Keywords: Atomic Clock006.jpg Charles Snider of the Radio Standards Laboratory pours liquid nitrogen over a cold trap of the new cesium beam frequency standard as Roger Beehler adjusts the atomic beam detector The U-shaped resonant cavity used to excit the cesium transition is suspended above the center of the machine National Institute of Standards and Technology National Institute of Standards and Technology PD-USGov-NIST PD-USGov National Bureau of Standards National Institute of Standards and Technology Atomic clocks |