Determination of $1p$ and $2p$ stripping excitation functions for $^{16}$O+$^{142}$Ce using a Recoil Mass Spectrometer

Abstract

We report the first direct measurement of differential transfer cross sections using a Recoil Mass Spectrometer. Absolute differential 1p and 2p-stripping cross sections at θ c.m. = 180 • have been determined for the system 16 O+ 142 Ce by detecting the heavier target-like ions at the focal plane of the Heavy Ion Reaction Analyzer. Focal plane spectra have been compared with the results of a semi-microscopic Monte-Carlo simulation to unambiguously identify the transfer channels. Transmission efficiency of the target-like ions through the spectrometer has also been estimated using the simulation which has been crucial to extract the cross sections from the yields of ions measured during the experiment. The methodology adopted in this work can be applied to measure multi-nucleon transfer cross sections using other similar recoil separators. The experimental excitation functions for the reactions 142 Ce( 16O, 15 N) 143 Pr and 142 Ce( 16 O, 14 C) 144 Nd have been compared with coupled reaction channel calculations. An excellent matching between measurement and theory has been obtained. For 1p-stripping, major contribution to the cross section has been found to be the transfer of a proton from 16 O to the 2d 5 2 excited state of 143 Pr, leaving behind 15 N in the 1p 1 2 ground state. Transfer of a cluster of two protons from 16 O to the 2 + excited state of 144 Nd, resulting in 14 C in the 0 + ground state, appears to be the most probable cause for 2p-stripping. Measured transfer probabilities for 1p and 2p channels have been compared with Time-Dependent Hartree-Fock calculations. Proton stripping channels are found to be more favourable compared to neutron pick-up channels. However, the theory overpredicts the measurement hinting at the need for extended approaches with explicit treatment of pairing correlations in the calculations.