Okay, it has been a while since I reviewed ⁹⁰Sr, so, I went to my ole friend Wikipedia:

Strontium-90 (⁹⁰Sr) is a radioactive isotope of strontium, with a half life of 28.8 years. ⁹⁰Sr undergoes beta decay with decay energy of 0.546 MeV to the yttrium isotope ⁹⁰Y, which in turn undergoes beta decay with half life of 64 hours and decay energy 2.28 MeV for beta particles to 90Zr (zirconium), which is stable.
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⁹⁰Sr is a product of nuclear fission. It is present in significant amount in spent nuclear fuel and in radioactive waste from nuclear reactors and in nuclear fallout from nuclear tests.
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Strontium has biochemical behavior similar to calcium. After entering the organism, most often by ingestion with contaminated food or water, about 70-80% of the dose gets excreted. Virtually all remaining strontium is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues. Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia.
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Accidental mixing of radioactive sources containing strontium with metal scrap can result in production of radioactive steel.
[and notice this!]
Discarded radioisotope thermoelectric generators are a major source of ⁹⁰Sr contamination in the area of the former Soviet Union.

I don't like it. I would ban all fission from this biosphere and put all products of fission under armed guard. This is nasty stuff and nasty people would love to have enough to ruin a lot of peoples' day. As in a dirty bomb. Encasing in diamond is not going to stop them. Reviewing this article only reenforced my feelings on this. I think that finding a way to storage more hydrogen in a vehicle would be a better solution, or ultra-capacitors. Ultra-capacitors for electric cars looks very promising to me.

That has got to be fixed. Or least banned at the state level.

Where are the Chinese mining it? Where they once tested nuclear weapons? Once the waste dumps and contaminated sites are deleted, you are going to have to reprocess fuel rods to get it. This has been tried, to recover the plutonium. No place in the U.S., where this has been tried has it been successful with making a huge mess. Karen Silkwood knew something about this. And they murdered her for it.

Again, I have to vote no on this idea. ⁹⁰Sr shorter half-life may seen to make it easier to handle but you have to think the whole industrial cycle you are going to need, because the problem of making large amount available for terriorism and you cannot just make ⁹⁰Sr by itself.