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Element 115
1 March 2004
Nuclei of transuranium element 115 have been created at
the Joint Institute for Nuclear Research in Dubna, Russia,
in collaboration with a team from the Lawrence Livermore
National Laboratory in the US. The researchers used a gas-
filled separator to detect the products of the nuclear
reactions caused by the collision of a 48Ca beam with an
243Am target. Their first experiment, in which the energy of
the nuclei in the beam was 248 MeV, revealed three reaction
chains, each consisting of five alpha decays. Based on the
decay characteristics, the reaction chains started with the
decays of the isotopes of an element 115 with an atomic
weight of 288. The second experiment, with a beam energy
of 253 MeV, revealed one chain of four alpha decays, whose
initial nucleus is likely to be among the isotope of an
element 115 with an atomic weight of 287. According to a
theoretical analysis, in both experiments the compound 291115
nucleus formed prior to the alpha decays, from which three
or four neutrons evaporated.
Source: Phys. Rev. C 69 021601(R) (2004)
Resonance condensation of fermions
1 March 2004
A team of researchers from the National Institute of
Standards and Technology (NIST) and the University of
Colorado (also in Boulder, USA) have observed for the first
time the condensation of pairs of fermionic atoms under
conditions covered by the Bardeen - Cooper - Schrieffer
(BCS) theory in the vicinity of the Feshbach resonance. In
earlier studies, the Bose - Einstein condensation of the
bosonic 40K2 and 6Li2
molecules consisting of two fermionic
atoms was already observed. Unlike this type of condensation,
in the new experiments atoms were not bound into
molecules but rather paired up due to collective effects. A
similar process is realized when the Cooper pairs of electrons
condense in superconductors governed by the BCS theory. To
cool the gas of 40K atoms, first evaporative and then
magneto-optical techniques were applied. The experiment
enabled the external magnetic field to be varied near the
Feshbach resonance whose exact position was determined to
a high accuracy from the molecular dissociation. Increasing
(decreasing) the magnetic field with reference to its resonance
value led to an attractive (repulsive) interaction between the
atoms, thus allowing the smooth transition from the Bose -
Einstein condensation of molecules to the BCS type condensation
to be traced. In the latter case, the condensate of
40K atoms is called a fermionic condensate. The fermionic
condensate was found to live much longer before breaking the
coherence than the condensate of bosonic molecules. On
completing the experiment, the gas cloud was freed from the
trap and the momentum distribution of the particles was
measured. On evidence derived from these measurements it
may be argued that the atoms were in the fermionic
condensation state when trapped.
Source: Phys. Rev. Lett. 92 040403 (2004)
Nanotube gels
1 March 2004
A polymer-dissolved liquid polymer (gel) of carbon nanotubes
has been created at the University of Pennsylvania.
Nanotubes in a gel are about half a micron in size and are all
aligned in the same direction. The new gel is suggestive in part
of a liquid crystal, including such its properties as optical
anisotropy and the character of the topological defects. The
gel was obtained by mixing nanotubes with a solvent and then
compressing the mixture.
Source: Physics News Update, Number
672
A distant galaxy
1 March 2004
An international team of astronomers using the Hubble
Space Telescope and the ground-based Keck telescope in
Hawaii has discovered the most distant galaxy ever seen. The
galaxy is 13 billion light years away, its look-back time being
just 5% of its present age. Just as with the former record
holder, the new galaxy is seen due to its image being amplified
by a gravitational lens (cluster of galaxies Abell 2218) lying on
the line of sight. Based on the angular distance between the
two images the researchers detected from the galaxy, the
redshift of the galaxy is in the range 6.6 - 7.1. Despite its being
25-fold amplified by the gravitational lens, the galaxy's image
is very faint, pushing the telescopes to their sensitivity limits.
The galaxy has a size of about 2,000 light years and is
undergoing an intense star formation period. Two unusual
things about the galaxy's spectrum are that it does not exhibit
a bright hydrogen emission line and that its ultraviolet
radiation is much more powerful than that of similar galaxies
observed at the present epoch. Studying distant galaxies is
important for understanding their evolution and what
mechanisms control the re-ionization of the universe.
Source: http://www.stsci.edu/
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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources.
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