Indirect Measurements of Neutron Induced Radiative Capture Cross Sections on Rare Earth Elements

Radiative capture reactions involving neutrons are of particular importance to var- ious nuclear applications. Experimental constraints, however, make measurements of these types of cross sections nontrivial. Therefore, it is essential to have a reliable method for predicting (n, γ) and (γ, n) reaction cross sections. Indirect measure- ments of compound nuclear reactions can be performed using more easily accessible reaction channels as a way of studying the reaction of interest. Two methods of extracting (n,γ) cross sections from indirect measurements are the Oslo method and the surrogate method. For this Ph.D. dissertation, indirect measurements of 145,146Sm(n, γ)146,147Sm and 159,160Dy(n, γ)160,161Dy were attempted using both meth- ods.

Data for this thesis was taken at Texas A&M University, using the Hyperion particle-γ detector array. Reactions measured include 148Sm(p, d)147Sm, 148Sm(p, t)146Sm, 162Dy(p, d)161Dy, and 162Dy(p, t)160Dy. Eex − Eγ matrices were generated for 147Sm, 160Dy, and 161Dy using particle-γ coincidence measurements, and were then run through the Oslo method fitting algorithms to simultaneously extract γ-strength function and nuclear level density. The data taken explores the existence of the low energy enhancement of the γ-strength function in a spherical

and deformed nuclear system, and verifies the robustness of the method to differ- ent indirect reaction channels. Surrogate measurements of (n,γ) cross sections were attempted, and γ-decay probabilities were extracted for 146Sm, 147Sm, and 160Dy. Extracted γ-decay probabilities exhibit spin inhibition, where neutron evaporation cannot occur in a compound nucleus until conservation of both energy and angular momentum are conserved.