Peter Jani

A new method for the simultaneous measurement of aerosol particle size, complex refractive index and particle density

Particle size measurement by means of optical spectrometry of single particles depends substantially on the angular range of light scattering and the refractive index of the particle. Knowledge of the latter determines implicitly the accuracy of measurement. In contrast to commonly used instrumental systems the configuration of the design concept presented here consists of two laser illumination sources with different wavelengths and four angular ranges for the collection of scattered light. As a result a set of four independent pulses from each measured particle can be obtained allowing simultaneous assessment of particle size and its complex refractive index. Based on the Mie theory of light scattering, light collection angles yielding a single-valued aerosol size measurement were identified and used to design a new optical system. Based on the modelling of the performance for an assumed instrumental arrangement the sizing errors were found to be about 2%. The accuracy of assessment of the complex index of refraction was found to be of the order of 10% over the range of particle diameters investigated (0.1-10 µm). The theoretical results show clearly the capability of this novel instrumental design for the measurement of aerosol particle sizes, their density and optical properties. Based on these model calculations an experimental set-up is under construction.

New design for a light-scattering airborne particle counter and its applications

A light-scattering airborne particle counter with a new optical design having the optical sampling chamber outside the laser resonator is presented. This device can be used to measure the size distribution of particles from a diameter of 0.3 μm in a wide concentration range with high reliability and stability. Some results of the applications of the device in highly contaminated environments are reviewed.

Interaction of Failed Fuel Rods Under Air Ingress Conditions

Abstract In the late phase of a severe reactor accident, the molten corium interacts with the vessel wall, and it can lead to the failure of the lower head. Through the failed bottom wall, part of the corium can flow into the cavity, and air can enter the primary circuit. The residual fuel in the core periphery will be further oxidized in air atmosphere. The degradation process will accelerate, and new chemical species will be formed, which can have an impact on the release of radioactive materials. Two experiments were carried out with electrically heated nine-rod pressurized water reactor-type bundles in the CODEX (COre Degradation EXperiment) facility to provide experimental data on the behavior of real fuel bundles under air oxidation conditions. The main objective of the tests was the investigation of oxidation phenomena, and some other important aspects (e.g., enhanced fission product release) were not addressed. The CODEX air ingress tests indicated the acceleration of oxidation phenomena and core degradation processes during the late phase of the vessel melt through accident, when air can have access to the residual fuel bundles in the reactor core. The degradation process was accompanied with zirconium-nitride formation and release of uranium-rich aerosols.

Photothermal deflection technique for measuring thermal nonlinearities in semiconductor glasses

The photothermal deflection technique is used to determine the thermal nonlinearity in samples of glasses doped with CdS(x)Se(1-x). Values of the nonlinear refractive index are derived at low frequencies; they compare with recently obtained dc values in similar, but not equal, glasses.

Behavior of VVER Fuel Rods Tested Under Severe Accident Conditions in the CODEX Facility

The early phase of severe accidents in VVER reactors was simulated in the CODEX (COre Degradation EXperiment) facility with electrically heated fuel rod bundles. The selected test conditions and applied measurement techniques made possible the observation of some specific phenomena, such as the protective role of oxide scale during quenching of high-temperature bundles, the composition of gases produced during the oxidation of boron-carbide control rods, and the interlink between the aerosol release and the oxidation process. The general behavior of the VVER bundles did not differ significantly from that of the Western-design light water reactor bundles tested under similar high-temperature conditions, but the experiments emphasized that the application of VVER-specific material properties and models is essential for comprehensive numerical simulations.

Measurement of quantum efficiency using correlated photon pairs and a single-detector technique

A new approach is proposed to the calibration of photodetectors and the determination of the absolute value of the quantum efficiency of photon-counting photomultipliers using entangled-photon pairs. It is based on a new single-photodetector technique and a special modulation of the entangled-photon flux. The absolute values of the quantum efficiency have been determined for several photon-counting photomultipliers.

Nanoparticle size distribution measurement in photon correlation experiments

We propose the measurement of particle size, which is based on the visibility measurement of the pre-detection signal corresponding to particle transit of the sensing volume in a photon correlation LDA arrangement. It is shown that a good estimate of the visibility is the ratio of the contents of two specific channels of the Fourier transform of the autocorrelation function. We show that in a wide range of experimental conditions this ratio is a monotonous function of particle size. This circumstance leads to the possibility of defining calibration curves for practical devices.

Lee filtered burst selecting in the photon correlation LDA signal processing

The photon correlation Laser Doppler Anemometers were developed to measure the flow velocity also in the nanometer particle range. An LDA signal processing method has been developed for dividing the raw data line of photon correlation LDA into shorter parts corresponding to single particle transit (burst). The commonly used Lee filter was applied with some modification and an intelligent burst finding algorithm was developed. By this way the LDA system was adapted for single particle counting. The complete simulation algorithm gives an opportunity for discussing the burst selecting and so the particle counting efficiency as a function of the SNR. Size estimation from the burst size was discussed and compared to the model-based signal processing technique. The minimum detectable particle size was estimated.

Probability distribution of scattered intensities

The probability distribution of scattered light intensity is derived when both the size and the number of scattering aerosol particles are random variables. When light is scattered from an ensemble of aerosol particles, the scattered intensity is a random variable itself. Analytical derivation is found for the distribution of scattered intensities. It is shown that in a wide range of experimental conditions the scattered intensity follows Gaussian statistics. For a given sort of aerosols the ratio of the mean value to the standard deviation is shown to be dependent only on the mean number of particles present in the measurement volume. Monte-Carlo simulations and experiments were carried out to prove the expectations of the theory.

Development of a new particle counter for simultaneous measurement of the size distribution, concentration, and estimation of the shape factor of liquidborne particles

A new liquid-borne particle counter is described that utilizes an optimized optical setup to determine the size distribution and concentration by two different methods and to estimate the shape-factor of the suspended particles. The aim of this optimization was to achieve the appropriate optical conditions for such type of measurement, viz. determining the geometry of the illumination and detection, and calculating the testing volume and dependence of the parameters of detected signal on the particle size for pulse height and pulse duration methods performed at the same illumination and detection conditions. The main benefit of the developed device is the high dynamic range of the size determination of the micron-size liquid-borne particles and the possibility of estimating their shape-factor. The proposed measurement method was incorporated in a PC- controlled LQB-1-200-L-T liquid-borne laser particle counter developed on the basis of our previous APC-03-2 and APC-03- 2A air-borne particle counters and a LQB-1-200 liquid-borne particle counter.