From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Sep 28 2005 - 18:18:00 UTC
>From: physnews_at_aip.org
>Reply-To: physnews_at_aip.org
>To: ljk4_at_MSN.COM
>Subject: Physics News Update 747
>Date: Wed, 28 Sep 2005 14:10:11 -0400
>
>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 )
>
>***********
>PHYSICS NEWS UPDATE is a digest of physics news items arising
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