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.
In the past, the Cryonics Institute has had a policy that said that they would not accept anyone who is not a member. This has changed. The policy now is that someone who has full legal authority over your body can sign you up after you die. It costs $36,250 to be frozen if you are not signed up, which is more expensive. They also will not do anything until you have been on dry ice for 2 weeks after they have been contacted, so not being a member is more risky.
This is very important news for anyone who is currently cryocrastinating. It means that you can drastically increase your chances of survival without filling out any forms. All you have to do is tell a loved one you want to be frozen upon death, and that you would like them to take responsibility for making sure this happens. This takes literally 30 seconds. Do it now!
This news might also be a reason to not sign up right away, if you think something better (like radical life extension or uploading) will come along in your lifetime. We should discuss this in the comments.
Edit: The general consensus of this discussion is that this is a really bad reason not to sign up for cryonics.