I doubt it was from the betas, they are all fairly low energy for typical radium. It was probably from the gammas produced by Ra-226. Ra-226 produces a 186 k

I doubt it was from the betas, they are all fairly low energy for typical radium. It was probably from the gammas produced by Ra-226. Ra-226 produces a 186 keV gamma in 3.3% of decays. Cherenkov radiation flashes in the eye are observed by patients undergoing clinical radiation therapy (see this interesting paper where this was explored and tested: https://www.redjournal.org/article/S0360-3016(19)33947-1/fulltext https://www.redjournal.org/article/S0360-3016(19)33947-1/ful... ). The test done in the paper was with much higher energy gammas, but it is feasible that the 186 keV lines could cause the same effect. I've never observed this when working with radium, but then I don't stick it in my eye.