In-beam gamma ray spectroscopy of 58Co

Abstract

The odd-odd 58 Co nucleus has been studied with the 51 V( 10 B, p2n) reaction at 33-MeV incident energy and the γ-spectrometer Saci-Pererê. Excited states up to 8.0 MeV and spin up to 11 + have been observed. The results are compared to Shell Model calculations using the GXPF1 effective interaction, developed for use in the fp shell. The πf −1 7/2 ⊗ν(p 2 3/2 f 1 5/2 ) configuration was assigned to the yrast levels.Nuclei close to doubly magic shell closures are the object of extensive experimental and theoretical investigations [1][2][3]. Spectroscopic data from these nuclei provide essential information for the parameter sets of spherical shell-model calculations. They apply severe constraints on the outcome of such calculations and, consequently, define the effective nuclear forces. During recent years both experimental and theoretical efforts have been used to understand the nuclei near the Z=N=28 shell closure. There is an N or Z=28 "magic" number inside the major shell with the oscillator quantum number N=3. The shell gap at N=Z=28 is due to the spin-orbit lowering of the f 7/2 orbital. This gap is relatively small so that the particle-hole excitation across the gap has relatively low energies. For shell model calculations around this magic number, 56 Ni has often been assumed as an inert core. However, it has been shown that this core is rather soft and only a very limited description is provided by the closed-shell model for the magic number 28 [4]. These structures were successfully described for N or Z = 28 nuclei only after considering the existence of significant core-excitations in low-lying non yrast states as well as in high-spin yrast states [3]. These calculations were performed for the 53 Mn, 54 Fe, 55 Co and 56,57,58,59 Ni nuclei.In this study we present new results on excited states of 58 Co, thus enriching the systematics of the nuclear structure along the N=31 chain. This nucleus has three particles and one hole relative to the 56 Ni core and has been studied so far with proton and α particle induced reactions [6-8], therefore very little was known regarding its high-spin structure.The 58 Co nuclei were produced with the fusion-evaporation reaction 51 V( 10 B,p2n) at 33 MeV bombarding energy, with the 8MV Pelletron accelerator of the University of São Paulo (USP). The target consisted of a stack of 3 self-supporting natural 51 V foils of 200 µg/cm 2 . Gamma-gamma-charged particle coincidences were measured with the Saci-Pererê γ-ray spectrometer. Saci [9] (Sistema Ancilar de Cintiladores) is a 4 π-charged particle system consisting of 11 plastic phoswich scintillator E-E telescopes. Pererê Gamma-ray spectrum from the 10 B on 51 V (E=33MeV) gated on the 321keV low-lying transition of the 58 Co nucleus, and on protons detected by the SACI array. These gamma-rays were assigned to the 58 Co nucleus.Canberra REGe of 60% efficiency). Two of these detectors were placed at 37 o and the other two at 101 o with respect to the beam direction. Events were collected when at least two HPGe detectors fi...

Propriedades Eletromagnéticas de Estados Nucleares

“…Serão apresentados e discutidos os estudos realizados em núcleos par-par e ímpar-ímpar, com ênfase na estrutura de núcleos da região de massa A=50, interpretadas com base no Modelo de Camadas de Larga Escala. Esse texto é baseado principalmente nas referências [11,13,16,18,17,20,21,22,23,24,25,26 [12,14,15,19,27,28,29,30,31,32,33] …”

“…Serão apresentados e discutidos os estudos realizados em núcleos par-par e ímpar-ímpar, com ênfase na estrutura de núcleos da região de massa A=50, interpretadas com base no Modelo de Camadas de Larga Escala. Esse texto é baseado principalmente nas referências [11,13,16,18,17,20,21,22,23,24,25,26 [12,14,15,19,27,28,29,30,31,32,33] onde T i é o operador energia cinética do i-ésimo núcleon e V ij é a interação entre o par ij.As auto-funções desta hamiltoniana são descritas como um produto de funções de onda para cada uma das partículas. Porém, como os núcleons são férmions, o princípio de exclusão de Pauli implica que a função de onda de cada estado deve ser antissimétrica.…”