Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure
Authors: LAOUET Nadjet , BENRACHI Fatima , GUERRAICHE Habiba , BENHIZIA Karima 
Published: December 2019

Bitlis Eren Universıty  Journal of scıence and technology 00 (2013) 000–000                                              Available online at www.dergipark.ulakbim.gov.tr/beuscitech/   Journal of Science and Technology                                                                   E-ISSN 2146-7706                                                                                                     ﻿Study of the shell evolution effect on the nuclei structure around the 78Ni core    Nadjet Laouet * , Fatima Benrachi, Habiba Guerraiche, Karima Benhizia LPMPS Laboratory, Frères Mentouri Constantine-1, 25107,Constantine AlgeriaA R T I C L E  I N F O Article history: Received 00 December 0000 Received in revised form 00 January 0000 Accepted 00 February 0000   Keywords: Nuclear shell modelDoubly magic core 78NiMonopole interactionNuclear structure propertiesNuShellX@MSU code   A B S T R A C T The interactions between the core which is anymore inert and the valence nucleons play a very important role in the interpretation of nuclear properties far from stability. The work done in this study is based on the calculations of energy spectra and electromagnetic properties for even-even isotones with N=52, in the 78Ni region. Based on the interaction jj45apn with the space model jj45pn, we have realized some modifications considering the monopole interaction and a new interaction called jj45am is introduced. The calculations are performed in the framework of the nuclear shell model using the NuShellX@MSU code. The shell evolution, studied by estimating the effective single particle energies in this region, show an important influence on the nuclear structure properties. The obtained results using the new interaction jj45am are in good agreement with the experimental data, and better than those given by the original one jj45apn.    © 2017. Turkish Journal Park Academic. All rights reserved.  1. Introduction Nuclei close to doubly magic cores that are in the limit of the nuclear chart are good candidate to test new theoretical predictions in order to explain the experimental observations in such systems. Experimental studies and spectroscopic calculations, in these regions, can prove and expect new phenomena as the disappearance of some habitual magic numbers and the appearance of new ones (Dobaczewski et al., 1994; Otsuka et al., 2005). These observations may result from the so-called shell evolution. 78Ni is one of the best exotic doubly magic cores, which is considered as the closest core to the neutron drip-line. This region offers best opportunity to develop a comprehensive understanding of shell evolution. In this context, we have studied N=52 isotones, which cover a large range from the neutron drip line to the neutron one near 78Ni core. Indeed, there are few experimental data in the considered mass region. 78Ni is an exotic nucleus that situated in the limit of nuclear chart and it is very difficult to study experimentally. The two neutrons in N=52 isotones are situated on d5/2 shell for low excitation energies. For high ones, one or two neutron can move to other orbits. These isotones have been studied by (Czerwinski et al., 2013). In their work, the 86Se and 88Kr nuclei have been investigated following, respectively, spontaneous fissions of 248Cm and 252Cf by means of prompt-g -ray-spectroscopy methods using the Gamma sphere Ge array (Czerwinski et al., 2013). In addition, they have predicted the Energies of the first 2+ and 4+ levels in the 82Zn nucleus using systematics shown in Figure 1, that presents the calculated excitation systematics in comparison with the available experimental data (see (Czerwinski et al., 2013) for more details).                                                                                                                Figure 1. Calculated excitation systematic in comparison with the available experimental data (Czerwinski et al., 2013).2. Theoretical framework One of the most important phenomena used to study such nuclear systems is the monopole effect; which has been focused on after the discovering of new nuclei more and more exotic and the appearance of unexpected observation as the appearance of new magic numbers, as a result of shell evolution (Cortes and Zuker, 1979; Sorlin and Porquet, 2008). This effect comes from the interactions between the core and the valence nucleons (Otsuka et al., 2010; Smirnova et al., 2010). In this approximation, a nuclear system can be presented in terms of a monopole and a multipole Hamiltonians.                                                           (1)  The monopole part is expressed as a function of single particle energies es, occupation nst, isospin Tst operators, and Vj which presents an energy average over the spin J (Poves and Zuker, 1981; Otsuka et al.,2010):  ﻿                                                             (2)  ﻿ The TBMEs of the using interaction are modified taking in consideration the proton-proton, neutron-neutron and proton-neutron monopole effects for even-even nuclei in the 78Ni region and a new interaction is introduced. 3. Results and discussions For our calculations, we have used jj45pn as a single particle state (SPS). The single particle energies (SPE) were taken from the experimental data and from Grawe et al., for some shells (Grawe et al., 2007; nndc.bnl.gov, 2019). The used interaction is obtained starting from jj45apn original one, based on the G matrix for 132Sn region (Jensen et al., 1995; Rejmund et al., 2016), considering the monopole effect. One of the well-known codes, the NuShellX@MSU is used to carry out the spectroscopic calculations achieved in this work. It presents a development of NuShellX code; which contains a set of computed codes written by Rae (Brown and Rae, 2014). The calculation results in comparison with the experimental data are reported in Figure 2. Figure 2. Calculated energetic spectra using jj45apn and jj45am interactions in comparison with the available experimental data (nndc.bnl.gov, 2019). These spectra are used to plot the energetic systematics for N=52 isotones with Z=30-50. The results are shown in Figure 3:Figure 3. Calculated systematics by means of  jj45am (right) in comparison with the experimental ones (left), in N=52 isotones. For the experimental energies (left), the spectra show a peak for Z=38 isotope. The peak is clear for 4+, 6+ and 8+ states. The available data for 2+ and 4+ states show also a peak for Z=50. These two peaks are clear in the calculated systematics (right). The peaks is clear for all excited states. The explanation of the Z=50 peak is clear as this charge number is a habitual magic number. The other peak in Z=38 is a sign of a possible new magic number which can be a result of shell evolution in 78Ni. 4. Conclusions This work is based on the energetic spectra calculations, for even-even N=52 isotones, with two neutrons and few protons in their valence spaces. The calculations are realized in the framework of the nuclear shell model, by means of NuShellX@MSU nuclear structure code. Using the jj45apn original interaction of the code, we carried out some modifications based on the monopole interaction to get jj45am one. Most of the calculated spins and parities of the studied nuclei are in agreement with the experimental ones. The excited states calculated using the elaborated interaction jj45am are close to the available experimental data, in comparison with those calculated using the original interaction without monopole terms, which are underestimated in this case. The calculated results give a prove of the magic nature of the number Z=38. This may give an important indication of the monopole interaction consideration role on the explanation of spectroscopic properties.  Acknowledgements Authors of this article thanks to the organizers of the “XII. International Conference on Nuclear Structure Properties NSP 2019, October 11th-13th 2019, Bitlis-Turkey’, for the organization and the support provided during the conference. Special thanks are owed to B. A. 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