This isn't a cheat but it's helpful.

1: The scientist will only steal the gun you're equiped with.
2: The scientist will not take you're gun if it's empty.
3: The scientist never stays in one area.
4: If you hear a strange noise near you, it means the scientist is coming.
5: If you want to survive the scientist, always run through teleporters and away from the scientist.
6: The scientist will not go away until he steals you're gun.