicate triaxial deformation. The phenomenon of signature inversion has been observed in 114Rh at I = 12 ħ. The observed signature inversion of 114Rh is interpreted successfully in terms of the triaxial projected shell model. Theoretical calculations suggest that the negative-parity, yrast band of 114Rh has the two-quasi-particle configuration of πg9/2 ⊗ νh11/2, consistent with the systematics of odd-odd Rh isotopes. The signature inversion at spin 12 ħ may be attributed to the change of rotational mode, from quasi-particle aligned rotation at low spins to collective rotation at high spins. [ABSTRACT FROM AUTHOR]