Using the CUSB-II detector at the Cornell Electron Storage Ring, we have made precision measurements of the electric dipole transition rates from Y« to χ' b , which are in excellent agreement with theory. The fine-structure splitting is found to be M(χ' b2 )-M(χ' bl )=13.5±0.4±0.5 MeV and M(χ' bl )-M(χ' bo )=23.2 ± 0.7 ± 0.7 MeV, leading to a ratio R=0.584 ± 0.024 ± 0.02. The fine structure measures the relative contributions of the spin-orbit interaction a=9.5±0.2±0.1MeV and tensor interactionb=2.3±0.1±0.1 MeV