Evidence for the existence of the astrophysically important 6.40-MeV state of 31S

Proton-unbound excited states of 31S have been populated with the 32S(d,t)31S reaction at a beam energy of 24 MeV. Tritons corresponding to 31S states with Ex(31S)≈6.3–7.1 MeV were momentum analyzed with a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph at six angles ranging from θlab=15∘ to 58.5∘. We report a statistically significant detection of an astrophysically important state at Ex(31S)=6402 (2) keV, whose existence as a third state in this region has been under debate. Using updated A=31 nuclear structure information, we present a new set of proposed 31S-31P mirror assignments for 31S, in which this state is tentatively assigned a spin of 7/2. This level, corresponding to a 30P + p resonance at 271 keV, is likely to have a significant influence on the 30P(p,γ)31S reaction rate in explosive hydrogen burning in classical novae.