Influence of neutron surface onE1 resonance properties

Abstract

Abstract. The E1 strength distributions in even-even Si isotopes were calculated in the "particle-core coupling" version of the shell model taking into account the fragmentation of the hole configuration among the states of the daughter nuclei. The comparison of calculated strength distributions in different isotopes of the same element shows the peculiarities of a neutron surface influence on the E1 resonance fragmentation.The problem of theoretical description of the excited states of light nuclei has been discussed for many years. Various model approaches have achieved success in the study of highly excited nuclear states, primarily E1 resonance, as this state is the most studied experimentally [1]. From comparison of the experimental photo-excitation cross sections it is seen that a consistent increase in the number of neutrons in the isotopic chain changes drastically the resonance structure. Especially, these changes are critical in the area of light nuclei A < 50, where the resonance structure is important. Theoretical description of dipole resonances in some even isotopes of Ti and Ca was performed in the previous paper [2]. In this work the structure of excitations of 28 Si and 30 Si isotopes is discussed. Particle-core coupling shell modelThe increasing amount of experimental data on structure of multipole giant resonances (GR) in the cross sections of nuclear reactions has shown that microscopic approach considering only particle-hole configurations cannot reproduce a complicated structure of GR. One of the possible ways to build a set of basic configurations which could be used as doorway states in the microscopic description of nuclear resonances is to take into account the distributions of the "hole" configurations among the states with total momentum J, excitation energy E and isospin T (JET ) A−1 of residual nuclei with mass number (A − 1). In the Particle Core Coupling version of Shell Model (PCC SM) these distributions are taken into account in microscopic description of multipole resonances (MR) [3,4]. Theoretical description of MR in 1p-shell nuclei based on the PCC SM has shown good agreement with experimental data for nuclei 7 ≤ A ≤ 15 [4].The wave functions of excited states of a nucleus in the PCC SM constructed as a product of the wave functions of the final nucleus (A − 1) and the wave functions of the a e-mail: n.g.goncharova@gmail.com nucleon(1) The set of states of the final nucleus in (1) has to include all states with the significant genealogical connection to the ground state of the target nucleusThe way to determine the probabilities of the various core states which appear when one of the nucleons would be extracted from the parent nucleus is to use the experimental data on the spectroscopic factors S i of direct pick-up reactions to estimate the coefficients of fractional parentageMGR probabilities could be calculated via the E1 form factorswhere the excitation matrix element is expressed in terms of matrix elements of one-nucleon transitions

Influence of surface tension on nuclear collective properties

“…The low values of surface tension for 28 Si apparently lead to the deviation of this nucleus from the spherical shape. The effect of this deviation on the structure of E1 resonance was traced in [9].…”