PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 747   September 28, 2005  by Phillip F. Schewe, Ben Stein

NUCLEAR SEISMOLOGY.  Physicists at the GSI lab in Darmstadt, Germany have
discovered a new excited nuclear state, one in which a tide of neutrons
swells away from the rest of the nucleus.  Ordinarily, in its unexcited
state, a typical atomic nucleus consists of a number of constituent
neutrons and protons (collectively known as nucleons) bobbing around inside
a roughly spherical shape.  However, if struck by a projectile from
outside, such as a beam particle supplied by an accelerator, the nucleus
can be set to spinning, or it might distend.  In one kind of excited mode
called a dipole resonance, the protons can move slightly in one direction
while the neutrons go the other way.  In another type of excitation, a
nucleus might consist of a stable core blob of nucleons surrounded by a
surplus complement of one or two neutrons, which constitute a sort of halo
around the core (see http://www.aip.org/pnu/2004/split/702-3.html ).
In the new GSI experiment, yet another nuclear mode has been observed.  The
nuclei used, two isotopes of tin, are the most neutron-rich among the
heavier nuclei that can be produced at this time.  Sn-130 and Sn-132 are so
top-heavy with neutrons that they are quite unstable and must be made
artificially in the lab.  At GSI this is done by shooting a uranium beam at
a beryllium target.  The U-238 nuclei, agitated by the collision,
eventually fission in flight, creating a swarm of more than 1000 types of
daughter nuclei, from which the desired tin isotopes can be extracted for
study.  The tin nuclei are excited when they pass through a secondary
target, made of lead.  The excited tin states later disintegrate; the
debris coming out allows the researchers to reconstruct the turbulent
nature of the tin nuclei.  The dipole resonance was seen, as expected, but
also a new resonance: an excess of neutrons pushing off from the core
nucleus.  Furthermore, the neutron resonance appears at a lower excitation
energy than does the dipole resonance.  Team leader Hans Emling
(h.emling{at}gsi.de) says that there was some previous evidence for the
existence for the neutron mode in work with lighter nuclei, but not the
actual oscillation observed in the present work.  (Adrich et al., Physical
Review Letters, 23 September 2005.)
                                                
HYDROPHOBIC WATER sounds like an impossibility.  Nevertheless, scientists
at Pacific Northwest National Lab have produced and studied monolayers of
water molecules (resting on a platinum substrate) which prove to be poor
templates for subsequent ice growth.  Picture the following sequence: at
temperatures below 60 K, isolated water molecules will stay put when you
place them on a metallic substrate.  At higher temperatures, the molecules
become mobile enough to begin forming into tiny islands of two-dimensional
ice.  New molecules landing on the crystallites will fall off the edges
into the spaces between the islands.  In this way the metal surface becomes
iced over completely with a monolayer.  But because the water molecules'
four bonds are now spoken for (1 to the Pt substrate and 3 to their
neighboring water molecules), the addition of more water does not result in
layer-by-layer 3D ice growth.  Only when there is an amount of overlying
water equivalent to about 40 or 50 layers does 3D crystalline ice
completely cover the hydrophobic monolayer.  The PNL researchers (contact
Greg Kimmel,  509-376-2501, gregory.kimmel{at}pnl.gov) are the first to
observe this effect.  For the novel hydrophobic property to show itself,
the water-substrate bond has to be strong enough to form a stable
monolayer.  Weaker bonding results in a "classic" hydrophobic
state, in which the water merely balls up immediately; in other words, not
even a first monolayer of ice forms.  This research should be of interest
to those who, for example, study the seeding of clouds, where ice is
nucleated on particles in the atmosphere.  (Kimmel et al., Physical Review
Letters.)

VISA PROBLEMS CONTINUE FOR FOREIGN STUDENTS attempting to enter physics
departments at US universities.  A new survey conducted by AIP's
Statistical Research Center shows that in 2004 half the PhD-granting
physics departments reported that at least one admitted student was either
denied a visa or considerably delayed by visa problems.  About 60% of the
departments also reported visa problems for foreign students returning to
the US after trips abroad.  The AIP survey estimates that ultimately 12% of
admitted foreign physics graduate students in the Fall of 2004 were (at
least initially) denied entry.  This actually represents an improvement; in
2002 the same fraction was 20%.  The falloff in foreign graduate physics
enrollment is matched by a substantial increase in US students admitted: a
growth of 42% in four years.  (Report text at
http://www.aip.org/statistics/trends/intltrends.html; contact Patrick
Mulvey or Michael Neuschatz at stats{at}aip.org )

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