Two-proton spectroscopy of low-lying states in ¹⁷Ne

The decay of the first two excited states of ¹⁷Ne (I^π=3 / 2^-, 5 / 2^-) has been studied via intermediate energy Coulomb excitation of a radioactive ¹⁷Ne beam on a ¹⁹⁷Au target using a particle detector setup allowing a kinematically complete detection of the reaction products. Despite the first excited state being bound to single proton emission but unbound with respect to two proton emission, no evidence for a simultaneous two proton decay competing with the known γ decay of the 3 / 2^- state could be observed. The 5 / 2^- state decays via sequential two-proton emission to the ground state of ¹⁵O. The transition matrix elements B(E2,1 / 2^-→3 / 2^-)=66_-25⁺¹⁸ e² fm⁴ and B(E2,1 / 2^-→5 / 2^-)=124(18)e² fm⁴ have been deduced. From the nonobservation of the simultaneous two-proton emission of the 3 / 2^- state a lifetime limit τ_2p>26 ps could be deduced in agreement with recent theoretical calculations.