From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Oct 18 2007 - 08:54:26 PDT
>From: physnews_at_aip.org
>Reply-To: physnews_at_aip.org
>To: ljk4_at_MSN.COM
>Subject: Physics News Update 843
>Date: Thu, 18 Oct 2007 11:46:43 -0400
>
>PHYSICS NEWS UPDATE
>The American Institute of Physics Bulletin of Physics News
>Number 843 October 18, 2007 by Phillip F. Schewe
>www.aip.org/pnu
>
>RELATIVISTIC THERMODYNAMICS. Einstein*s special theory of
>relativity has formulas, called Lorentz transformations, that
>convert time or distance intervals from a resting frame of reference
>to a frame zooming by at nearly the speed of light. But how about
>temperature? That is, if a speeding observer, carrying her
>thermometer with her, tries to measure the temperature of a gas in a
>stationary bottle, what temperature will she measure? A new look at
>this contentious subject suggests that the temperature will be the
>same as that measured in the rest frame. In other words, moving
>bodies will not appear hotter or colder.
>You*d think that such an issue would have been settled decades ago,
>but this is not the case. Einstein and Planck thought, at one time,
>that the speeding thermometer would measure a lower temperature,
>while others thought the temperature would be higher. One problem
>is how to define or measure a gas temperature in the first place.
>James Clerk Maxwell in 1866 enunciated his famous formula predicting
>that the distribution of gas particle velocities would look like a
>Gaussian-shaped curve. But how would this curve appear to be for
>someone flying past? What would the equivalent average gas
>temperature be to this other observer? Jorn Dunkel and his
>colleagues at the Universitat Augsburg (Germany) and the Universidad
>de Sevilla (Spain) could not exactly make direct measurements (no
>one has figured out how to maintain a contained gas at relativistic
>speeds in a terrestrial lab), but they performed extensive
>simulations of the matter. Dunkel
>(joern.dunkel_at_physik.uni-augsburg.de ) says that some astrophysical
>systems might eventually offer a chance to experimentally judge the
>issue. In general the effort to marry thermodynamics with special
>relativity is still at an early stage. It is not exactly known how
>several thermodynamic parameters change at high speeds. Absolute
>zero, Dunkel says, will always be absolute zero, even for
>quickly-moving observers. But producing proper Lorentz
>transformations for other quantities such as entropy will be
>trickier to do. (Cubero et al., Physical Review Letters, 26 October
>2007; text available to journalists at www.aip.org/physnews/select)
>
>NUCLEAR SYRUP. A new measurement of how long it takes certain
>nuclei to fission into large fragments suggests that the
>*liquid-drop* model of the nucleus should be replaced with a
>*nuclear syrup*model. Fission is the most dramatic form of
>radioactivity, when a nucleus loses not merely a small fragment-such
>as an electron, gamma ray, or an alpha particle-but actually splits
>in half. The fission of many nuclei has been studied through the
>years, most famously
>uranium-235. As early as 1939 Niels Bohr and John Wheeler tried to
>model the nature of fission by saying that the nucleus is like a
>drop of water in which the tendency of the drop to fly apart is
>checked by the force of surface tension; something like this, they
>said, kept a nucleus intact until such time as the rapid
>oscillations of an unstable nucleus became so large that the
>*surface tension* normally keeping the nucleus together was
>overcome. Sometimes as a prelude to fission, the nucleus relieves
>some of its instability and effectively reduces its internal
>*nuclear temperature* by flinging out neutrons or gamma rays. In
>fact, the lifetime for fission has been indirectly measured by
>observing those cast-off neutrons. The results suggest that the old
>liquid-drop model was off by a factor of ten or so
> in predicting
>lifetimes. Some scientists have begun to think that an additional
>stickiness in the nuclear substance is at work, which slows up the
>fission process.
>An experiment at Oak Ridge National Laboratory has probed this
>proposition by creating several fissionable nuclei artificially with
>heavy-ion beams bombarding a tungsten target; the projectile and
>target nuclei temporarily fuse together, travel a short distance
>through the tungsten crystal, and then fission. The spacing of the
>atoms in the crystal is used as a reference to measure the recoil of
>the composite nucleus before fission. According to team member Jens
>Andersen of the University of Aarhus in Denmark (jua_at_phys.au.dk,
>45-8942-3713), the Oak Ridge experiment suggests that the fission
>lifetimes are even longer (an additional factor of ten to one
>hundred) than those derived with the more indirect neutron-emission
>method. This could imply that the nuclear shape does not oscillate
>as rapidly as a water droplet would but instead deforms very slowly
>like a drop of syrup. (Andersen et al., Physical Review Letters, 19
>October 2007; journalists can obtain the text from
>www.aip.org/physnews/select)
>
>***********
>PHYSICS NEWS UPDATE is a digest of physics news items arising
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