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 e²fm⁴ and B(E2,1/2^-→5/2^-)=124(18)e²fm⁴ 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.