thorium-229

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Vietnam War. U.S. President Lyndon B. Johnson awards the Distinguished Service Cross to First Lieutenant Marty A. Hammer, during a visit to military personnel, Cam Ranh Bay, South Vietnam, October 26, 1966. President Johnson

Vietnam War Timeline

New Zealand. Political/Physical map. Includes locator.

Where Is “Old Zealand”?

Portrait of Marie Antoinette by Jean-Francois Janinet, 1777. Color etching and engraving with gold leaf printed on two sheets, 30x13.5 in.

Did Marie-Antoinette Really Say “Let Them Eat Cake”?

Black widow spider

9 of the World’s Deadliest Spiders

Queen Elizabeth II addresses at opening of Parliament. (Date unknown on photo, but may be 1958, the first time the opening of Parliament was filmed.)

All 119 References in “We Didn’t Start the Fire,” Explained

Flags of the countries of the world (flagpoles).

How Many Countries Are There in the World?

Computer mapping, woman at early 1990s computer

Timeline of the 1990s

thorium-229

chemical isotope

Learn about this topic in these articles:

half-life

In thorium
Synthetic isotopes have been prepared; thorium-229 (7,880-year half-life), formed in the decay chain originating in the synthetic actinoid element neptunium, serves as a tracer for ordinary thorium (thorium-232).
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