Answer:
Neither? If it must be one then fission.
Step-by-step explanation:
I actually didn't know they had fission, but I can absolutely gaurantee that they don't use fusion, nuclear fusion is a process that fuses hydrogen atoms together and releases a massive amount of energy, it used in hydrogen bombs and by our sun. It's a process that needs a massive amount of energy to kickstart and there's no way that technology would fit in a tanning bed. If I'm wrong then please tell me.
Hope this is a good answer.