Why does Y90 and Sr90 beta emissions have the same range in air if they have different energy averages (0.935 MeV, 0.196 MeV, espectively)? I would assume that their average energy would indicate different ranges in the same medium. Does this apply to other mediums as well?
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90Sr decays to 90Y which decays to 90Zr, which is stable. I notice in your datasheet for 90Sr that it lists two "major betas," one for the 90Sr decay, and one for the subsequent 90Y decay. I would guess then that the 90Sr datasheet, when they calculate the range in air, they include the subsequent decay of 90Y. After all, if you had a chunk of 90Sr, and you wanted to know what safety measures to put in place, you would have to be aware that two betas will come from each atom, because it decays twice.
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$\begingroup$ In support of this hypothesis, note that these data sheets are hosted by the Environmental Health & Safety office (EHS) at U. Missouri. $\endgroup$ Commented Jun 20 at 21:34