Invariant-mass spectroscopy of Ne18, O16 , and C

Abstract

Neutron transfer reactions with fast secondary beams of 17 Ne, 15 O, and 9 C have been studied with the HiRA and CAESAR arrays. Excited states of 18 Ne, 16 O, and 10 C in the continuum have been identified using invariant-mass spectroscopy. The best experimental resolution of these states is achieved by selecting events where the decay fragments are emitted transverse to the beam direction. We have confirmed a number of spin assignments made in previous works for the negative-parity states of 18 Ne. In addition we have found new higher-lying excited states in 16 O and 18 Ne, some of which fission into two ground-state 8 Be fragments. Finally for 10 C, a new excited state was observed. These transfer reactions were found to leave the remnant of the 9 Be target nuclei at very high excitation energies and maybe associated with the pickup of a deeply-bound 9 Be neutron.

Invariant-mass spectroscopy of O14 excited states

“…As we are only interested in relative yields, the uncertainties in the cross sections quoted in this work are statistical only. However, based on past experience [12] we expect an overall ±15% systematic uncertainty.…”

“…In this experiment, the array consisted of fourteen E-∆E telescopes which were arranged around the beam axis and subtended polar angles from 2 • to 13.9 • . 13 N and 12 C fragments were only identified in the inner two telescopes where their yield was greatest.…”

“…For this experiment, the array consisted of 158 CsI(Na) crystals covering polar angles between 57.5 • and 142.4 • in the laboratory, with complete azimuthal coverage. The only use of this array in this study was to verify that the invariant-mass peaks obtained with the detected 2p+ 12 C channel involved decays to the ground state of 12 C rather than the γ-decaying first-excited state.…”

Using spin alignment of inelastically-excited fast beams to make spin assignments: the spectroscopy of 13O as a test case

“…The best invariant-mass resolution is obtained by only including events that decayed transversely, i.e. the heavy core fragment is emitted transversely to the beam axis from the moving parent 13 O * fragment [22,23]. The transverse gate used to produce these spectra is |cos θ C | < 0.2 where θ C is the emission angle of the core from the beam axis in the parent's center-of-mass frame.…”

“…The spins of the 12 remained in its ground state. These distributions have been corrected for the detection efficiency determined with Monte Carlo simulations [22]. Forward emission parallel to the beam axis corresponds to θ p =0 • .…”