β-delayed α spectrum of 16N and the 12C(α,γ)16O cross section at low energies

The α spectrum following the β decay of 16N from the isotope separator TISOL has been measured by detecting 106 α particles in coincidence with 12C nuclei. These data, which show a low-energy interference anomaly accompanying the main α peak, permit a more precise determination of the p-wave amplitude of the astrophysically important reaction 12C(α,γ)16O. The α spectrum and previous γ-ray data have been fitted simultaneously by a K-matrix parametrization; a value of S(E=0.3 MeV)=57±13 keV b has been obtained for the E1 part of the 12C(α,γ)16O reaction

Constraints on the low-energy E1 cross section of 12C(α,γ)16O from the β-delayed α spectrum of 16N

The shape of the low-energy part of the β-delayed α-particle spectrum of 16N is very sensitive to the α+12C reduced width of the 7.117 MeV subthreshold state of 16O. This state, in turn, dominates the low-energy p-wave capture amplitude of the astrophysically important 12C(α,γ)16O reaction. The α spectrum following the decay of 16N has been measured by producing a low-energy 16N14N+ beam with the TRIUMF isotope separator TISOL, stopping the molecular ions in a foil, and counting the α particles and 12C recoil nuclei in coincidence, in thin surface-barrier detectors. In addition to obtaining the α spectrum, this procedure determines the complete detector response including the low-energy tail. The spectrum, which contains more than 106 events, has been fitted by R- and K-matrix parametrizations which include the measured 12C(α,γ)16O cross section and the measured α+12C elastic scattering phase shifts. The model space appropriate for these parametrizations has been investigated. For SE1(300), the E1 part of the astrophysical S factor for the 12C(α,γ)16O reaction at Ec.m.=300 keV, values of 79±21 and 82±26 keV b have been derived from the R- and K-matrix fits, respectively

A study of beta delayed alpha emission from ^(16)N

The low energy part of the beta delayed, alpha spectrum of ^(16)N can be used to determine the p-wave capture amplitude of the astrophysically important reaction ^(12)C(α ;y)^(16)O. Experimental details of a measurement of the emitted a spectrum in coincidence with the ^(12)C recoil nuclei, performed at the TRIUMF isotope separator, TISOL is presented

The β-Delayed α-Particle Spectrum of ^(16)N and the ^(12)C(α,y)^(16)O Cross Section at Low Energies

We have measured the ɑ-particle spectrum from the decay of ^(16)N by selecting a low-energy ^(16)N beam with the TRIUMF isotope separator, TISOL, stopping the ^(16)N nuclei in a foil, and counting the α, particles and ^(12)C recoil nuclei, in coincidence, in thin surface-barrier detectors. The spectrum has been fitted by R- and K-matrix parametrizations which include the measured ^(12)C(α, y)^(16)O and ^(12)C(α,y)^(12)C cross sections. Best fit values for S_(E1)(0.3) have been derived for the El part of the ^(12)C(α,y)^(16)O reaction. These are S_(E1)(0.3)=75±20 keV·barn and S_(E1)(0.3)=62±15 keV·barn for the R- and K-matrix parametrizations, respectively

The β-delayed α spectrum of ^(16)N and the low-energy extrapolation of the ^(12)C(α, γ)^(16)O cross section

The low-energy part of the βα-decay spectrum of ^(16)N permits the determination of the reduced α-width θ^2_ɑ of the 7.12 MeV subthreshold state of ^(16)O, which dominates the low-energy p-wave capture amplitude of the astrophysically important reaction ^(12)C(α, γ)^(16)O. In a first run, a total of 7.1 x 10^3 a particles from the decay of ^(16)N nuclei, selected by the TRIUMF isotope separator TISOL, have been observed in a 10.6 μm detector in coincidence with the recoiling ^(12)C nuclei in a second detector, thus removing most sources of low-energy a background. These new data show a narrower width for the main a peak than previously determined. In addition, there is an indication of the low-energy interference anomaly predicted by several authors. The spectrum obtained can be parametrized in K- and R-matrix calculations, which also include the previously-measured ^(12)C(α, γ)^(16)O cross sections and elastic scattering phase shifts. Results of a data collection run in June with much higher α yields will be presented

The β-delayed ɑ spectrum of ^(16)N and the low-energy extrapolation of the ^(12)C(ɑ,y)^(16)O cross section

The low-energy part of the βɑ-decay spectrum of ^(16)N permits the determination of the reduced ɑ-width θ_ɑ^2 of the 7.12 MeV subthreshold state of ^(16)O, which dominates the low-energy p-wave capture amplitude of the astrophysically important reaction ^(12)C(ɑ, y)^(16)O. In a first run, a total of 7.1x10^3 α particles from the decay of ^(16)N nuclei, selected by the TRIUMF isotope separator. TISOL, have been observed in a 10.6 µm detector in coincidence with the recoiling ^(12)C nuclei in a second detector, thus removing most sources of low-energy alpha background. These new data show a narrower width for the main ɑ peak than previously determined. In addition, there is an indication of the low-energy interference anomaly predicted by several authors. The spectrum obtained can be parameterized in K- and R-matrix calculations, which also include the previously-measured ^(12)C(ɑ, y)^(16)O cross sections and elastic scattering phase shifts. Results of a data collection run in June with much higher alpha yields will be presented