Measurement of the $E_r^{\mathrm{c}.\mathrm{m}.}=259$ keV resonance in the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction

The ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction regulates the power generated by the CN cycle and thus impacts the structure and evolution of every star at some point in its life. The lowest positive-energy resonance in this reaction is located at $E_r^{\mathrm{c}.\mathrm{m}.}=259$ keV, too high in energy to strongly influence quiescent stellar burning. However, the strength of this resonance is used as a cross-section normalization for lower-energy measurements of this reaction. We report on new measurements of the energy, strength, and $\gamma$-ray branching ratios for the 259-keV resonance, using different detection and data-analysis schemes. We have also reevaluated previous results, where possible. Our new recommended strength of $\omega \gamma =12.6\left(3\right)$ meV is in agreement with the previous value of 13.1(6) meV, but is more precise and thus provides a more reliable normalization for low-energy $(p,\gamma )$ measurements.

Figure 1

RBS spectra from an implanted target (blue) and a tantalum backing (grey). The simnra [27] fit is shown in red.

Figure 2

Relative concentration of ${}^{14}\mathrm{N}$ in the region of saturation density. Each pair of closely spaced points corresponds to a different target, with two measurements at different locations on the same target. Note that only statistical uncertainties are shown. The average is denoted by the red point and the uncertainty calculated via bootstrapping is indicated by the dashed lines.

Figure 3

Cutaway view of the geant4 geometry used in the Monte Carlo simulation of the APEX detector. The beam enters the target chamber from the right.

Figure 4

Reconstructed positions of 1333-keV $\gamma$ rays from a ${}^{60}\mathrm{Co}$ source after position calibration. The compilation of histograms are for one NaI(Tl) segment as the source was moved in 3.5 cm increments along the length of the detector.

Figure 5

Levels in ${}^{15}\mathrm{O}$ populated in the $\gamma$-ray decay of the 259-keV resonance. Energies (in keV) are from Table 1 and Ref. [17].

Figure 6

Spectrum of the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction taken at $E_p^{\mathrm{lab}}=284$ keV with the HPGe detector. Gamma rays associated with the decay of the 259-keV resonance are labeled in red, background lines are denoted in purple.

Figure 7

The result of the best fit, shown in green, to HPGe data for the 259-keV resonance in the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction, shown in black, as derived using the TFractionFitter [46] class of root [47] as described in the text and in Refs. [48, 49]. Note that the data are not easily distinguished from the fit. Full-energy peaks for primary and secondary transitions are indicated by arrows and the corresponding templates are also shown in light and dark blue. The room-background spectrum is shown in red.

Figure 8

Branching ratios measured using the HPGe detector at distances of 1.62, 6.62, 11.62, and 21.62 cm from the target to the detector crystal. The dashed lines are the weighted averages of the individual measurements for each transition, which are listed in Table 3.

Figure 9

Reconstructed APEX energy spectra of $\gamma$ rays from the decay of the 259-keV resonance with imposed multiplicity-1 and -2 cuts. The ground-state and secondary $\gamma$ rays for transitions to the 5181-, 6172-, and 6792-keV states are indicated as well as their corresponding single-escape peaks.

Figure 10

Maximum-likelihood fit of the multiplicity-1 data collected with the APEX detector. The data are denoted by the black points, the fit by the green line and the individual templates are displayed as the colored histograms.

Figure 11

An example of a yield curve for the 259-keV resonance. The Markov chain Monte Carlo fit is denoted by the red line.

Figure 12

Resonance strengths extracted from independent yield-curve measurements on 23 separate targets (blue points). The red point and dashed lines represent the weighted average of the individual points. Note that only statistical uncertainties are shown.