One-nucleon knockout reactions at intermediate and high energies in inverse kinematics have proven to be a powerful tool for probing the single-particle structure of rare isotopes away from the valley of β stability. The spectroscopic factors and orbital angular momenta of the removed nucleons can be deduced by comparison of the experimental cross sections and longitudinal-momentum distributions to those calculated in the eikonal reaction theory. In one-nucleon knockout experiments on near-drip-line nuclei, the ratio of the experimental and theoretical cross sections is found to be as small as 0.24 for the knockout of strongly bound valence nucleons at intermediate incident energies below 100 MeV/n. The origin of such a small ratio is still not well understood. Both the nuclear structure model and the reaction theory have been questioned. 

Researchers at the Institute of Modern Physics, Chinese Academy of Sciences have investigated the knockout reactions from ¹⁴O at around 300 MeV/n at the Heavy Ion Research Facility in Lanzhou and obtained some interesting results. 

In this work, the measured cross section of ¹²N was 30(6) mb. Such a large cross section is expected to receive a contribution from an indirect process, namely, one-neutron knockout followed by proton emission. If this was the case, the missing one-neutron knockout strength from ¹⁴O could be found in the unbound ¹³O, and the eikonal reaction model then might be not valid for the cases of knockout of strongly bound valence nucleons. 

The results have been published in Physical Review C 90, 037601 (2014). 

The article can be linked as follows: http://link.aps.org/doi/10.1103/PhysRevC.90.037601 

The particle identification spectrum of the cocktail beams