Speaker
Description
Transfer reactions have been proven to be a powerful tool to understand nuclear structure. Two different physical aspects are being investigated with the use of transfer reactions on $^{56}Ni$, which is a $N=Z$ unstable doubly magic nucleus.
$i)$ To probe the gap of $N=28$, we study the spectroscopy of the $N=29$ and $N=27$ isotones by the $(d,t)$, $(p,d)$ and $(d,p)$ one nucleon transfer reactions on $^{56}Ni$ ($N=28$ isotone) and extract information on the single-particle configuration around the Fermi surface.
$ii)$ To study the $np$ pairing in the self-conjugate nucleus $^{56}Ni$, we have measured the two-nucleon transfer reactions $^{56}Ni(p,^3He)^{54}Co$ and $^{56}Ni(d,α)^{54}Co$. In the $(p,^3He)$ reaction, the ratio of the population of the $T=0$ and $T=1$ states indicates a predominance of $T=1$ pairing. The selectivity of the $(d,α)$ reaction enables the investigation of the $T=0$ channel with better precision.
During spring 2014 the experiment aiming to these studies took place at GANIL-Caen, France. The radioactive beam of $^{56}Ni$ at $30MeV/u$ was produced by fragmentation of $^{58}Ni$ and purification. Measurements were performed in inverse kinematics on CH$_2$ and CD$_2$ targets. The experiment included a 4π coverage for the study of the charged projectiles with the MUST2 and TIARA detectors, while 4 clovers of EXOGAM were also used for γ-particle coincidences in order to identify the populated state of the residue. The analysis of the $^{56}Ni(d,t)^{55}Ni$ and $^{56}Ni(d,p)^{57}Ni$ reactions yield the differential cross-section for transfer reaction to the ground state and the excited states of 55Ni and $^{57}Ni$ giving information about the shell closure and depicting the Fermi surface of $^{56}Ni$. I will present the angular distribution and compare with the results for the $(p,dγ)$, $(d,tγ)$ and $(d,pγ)$ reactions, as well as with DWBA calculations. The results for the transfer reaction $^{56}Ni(d,α)^{54}Co$ will be also presented, completing the information about the strength of the isoscalar $np$ pairing in the closure of the $fp$ shell.
