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Speaker 1: Welcome to brain Stuff, the how stuff works podcast that

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Speaker 1: can make you smarter in sixty seconds. Hi Marshall, brain

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Speaker 1: You've probably seen all kinds of glow in the dark toys.

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Speaker 1: You hold them up to a light and then they

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Speaker 1: glow in the dark for half an hour. Occasionally you'll

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Speaker 1: see something glowing, but it doesn't need charging like this.

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Speaker 1: The most commonplace is on the hands of expensive watches.

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Speaker 1: In these products, the phosphor is mixed with a radioactive

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Speaker 1: element and the radioactive emissions energized the phosphor continuously. Does

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Speaker 1: it last forever? Well, no, but it can last a

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Speaker 1: pretty long time. In the past, the radioactive element was radium,

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Speaker 1: which has a half life of sixteen hundred years. Today,

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Speaker 1: most glowing watches use a radioactive isotope of hydrogen called tritium,

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Speaker 1: which has a half life of about twelve years, or prometheum,

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Speaker 1: a man made radioactive element with a half life of

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Speaker 1: around three years. Do you have any ideas or suggestions

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Speaker 1: for this podcast? If so, please send me an email

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Speaker 1: at podcast at how stuff works dot com. For more

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Speaker 1: on this and thousands of other topics, go to how

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Speaker 1: stuff works dot com.