Determination of temperature and emissivity of opaque heated bodies via thermal radiation spectrum: simulation of measurements in spectral window

Computer simulation of emitted radiation intensity spectrum of tantalum object was carried out. Simulation measurements occurred in a narrow spectral window, which moved along the spectrum with the given step. In this way, spectral ranges at which the dependence of the emissivity (or its logarithm) on the wavelength is the simplest and fairly accurate, in particular linear, were sought for. In the case of successful search for the specified spectral range, the required temperature was determined in the spectral window with the least squares technique. If the emissivity (or its logarithm) is linearly dependent on the wavelength then the alternative estimation of the true temperature is possible. In this case, the required temperature is determined via the change of the convexity of the spectral emissivity dependence at selection of its numerical value from the values lower than the true temperature value to the values higher than the true temperature value. This approach is simple, does not require solution of the system of equations and can significantly narrow temperature range to which the true temperature belongs.     

Temperature recovery of opaque bodies by thermal radiation spectrum: the use of relative emissivity to select the optimal spectral range

The approach based on relative emissivity was tested and developed using the experimental data. It was assumed that the medium separating an opaque body and measuring device was diathermic or nonradiating (it is characterized by its transmittance); radiation source emissivity and medium transmittance were unknown. Data on comparison of spectral radiances (spectral intensities), obtained within 220–2500 nm for the temperature lamps in the metrological laboratories of Europe, Russia, and USA were used as the initial experimental data. It is shown that the use of relative emissivity allows graphical interpretation for the solution to the initial nonlinear system of equations. In this case, the problem of determining the true temperature of the body by the thermal radiation spectrum in a graphical interpretation is reduced to the choice depending on relative emissivity at the desired temperature. It is shown that to narrow the interval, which includes the true temperature, the criterion was based on a change in convexity of spectral dependence of the relative emissivity in the process of desired temperature selection. The use of relative emissivity in a spectral range, where the Rayleigh—Jeans approximation is satisfied, allows unambiguous determination for the shape of emissivity dependence on the wavelength. The relationship for determination of the peak wavelength within the registered thermal radiation spectrum on the basis of data about the true temperature of the body and its spectral emissivity is presented.     

Determining the energy spectrum slope of diffuse superhigh-energy gamma radiation

We evaluate the primary gamma quanta (PGQ) energy spectrum slope at E _γ > 10¹⁴ eV. To accomplish this, a new method based on analyzing the data obtained in high-mountain experiments with large-scale X-ray emulsion chambers (XECs) is used.     

Effective temperature of thermal radiation from non-uniform temperature distributions and nanoparticles

We study thermal radiation properties from non-uniform temperature distributions and nanoparticles, and define effective temperature. Conventionally, the temperature of a body is measured by fitting with the blackbody radiation spectrum, which assumes a uniform temperature throughout the body. We show the energy density of thermal radiation for non-uniform temperature distribution of the body and derive the effective temperature. Furthermore, the energy density of thermal radiation from nanoparticles is derived and the effective temperature of the body is shown to depend on the particle size.     

Measurement of ultrasonic exposure with radiation force and thermal methods

It is the purpose of this paper to discuss briefly the factors that influence the interaction of the ultrasonic field and medium being irradiated, and to collect together the various techniques that have been suggested for measuring energetic parameters of the ultrasonic field. The calorimetric and radiation force methods are then discussed in more detail. The former is discussed as a technique whose capabilities have not been fully exploited while the latter demands attention both because of its simplicity and its controversial theoretical basis. Areas in which further work is needed are indicated in the summary and conclusion. It is hoped that the paper will be of practical use to workers in the field.     

Depth profiling the thermal reflection coefficient of an opaque solid via an inverse thermal wave scattering theory based on the Method of Images

A new formulation of the inverse problem of depth profiling the thermal properties of an opaque solid based on one-dimensional photo-generated thermal waves is presented. The inverse problem as posed is linear in a set of lumped thermal reflection coefficients which account for the return of energy to the surface by all significant heat conduction channels. An analysis based on the Method of Images relates these coefficients to individual values of the interface thermal reflection coefficients in the material. No weak backscattering assumption is invoked to linearize the problem. The method yields a unique solution subject to a given condition of regularization. Solutions recovered by the method are stable at experimentally feasible error levels. Received: 27 September 1999 / Published online: 16 June 2000     

A built-in scale in the initial spectrum of density perturbations: Evidence from cluster and CMB data

We calculate the temperature anisotropies of the cosmic microwave background (CMB) for several initial power spectra of density perturbations with a built-in scale suggested by recent optical data on the spatial distribution of rich clusters of galaxies. Using cosmological models with different values of the spectral index, baryon fraction, Hubble constant, and cosmological constant, we compare the calculated radiation power spectrum with the CMB temperature anisotropies measured by the Saskatoon experiment. We show that spectra with a spike at 120h ⁻¹ Mpc are in agreement with the Saskatoon data. The combined evidence from cluster and CMB data favors the presence of a peak and a subsequent break in the initial matter power spectrum. Such a feature is similar to the prediction of an inflationary model wherein an inflaton field is evolving through a kink in the potential. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 373–378 (25 September 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse are studied based on the sudden perturbation approximation. The excitation and ionization probabilities, the spectra of pulse reradiation by the atom, and the reradiation cross sections are calculated. It is concluded that the reradiation of ultrashort electromagnetic pulses by multielectron atoms is of a coherent nature.     

On the possibility of a thermal spectrum of particles produced by an electric field

The exponentially damped electric field is shown to produce particles with a thermal spectrum from vacuum if the residual action of the field on the particles produced may be neglected.     

O--ion radiation in the spectrum of an oxygen arc plasma

The radiation emitted from the axis of a wall-stabilized, low-current cylindrical arc in pure oxygen at temperatures around 9000 K was measured quantitatively in the wavelength range from 2000 to 9000 A. In the near i.r. region, the two first thresholds of the affinity continuum appear at 8615 and 8465 A, respectively, yielding an electron affinity (EA) of 1.465 eV and a ground-state splitting Δ = 26 meV for the negative oxygen ion. Another threshold occurs in the u.v. region at 3630 A and involves a transition to O^- from the first exited state of atomic oxygen. The continuous spectrum can be shown (Fig. 17) to be dominated in the u.v. and visible regions by the affinity continuum due to the negative oxygen ion. Additional contributions, which become increasingly important towards longer wave-lengths, are the Kramers-Unsöld continuum and O₂⁺-association radiation. In the u.v., the recombination of two neutral oxygen atoms forms a small contribution. A broad peak structure centered around 7000 A cannot be definitely explained. Applying Kirchhoff's law, the photodetachment cross section of O^- is obtained as a function of photon energy. Deviations from local thermodynamic equilibrium (LTE) are accounted for.     

Approximate twofold photocount statistics of superposed coherent and thermal radiation with arbitrary spectrum

An approximate formula is suggested for the twofold photocounting statistics of superposed coherent and thermal light with an arbitrary spectrum, when the counting interval and the detector area are arbitrary. The approximate moment of order (2, 1) is compared to its exact value for Lorentzian light, and curves for the approximation error are given.     

Diagnostics of the temperature of a plasma created by a CO2 laser,from the UV radiation spectrum

Delivered at the Fifth All-Union Conference on Diagnostics of a High-Temperature Plasma (18–22 June, 1990, Minsk).