BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Shedding new light on the structure of $^{56}$Ni using (n\,3n) rea ction at NFS DTSTART;VALUE=DATE-TIME:20240530T103000Z DTEND;VALUE=DATE-TIME:20240530T105000Z DTSTAMP;VALUE=DATE-TIME:20260611T094624Z UID:indico-contribution-23096@indico.ific.uv.es DESCRIPTION:Speakers: Hemantika Sengar (GANIL)\nSystematic studies of nucl ear reactions are essential to the development of nuclear physics.\nUnders tanding and predicting the evolution of nuclear structure and the novel ph enomena in atomic nuclei has long been a pursuit of scientific curiosity. \nConventional methods such as charged particle probes\, $\\beta$-decay\, Coulombic-excitation\, and heavy-ion fusion evaporation reactions have bee n employed so far in the phase space of Shell structure\, magic numbers\, angular momentum\, and excitation energy. However\, the horizon of possibi lities expands when we delve into the uncharted territories of fast-neutro n probes. The (n\,xn) reactions are a long-standing reaction mechanism use d in the cross-section data evaluation\, but rarely used in the framework of nuclear structure.\nThis might unveil a treasure trove of reactions\, p articularly the (n\,xn) reactions with high production thresholds\, which\ , until now\, have not been looked at from the eye of nuclear structures.\ nAs a result\, we know very little about their reaction mechanisms.\n\n\nW hile the structure of $^{56}$Ni has been previously investigated using cha rged particle and heavy ions collisions as shown in Fig.1. ![Yrast Diagram ][1]\, a pure neutron probe was never used.\nFor the first time\, using t he unprecedented neutron flux at $\\sim$20 - 40 MeV at the Neutrons for Sc ience (NFS) facility of GANIL--Spiral2\, $^{56}$Ni can be populated from $ ^{58}$Ni in a (n\,3n) reaction which has a cross-section of 2 mb at $\\sim $30 MeV\, opening a new probe and possibly new aspects of the nuclear stru cture of this doubly magic nucleus.\nThe TALYS cross-section calculation a s a function of incident neutron energy is shown in Fig.2. ![^{56}Ni cross -section][2].\nThe maximum cross-section is predicted to be at 40 MeV\, sl ightly higher than the end-point of NFS.\np + Li / Be allows reaching the [20-30] MeV range\, whereas d + Be allows up to a broader [25-40] MeV rang e.\nWith $^{58}$Ni target\, studying pure neutron channels is the main int erest alongside Co isotopes that are produced from (n\,p/d/t) reaction. \n \nThe nuclei near $^{56}$Ni are of particular interest as they are amenabl e to different microscopic theoretical treatments while studying the compe tition between single-particle and collective excitations. The collective states in $^{56}$Ni involve multiparticle multi-hole excitations across th e $N=Z=28$ shell gap from the 1f$_{7/2}$ shell to the 2p$_{3/2}$\, 1f$_{5/ 2}$\, and 2p$_{1/2}$ orbits. Excitation to the higher lying 1g$_{9/2}$ orb it are necessary to explain the observed rotational bands in Cu and Zn. At high excitation energies\, reaction studies have revealed evidence for hy per-deformed resonances in the $^{56}$Ni compound. \n\n\nIn this project\, we performed prompt-$\\gamma$ spectroscopy of $^{56}$Ni using the EXOGAM array at NFS.\nFrom nuclear structure's point of view\, the main motivatio n is the search for low spin (J=2 or 4) states from 3 to 10 MeV excitation energy possibly populating the $0^{+}$ states at 3956 keV\, 6654 keV and 7903 keV observed only in $^{58}$Ni(p\,t)$^{56}$Ni and $^{58}$Ni($^{3}$He\ ,n)$^{56}$Ni reactions. New spectroscopic information that will be collect ed is also relevant for nuclear reaction mechanism formalism (like TALYS) and nuclear data evaluation libraries.\n\n\n\nThe experiment was carried o ut in October 2023. During an effective beam time of ~11 days\, a high ene rgy neutron beam produced by a primary beam of 10 $\\mu$Amps of $^{2}$H\, bombarded a 1mm thick Ni target.\nThe prompt gamma rays selected on the fa stest neutron using the Time of Flight information have been detected by 1 2 EXOGAM clovers placed at 15 cm off the beam axis. \nAbout $1.6 \\times 1 0^{10}$ $\\gamma\\gamma$ coincidences have been sorted after the AddBack p rocedure.\nThe $^{56}$Ni decay was observed and a large number of $\\gamma \\gamma$ coincidences for $^{57}$Ni and Co isotopes were sorted.\nThe very preliminary analysis of the experiment\, focusing mainly on the pure neut ron channels\, will be presented.\nThe (n\,2n) channel that produces $^{57 }$Ni has a much larger cross-section\, reaching a maximum of $\\sim$90 mb at around 23 MeV\, making it easier to study. Additionally\, $^{57}$Ni is only one neutron away from the doubly magic $^{56}$Ni\, making spectroscop y of single particle\, core-coupled\, and collective states of great inter est. The primary focus of the talk will be to provide a comprehensive desc ription of its level scheme and excitation functions. This isotope has a h alf-life of 35.6 hours and undergoes $\\beta^{+}$ decay to produce $^{57}$ Co in the system\, which interestingly is also populated by the (n\,d) and (n\,n$'$p) channels. \nThe question of whether large germanium volume det ectors can be used for $\\gamma$ spectroscopy in a high flux high neutron energy environment will also be addressed.\n\nThis experiment is a pioneer ing work in the study of the nuclear structure studies using large gamma a rray and fast neutron and is only possible at GANIL-Spiral2 as of today.\n If successful\, this program will open a new door for nuclear structure st udies.\n\n\n [1]: https://gitlab.com/H_sen1122/open_gaca/-/raw/main/Yrast _dobara.png?ref_type=heads\n [2]: https://gitlab.com/H_sen1122/open_gaca/ -/raw/main/Ni58to56cs.png?ref_type=heads\n\nhttps://indico.ific.uv.es/even t/7332/contributions/23096/ LOCATION:ADEIT - Valencia URL:https://indico.ific.uv.es/event/7332/contributions/23096/ END:VEVENT END:VCALENDAR