Measurement of the Total Cross-Section for the $^{9}$Be($\gamma $,n$\alpha )\alpha $ reaction

The $^{9}$Be($\gamma $,n$\alpha )\alpha $ cross section is key to understanding isotopic abundances of nuclei produced during the r-process. The inverse reaction bridges the unstable mass gaps at A=5 and 8 leading to $\alpha (\alpha $n,$\gamma )^{9}$Be($\alpha $,n)$^{12}$C and so on, producing seed nuclei for the r-process and setting the neutron-to-seed nucleus ratio that drives universal isotopic abundance predictions [Ref 1,2]. In order to make high precision measurements ($\pm $ 5{\%}) of the $^{9}$Be($\gamma $,n$\alpha )\alpha $ cross-section which includes narrow resonances, tunable gamma ray beam with small $\Delta $E/E is required along with gamma and neutron detectors whose efficiencies are well known. We used TUNL's high intensity gamma ray source (HI$\gamma $S) to measure the cross sections for $^{9}$Be($\gamma $,n) in the energy range of 1.55 to 5.0 MeV with beam energy resolutions between 14 and 150 keV as determined by large Ge detector. The neutrons were detected using $^{3}$He proportional counter. Experimental details will be discussed and the results as well as their astrophysical consequences will be presented. [Ref 1] B. Meyer \textit{et al.}, Astro J., \textbf{399} 656-664 (1992). [Ref 2] T. Kajino \textit{et al.}, Nuc. Phys. A, \textbf{704}, 165c-178c (2002)