Small spectroscopic factors of low-lying positive parity states in 31Mg

The single particle structures of even-odd nuclei around the so-called ``island of inversion'' would give us the direct evidence of such a shell evolution in this region. We measured the proton resonance elastic scattering on $^{30}$Mg re-accelerated upto 2.92 MeV/nucleon by REX-ISOLDE to study the isobarig analog resonances (IARs) of the low-lying bound states in $^{31}$Mg. The proton resonance elastic scattering is a complementary method of (d,p) reaction. We observed three resonances which can be regarded as the IARs of $^{31}$Mg. The proton widths of the first two resonances give a rise to the spectroscopic factors for the two positive parity states in $^{31}$Mg which were found to be strongly quenched compared to those for the $^{35}$S and $^{37}$Ar. Comparison with a modern shell model calculation suggests that the degrees of the $\nu$(2p-2h) configuration in $^{30}$Mg would be less than considered [1].\\[4pt] [1] N. Imai, {\it et al.}, Phys. Rev. C, in press.