I was using atheist as a synonym of irreligious

So was I. I was under the impression physicists were only more irreligious than baseline, rather than most of them being irreligious; although "top" scientists are much more so.

Trying to look up the actual statistics ... OK, a lot of it is behind paywalls and frankly I'm too lazy to do much beyond a quick Google, but Wikipedia claims scientists in general are about equal numbers atheists, agnostics and theists (i.e. 2/3rds non-theist.) And physicists are just under that, apparently (29%). But I can't read the actual sources for these vaguely-worded assertions (they have some, though!)

The most - practically the only, in popular discussions of this - cited study on this topic seems to be this, which, naturally, isn't much good (short, though.)

So going with WPs figure ... eh, it's a bit higher than I expected offhand, so hey, new data! I wouldn't call that "usually", but ultimately that's a semantic question of usage. I don't attach huge confidence to Wikipedia's figures, though I would say they're in the right ballpark; do you by any chance have better ones?

We may be getting offtopic, though, since I'm not sure how much bearing atheism has on reactions to cryonics in practice.