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| Issue 11, 2024 |
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Extracts from the Internet | ||
Element 1151 March 2004Nuclei 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 fermions1 March 2004A 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 gels1 March 2004A 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 galaxy1 March 2004An 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/ |
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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