Resonance strengths in the 14N(p,gamma)15O astrophysical key reaction measured with activation

Abstract

The 14N(p,gamma)15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p,gamma)15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p,gamma)15O reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam gamma-spectroscopy and are free from some of their systematic uncertainties. Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced 15O isotopes was measured by detecting the 511 keV positron annihilation gamma-rays. The strength of the Ep = 278 keV resonance was measured to be 13.4 +- 0.8 meV while for the Ep = 1058 keV resonance the strength is 442 +- 27 meV. The obtained Ep = 278 keV resonance strength is in fair agreement with the values recommended by two recent works. On the other hand, the Ep = 1058 keV resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the 14N(p,gamma)15O reaction and therefore the astrophysical consequences are not changed by the present results.