 In the US and Europe, there are several "radon spas", where people sit for minutes or hours in a high-radon atmosphere in the belief that low doses of radiation will invigorate or energize them.Radon has been produced commercially for use in radiation therapy, but for the most part has been replaced by radionuclides made in particle accelerators and nuclear reactors.Radon has been used in implantable seeds, made of gold or glass, primarily used to treat cancers, known as brachytherapy.