Measuring the cross section of the ${}^{15}$N($\alpha$,$\gamma$)${}^{19}$F reaction using a single-fluid bubble chamber

Abstract

${}^{15}$N($\alpha$,$\gamma$)${}^{19}$F is believed to be the primary means of stellar nucleosynthesis of fluorine. Here we present the use of a single-fluid bubble chamber to measure the cross section of the time-inverse photo-dissociation reaction. The method benefits from a luminosity increase of several orders of magnitude due to the use of a thicker liquid target -- when compared to thin films or gas targets -- and from the reciprocity theorem. We discuss the results of an experiment at the Thomas Jefferson National Accelerator Facility, where the cross section of the photodisintegration process ${}^{19}$F($\gamma$, $\alpha$)${}^{15}$N was measured by bombarding a superheated fluid of C${}_3$F${}_8$ with bremsstrahlung $\gamma$-rays produced by impinging a 4 - 5.5 MeV electron beam on a Cu radiator. From the photodissociation yield the cross section was extracted by performing a convolution with a Monte Carlo-generated $\gamma$-ray beam spectrum. The measurement produced a cross section that was then time inverted using the reciprocity theorem. The cross section for the ${}^{15}$N($\alpha$,$\gamma$)${}^{19}$F reaction was determined down to a value in the range of hundreds of picobarns. With further improvements of the experimental setup the technique could potentially push cross section measurements down to the single picobarn range.

arXiv commentCorrected Typos. Accepted for Publication in Physical Review C

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