On EAS spectrum with extremely low content of hadrons in the primary-energy range ∼10<Superscript>14</Superscript>−10<Superscript>15</Superscript> eV

The distribution of energy fluxes of the hadron component of extensive air showers through an ion-ization calorimeter in the primary-energy range ～3 × 10¹³?10¹⁶ eV is considered. Extensive air showers with zero and minimum energy fluxes of the hadron component are selected. It is concluded that the primary-energy range E ₀ ≈ 1 × 10¹⁴?2 × 10¹⁵ eV contains isotropic γ radiation with a spectrum close to bell-shaped, having a maximum near E ₀ ≈ 2.2 × 10¹⁴ eV and an additional peak near E ₀ ≈ 1.6 × 10¹⁵ eV.     

An interpretation of the energy-momentum tensor of the dirac field with anomalous magnetic moment

The ground state radiative widths of the 1.56 MeV (3/2⁺) and the 1.35 MeV (5/2^?) levels in¹⁹F were determined by inelastic electron scattering. The measured cross sections have been analysed using DWBA calculations. The resultsΓ _y ⁰ (5/2^?→1/2^?,E3)=(8.1±1.7)·10^?10eV andΓ _y ⁰ (3/2⁺→1/2⁺,E2=(1.76±0.15)·10^?4eV are in agreement with, but more accurate than, former measurements.     

Experimental estimation of the possible subbarrier penetration of ultracold neutrons through vacuum-tight foils

The probability of subbarrier penetration of ultracold neutrons through 15 μm-thick vacuum-tight beryllium foil (boundary energy for beryllium is E _{lim Be}=249 eV) was measured. It is equal to (?1.2±1.0) × 10^?8 per collision of neutrons with energy lower than ～160 neV.     

Spatial distribution of EAS radio emission at 32 MHz

The results of the reprocessing of the experimental data on radio emission from extensive air showers (EAS) earlier obtained at the EAS facility (Moscow State University) are reported. The maximum depth distribution of showers is found from analysis of the width of the spatial distribution of radio emission. The average maximum depth is X _max = 655 ± 8 g/cm² for the primary particle energy E ₀ ～ (3–4) × 10¹⁷ eV. The normalized field strength at E ₀ = 10¹⁷ eV is 3.2 ± 0.6 and 2.8 ± 0.4 μV/(m MHz) at distances of 50 and 100 m from the axis, respectively. The accuracy of E ₀ determination from the radio emission field strength at 50 m from the axis is about 20%.     

The exciton absorption in deformed germanium

Absorption spectra at 77° K near the direct (κ = 0) exciton transition are reported for deformed and undeformed single-crystal films of n-type Ge oriented on (111); Elliott's theory is applied. The optical width of the forbidden band for this transition is found as E_{g 0} = (0.8821 ±±0.0002) eV, while the exciton binding energy is found as E_ex(0) = = (0.0016±0.0003) eV for undeformed Ge at 77 ° K. The mean temperature coefficient of E_g for κ = 0 in the range 77 °–297 ° K is (dE_g/ /dT)_p =?3.50 · 10^?4 eV/deg. The effects of thermoelastic deformation on the exciton spectrum give (dE_g/dT)_d = (?1.5±0.1) · 10^?4 eV/deg. The half-width σ ≈ 5 · 10^?4 eV of the exciton peak gives the exciton lifetime as gt ≥ 10^?12 sec.     

A new approach to the problem of electron-atom collision cross section measurements in the low-energy range

Momentum-transfer cross sections for He and Ar have been determined in the energy ranges 5×10^-3?3 eV and 5×10^-3?0.6 eV, respectively using a modified effective-range analysis of the shape of experimental ECR-absorption lines, registered in the afterglows. The following values have been obtained for the scattering length: 1.17±0.01a³₀ for He and 1.53±0.01a³₀ for Ar.     

Untersuchung der vier ersten angeregten Zustände des6Li-Kernes durch Elektronenstreuung

Inelastic electron scattering cross sections were measured for energies below 60 MeV and momentum transfersq between 0.2 and 0.6 fm^?1. Ground state radiative widths Γ _γ ⁰ and transition radiiR _tr were deduced. 2.18 MeV: Γ _γ ⁰ (E2)=(4.40±0.34) · 10^?4 eV,R _tr=(4.28±0.39)fm; 3.56MeV: Γ _γ ⁰ (M1)=(8.31±0.36)eV,R _tr=(2.90±0.10)fm; 4.27 MeV: Γ _γ ⁰ (E2)=(5.4±2.8) · 10^?3 eV,R _tr=(3.4±1.2) fm. The excitation of the 5.37 MeV level shows a transverse angular dependence.     

Messung der Verweilzeit von He-Atomen an Glasoberflächen

Mean sticking times of helium on a glass surface are determined at very low pressures from nonstationary molecular flow through glass capillaries. The temperature range covered is 13.8 °K to 20.4 °K. Resulting sticking times are of the order of 10^?7 to 10^?5 sec. They show a characteristic dependence on temperature and pressure. These measurements can be interpreted by means of a simple model: He-atoms mostly are bound to the surface with an adsorption energyE of 229 cal/mol?0.01 eV (±20%). However with a probability of 10^?4 the energy is 530 cal/mol?0.023 eV (±6%). In both cases sticking times τ follow the equation τ=τ₀exp(E/RT) where τ₀ is about 10^?9 to 10^?10 sec.     

Astrophysical and structural peculiarities of extensive air showers with energy E 0 ≥ 1017 eV from Yakutsk EAS array data

The astrophysical characteristics of primary cosmic rays (PCRs) and the structure of extensive air showers (EASs) with energy E ₀ ≥ 10¹⁷ eV are simultaneously analyzed using the Yakutsk EAS array data acquired in the period 1974–2005. Enhanced and reduced particle fluxes are shown to come from the disk of the Supergalaxy (the Local Supercluster of galaxies) at E ₀ ≥ 5 × 10¹⁸ eV and E ₀ ≤ (2?3) × 10¹⁸, respectively. The development of air showers with E ₀ ≥ (3?5) × 10¹⁸ eV differs significantly from that at lower energies. This is interpreted as a manifestation of the possible interaction between extragalactic PCRs and the matter of this spatial structure.     

Migration and stabilization of hydrogen atoms in KCl

Stabilities of hydrogen atoms at the interstitial (H⁰_i), cation and anion sites (H⁰_sc and H⁰_sa) in KCl have been studied with ESR and thermoluminescence. The close pair between H⁰_i and S^? formed by UV-irradiation of KCl:SH^? recombines first with the activation energy of 0.17±0.02 eV following the emission of light and then H⁰_i becomes mobile with the energy of 0.20±0.02 eV. The energies determined from the decay of ESR signal intensity of H⁰_sc and H⁰_sa are 0.24±0.02 eV and 0.43±0.03 eV, respectively.     

Energy spectrum and anisotropy of cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript>≥10<Superscript>17</Superscript> eV from Yakutsk EAS array data

Data from the Yakutsk extensive air shower array for the period 1974–2004 are used to analyze the energy spectrum and anisotropy of primary cosmic rays (PCRs) with energy E₀≥10¹⁷ eV. The spectra from different regions of the sky are shown to differ in shape. Enhanced and reduced particle fluxes come from the disks of the Galaxy and the Supergalaxy (the Local Supercluster of galaxies) at E₀≥5×10¹⁸ eV and E₀≤ (2?3)×10¹⁸ eV, respectively. This is interpreted as a manifestation of the possible interaction between extragalactic PCRs and the matter of these spatial structures.     

Simulation of the thermal fragmentation of fullerene C60

Defect formation and annealing processes in fullerene C₆₀ at T = (4000–6000) K are studied using molecular dynamics with a tight-binding potential. The cluster lifetime until fragmentation, which proceeds, as a rule, through the loss of a C₂ dimer, has been found as a function of temperature. The activation energy and the frequency factor in the Arrhenius equation for the fragmentation rate have been found to be E _a = (9.2 ± 0.4) eV and A = (8 ± 1) × 10¹⁹s^?1. It is shown that fragmentation can occur already after the C₆₀ cluster loses its spherical shape. This fact must be taken into account in theoretical calculations of E _a.     

Fraction of protons in primary cosmic rays according to data from the PAMIR experiment in consideration of the response of X-ray emulsion chambers

Adjusted data on the fraction of protons in the mass composition of primary cosmic rays (PCRs) in the energy range of 10¹⁵–10¹⁷ eV are presented. Adjustments are made according to detailed calculations of the response of the X-ray emulsion chamber in the PAMIR experiment. It is demonstrated that the fraction of protons in a PCR is 16–18% for E ₀ ≈ 10¹⁵–10¹⁶ eV and does not change within the error for E ₀ ≈ 10¹⁶–10¹⁷ eV.     

Constraints on the fraction of primary gamma rays at ultra-high energies from the muon data of the Yakutsk EAS array

By using data on the total signal and on the muon component of air showers detected at the Yakutsk array, the possible upper limits on the fraction of primary gamma rays at ultra-high energies is analyzed in the framework of the recently suggested event-by-event approach. Upper limits on the photon fraction in the integral flux of primary cosmic rays are derived. At 95% C.L., these limits are 22% for primary energies E ₀ > 4 × 10¹⁹ eV and 12% for E ₀ > 2 × 10¹⁹ eV. Despite the presence of muonless events, the data are consistent with the complete absence of photons at least at 95% C.L. The sensitivity of the results to systematic uncertainties, in particular to those of the energy determination for nonphoton primaries, is discussed. The text was submitted by the authors in English.     

Simulation of the thermal decomposition of the C9H10 methylcubane molecule

The thermal stability of the C₉H₁₀ methylcubane molecule was studied over the temperature range 1100–2100 K by molecular dynamics simulation with the tight binding potential. The temperature dependence of its lifetime to the decomposition moment was determined. The activation energy E _a = 1.7 ± 0.2 eV and frequency factor A = 10^{15.63 ± 0.53} s^?1 of the Arrhenius equation were found. Possible channels and final products of molecule decomposition were studied.     

Muons in extensive air showers of energies E 0=1016.6–1019.8 eV

Data on muons with the threshold energy E _μ≈1.0×secθ GeV in extensive air showers of energies E ₀≥4×10¹⁶ eV measured on the Yakutsk and Akeno arrays are jointly analyzed. The results are compared with the calculations by the quark-gluon-string model with jets. It is shown that this model does not contradict the data measured for energies E ₀≤10¹⁸ eV on both arrays under the assumption that the primary particle composition differs from the composition where heavy nuclei dominate over protons. Experimental data for energies E ₀≥3×10¹⁸ eV indicate that the shower development differs from that predicted by the quark-gluon-string model with jets.     

Measurement of the 15N(α, γ)19F resonances at Ec.m. = 536 keV and 542 keV

The E_c.m. = 536 keV and E_c.m. = 542 keV resonances in the ¹⁵N(α, γ)¹⁹F reaction have been studied using a thick Ti¹⁵N target, determining ωγ = (9.7 ± 2.0) × 10⁻⁵ eV and ωγ < 1 × 10⁻⁵ eV for these two resonances, respectively. For the 542 keV resonance this value is substantially smaller than had been assumed in earlier model calculations, and this reduces the rate of the analog ¹⁵O(α, γ)¹⁹Ne reaction (connecting the Hot CNO cycle and the rp-process) by a factor of ≈ 3 for temperatures in the region of T₉ = 1.     

Zenith-angle dependences of ρ s,600 and ρ μ,600, in giant air showers

Results of a global analysis of data from the Yakutsk array and AGASA are presented. The zenith-angle dependences ρ _s,600(θ) and ρ _μ,600(θ) of the densities of all charged particles and muons (the threshold energy is E _μ ≈ 1.0·secθ GeV) at a distance of 600 m from the axis of giant air showers (GAS) of energies E ₀≥10¹⁹ eV are considered. These dependences are compared with the results of the calculations based on the QGSJET model and performed for the case of primary protons. The results of the calculations within this model agree well with data from both arrays at E ₀≤2×10¹⁸ eV, but they are in a glaring contradiction with GAS data. The experiments indicate that the lateral structure of showers changes at E ₀≥(3–5)×10¹⁸ eV. In all probability this is due to some new processes accompanying their evolution. The neglect of this fact can lead to considerably overestimating the GAS energy (by a factor of 1.5–2.5).     

Temperature dependence of the energy gap of MgxZn1−xTe semiconductors alloys

Wavelength-modulation spectroscopy is used to obtain the temperature dependence of the near band gap reflectivity spectrum E_o of Mg_xZn_1?xTe ternary semiconducting alloys. Results are given in the range 80–100 K for the cubic materials: 0〈x〈0.5. The analysis of the line shapes as a function of x and T confirms the hypothesis of an exciton bound to the complex defect associated with zinc vacancy, as ZnTe. The E_o(x) curve is parabolic. The bowing parameter is C=0.45 ± 0.1 eV at 80 K, C=0.6 ± 0.1 eV at 300 K. Within experimental scattering the temperature coefficient dE₀dT is nearly constant with x:-4.5±0.3 × 10^?4eVK^?1. This data is smaller than the value calculated in the literature for ZnTe from pseudo potential method.     

High spin states and neutron multiplicities after pion capture in181Ta and209Bi

The absorption of stoppedπ ^? in¹⁸¹Ta and²⁰⁹Bi has been investigated by studying prompt and delayedγ-ray spectra. Absolute cross-sections for the yield of isotopes per capturedπ ^? in (π ^?, xn) reactions, as well as the relative probability of populating nuclear states of different spins have been measured for the hafnium and lead isotopes, respectively. A spin as high as 20 has been observed in the production of²⁰⁴Pb. The ground-state rotational bands of the hafnium isotopes are excited to spin values up to 16. Neutron multiplicities as large as 15 have been observed for both targets. A neutron multiplicity of ?8 is most probable for both tantalum and bismuth targets. The strong interaction monopole energy shift? ₀ and widthΓ ⁰ for the 4f level are found to beε ₀(¹⁸¹Ta)=540±100eV; ?₀(²⁰⁹Bi)=1790±150 eV;Γ ₀(¹⁸¹Ta)=225±57 eV;Γ ₀(²⁰⁹Bi) =1166±70 eV. The quadrupole moments, determined from the hyperfine splitting of the 4f pionic atom level, areQ=3.30±0.06b andQ=}-0.50±0.08b for¹⁸¹Ta and²⁰⁹Bi, respectively.