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A study of the 6Li([pi]+,3He)3He reaction at 60, 80 and 100 MeV McParland, Brian James


An experimental study of the pion-induced fission, ⁶Li (π⁺, ³He) ³He, has been performed at TRIUMF using 60, 80 and 100 MeV pions. Angular distributions for this reaction at these energies, along with the energy dependence at fixed center-of-mass angles, are presented. Two theoretical models of this reaction predict widely differing angular and energy dependences. Prior to this experiment, the available data on the ⁶Li (π⁺, ³He) ³He reaction (and its inverse, ³He (³He, π⁺) ⁶Li) were insufficient to determine which of the two calculations better represent the reaction. The new data presented here have thoroughly tested these two models in this energy regime and have determined their suitability in their descriptions of the ⁶Li (π⁺, ³He) ³He reaction. From these data (and from results previously published for the inverse ³He (³He, π⁺) ⁶Li reaction at an equivalent pion energy of 15.4 MeV), the differential cross-sections were fit to an orthogonal Legendre polynomial series at each energy. These fits allowed the total cross-section to be extracted as a function of pion energy between 15.4 and 100 MeV. The total cross-section, and the center-of-mass differential cross-section at a fixed center-of-mass angle, were found to exhibit an exponential decrease with pion energy over this range. The coefficients of these polynomial fits also clearly show the growing importance of higher-order partial-waves with increasing energy. Finally, a phenomenological search for systematics in the world data of the ⁶Li (π⁺, ³He) ³He and ³He (³He, π⁺) ⁶Li reactions was made. This attempt was successful in finding a dependence of the reaction upon the spin-state of the exit channel which is similar to that previously seen in (p, π⁺) experimental data.

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