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| Issue 12, 2024 |
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Extracts from the Internet | ||
Element 117 has been synthesized1 May 2010A team of researchers from Russia and the U.S. under the guidance of academician Yu.Ts. Oganesyan have synthesized for the first time six nuclei of the chemical element with atomic number 117. Its isotopes 293117 and 294117 were created on a heavy ion accelerator — the U-400 cyclotron at the JINR (Dubna, Russia) in collisions of the beam of nuclei 48Ca with a target of the radioactive isotope 249Bk. 22.2 mg of 249Bk nuclei were produced at the Oak Ridge National Laboratory (USA) and prepared for use at the RIAR (Dimitrovgrad, Russia); they were incorporated into the target by deposition of oxide BkO2 onto titanium foil. The experimental data was processed at JINR, at the E. Lawrence Livermore National Laboratory (Berkeley, USA) and at two American universities. The method used for the identification of nuclei was the determination of spatio-temporal correlations in the gas-filled fragment recoil separator; it revealed the characteristic chain of α-decays of nuclei which included the sequence of 11 intermediate neutron-rich isotopes. The half-lives of the nuclei 293117 and 294117 are about 14 and 78 ms, respectively. The properties of the observed chains of decay indicate that the experiments have now moved closer to the border of the “island of stability” — that region of long-lived superheavy nuclei whose existence was predicted theoretically. Among the nuclei produced by now, the atomic number is the highest in the nucleus of the element 118 obtained at JINR in collaboration with the Lawrence Livermore National Laboratory in 2006 (see Phys. Usp. 49 1221 (2006)). Source: Phys. Rev. Lett. 104 142502 (2010) Superconductivity on the nanoscale1 May 2010Researchers at Ohio State University (USA) together with colleagues from Japan and Germany found that superconductivity can emerge in samples consisting of only four pairs of molecules of organic salt (BETS)2GaCl4 where BETS is a complex-structure organic compound bis(ethylenedithio)tetraselenafulvalene acting as donor of charges in the salt molecule. The temperature of superconducting transition in a macroscopic specimen of this substance is Tc ≈ 8 Ê; specimens possessed two-dimensional layered structure resembling the structure of high-Tc cuprate superconductors. The electron spectrum of a single layer of (BETS)2GaCl4 on silver substrate at temperatures from 5.8 to 15 K has been studied by scanning tunneling spectroscopy. The superconducting gap was established; its width was a function of temperature and specimen size (length of paired molecular chains of (BETS)2GaCl4). With the shortening of molecular chains down from 50 nm, the gap diminished and superconducting properties decreased correspondingly. However, the gap persisted even in samples measuring about 3.5 nm and consisting of only four pairs of molecules (BETS)2GaCl4. The mechanism of superconductivity in (BETS)2GaCl4 has not yet been identified. It is possible that these molecular-scale superconductors may find applications in nanoelectronics. Source: Nature Nanotechnology 5 261 (2010) Ionization of atoms near the nanotube1 May 2010Ionization of rubidium atoms by electric field created by carbon nanotube has been studied at the Harvard University (USA). Rubidium atoms cooled in a magneto-optical trap to a temperature of 200 µK were sent to the nanotube in the plane perpendicular to its axis. If the angular momentum of the atom with respect to the nanotube did not exceed a certain critical value which was a function of electric potential of the nanotube, the atom began to rotate around the nanotube, approaching it along a spiral trajectory and at the same time greatly accelerating. Then one of the outer electrons of the atom tunneled to the nanotube while the resulting ion felt the Coulomb repulsion and accelerated away from the nanotube at a high velocity. Measurements of the momentum distribution in receding ions as a function of the potential of carbon nanotubes showed good agreement with the predictions of the theoretical model. The effect of ionization of atoms near the nanotube can be used to create high-sensitivity detectors of ultracold atoms. Source: Phys. Rev. Lett. 104 133002 (2010) Adiabatic Landau – Zener transition in Rydberg atoms1 May 2010N. Saquet and his colleagues at the Aime Cotton Laboratory (Orsay, France) studied the dipole-dipole interaction of sodium atoms in Rydberg states, accompanied with electron transitions ns + ns → np + (n – 1)p in the vicinity of n = 48 driven by the Landau – Zener mechanism. A beam of sodium atoms was created by laser-driven ablation of atoms from the surface of a solid specimen. Resonance excitation and irradiation by pulses of infrared laser in the beam produced a concentration of 108 cm-3 of rubidium atoms in Rydberg ns-state. Dipole-dipole interaction of Rydberg atoms combined with a slowly varying external electric field resulted in adiabatic transitions to np levels in the Landau – Zener configuration of nearly intersecting potential energy surfaces of two electronic states. The number of atoms in np states in the beam was measured at the output. This experiment succeeded in inducing Landau – Zener transitions in Rydberg atoms in a controlled manner; a similar technique could be used in the future to produce Rydberg atoms in quantum-entangled states. Source: Phys. Rev. Lett. 104 133003 (2010) White dwarfs in the Galactic halo1 May 2010M. Kilic and his colleagues from the U.S. and Germany have discovered using ground-based optical telescopes three white dwarfs at a distances of 70-80 pc from the Sun; in all likelihood, they belong to the population of very old stars from the galactic halo. Once white dwarfs are formed, they start to cool down and their observed temperature is a measure of their age. The study of white dwarfs is thus an important source of information about the history of star formation in various subsystems in the Galaxy. The three white dwarfs found, two of which form a binary, are among the coldest of the known white dwarfs. Their effective temperature is 3700-4100 K, which corresponds to the age of stars approximately 10-11 billion years. The type of motion of white dwarfs shows that they are likely to belong to the Galactic halo, while their belonging to the disk is rejected at the 2 σ confidence level. A comparison with the stars of the galactic disk led to a conclusion that there was a time gap of one to two billion years between the epoch of star formation in the halo and the beginning of star formation in the galactic disk. A similar result was obtained earlier using Hubble telescope observations of cold white dwarfs in two globular star clusters. Source: arXiv:1004.0958v1 [astro-ph.GA] |
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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