How do I make the energy level never drop below 1?

I have a radioactivity field and have rules set up to add energy to it when its node is commented on or flagged. This is working just fine if there is above 0 energy, but when it is down to 0, rules energy won't add to the field. I have my rule set up to set a data value in the energy field and add an offset to add energy to the field. I figure that if I can make the field stop decaying win it hits 1, it will always have a little bit of energy and still be able to "receive" energy. I have tried making the energy cut off 10, but no luck. It still goes all the way to 0. Any suggestions? Is there a better way for me to do this not using rule like I do? Thanks.