A New Measurement of the Total Cross Section for the Photodisintegration of $^{9}$Be Near Threshold*

The hot and neutron rich dense matter in Type II supernovae is a plausible environment where r-process nuclei are synthesized. The $\alpha(\alpha n,\gamma)^{9}Be(\alpha,n)^{12}C$ sequence is the favored reaction chain for synthesizing carbon in this explosive environment. Nucleosynthesis network models indicate that the ratio of neutrons to seed nuclei at the onset of the r-process is highly sensitive to the rate of the $\alpha(\alpha n,\gamma)^{9}Be(\alpha,n)^{12}C$ chain relative to the $\alpha(\alpha\alpha,\gamma)^{12}C$ reaction. The rate of the $\alpha(\alpha n,\gamma)^{9}Be$ reaction is derived from the measured cross section for photodisintegration of $^{9}Be$. New cross section measurements for this reaction have been made from threshold to 5 MeV using the High Intensity Gamma-ray Source (HI$\gamma$S) at TUNL. The low energy spread (as low as 1\%) of the beam at HI$\gamma$S enabled high precision measurements at the reaction threshold energy and of the narrow resonance at 2.43 MeV. Experimental techniques and results will be presented and astrophysical consequences will be discussed.