h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm updating the entry "A Chronology of Time" at the moment. I came across the following:

"1948 USA First atomic clock. The most precise time meter, it measures decay of radioactive material."

I'm pretty sure that atomic clocks don't use radioactive decay in any shape or form. Can anyone else confim this?

Wikipedia agrees with me:

"The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics and using the microwave signal that electrons in atoms emit when they change energy levels."

But I'd never trust anything I read in Wikipedia without checking it with you lot first.

HI Gnomon

As Clarkson would say "I was looking on the internet and found this" http://www.npl.co.uk/educate-explore/what-is-the-time/how-do-atomic-clocks-work which is from the National Physical Laboratory and explains Caesium clocks.

I'm with you on the atomic decay point. This site has more information on the history - http://www.atomic-clock.galleon.eu.com/atomic-clock/atomic-clock.htm although it is a commercial site they say the first atomic clock was invented in the USA in 1949.

None seems to use atomic decay. To quote Galleon: -

'An atomic clock is not radioactive, it doesn’t rely on atomic decay. Rather, an atomic clock has an oscillating mass and a spring, just like ordinary clocks.

The big difference between a standard clock in your home and an atomic clock is that the oscillation in an atomic clock is between the nucleus of an atom and the surroundin electrons. This oscillation is not exactly a parallel to the balance wheel and hairspring of a clockwork watch, but the fact is that both use oscillations to keep track of passing time. The oscillation frequencies within the atom are determined by the mass of the nucleus and the gravity and electrostatic "spring" between surrounding it.'

t.

Thanks. I've changed the sentence to "The most precise time meter, it measures oscillations of electrons in an atom."

PING

A bit late, but i#d add that using radioactive decay wouldn't be much good for an accurate clock, since it is fundamentally uncertain - it is one more thing that prevents you knowing exactly what would happen in the universe if you know where everything was and what speed it travels at.
Radioactive decay is only accurate in really big terms (relatively that is), not in nano or pico seconds