  We report on a study of exclusive radiative decays of the Upsilon(1S)
resonance into a final state consisting of a photon and two K0s candidates. We
find evidence for a signal for Upsilon(1S)->gamma f_2'(1525);
f_2'(1525)->K0sK0s, at a rate (4.0+/-1.3+/-0.6)x10^{-5}, consistent with
previous observations of Upsilon(1S)->gamma f_2'(1525); f_2'(1525)->K+K-, and
isospin. Combining this branching fraction with existing branching fraction
measurements of Upsilon(1S)->gamma f_2'(1525) and J/psi->gamma f_2'(1525), we
obtain the ratio of branching fractions: B(Upsilon(1S)->gamma
f_2'(1525))/B(J/psi->gamma f_2'(1525))=0.09+/-0.02, approximately consistent
with expectations based on soft collinear effective theory.
