I solicited an opinion from someone who is currently a NPP safety consultant. She read the criminal case and responded but does not want her name to be mentioned:
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XX: It is difficult to draw a conclusions. There is not enough information. Did the students have classes and exercises in nuclear physics? In those years, the rules were not very strict and it is possible that they got infected in the laboratories.
It's a pity they didn't do an isotopic analysis. Just beta contamination, more like work/test/experiment contamination. We o not know exactly what the radioactive material is, for example, Cs-137 (cesium) or another substance - strontium.
Teddy: The one the contaminated clothes belong to was a nuclear physics student (
Kolevatov).
XX: Perhaps he contaminated the rest.
Teddy: But only his clothes were contaminated, he and one more participant who worked on Chelyabinsk-40 when there was an accident (
Krivonischenko).
XX: Most likely, this is the reason. In those years, there were still no such strict rules for safe work with radioactive substances.