
Radioactivity detected from a half-life of once every trillion universes - okket
https://arstechnica.com/science/2019/04/dark-matter-detector-identifies-extraordinarily-rare-radioactive-decay/
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gus_massa
Note that this is almost "as expected". If you have only one xenon atom in a
box, to see that it decayed you should wait a "1.8 x 10^22 years—or about a
trillion times the age of the Universe".

If you have two atoms in a box, you must wait approximately half of the time
to see the decay.

They have 2 tons of xenon. I'm not sure if 1 ton = 1000kg or 907 kg, but it
doesn't change the result too much. With 2 tons you have 2 x 907 * 1000 / 131
x 6.02x10^23 = 8E28 xenon atoms, so you expect to have a few decays per hour
(if I did the calculations correctly).

I'm not sure if they can detect the 100% of the decays and the noise level, so
it probably takes a longer time to detect a good signal.

