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| Issue 11, 2024 |
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Extracts from the Internet | ||
Superheavy hydrogen1 October 2001For over forty years physicists have searched for nuclei of superheavy hydrogen 5H, consisting of four neutrons and one proton. Now, for the first time, these nuclei have been reliably detected in an experiment conducted by Russian scientists from the Joint Institute for Nuclear Research in Dubna and Kurchatov Institute in collaboration with their colleagues from France and Japan. Produced in the reaction 1H(6He,2He)5H, the nuclei of the isotope 5H were identified by the kinetics of the decay of 2He into two protons. The energy spectrum of the protons shows a resonance which, according to calculations, corresponds with the nucleus of superheavy hydrogen as the second reaction product. The discovery became possible thanks to a combination of a cryogenic target, special kinds of detectors, and a unique source of 6He nuclei developed at Dubna. Source: Phys. Rev. Lett. 87 092501 (2001) Cancellation of magnetic moments1 October 2001H Adachi and his colleagues in Japan have discovered that the compound Sm0,976Gd0,024Al2 may have zero macroscopic magnetization even with the spins (and intrinsic magnetic moments) of its electrons all aligned in a single direction as in a common ferromagnet. Spin magnetization and that due to the orbital motion of atomic electrons are different in their temperature dependence. At a temperature of 67.5 K the perfect cancellation of the two magnetizations occurs, although both above and below this temperature the substance does have a magnetic moment. The alignment of electron spins was discovered by studying the Compton scattering of polarized X rays from a sample. The effect was predicted theoretically by the Australian physicist A Stewart in 1972. It may prove useful in experiments which require spin polarization but in which the effect of a macroscopic magnetic field is undesirable. Source: Phys. Rev. Lett. 87 127202 (2001) An anomalous acoustoelectric effect1 October 2001The normal acoustoelectric effect is the appearance in a material of an electric current parallel to the sound wave propagation direction. The study of this effect may be useful in understanding interactions between electrons and the vibrations of the crystal lattice. A collaboration of scientists from Russia (Ioffe Physical Technical Institute, St. Petersburg), Ukraine, and Poland studied the propagation of acoustic surface waves in a thin film of La0,67Ca0,33MnO3 laid onto a substrate of piezodielectric material LiNbO3. It is found that, along with the ordinary current, an additional current is generated in a material, which does not depend on the direction of the sound wave and which in a certain temperature range exceeds the current due to the normal acoustoelectric effect. A detailed study showed that the additional current is due to the properties of the piezodielectric substrate and is produced by the electric fields resulting from the compressions and rarefactions in the field of the acoustic wave. Source: Physics News Update, Number 557 Superconductivity in the fullerene1 October 2001In a pure crystal of fullerene C60 the distance between the molecules is 1.415 nm, and the temperature at which such a crystal becomes superconducting is Tc= 18 K. It is known that inducing hole superconductivity (hole injection) and doping the crystal with certain substances may lead to a higher transition temperature. A record high transition temperature of Tc=117 K was achieved by B Battlog and his colleagues from Lucent Technologies by doping a C60 crystal with molecules of tribromo-methane Br3CH. Placed in the space between fullerene molecules, the Br3CH molecules increase the lattice parameter to 1.445 nm, causing Tc to rise to a temperature characteristic of high-temperature superconductors. Source: www.science.com An X-ray burst1 October 2001For the first time, a short powerful burst of X-ray radiation from the object Sgr A* at the centre of our galaxy has been detected by the space-based Chandra Observatory. Within a few minutes the source's brightness increased 45 times, then decreased by a factor of 5 within the next ten minutes, and then returned to its normal level over a period of several hours. According to the infrared telescope data on the kinematics of stars at the centre of the Galaxy, the location of the source Sgr A* coincides with the supposed location of the central black hole with a mass of about 2,6.106 solar mass. Previously, only weak constant-brightness radiation at radio and X-ray wavelengths has been observed to come from this object. The burst can be explained either by the infall of a comet head into the black hole, or alternatively by the reconnection of magnetic field lines in the black hole's magnetosphere. Either scenario leads to the formation of shock waves and also involves the acceleration of electrons to subrelativistic speeds - and thereby X-ray radiation. Powerful variable-brightness radiation is characteristic of quasars, where it is due to the intense unsteady accretion on supermassive black holes. Modern galaxies also may have passed through a quasar stage in the dim past, but today their central black holes are calm - except for rare events one of which was presumably detected by Chandra. Source: http://unisci.com |
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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