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%.     

Asymptotic normalization coefficients (nuclear vertex constants) for p + 7Be → 8B and the direct 7Be(p, γ)8B astrophysical S factors at solar energies

A new analysis of the precise experimental astrophysical S factors for the direct-capture reaction ⁷Be(p, γ)⁸B [A.J. Junghans et al., Phys. Rev. C 68, 065803 (2003) and L.T. Baby et al., Phys. Rev. C 67, 065805 (2003)] is carried out on the basis of a modified two-body potential approach in which the direct astrophysical S factor, S ₁₇(E), is expressed in terms of the asymptotic normalization constants for p + ⁷Be → ⁸B and two additional conditions are involved to verify the peripheral character of the reaction under consideration. The Woods-Saxon potential form is used for the bound-(p + ⁷Be)-state wave function and for p ⁷Be-scattering wave function. New estimates are obtained for the “indirectly measured” values of the asymptotic normalization constants (the nuclear vertex constants) for the p + ⁷Be → ⁸B and S ₁₇(E) at E ≤ 115 keV, including E = 0. These values of S ₁₇(E) and asymptotic normalization constants have been used for obtaining the indirectly measured values of the s-wave average scattering length and the p-wave effective-range parameters for p ⁷Be scattering. The text was submitted by the authors in English.     

Radio emission of extensive air showers as a method for detecting ultra-high energy cosmic rays

Recording radio emission from extensive air showers (EASs) is considered now as a new promising method for detecting ultra-high energy (E ₀ > 5 × 10¹⁶ eV) cosmic rays. The results of calculation of EAS radio emission at frequencies from 40 to 80 MHz in the EAS energy range E ₀ = 10¹⁴–10¹⁷ eV are reported here, and the possibilities of determining EAS parameters from the radio emission lateral distribution are discussed.     

Coulomb breakup of 8B and the flux of 8B neutrinos from the Sun

A kinematically complete measurement was made of the Coulomb dissociation of ⁸B nuclei on a Pb target at 83 MeV/nucleon. The cross-section was measured at low relative energies in order to infer the astrophysical S-factor for the ⁷Be(p,γ)⁸B reaction. A first-order perturbation theory analysis of the reaction dynamics including E1, E2, and M1 transitions was employed to extract the E1 strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross-section from E _rel = 130 keV to 400 keV, we find S ₁₇(0) = 17.8^+1.4 _-1.2 eV b. Semiclassical 1st-order perturbation theory and fully quantum-mechanical continuum-discretized coupled-channels analyses yield nearly identical results for the E1 strength relevant to solar-neutrino flux calculations, suggesting that theoretical reaction mechanism uncertainties need not limit the precision of Coulomb-breakup determinations of the ⁷Be(p,γ)⁸B S-factor. A recommended value of S ₁₇(0) based on a weighted average of this and other measurements is presented. This recommendation implies a revised value for the theoretical flux of ⁸B solar neutrinos, which is also given.-1 Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"Present address: Kernfysisch Versneller Instituut, Zernikelaan 25, 9747 AA Groningen, The Netherlands; e-mail: davids@kvi.nl     

Radio emission from extensive air showers as a method for cosmic-ray detection

At the present time, radio emission from extensive air showers (EASs) is being considered as a new promising method for detecting cosmic rays of energy in the region E ₀ > 5 × 10¹⁶ eV. Radio emission from an EAS whose development is simulated by the Monte Carlo method is calculated here. The field of radio emission from an EAS is calculated on the basis of two representations of a shower: that as a set of individual particles and that as a continuous set of currents. The sensitivity of radio emission to EAS parameters in the frequency range 10–100 MHz is investigated. The results can be used to analyze experiments that being presently performed (CODALEMA and LOPES) and those that are being planned for the future.     

Resonance structure of the beta-strength function

The beta-decay strength function S _β(E) is described within two approaches: numerical solution of equation of the theory of finite Fermi systems for the effective nuclear field and solution of these equations using the quasi-classical approximation. Calculations were carried out for the isotopes ⁷¹Ge and ¹²⁷Xe. A comparison with experimental data showed their good accuracy. The resonance structure of the function S _β(E) and the quenching-effect resulting from the effective charge of quasiparticles in the nucleus are discussed.     

Estimation of soft X‐ray and EUV transition radiation power emitted from the MIRRORCLE‐type tabletop synchrotron

The tabletop synchrotron light sources MIRRORCLE‐6X and MIRRORCLE‐20SX, operating at electron energies E_el = 6 MeV and E_el = 20 MeV, respectively, can emit powerful transition radiation (TR) in the extreme ultraviolet (EUV) and the soft X‐ray regions. To clarify the applicability of these soft X‐ray and EUV sources, the total TR power has been determined. A TR experiment was performed using a 385 nm‐thick Al foil target in MIRRORCLE‐6X. The angular distribution of the emitted power was measured using a detector assembly based on an NE102 scintillator, an optical bundle and a photomultiplier. The maximal measured total TR power for MIRRORCLE‐6X is P_max? 2.95 mW at full power operation. Introduction of an analytical expression for the lifetime of the electron beam allows calculation of the emitted TR power by a tabletop synchrotron light source. Using the above measurement result, and the theoretically determined ratio between the TR power for MIRRORCLE‐6X and MIRRORCLE‐20SX, the total TR power for MIRRORCLE‐20SX can be obtained. The one‐foil TR target thickness is optimized for the 20 MeV electron energy. P_max? 810 mW for MIRRORCLE‐20SX is obtained with a single foil of 240 nm‐thick Be target. The emitted bremsstrahlung is negligible with respect to the emitted TR for optimized TR targets. From a theoretically known TR spectrum it is concluded that MIRRORCLE‐20SX can emit 150 mW of photons with E > 500 eV, which makes it applicable as a source for performing X‐ray lithography. The average wavelength, = 13.6 nm, of the TR emission of MIRRORCLE‐20SX, with a 200 nm Al target, could provide of the order of 1 W EUV.     

Photodisintegration of 4He and the Supermultiplet Potential Model of Cluster-Cluster Interactions

p+³H and p+³He elastic collisions are described in terms of a supermultiplet model with [ƒ]-dependent potentials. The phase shifts δ ^[ƒ] _L,t,S (E) with [ƒ] = [4], t = S = 0, L = even are reconstructed from the observable nuclear phase shifts δ _L,S (E) of the above collisions. So, the initial-state interaction V ^[4] _L,0,0 (R) of the ⁴He +Υ→³H +p(³He +n) reaction can be found unambiguously, while the final-state interaction V ^[31] _{L, 1, 0} (R) is defined by the observablesδ _L,0 (E) of p+³He scattering. The data on the proton momentum distribution in ⁴He and on the charge-exchange reaction ³H +p→³He +n confirm the model. In calculating the above photonuclear reactions, in addition to the initial-state and final-state antisymmetrizations, preserving the corresponding symmetry [ƒ], the nucleon-nucleon correlations in the ³H (³He) subsystem were also taken into account. The results are in good agreement both with recent experimental data and theoretical investigations by sofianos, Fiedeldey, and Sandhas, who followed a rather different approach. Received August 5, 1994; revised November 30, 1994; accepted for publication December 30, 1994     

Electric dipole moment and charge transfer in alkali-C molecules

Electron excitation rate coefficients for 2p (2p₁, 2p₂, 2p₃, 2p₄, 2p₅, 2p₆) and 3p(3p₅, 3p₆, 3p₇, 3p₈, 3p₁₀) (in Paschen notation) levels of xenon atom have been measured by using electron drift tube technique. The absolute excitation coefficients were obtained from the optical signal at the anode in Townsend xenon discharges, after correction for detector quantum efficiency. The ionization coefficients were determined from the spatial emission profile. The measurement were made for the electric field to xenon atom number density ratios (E/N) from Vm² to Vm². The data were obtained between moderate E/N values where electrons are in equilibrium and very high E/N values where electrons may not be in equilibrium with the local field. It was found that at the highest values of E/N heavy particles do not contribute to the excitation under the present conditions. The absolute excitation coefficients for the studied levels of xenon are to our knowledge the only experimental data available in the literature. Received 17 March 1999 and Received in final form 9 August 1999     

Fine structure of strength functions for beta decays of atomic nuclei

The β transition strength function S _β(E) is the nuclear excitation energy distribution of moduli squared of the β-decay-type matrix elements. The function S _β(E) determines the characteristics of β decay, the spectra of accompanying radiation, and the probabilities of delayed processes following the β decay. Until recently, tools widely used for experimental investigation of the S _β(E) structure have been total absorption gamma spectrometers and total absorption gamma-ray spectroscopy (TAGS) which could not provide high energy resolution. Development of experimental techniques allows nuclear spectroscopy methods with high energy resolution to be used for studying the fine structure of S _β(E). A thorough investigation of this kind has been carried out for a number of nuclei produced at the YASNAPP-2 facility in Dubna. In this review, studies involving works on measuring the fine structure of S _β(E) in spherical and deformed nuclei are analyzed. Modern nuclear spectroscopy methods made it possible to identify the splitting of peaks from nuclear deformation in S _β(E) for Gamow-Teller (GT) transitions. The resonance nature of S _β(E) for first-forbidden (FF) transitions in both spherical and deformed nuclei is experimentally proven. It is shown that for some nuclear excitation energies, FF transitions can be comparable in intensity with GT transitions. Criteria for verifying the completeness of nuclear decay schemes are considered. The S _β(E) functions obtained by TAGS and by the high-resolution spectroscopy are compared.     

Molecular orbital study of excited state geometry of substituted benzenes

The liquid-like structure of a polystyrene latex solution of particle size 109 nm and its dependence on the ionic strength of added sodium chloride is investigated via the static light scattering structure factor S(Q). The experimental S(Q)s are compared with structure factors derived in the rescaled mean spherical approximation (RMSA) of Hansen and Hayter. After adjustment of the macromolecular charge Z _M such that the neat (salt free) latex solution is best represented by the RMSA, the experimental structure factors obtained after addition of salt can adequately be accounted for in terms of the RMSA by merely readjusting the ionic strength in the calculations. Our investigation indicates that the RMSA and the underlying screened Coulomb potential are suited for a detailed simulation of the structure and structural changes due to a variation of the ionic strength of liquid-like ordered solutions.     

Diffusion activation energy versus the favourable energy in two-order-parameter model:A molecular dynamics study of liquid Al

In the present work, we find that both diffusion activation energy E_a(D) and E_a(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex(T,P)/k_B=a(P)+b(P)T+c(P)exp(E_f/k_BT), which together with the small ratio of E_f/k_BT leads to the relationship of excess entropy to temperature and pressure, i.e. S^ex≈-cE_f/T, where c is about 12 and E_f (=Δ E-PΔV) is the favourable energy. Therefore, there exists a simple relation between E_a(S^ex) and E_f, i.e. E_a(S^ex)≈cE_f.     

Generation of far-infrared radiation by hot holes in germanium and silicon inE ⊥H fields

The experimental results obtained by the investigation of stimulated FIR emission from dopedp-type germanium andp-type silicon by hot holes in crossedE andH fields at = 10 and 80 K are reported. The analysis of the emission intensity fromp-type germanium as a function ofE andH fields permits us to draw a conclusion about the important role of quantization of the energy spectrum of light holes and the contribution of light hole transitions with n = 2 to the amplification of FIR radiation. A new region of generation is demonstrated inp-type germanium under uniaxial stress. The first experimental results on stimulated FIR emission fromp-type silicon are reported.     

Tuning of the open‐circuit voltage by wide band‐gap absorber and doped layers in thin film silicon solar cells

We present an experimental study combined with computer simulations on the effects of wide band‐gap absorber and window layers on the open‐circuit voltage (V_oc) in single junction thin film silicon solar cells. The quantity ΔE_p, taking as the difference between the band gap and the activation energy in ?p? layer, is treated as a measure of the p‐layer properties and shows a linear relation with V_oc over a range of 100 mV with a positive slope of around 430 mV/eV. Two limiting mechanisms of V_oc are identified: the built‐in potential at lower ΔE_p and the band gap of the absorber layer at higher ΔE_p. The results of the experimental findings are confirmed by computer simulations. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Fine structure of the strength function for β<Superscript>+</Superscript>/<Emphasis Type="Italic">EC</Emphasis> decay of <Superscript>160<Emphasis Type="Italic">g</Emphasis></Superscript>Ho (25.6 min)

A strength function for the β⁺/EC decay of the deformed ^160g Ho (25.6 min) nucleus has been obtained from experimental data. The fine structure of the strength function S _β(E) is analyzed. It is found to have a pronounced resonant structure for Gamow-Teller transitions. In S _β(E) with μ_τ = +1 the Gamow-Teller resonance has been observed to split into two components. This splitting is associated with anisotropy of isovector density oscillation in deformed nuclei. The β⁺/EC strength function for first-forbidden transitions is obtained in the Coulomb (ξ) approximation. It is shown that S _β(E) for first-forbidden transitions does not have a pronounced resonant structure. The text was submitted by the authors in English.     

Thermal stability and crystallization kinetics of Ge–Se–Cd glasses

The effect is reported of varying cadmium concentration on the glass transition, thermal stability and crystallization kinetics of Ge₂₀Se_{80? x} Cd _x (x = 2.5, 5, 7.5 and 10 at. %) glasses. Differential scanning calorimetry results under non-isothermal conditions for the studied glasses are reported and discussed. The values of the glass transition temperature (T_g ) and the peak temperature of crystallization (T_p ) were found to be dependent on heating rate and Cd content. From the heating rate dependence of T_g and T_p , the values of the activation energy for glass transition (E_g ) and the activation energy for crystallization (E_c ) were evaluated and their composition dependence discussed. The thermal stability of the glasses was evaluated using various thermal stability criteria such as ΔT, H_g and S. The stability calculations emphasize that the thermal stability decreases with increasing Cd content.     

Electronic structure and X-ray spectra of transition metal sulfides NiS,CuS, and ZnS

A numerical electronic band structure calculations for sulfides NiS, CuS, and ZnS are carried out. Using the results a detailed analysis of a valence states is performed; obtained partial densities of states are compared with X-ray SL _2,3 and $ SK_{\beta _{1,3} } $ SK_{\beta _{1,3} } -emission spectra. We showed that spectrum lineshape depends on hybridization strength between various Me(3d)-orbitals and 3p-states of sulfur. The hybridization strength and the symmetry of hybrid Me(3d)-orbitals are defined by crystal lattice structure. Finally a well splitted in energy bonding and antibonding states Me(3d)-S(3p) appear while weakly hybridized Me(3d)-states mainly contribute to spectra intensity in the energy between them. A good agreement between the theoretical and the experimental spectra of valence band for considered sulfides is obtained.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

Crystallization kinetics and thermal stability of Se98-x Zn2In x chalcogenide glasses

In this paper, we report on the non-isothermal crystallization kinetics of Se_{98 ?x} Zn₂In _x (0 ≤ x ≥ 10) chalcogenide glasses. The onset crystallization activation energy E _c, peak crystallization activation energy E _p and overall crystallization activation energy E have been determined by different approaches. The values of E _c, E _p and E have minima at a composition corresponding to 6 at% In. However the stability factor S and the crystallization rate constant stability factor K have a maximum and a minimum, respectively, at in the same composition. The nucleation and growth order parameter n, and the dimension order parameter m, are also determined and discussed for the present glasses.     

(EC+β +) decay of 130Nd and 140Tb

The available astrophysical S(E) factor data for the reaction ⁷Li (p,α)α at 10 < E < 1000keV exhibit an exponential increase at low energies due to the effects of electron screening. A parametrisation of the data using a non-resonant, direct process and two subthreshold resonances reproduces the data at energies E≥ 100keV, while at lower energies this calculated S _b(E) factor curve for bare nuclides drops below the data, which in turn represent the case of electron-shielded nuclides, i.e. the electron-shielded S _s(E) factor. The comparison between S _b(E) and S _s(E) leads to an electron-screening potential energy U _e = 350eV, which is much higher than the adiabatic limit of 175eV and not understood at present. The deduced value of S _b(0) is considerably smaller than the previously adopted value of 59keV b, significantly increasing the calculated abundance of ⁷Li in big-bang nucleosynthesis. The Trojan-horse method was applied to the reaction ⁷Li (p,α)α to determine the energy dependence of the S _b(E) factor for 10 < E < 370keV, free from the effects of the Coulomb barrier and electron screening. The THM results are close to the calculated S _b(E) curve and suggest that the THM may become a powerful way to obtain improved information on low-energy cross-sections and associated electron-screening effects in a model-independent way. Received: 9 September 2000 / Accepted: 5 December 2000