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Hiroshima scientists turn any smartphone into a radiation detector
(techxplore.com)
This is a most excellent place for technology news and articles.
It's not an "if" detector, it's a "how much" detector. It looks like it's using the LED chamber to light the film in a consistent way, and then the phone camera measures the color change to quantify how much radiation it was exposed to.
Ah. I missed that. Ok, this makes total sense then. But the films activate at high doses anyway; doses you'll notice. I guess this system will be especially useful if those films ever become more sensitive.