Invariant-mass spectroscopy of O14 excited states

Abstract

Excited states in 14 O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast 15 O beam and the invariant-mass technique was employed to isolate the 1p and 2p decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2 + state that we find is in near degeneracy with the third 0 + state. An interesting case of sequential 2p decay through a pair of degenerate 13 N excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons.

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.…”

Reanalysis of $^{13}$N($p,γ$)$^{14}$O reaction and its role in stellar CNO cycle

“…It is done primarily due to a fact that carbon component burns out in a series of processes known as hot CNO cycle (HCNO-I), which occurs at temperatures starting from 0.2 T 9 [1]. The synthesized isotope 14 O is considered as a waiting point, which is overcome by a chain of reactions, starting with 14 O(α, p) 17 F when temperature is above 0.4 T 9 . The review [1] presents the comprehensive and consistent illustrations of CNO and HCNO-I cycle chains, as well as evolution of CNO isotope abundance with time for different density and temperature conditions, the calculations of which are directly based on the reaction rates.…”

“…The pioneering measurement with a rare-isotope beam was the first direct determination of the 13 N(p, γ) 14 O reaction cross section using a radioactive 13 N beam [6][7][8]. In the reaction 13 N(p, γ) 14 O the s−wave capture on the broad 1 − resonance dominates the reaction rate and over three decades many efforts have been made to determine the parameters for the resonance using different experimental approaches: transfer reactions [7,[9][10][11], Coulomb dissociation of high energy 14 O beam in the field of a heavy nucleus [12][13][14], a rare-isotope beam [6][7][8], using the unstable ion beam by indirect measurements [15,16], and, the most recently, via neutron-knockout reactions with a fast 15 O beam [17]. Ref.…”

“…Therefore, it is relevant to consider these data for analysis of the 13 N(p, γ) 14 O reaction. Moreover, another incentive for these calculations is the data from the latest experimental research [17] that will be also brought to our discussion.…”

“…Calculations of the rate for the 13 N(p, γ) 14 O reaction and the astrophysical S-factor were performed within potential models using a shell-model, cluster model and R-matrix approaches [19][20][21][22][23]. There are significant differences between the various calculations of the 13 N(p, γ) 14 O reaction as well as in the light of a new experimental study [17], an independent and well established approach is greatly needed to analyze this process. Continuing our studies of the processes of radiative capture on light atomic nuclei (see Refs.…”