Human-Made Sources:

Radioactivity is generated by a diversity of human activities. The most familiar in the early years of atomic research was the fission bomb. Its modern successor is the greatly more powerful hydrogen fusion bomb. Such a weapon, whenever detonated, generates an instant, intense burst of ionizing radiation. The high-speed subatomic particles produced in the initial blast, particularly when the explosion takes place at or near the ground, cause large quantities of material to become radioactive. The resultant radioactive dust, known fallout, precipitates back to Earth over a time period. Some fallout, particularly from the largest nuclear bombs, can increase high into the troposphere and come in the jet streams, where it is carried about the globe.

The Nuclear fission reactors have radioactive elements. The heat from the decay of such elements is used to produce electrical power. Various by-products of fission are radioactive, and since they cannot be reused to produce more power, they symbolize radioactive waste. Disposal of such waste is a problem since it takes many years, even centuries, to decay. When a fusion reactor is ever developed and place into use, it will be a huge improvement over the fission reactor since controlled hydrogen fusion generates no radioactive waste.

The Radioactive isotopes can be generated by bombarding the atoms of certain elements with high-speed subatomic particles or energetic gamma rays. The charged particles are accelerated to relativistic speeds by particle accelerators, also termed informally as atom smashers. The linear particle accelerator is a long, evacuated tube which employs a high voltage to accelerate particles like alpha particles, protons, and electrons to speeds too great that they can modify or split some atomic nuclei that they strike. The cyclotron is a large ring-shaped chamber which uses alternating magnetic fields to accelerate the particles to relativistic speeds.