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| Issue 12, 2024 |
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Extracts from the Internet | ||
Hyperhydrogen Λ6H1 March 2012FINUDA Collaboration operating in Frascati Laboratory (Italy) has reported for the first time hypernuclei consisting of four neutrons, a proton and a Λ-hyperon. The possibility of the existence of the Λ6H was predicted in 1963. Two redundant neutrons form a nuclear “halo”. In the absence of the Λ-hyperon they would be ejected from the nucleus over a time 10-22 s but the Λ-hyperon stabilizes 5H, increasing its lifetime to 0.1 ns. Λ6H nuclei were produced in the accelerator in collisions of K mesons with the lithium target in the reaction K- + 6Li → Λ6H + π+ and then decayed by the weak channel Λ6H → 6He + π-. A search for correlated pairs π+π- was conducted; as a result, three events of production of Λ6H were identified in five years among ≈ 3 × 107 interactions of K- with the target. The mass of these nuclei was 5801.4 ± 1.1) MeV, and their binding energy was (4.0 ± 1.1) MeV energy of separation into 5H + Λ). Masses of nuclei found in production reactions are higher by approximately 1 MeV than masses found in decay reactions. This is an evidence of production of Λ6H in the first excited state, fast transition of nuclei to ground state and emission of a photon (photons were not recorded), followed by decay in the ground state. Source: Phys. Rev. Lett. 108 042501 (2012) Photon formation length1 March 2012Ê. Andersen (Aarhus University, Denmark) and his colleagues investigated effects of finite photon formation in matter. The experiment NA63 performed at CERN measured the spectrum of radiation by 197 GeV electrons flying across two sheets of gold foil. After transit, the electrons were deflected in magnetic field and the spectrum of the emitted photons was measured by a detector on the beam line. While in the foil, electrons undergo Coulomb interactions with atoms and emit photons as a result of accelerations (bremsstrahlung radiation) with the Bethe – Heitler spectrum (modified by the Landau – Pomeranchuk – Migdal effect in the range of low energies). An individual photon is formed not at a point but over a certain length. A maximum was observed in the emission spectrum ≈ 0,5 GeV when the gap between the two gold foils was 45 µm. The phenomenon responsible for this specific feature of the spectrum was the fact that the emission of the photon would start within the first foil but would be completed in the second one. This extension of the formation length beyond the physical limits of the structured target is described by the Ternovskii – Shulgin – Fomin effect. Calculations using the formalism developed by R. Blankenbecler fit experimental data quite well. Source: Phys. Rev. Lett. 108 071802 (2012) Rate of propagation of quantum correlations1 March 2012Ì. Cheneau (Max Planck Institute of Quantum Optics, Germany) and his colleagues measured for the first time the speed of propagation of quantum correlations. For some many-body systems, such as spins on a lattice, we are aware of the maximum speed, known as the Lieb – Robinson bound, that limits the speed of propagation of quantum information, in an analogy to the speed of light setting the limit in relativity theory. In their experiment Ì. Cheneau et al. created one-dimensional sequences of 87Rb atoms placed in an optical lattice, one atom per each potential well. These wells are separated by potential barriers — dark areas of the lattice. Rapid reduction of barrier hight produces quasiparticles — doublons (pairs of particles in one potential well) and neighboring holons (empty vacancies — holes). These quasiparticles were quantum-correlated: if a doublon was observed, this meant that that second particle was a holon, and vice versa. Quasiparticles's positions were not fixed — they could tunnel into neighboring potential wells. Fluorescent emission of atoms was monitored through a microscope and speeds of quasiparticles were measured by recording the time quasiparticles took to move over a specific distance. These speeds were approximately twice larger than the speed of sound in superconducting gas and were always below the Lieb – Robinson bound. Source: Nature 481 484 (2012) Generation of magnetic field in shock waves1 March 2012G. Gregori (Oxford University, United Kingdom) and his colleagues conducted an experiment at the LULI laboratory (France) on generation of magnetic field in shock waves. The mechanism of generation was described theoretically by L. Biermann (the “Biermann battery” process). Closed currents emerge in asymmetric shock waves with pressure and temperature gradients, producing magnetic field as a result. Note that this process requires no seeding magnetic fields. In this experiment, powerful laser pulses heated a small carbon rod in a vessel with helium at low pressure. Solenoids recording magnetic field in three planes (via induced currents) were placed around the rod at a distance of about 3 cm. A microexplosion in carbon produced a shock wave in helium which was observed by optical means, and 1-2 µs later surges of magnetic field of 10-30 gauss were detected in the shockwave plane. The experiment simulated generation f magnetic fields by shock waves in the gas which moved in gravitational fields at the early stages of galaxy formation. Despite scale differences, these very different conditions obey quantitatively simple scaling relations. Cosmic shock waves could generate fields up to 10-21 gauss; these fields could be amplified by turbulence and the dinamo effect and thus constitute an important factor for star formation. Source: Nature 481 480 (2012) New data from the Planck telescope1 March 2012New data collected by the Planck space radio telescope were reported at the scientific conference in Bologna. Among other things, the complete (all-sky) map of distribution of carbon monoxide ÑÎ in interstellar molecular clouds was produced. The main component of these clouds is molecular hydrogen, which is difficult to detect. Consequently, CO emission is typically used to study molecular clouds in Galaxy. The existence of diffuse glow (haze) from regions around the center of the Galaxy which resembles synchrotron radiation but has harder spectrum was also confirmed. The nature of this haze remains unclear. Among the suggested hypotheses are, for instance, those of the ejecta of supernova explosions and annihilation of particles of dark matter. The main task of the Planck telescope is the study of the microwave background radiation. The observations of the CO emission outlined above and of the diffuse glow are important not only as such but also for elimination of the noise they create for extraction of the microwave background signal. Source: www.esa.int |
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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