WEBVTT - How Glowing Watch Hands Work

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<v Speaker 1>Welcome to brain Stuff, the how stuff works podcast that

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<v Speaker 1>can make you smarter in sixty seconds. Hi Marshall, brain

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

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<v Speaker 1>You hold them up to a light and then they

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<v Speaker 1>glow in the dark for half an hour. Occasionally you'll

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

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<v Speaker 1>The most commonplace is on the hands of expensive watches.

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<v Speaker 1>In these products, the phosphor is mixed with a radioactive

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<v Speaker 1>element and the radioactive emissions energized the phosphor continuously. Does

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<v Speaker 1>it last forever? Well, no, but it can last a

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<v Speaker 1>pretty long time. In the past, the radioactive element was radium,

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<v Speaker 1>which has a half life of sixteen hundred years. Today,

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<v Speaker 1>most glowing watches use a radioactive isotope of hydrogen called tritium,

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<v Speaker 1>which has a half life of about twelve years, or prometheum,

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<v Speaker 1>a man made radioactive element with a half life of

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<v Speaker 1>around three years. Do you have any ideas or suggestions

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<v Speaker 1>at podcast at how stuff works dot com. For more

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