Sitting in a hot bath or spa has always been a great prescription for dealing with sore muscles. People used to believe that it was even more beneficial to immerse themselves in radioactive hot springs and drink water containing radioactive materials (some still do). In the early 1900's, people spent millions of dollars on treatments and "radioactive water" with the belief that all of their ills would be taken care of. Radioactivity in the water was usually due to radon gas that leaked up from deep underground, formed by decay of other radioisotopes. If you're feeling sore, find a hot pool and sit back and relax.

We are all exposed to a small amount of radiation in our daily lives. This background radiation comes from naturally occurring sources and from human-produced radiation. Exposure to x-rays and nuclear medicine isotopes, ground sources, and cosmic radiation account for almost half of the background exposure of the average American. Radon gas, formed from the decay of uranium and thorium isotopes, is responsible for a little over half the total amount of background radiation. See the table below for background sources.

 Table 24.5.1: Sources of Background Radiation radon $$54\%$$ consumer products $$3\%$$ nuclear medicine $$4\%$$ cosmic radiation $$8\%$$ terrestrial $$8\%$$ internal $$11\%$$ x-rays $$11\%$$ other $$1\%$$

Small amounts of uranium and thorium are found in the soil of a large number of areas in the U.S. When radioactive isotopes of these elements decay, radon is one of the products formed. Radon is a colorless, odorless gas and is chemically inert, as it is one of the noble gases.