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

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.)