Investigation of surrogate reactions near A=100: $^{102,104}Ru(\alpha,\alpha')$ for $^{101,103}Ru(n,\gamma)$

For two-step, neutron-induced reactions proceeding through an equilibrated intermediate state, an alternate, ``surrogate reaction'' technique \footnote{J.D. Cramer and H.C. Britt, Nucl. Sci. Eng., {\bf{41}}, 177 (1970).} is applicable. Measured decay probabilities for the intermediate nucleus formed via a light-ion reaction are combined with optical-model calculations for the formation of the same intermediate nucleus via the n- induced reaction, and result in the overall (n, $\gamma$/n/2n) cross sections. $^{102,104}Ru(\alpha,\alpha')$ were studied separately as surrogate reactions for $^{101,103}Ru (n,\gamma)$. The test, $^{101}Ru(n,\gamma)$, has been previously measured directly (EXFOR). The unknown, $^{103}Ru (n,\gamma)$, is a branch in the s-process. Energies of scattered $\alpha$ particles were detected in double-sided silicon detectors (STARS) over scattering angles of 42-60 degrees. Ge clover detectors (LiBerACE) were used to count $\gamma$-rays in coincidence with $\alpha$ particles scattered at energies corresponding to 0-3 MeV equivalent neutron energy in the desired (n,$\gamma$) reaction. Work performed under the auspices of the U.S. DOE by the Univ. of CA, LLNL contract No. W-7405-Eng-4, and DOE grants DE-FG02-91ER-40609 and DE-FG03- 03NA00081, LDRD-04-ERD-057.