image credit: F. Gauthier-Lafaye; image source; larger image

The Oklo Fossil Fission Reactors

This photo shows part of a natural nuclear reactor-- an underground uranium deposit where a chain reaction occurred spontaneously. In fact, such a natural reactor was predicted, beginning in 1956, and then discovered in 1972.

To find the reactor, physicists search for a deposit of uranium with a slightly lower concentration of U-235 than is found elsewhere on Earth. This U-235 deficit would be caused by the chain reaction of a small fraction of the U-235 nuclei. To learn more, visit The Oklo Fossil Fission Reactors and also this Astronomy Picture of the Day page.

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What is Radioactivity?

Check out What is Radioactivity? to learn about isotopes and radioactivity.

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image credit: U.S. Department of Energy; image source; larger image

Radioisotope Power Systems

The glowing pellet is an oxide of plutonium, the fuel for a radioisotope thermoelectric generator (RTG). It is photographed in the light it emits, because its radioactive decay produces considerable heat. The RTG converts this heat into electricity.

RTGs power the spacecraft that visited Mars, Jupiter, and Saturn--and the RTG keeps working over decades. To find out more, visit Radioisotope Power Systems.

Ionizing Radiation and Humans – The Basics

Radioactivity is all around us--in soil, rocks, and even food--but small doses of it are not harmful. Visit Ionizing Radiation and Humans – The Basics to learn how exposure to radiation is part of our daily lives.

For more, check out this Fact Sheet from the Health Physics Society. Also see, from a previous Physics at Home, Calculate Your Radiation Dose.