[thamer]

That's the method described in https://arxiv.org/pdf/1604.03304.pdf on page 11:

> A fast clock (down) is used to increase a counter. Whenever a detection is made (up), the counter is read and reset, generating one random number.

> We restrict to a counter that generates values from 0 to M −1, a modulo M counter. When M = 2 we have a binary random number generator.

It doesn't have to be a millisecond timestamp, any clock that's much faster than the rate of decay should work. Every time a decay is detected, take the elapsed time in clock units mod 2 and that's your random bit.