Ne

The location of the neutron drip line is one of the important questions in nuclear physics, since it has been established only up to Z=8. One of the puzzles relevant to this issue is oxygen anomaly, where there is a sudden gap of the location of the drip line from oxygen (24O) to fluorine (31F or heavier isotopes). In order to determine the location of the drip line, it is important to understand the nuclear force for extremely neutron rich nuclei near and beyond the drip line. In this talk, we will show the recent experimental study of 28F produced by the (n,p) type charge-exchange reaction of 28Ne. 28F is considered to be a key nucleus to pin down the nucleon-nucleon force near the drip line, since 28F may have a structure made by one proton-one neutron hole upon the possible doubly magic nucleus 28O. In this experiment, the invariant mass spectroscopy of 28F was performed using the charge exchange reaction of 28Ne with a carbon target at 230MeV/nucleon at RIBF, RIKEN. Decay products, 27F and a neutron, were detected in coincidence by the SAMURAI spectrometer. In the presentation, we will report on the preliminary results.