It's really easy to build a basic visible cosmic ray detector - they're called cloud chambers. Here [1] is a random video, but you can find countless sources just searching for 'how to build a cloud chamber.'
If you haven't seen one of these before, it might sound more cool in paper than in practice. Cosmic rays are absurdly abundant to the point that dozens to hundreds are passing through you per second. So a cosmic ray detector ends up turning more into something like a really neat art show than a search for a signal. Of course there is the search for 'the big one', but somehow it's not quite so romantic when you're getting plowed by these guys constantly.
If you haven't seen one of these before, it might sound more cool in paper than in practice. Cosmic rays are absurdly abundant to the point that dozens to hundreds are passing through you per second. So a cosmic ray detector ends up turning more into something like a really neat art show than a search for a signal. Of course there is the search for 'the big one', but somehow it's not quite so romantic when you're getting plowed by these guys constantly.
[1] - https://www.youtube.com/watch?v=gt3Ad5_Z5IA