In the USA there are over 20 million nuclear medicine procedures per year among 311 million people, and in Europe about 10 million among 500 million people.In Australia there are about 560,000 per year among 21 million people, 470,000 of these using reactor isotopes.All minerals and raw materials contain radionuclides of natural origin.
These elements have always been present in the Earth's crust and atmosphere, and are concentrated in some places, such as uranium orebodies which may be mined.
The reason is that energy and frequency of a gamma ray which is emitted by a radioactive element, is far beyond that of the radio band of electromagnetic spectrum! Every nucleus contains neutrons as well as protons.
Neutrons are neither positively charged, nor negatively charged, they are neutral particles. As you might remember from high school physics, like charges repel each other while unlike charges attract each other.
Thorium metal is silvery and tarnishes black when exposed to air, forming the dioxide.
Thorium is weakly radioactive: all of its known isotopes are unstable.