1 March 2020
The Borexino collaboration, in which Russian scientists take part, presented the results of 12-year measurements of geoneutrino – antineutrino anti-ν generated inside the Earth upon the fission of radioactive element nuclei and, perhaps, other processes. The possibility of recording geoneutrinos was pointed out by G.A. Gamov as far back as 1953. In 1960, M.A. Markov suggested that the reactions of inverse beta-decay should be used for their registration, and they were first registered in 2016 using Borexino and KamLAND detectors. The Cherenkov Borexino detector is located in the mountain tunnel at Gran Sasso National Laboratory in Italy. (see UFN 171 977 (2001) [Phys. Usp. 44 931 (2001)], UFN 183 315 (2013) [Phys. Usp. 56 296 (2013)] and UFN 184 555 (2014) [Phys. Usp. 57 512 (2014)]. The analysis of the spectra of geoneutrinos and the background from reactor neutrinos gives the total number of registered geoneutrinos (≈ 53). After subtraction of events from the Earth crust, the number of anti-ν from the mantel is 23.7+10.7−10.1. Radioactive decays are accompanied by heat release. This allows the total radiogenic heat release of the lithosphere (38.2+13.6−12.7 TW) to be found from the geoneutrino flux, which is well consistent with the silicate models of the Earth structure. The neutrinos interact weakly and leave freely the Earth center. Therefore, their observation provides unique insight into the processes inside the planet. According to one of these hypotheses, a natural nuclear reactor may function inside the Earth core. The observed geoneutrino flux gives a restriction on its possible power W<2.4 TW.
Source: Phys. Rev. D 101 012009 (2020)
Deformation of atomic nuclei
1 March 2020
Many atomic nuclei can be deformed and take different shapes. However, in all hitherto known cases, deformed nuclei could be either only symmetric about the mirror reflection in the equatorial plane or only asymmetric (e.g. pear-shaped). Yu.Ts. Oganesyan (JINR, Russia) with colleagues from China and USA discovered for the first time that one and the same atomic nucleus can take both symmetric and asymmetric shape. Gamma-ray photons emitted upon a spontaneous 252Cf nucleus fission were registered in the Berkeley National Laboratory (USA). Intranuclear transition energies in a daughter 144Ba nucleus were measured and the scheme of energy level positions was constructed. Six levels and several transitions between levels were revealed for the first time. The shape of the nuclei can be reconstructed using this information. It turned out that the 144Ba nucleus can be deformed as an octupole asymmetrically shaped about spatial reflection, but it can also have a quadrupole symmetric shape.
Source: Phys. Rev. Lett. 124 032501 (2020)
Quantum correlations of a massive mirror
1 March 2020
In 1967, V.B. Braginskii obtained the limit on the precision of measurements known as the Standard Quantum Limit conditioned bythe noises and by the backreaction effect of measurement on the system (UFN 114 41 (1974) [Sov. Phys. Usp. 18 644 (1975)]). This limit has already been surpassed earlier in micromechanical experiments at cryogen temperatures with the help of quantum nondestructive measurements. Laser LIGO/Virgo interferometers register gravitational waves from merging of black holes and neutron stars. H. Yu (LIGO collaboration) with co-authors has shown that the LIGO detector is also able to surpass the standard quantum limit. The interferometer operated in the normal mode like in gravitational wave registration except that the light with a high degree of quantum compression was used. It was established that the detector produced quantum correlation between the position of the 40-kg quartz mirror and 200-kW laser beam fluctuations, which allowed nondestructive quantum measurements 3 dB (a factor of 1.4) below the standard quantum limit. Impressive is the fact that quantum fluctuations of light affect the motion of such a massive mirror, and this influence can be measured even at room temperature.
Source: arXiv:2002.01519 [quant-ph]
Electrically pumped topological laser
1 March 2020
Topological lasers with valley edge electromagnetic modes used to generate lasing are of great interest for technical applications owing to high generation stability. The topological lasers created earlier were pumped using radiation of another laser. Y. Zeng (Nanyang Technological University, Singapore) with colleagues demonstrated for the first time an electrically pumped terahertz topological laser. In the principle of operation, it belongs to quantum-cascade lasers. Electrically generated lasing occurs in a photon crystal consisting of an array of quasi-hexagonal holes (triangles with cut angles) in flat semiconductor layers. In such a crystal, standing waves do not occur, but an electromagnetic field circulates along the perimeter of triangles and valley edge modes are excited. As a result, the radiation spectrum consists of several regularly positioned peaks near the frequency of 3.2 THz. The insertion of artificial defects into the photon crystal did not produce a substantial effect upon laser operation.
Source: Nature 578 246 (2020)
Periodic fast radio burst
1 March 2020
Although more than a hundred cosmic fast radio bursts have already been discovered, the mechanism of their generation has not yet been reliably established (see the review in UFN 188 1063 (2018) [Phys. Usp. 61 965 (2018)]. According to one of the hypotheses, bursts occur on magnetized neutron stars – magnetars. CHIME/FRB collaboration was the first to discover periodicity of fast radio bursts which, perhaps, will help to clarify their nature. The source FRB 180916.J0158+65 was observed during 400 days. All 28 bursts recorded within this time were found to get into phase windows four days wide and positioned with a period of 16.35 ± 0.18 days. Although no bursts occurred in half of these intervals, and from 1 to 5 bursts were noticed in other intervals, the above-mentioned periodicity of the phase windows have statistical significance of ≈ 5 σ. Its reason remains still unknown. The period of ≈ 16 days is likely to correspond to the orbital period of neutron star motion around the companion star along an elongated orbit. It is not excluded that the periodicity is explained by eclipses or lensing by the other star or by the accretion disc. In the magnetar model, periodicity may perhaps be explained by a slow neutron star rotation.
Source: arXiv:2001.10275 [astro-ph.HE]
Possible identification of high-energy neutrino sources
1 March 2020
Cosmic neutrinos ν with energies above 50 TeV are registered by the IceCube detector located in the Antarctic ice (see UFN 184 510 (2014) [Phys. Usp. 57 470 (2014) and by the Baikal underwater telescope (see UFN 185 531 (2015) [Phys. Usp. 58 495 (2015)). The origin of these # is not yet known. It is only once that a neutrino event may have coincided with a gamma-ray burst on a blasar – an active galactic nucleus. A.V. Plavin (ASC of LPI RAS, MIPT), Yu.Yu. Kovalev(ASC of LPI RAS, MIPT, and Max Planck Institute for Radio Astronomy), Yu.A. Kovalev (ASC of LPI RAS), and S.V. Troitskii (INR RAS) reported the discovery of correlation between the neutrino events and galactic activity in the radio frequency band, which may testify to the origin of high-energy neutrinos in radio-bright galaxies. The observational data of 3388 galaxies by PATAH-600 radio telescope and very-long-baseline radio interferometers, as well as the IceCube data on 56 neutrino events with energies above 200 TeV were used. Radio galaxies located in the direction of ν arrival were revealed to exhibit a heightened activity with the probability of random coincidence of ≈ 0.2 %. Moreover, the ν recording time often gets into the period of galactic activity growth. Possibly ν are produced in the scattering of high-energy protons by photons emitted by the accretion disc around the central black hole or by other protons in a nearly pc-sized region. Radio emission may have been generated in farther jet regions.
Source: arXiv:2001.00930 [astro-ph.HE]
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.
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