1. Antimatter is the opposite of matter, where matter would have a positive charge Antimatter has a negative charge. If he isn't carful and concentrates his Antimatter will react with the normal matter around him and he will blow up. So yeah, he really has to not over do it or he latterly burns out.

2. You can go the old lock him in a deep dark hole thing. Honestly leaving him alone with his thoughts is the worst thing you can do to him.