Optical properties of natural magnetite in the region from 2.5 to 50 μm

Infrared transmission measurements at 300° K from 2.5 to 50 μm have been carried out on natural magnetite (Fe₃O₄) from Mineville, New York. The measurements were made on magnetite powder in the form of a pellet and for two concentrations of 0.5 and 1.0 per cent.The spectrum analysis gave characteristic absorptions though broad and weak between 1100 and 200 cm⁻¹. The absorption coefficient α, the refractive index n, the real ϵ₁ and imaginary ϵ₂ parts of the dielectric constant and the reflectivity R have also been calculated.     

The absorption spectrum of water in the 1.25 μm transparency window (7408–7920 cm)

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded between 7408 and 7920 cm⁻¹ by high sensitivity cw-cavity ring down spectroscopy (CW-CRDS). This region covers the low energy part of the 1.25 μm transparency window and corresponds to weak water absorption of the first hexad of interacting vibrational bands. The achieved sensitivity – on the order of α_min ∼ 2 × 10⁻¹⁰ cm⁻¹ – has allowed one to newly measure 2028 weak transitions with intensities down to 2 × 10⁻²⁹ cm/molecule at 296 K i.e. more than two orders of magnitude lower than previous observations. Three hundred and fourty-one new and corrected energy levels belonging to 26 vibrational states of H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O could be determined from the vibration–rotation analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the studied region by Fourier Transform Spectroscopy and existing databases have been critically evaluated. The most complete list for water in the region is provided as Supplementary Material.     

On the propagation of a light pulse in the “transparency window” of a medium with population inversion

The propagation of a light pulse through a layer of a substance with population inversion and, correspondingly, with an anomalous dispersion in the transparency range is considered. It is shown that, when the wave packet approaches the layer of the substance with a strong anomalous dispersion, two additional wave packets arise at the rear boundary of the layer. One of these packets has a negative energy and moves in the layer from its rear to the front boundary, while the other packet moves away from the rear boundary of the layer into a vacuum. As the initial wave packet comes into contact with the front boundary of the layer of the substance, it meets the packet of the negative energy. As a result, the two packets annihilate one another, after which only one packet remains, which moves away from the layer.     

π+ absorption on 12C in the Δ(1232) region

A search for possible structure in the energy spectrum of forward going protons from the ¹²C(π⁺, 3p)X reaction was undertaken. The measurement was done for π⁺ momenta of 355, 375, and 405 MeV/c. No narrow (less than 20 MeV) structure was found. A broad structure corresponding to a quasi-free scattering of the pion before capture, superimposed on a continuum background, was observed. The data indicate that additional free nucleons or light products are usually present in the final state.     

Analysis of the properties of the molecular–cluster xenon mixture in the mesoscopic phase transition region

We report on the results of calculation of the concentrations of cluster subcomponents in a molecular–cluster xenon mixture at temperatures and pressures at which the gas experiences a mesoscopic phase transition. The existence of such a transition follows from singularities of the temperature dependence of viscosity, from the behavior of the cluster thermodiffusion coefficient, and from the features of the distributions of cluster subcomponents in the centrifuge. The mesoscopic phase transition is manifested in the intermediate position of the molecular–cluster mixture between the gas and the liquid judging from its properties in the transition region.     

Polarization properties of baryons in the hadronic decays of the Δ(1232) resonance

The angular distribution of the probability for the Δ(1232)-resonance decay Δ(1232) → Nπ versus the polarizations of baryons and the vector of dynamical nucleon polarization are calculated.     

Decay properties of neutron-deficient nuclei in the region Z = 86–92

Neutron deficient isotopes of elements Z = 86-92 have been produced by heavy-ion fusion reactions ¹²C + ²⁰⁸Pb, ²⁰⁹Bi, ²²Ne + ²⁰⁸Pb, ⁵¹V + ¹⁷⁰Er, and ⁵⁰Ti + ¹⁷⁰Er. The evaporation residues were investigated by means of α- and α-γ-spectroscopy after in-flight separation from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si-detector. New or improved decay data for ^{225, 226}U, ^{216, 217m, 218}Pa, ^{215, 216, 217}Th, ^{214, 215, 216, 216m}Ac, ²¹⁴Ra and ²¹³Rn have been obtained. Received: 5 April 2000 / Accepted: 28 July 2000     

149Sm(n,α)146Nd cross sections in the MeV region

We have measured the (149)Sm(n,α)(146)Nd cross section at 4.5, 5.0, 5.5, 6.0, and 6.5 MeV. Measurements were performed at the 4.5 MV Van de Graaff accelerator of Peking University with monoenergetic neutrons produced via the (2)H(d,n)(3)He reaction using a deuterium gas target. Alpha particles were detected with a double-section gridded ionization chamber having two back-to-back (149)Sm(2)O(3) samples attached to the common cathode. Absolute neutron flux was measured using a small (238)U fission chamber and monitored by a BF(3) long counter. These are the first reported cross sections for this reaction at these energies, except at 6.0 eV, where our new data are in good agreement with our earlier result. The present results help to much better constrain the (149)Sm(n,α)(146)Nd cross section in a region where its energy dependence is changing fairly rapidly and there are large differences between evaluated nuclear data libraries.     

On the mechanism of formation of excited states of the 8Be nucleus in the reaction 12C(γ, 3α)

The reaction ¹²C(γ, 3α) was studied with the aid of a diffusion chamber placed in a magnetic field, filled with a methane-helium mixture, and irradiated with bremsstrahlung photons of endpoint energy 150 MeV. The total reaction cross section was measured in the energy range E _γ < 40 MeV. The ground state; the first, second, and unseparated third and fourth excited states; and highly excited states (in the range 19.9 < E _x < 25.2 MeV) of the ⁸Be nucleus manifested themselves in the distribution of events with respect to the energy of the relative motion of two alpha particles. A resonance that is characterized by the energy of E₀ = 0.72 MeV and the width of Γ = 0.80 MeV and which was identified as a ghost anomaly was found between the ground state and the first excited state. Partial cross sections were measured for various channels. Excited states are formed in narrow photon-energy intervals, and their partial cross sections are of a resonance shape. It is found that the energy corresponding to the maximum of the partial cross section for the ith level, E _m ⁱ , and the excitation energy of the next level, E ₀ ⁱ⁺¹ , are correlated: E _m ⁱ = E ₀ ⁱ⁺¹ + ?, where ? is the reaction threshold. The results are qualitatively explained on the basis of a model that assumes photon absorption by an alpha-particle pair.     

Estimate of the Δ(1232) component in the 12C nucleus

The cross section for the ¹²C(γ, π⁺ p) reaction was measured in the range of the Δ(1232) isobar. The data were analyzed using the models taking into account the nucleon and isobaric degrees of freedom of the ¹²C nucleus. The conclusion is drawn that in the large-momentum transfer range the π⁺ p pairs are produced in the course of the direct knocking-out of Δ⁺⁺ isobar from the nucleus. The probability of finding the Δ isobar in the ground-state ¹²C nucleus is estimated at 0.018±0.005 Δ isobars per nucleon.     

Optical properties of human jawbone and human bone substitute Cerabone® in the terahertz range

The refractive indices n(ω) and absorption coefficients α(ω) of the jawbone and the human bone substitute Cerabone® were determined in vitro by the terahertz (THz) time-domain spectroscopy (TDS) in a wide frequency range from 0.2 to 2.5 THz. It is shown that the refractive index of the human jawbone changes between the values of 2.075 and 2.157, and of the Cerabone® between 2.4 and 2.65. The absorption coefficient of the human jawbone increases depending on the frequency from 1.7 cm^–1 to 178.5 cm^–1, showing several resonance absorption lines at the values greater than 1.6 THz. The absorption coefficient of Cerabone® increases from zero to 80 cm^–1, and the resonance absorption occurs at 1.7 THz. The obtained results allow us to determine the proximity of the physical properties of the bone transplantation material Cerabone® with the natural bone matrix.     

Photoproduction of pion-nucleon pairs on nuclei in the Δ(1232)-resonance region

Data from three experiments performed at the linear accelerator in Saclay, the Tomsk synchrotron, and the MAMI accelerator in Mainz and devoted to studying single pion photoproduction on light nuclei that is accompanied by nucleon emission are analyzed. The behavior of respective experimental cross sections, which is inexplicable in the impulse approximation, is interpreted within a model where the formation of an intermediate quasibound isobar-nucleus state is followed by its decay to a final state involving a pion and a nucleon.     

Soft X-ray microscopy in the spectral region of “carbon window” with the use of multilayer optics and a laser-plasma source

This paper reports on the fabrication and testing of multilayer mirrors for X-ray optical systems operating in the “carbon window” region (at wavelengths from 4.5 to 5.0 nm) and the results of their application in soft X-ray imaging of the internal structure of organic objects. The developed approaches to the fabrication and control of graded Co/C multilayer coatings have made it possible to create an X-ray multimirror system with a maximum known entrance aperture and throughput. The use of the developed high-spatial-resolution X-ray optics can significantly extend the field of practical application of soft X-ray absorption microscopy based on compact laser-plasma sources.     

On the quantum efficiencies of twenty alkali halides in the 12–21 eV region

Absolute photoelectric yields of twenty alkali halides have been measured, using a rare gas ion chamber to determine the flux distribution of the He₂ continuum between 12.4 and 21.2 eV. In addition, semiquantitative absorption coefficients were obtained by evaporating AX (alkali halide) films on 300 Å thick Al₂O₃ windows. For most of these materials the photoelectric yield rises to values as high as 0.8 election/incident photon in the fundamental band beyond the stable exciton region. At photon energies near twice the threshold (or approximately 2 E_g the yield often reaches a distinct minimum of the order of 0.4 electron/incident photon. This region is likely characteristic of double exciton production. Beyond 2 E_g the yield generally rises to very large values, even over 1.0, strongly implying double excitation processes. Many broad diffuse bands, sometimes well correlated with the absorption coefficients, appear in the electron emission spectrum.     

Mathematical properties of the Kn(τ) functions

The K_n(τ) functions, which arise in the study of nongray radiative transfer, are investigated. Closed-form expressions for the triangular and exponential profiles are presented. The K_n(τ) and K₅(τ) functions for the rectangular, triangular, exponential, Doppler, and Lorentz profiles are tabulated.     

Investigation of the properties of the spontaneously fissioning isomer 241Pu in the reaction (γ, n)

The reaction ²⁴²Pu(γ, n) was studied in which a spontaneously fissioning isomer ²⁴¹Pu was formed with 23±1s half-life. The ratio of the cross sections for formation of the isomeric state and the ground state of ²⁴¹Pu was measured as (9±2) × 10⁻⁴ along with the threshold for the formation of the isomeric state (9.10±0.15 MeV). From the comparison of the thresholds for the formation of the ground state and the isomeric state the excitation energy of the spontaneously fissioning ²⁴¹Pu isomer was determined as −2.9 ± 0.15 MeV. The data obtained are compared with the analysis of subbarier resonances in the reaction ²⁴⁰Pu(n,f).     

Optical properties of thin anisotropic films of polyethyleneterephthalate in the spectral range of 700–760 cm−1

Using transmission coefficients of anisotropic polyethyleneterphthalate films measured in the range of 700–760 cm⁻¹ the optical functions n(v) and χ(v) are calculated in the film plane and perpendicular to its surface. Its shown that the asymmetric broadenings and shift of the maximum of the absorption band at 727 cm⁻¹ in the case of oblique incidence of p-polarized radiation are due to the influence of optical anisotropy and dispersion. A. A. Kuleshov Mogilev State University, 1, Kosmonavtov Str., Mogilev, 212022, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol 66, No. 3, p. 409–412, May–June, 1999.     

Optical properties of (F2 +) H centers in NaCl:OH− crystals

Abstract

In this work we present new data on the formation and destruction of the laser active (F₂ ⁺)