Neutron spectroscopic factors of Nickel-56 via Nickel(p,d)-56 Nickel-55 reaction in inverse kinematics

Transfer reactions have been the classic tool for studying the angular distributions, the excitation energies, and the spectroscopic factors of possible single-particles states. With the advent of radioactive beams, there has been a renewed effort to utilize these beams in transfer reactions in inverse kinematics. The exact shell structure of the unstable doubly magic nucleus 56Ni has attracted a lot of interest recently. To test if 56Ni has a closed f7/2 orbital, we have carried out the 56Ni(p,d)55Ni transfer reaction measurement with the radioactive 56Ni beam in inverse kinematics for the first time at the NSCL using the HiRA array and S800 spectrograph. The spectroscopic factor predicted by the independent particle model is 8, shell-model calculations give value of 6.8. We have extracted spectroscopic factors of the 56Ni(p,d)55Ni reaction, for the ground and two excited states of 55Ni. The neutron SF value of 7 for the 56Ni(p,d)55Ni ground state agrees with shell-model calculations supports the view that 56Ni is a closed shell nucleus. This result supports the use of 56Ni as a core in shell-model calculations. Another important goal was to study the structure of 55Ni by determining the spin and parities of excited states. We have assigned an ℓ value of 1 to first excited state of 55Ni for 2.089 MeV state of 55Ni. We have extracted a spectroscopic factor of 0.14 for this state. This serves as a second test of the shell model, and the results agree with the shell model calculations. We have confirmed the tentative ℓ = 0 assumption for 3.185 MeV state. A neutron spectroscopic factor of 1.2 was obtained for this state.