How can radioactivity be caused artificially?
Radioactivity can occur both naturally and through human intervention. An example of artificially induced radioactivity is neutron activation. A neutron fired into a nucleus can cause nuclear fission (the splitting of atoms). This is the basic concept behind the atomic bomb.
Neutron activation is also the underlying principle of boron-neutron capture therapy for certain brain cancers. A solution containing boron is injected into a patient and is absorbed more by the cancer than by other cells. Neutrons fired at the area of the brain cancer are readily absorbed (captured) by the boron nuclei. These nuclei then become unstable and emit radiation that attacks the cancer cells. Simple in its basic physics, the treatment has been complex and controversial in practice and after half a century is still regarded as highly experimental.