PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institut

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PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institute of Physics Number 178 May 10, 1994 THE LATTICE SPACING IN SILICON (220) has been measured to be 192015.569 fm (1 fm is 10**-15 m) with a relative uncertainty of 3 x 10**-8. Because silicon technology can provide the largest pure crystals with well-characterized dimensions (the <220> notation refers to the particular direction through which the crystal is viewed) a careful measurement of the spacing between atoms can facilitate a count of the atoms in the crystal. This in turn can be used to calculate a better value for the Avogadro constant, equal to the number of atoms in a mole. Scientists at the University of Torino in Italy, employing a combination of x-ray and optical interferometry to measure the lattice spacing, believe their work will also lead to a better determination of the wavelengths for thermal neutrons and for x rays and gamma rays. (G. Basile et al., Physical Review Letters, 16 May 1994.) HALTING AND REVERSING THE DESTRUCTION OF OZONE in the stratoshpere is a problem of great importance: the less protective ozone there is, the more harmful ultraviolet radiation reaches the Earth. Alfred Wong of UCLA studies this problem using a 2.4-m ozone-filled chamber. When CFCl-3 molecules are introduced and when an artificial source of sunlight starts to liberate free chlorine, the density of ozone in the chamber begins to fall, mimicking the catalytic destruction of ozone in the atmosphere. Wong's effort to counteract this effect is to inject a current of negatively-charged oxygen atoms and molecules. These attach themselves to the chlorine atoms which can then be collected on a positively-charged surface. Thereafter the ambient uncharged oxygen can reform as ozone now that it is spared the destructive presence of chlorine. Wong believes that much more research is necessary before a field test of this method can be attempted. He points out that the charge-induced approach is quite different from proposed chemical means for the regeneration of ozone since the negative charges are all recovered, leaving behind no greenhouse-inducing substances. (A.Y. Wong et al., Phys. Rev. Lett., 9 May.) NEUTRAL ATOMS HAVE BEEN TRAPPED WITH MICROWAVES, paving the way for new attempts to achieve Bose-Einstein condensation, a hypothesized state of matter in which cold atoms are so densely packed together that they all collapse into a single quantum state. A Harvard-NIST team (contact Isaac Silvera, 617-495-9075) has trapped cesium atoms with microwaves, and is ready to move on to atomic hydrogen, a highly promising candidate for Bose-Einstein condensation. In their design, the magnetic component of a microwave field traps atoms in their lowest-energy spin state. In earlier magnetic traps for atomic hydrogen, the atoms were confined in a high-energy spin state but could escape easily by dropping into their lower-energy state, depleting the large concentration of atoms needed for Bose-Einstein condensation to occur. (R.J.C. Spreeuw et al., Phys. Rev. Lett., 16 May.) CAMPHOR IS A SOURCE OF FULLERENES. Scientists at the Indian Institute of Technology in Bombay have deposited a film of camphor soot on a silicon substrate and observed the distinctive spherical shape of C-60 molecules with a scanning electron microscope. This represents the first time, the scientists say, that fullerenes have been derived from a natural source, a development which should promote a faster, cheaper means of producing buckyballs. Camphor is an extract of a tree found mostly in India and China. (Kingsuk Mukhopadhyay et al., Phys. Rev. Lett., 16 May.)

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