Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities

Differential cross sections for Compton scattering from the deuteron were measured at MAX-lab for incident photon energies of 55 MeV and 66 MeV at nominal laboratory angles of $45^\circ$, $125^\circ$, and $135^\circ$. Tagged photons were scattered from liquid deuterium and detected in three NaI spectrometers. By comparing the data with theoretical calculations in the framework of a one-boson-exchange potential model, the sum and difference of the isospin-averaged nucleon polarizabilities, $\alpha_N + \beta_N = 17.4 \pm 3.7$ and $\alpha_N - \beta_N = 6.4 \pm 2.4$ (in units of $10^{-4}$ fm$^3$), have been determined. By combining the latter with the global-averaged value for $\alpha_p - \beta_p$ and using the predictions of the Baldin sum rule for the sum of the nucleon polarizabilities, we have obtained values for the neutron electric and magnetic polarizabilities of $\alpha_n= 8.8 \pm 2.4$(total) $\pm 3.0$(model) and $\beta_n = 6.5 \mp 2.4$(total) $\mp 3.0$(model), respectively.Comment: 4 pages, 2 figures, revtex. The text is substantially revised. The cross sections are slightly different due to improvements in the analysi

The analysis of factors which cause weariness, and its influence on safety of work

Проаналізовані основні причини появи втоми у працівників та розглянуто її вплив на стан здоров’я людей та працездатність. Розроблені рекомендації щодо зменшення проявів втоми різних видів, в тому числі, і професійної, недопущення її глибоких стадій, а також прискорення відновлення сил і працездатності без шкоди для здоров’я працівників.Principal causes of occurrence of weariness at workers are analyses and its influence on a state of health people and work capacity is considered. Are resulted: degrees of weariness workers which arise under the influence of labour loads, their characteristic, symptoms and influence on fulfillment of the professional obligations. Including, and professional, not to an assumption of its deep stages, and also acceleration of restoration forces and work capacity without harm recommendations about reduction of displays weariness of different kinds are developed for health of workers.Проанализированы основные причины появления усталости у работников и рассмотрено её влияние на состояние здоровья людей и трудоспособность. Приведены: степени усталости работников, которые возникают под влиянием производственных нагрузок, их характеристика, симптомы и влияние на выполнение своих профессиональных обязанностей. Разработаны рекомендации по уменьшению проявлений усталости разных видов, в том числе, и профессиональной, недопущению её глубоких стадий, а также ускорению восстановления сил и трудоспособности без вреда для здоровья работников

Comment on ``Evidence for Narrow Baryon Resonances in Inelastic pp Scattering''

Compton scattering data are sensitive to the existence of low-mass resonances reported by Tatischeff et al. We show that such states, with their reported properties, are excluded by previous Compton scattering experiments.Comment: One page, submitted to PR

Extending the lining life in circulatory vacuum units at OAO EVRAZ NTMK

Practical methods for extending the life of submersible tubes in vacuum chambers are considered. The structure of periclase-chromite components is studied. Refractories corresponding to optimal vacuum-chamber operation in the converter shop at OAO EVRAZ NTMK are selected. © 2013 Allerton Press, Inc

Quasi-free Compton Scattering from the Deuteron and Nucleon Polarizabilities

Cross sections for quasi-free Compton scattering from the deuteron were measured for incident energies of 236--260 MeV at the laboratory angle -135 degrees. The recoil nucleons were detected in a liquid-scintillator array situated at 20 degrees. The measured differential cross sections were used, with the calculations of Levchuk et al., to determine the polarizabilities of the bound nucleons. For the bound proton, the extracted values were consistent with the accepted value for the free proton. Combining our results for the bound neutron with those from Rose et al., we obtain one-sigma constraints of alpha_n = 7.6-14.0 and beta_n = 1.2-7.6.Comment: 4 pages, 3 figures, accepted in PR

Low-Energy Compton Scattering of Polarized Photons on Polarized Nucleons

The general structure of the cross section of $\gamma N$ scattering with polarized photon and/or nucleon in initial and/or final state is systematically described and exposed through invariant amplitudes. A low-energy expansion of the cross section up to and including terms of order $\omega^4$ is given which involves ten structure parameters of the nucleon (dipole, quadrupole, dispersion, and spin polarizabilities). Their physical meaning is discussed in detail. Using fixed-t dispersion relations, predictions for these parameters are obtained and compared with results of chiral perturbation theory. It is emphasized that Compton scattering experiments at large angles can fix the most uncertain of these structure parameters. Predictions for the cross section and double-polarization asymmetries are given and the convergence of the expansion is investigated. The feasibility of the experimental determination of some of the struture parameters is discussed.Comment: 41 pages of text, 9 figures; minor revisions prior to publication in Phys. Rev.

Dirac-Foldy term and the electromagnetic polarizability of the neutron

We reconsider the Dirac-Foldy contribution $\mu^2/m$ to the neutron electric polarizability. Using a Dirac equation approach to neutron-nucleus scattering, we review the definitions of Compton continuum ($\bar{\alpha}$), classical static ($\alpha^n_E$), and Schr\"{o}dinger ($\alpha_{Sch}$) polarizabilities and discuss in some detail their relationship. The latter $\alpha_{Sch}$ is the value of the neutron electric polarizability as obtained from an analysis using the Schr\"{o}dinger equation. We find in particular $\alpha_{Sch} = \bar{\alpha} - \mu^2/m$ , where $\mu$ is the magnitude of the magnetic moment of a neutron of mass $m$. However, we argue that the static polarizability $\alpha^n_E$ is correctly defined in the rest frame of the particle, leading to the conclusion that twice the Dirac-Foldy contribution should be added to $\alpha_{Sch}$ to obtain the static polarizability $\alpha^n_E$.Comment: 11 pages, RevTeX, to appear in Physical Review

Non-thermal transport of energy driven by photoexcited carriers in switchable solid states of GeTe

Phase change alloys have seen widespread use from rewritable optical discs to the present day interest in their use in emerging neuromorphic computing architectures. In spite of this enormous commercial interest, the physics of carriers in these materials is still not fully understood. Here, we describe the time and space dependence of the coupling between photoexcited carriers and the lattice in both the amorphous and crystalline states of one phase change material, GeTe. We study this using a time-resolved optical technique called picosecond acoustic method to investigate the \textit{in situ} thermally assisted amorphous to crystalline phase transformation in GeTe. Our work reveals a clear evolution of the electron-phonon coupling during the phase transformation as the spectra of photoexcited acoustic phonons in the amorphous ($a$-GeTe) and crystalline ($\alpha$-GeTe) phases are different. In particular and surprisingly, our analysis of the photoinduced acoustic pulse duration in crystalline GeTe suggests that a part of the energy deposited during the photoexcitation process takes place over a distance that clearly exceeds that defined by the pump light skin depth. In the opposite, the lattice photoexcitation process remains localized within that skin depth in the amorphous state. We then demonstrate that this is due to supersonic diffusion of photoexcited electron-hole plasma in the crystalline state. Consequently these findings prove the existence of a non-thermal transport of energy which is much faster than lattice heat diffusion

АНАЛИЗ ЭЛЕКТРОННОЙ СТРУКТУРЫ ЭЛЕКТРИЧЕСКИ ИНДУЦИРОВАННОЙ КВАНТОВОЙ ТОЧКИ ВО ВНЕШНЕМ МАГНИТНОМ ПОЛЕ

 Numerical modeling of the electronic structure of a quantum dot, induced by an electric field of a nanosized disc-shaped gate, is carried out in the presence of external magnetic field. The dependences of an electronic energy spectrum on electric and magnetic fields are calculated using the finite element method. It has been found that a series of anti-crossing points for electronic levels takes place at relatively small magnetic fields. The existence of groups of close-energy levels (electronic shells) has been found. It has been shown that despite the essential distinction of the gate potential from the parabolic one, a model of a near-surface anisotropic harmonic oscillator can be effectively used for a qualitative description of the electronic structure of the electrically induced quantum dot. With the use of this model, the evolution of energy spectrum and wave function structure with magnetic and electric fields is described. In particular, the anisotropic oscillator model allows to predict anti-crossing points of electronic levels in external fields, as well as quasi-degeneracy of states having different values of the angular momentum projection.  Проведено численное моделирование электронной структуры квантовой точки, индуцированной электрическим полем наноразмерного дискообразного затвора и находящейся во внешнем магнитном поле. С помощью метода конечных элементов рассчитаны зависимости энергетического спектра электрона от величины магнитного поля и потенциала на затворе. Обнаружено наличие последовательности точек квазипересечения электронных уровней при относительно слабых магнитных полях, а также существование групп близких уровней энергии (электронных оболочек). Показано, что, несмотря на существенное отличие потенциала затвора от параболического потенциала, для качественного описания электронной структуры электрически индуцированной квантовой точки возможно использование модели приповерхностного анизотропного гармонического осциллятора. На основании этой модели описаны закономерности эволюции структуры волновых функций при изменении потенциала затвора и магнитного поля. В частности, модель анизотропного осциллятора позволяет предсказать появление точек квазипересечения электронных уровней при изменении внешних полей, а также квазивырождение состояний с различными значениями проекции орбитального момента импульса.