Resonant two proton decay from 14 O using a radioactive beam

Abstract

Two experiments were carried out to search for and identify the mechanism for two proton emission from the 7.77 MeV excited state in 14 O. The experiments were performed at the Radioactive Ion Beams Facility at Louvain­la­Neuve, in Belgium, using a 45 MeV beam of radioactive 13 N 3+ ions on a [CH 2 ] n target to populate the state. The protons and other particles were detected using the Louvain­Edinburgh Detector Array, LEDA, a large area annular silicon strip detector. Control experiments with a 12 C target and with a degraded beam energy were also made. Proton­proton coincidence measurements made in the commissioning run iden­ tified a two proton decay component. However, the large background (~90%) caused by evaporation protons from the fusion of 13 N with 12 C prevented an analysis of the decay mechanism. The follow up experiment utilised two LEDA detectors whereby the protons of interest would be stopped in the front detector with the back detector acting as a veto for high energy protons. Comparison of data with simulations for the decay mechanisms revealed the decay to be dominantly a sequential emission of two protons via the 2.37 MeV state in 13 N to the ground state in 12 C. This decay mode has a measured partial width of 125\Sigma20 eV which represents a 0.16% branching ratio. Theoretical predictions for this value give a width of 3 \Sigma 1 keV which gives a spectroscopic factor of ` 2 = 0:04. Simulations using a model for 2 He or diproton emission have resulted in an upper limit of 5% being set which corresponds to ~6 eV (95% confidence limit). Calculation for this width with a spectroscopic factor of unity give a value of 15\Sigma5 eV. Hence an upper limit for the spectroscopic factor of theta2 = 0:4 can be set which is above the value of 0.22 predicted by B.A. Brown.