The115In(γ, γ′) reaction as a test of the quasi-particle phonon model with complex configurations in odd-mass nuclei

Abstract

Abstract. The 115In(~;, ~/') reaction was measured at the S-DALINAC using bremsstrahlung with endpoint energies Eo= 3.1, 4.6 and 5.2 MeV. In the excitation energy range of 1-5 MeV in total 32 transitions were observed, 18 of which were hitherto| unknown. The results are compared to two quasiparticle-phonon model calculations, one with a model space of'quasiparticle | and one extended by 'quasiparticle| configurations. A substantial improvement is achieved in the description of low-lying ~SIn states by the consideration of the more complex configurations. The calculations quantitatively account for the summed l~SIn(~, 7') integrated cross sections and show a comparable amount of fragmentation of the individual transition strengths. The model interpretation of the microscopic structure of the experimentally observed transitions is discussed.

Population of isomers in the decay of the giant dipole resonance

“…Recently, essential progress in isomer photoexcitation has been achieved by using bremsstrahlung radiation at low values of an end-point energy [6][7][8][9]. The isomer yield in spherical nuclei as a function of the end-point energy was found to have a linear dependence in the energy interval of about one MeV, the line then breaks, and another linear dependence for one MeV takes place.…”

“…The application of the model in the case of isomeric states is described in detail in Refs. [6][7][8][9]. This model makes use of a separable form of the residual interaction which enables the diagonalization of the model Hamiltonian in a large dimensional configuration space.…”

“…This effect received its theoretical interpretation as follows: A level or a group of closely lying levels with very specific properties are located at the line break. The wave function of these excited states includes configurations which allow their intensive excitation from the ground state while some other configurations are responsible for a cascade decay from these levels at intermediate energies which lead to the isomeric state [6][7][8][9]. Usually the maximum value of the end-point energy in these bremsstrahlung experiments is 4-4.5 MeV.…”

“…For this reason, a microscopic calculation should be applied to explain the A-dependence of the isomer yield which is experimentally observed. For that purpose, we employ the Quasiparticle Phonon Model (QPM) which has already been successfully applied to the interpretation of the isomer population from the intermediate states at lower energies [6][7][8][9].…”

“…Considerable interest in the structure of the states at intermediate excitation energy in atomic nuclei has arisen recently [1][2][3][4][5][6][7][8][9][10]. The states are excited via different nuclear reactions and the deexcitation populates the low-lying excited states that have a simple structure [1].…”