The cross section and branching ratio for 3 He (a,y) 7 Be have been measured from E c#m# = 165 to 1170 keV by counting prompt y rays from a windowless, recirculating, 3 He gas target. Absolute cross sections were also measured at E CmTr)m = 945 and 1250 keV by measuring the 7 Be activity produced in a 3 He gas cell with a Ni entrance foil. The inferred zero-energy intercept is S M (Q) = 0.52± 0.03 keV b. The effect of this extrapolated value on the solar-neutrino problem is discussed.

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We propose a linewidth-narrowing mechanism in lasers by nonlinear absorptive wave mixing of the counterpropagating beams in the cavity. We give a theoretical analysis and report on a demonstration of the effect with an erbium-doped fiber laser. The system also exhibits bistability in the dependence of the oscillation intensity versus pump power.