No Subject

Yes, it's very hard to simulate cosmic radiation in the laboratory on
Earth. Cosmic rays are a low dose of very high-energy particles, to
which you may be exposed for a very long time. Many experiments
attempting to mimic them use higher doses for a short time, which might
not have the same biological effects. And in addition, most labs don't
have a big enough particle accelerator needed to produce the same kind
of radiation as cosmic rays anyway.

Moreover, even the ISS is no help here, as it's shielded from cosmic
rays by the magnetosphere.

This is the sort of research that would be best done on the Moon. You
could have an animal lab on the surface, with only minimal shielding
(perhaps enough to stop solar energetic particles, but not cosmic rays).
Unfortunately, the lab workers would be inadvertently experimenting on
themselves, too. But unlike the animals, they wouldn't need to be in
the lab all the time -- they could retreat to more heavily shielded
quarters when not actively tending the animals.