Cosmic rays and muons can initiate a nuclear reaction: they can have very high energy sometimes. If the metal plate is large enough, then it can be hit often en

Cosmic rays and muons can initiate a nuclear reaction: they can have very high energy sometimes. If the metal plate is large enough, then it can be hit often enough to produce significant output, when it is not shielded from cosmic rays. For example, lab at top floor or in mountain area may produce much more heat than lab in basement at sea level.