The adsorption coefficient is the fundamental parameter characterizing activated charcoal"s ability to adsorb 222Rn. The adsorption coefficient is determined for 222Rn activated charcoal detectors. In addition, a diffusion and adsorption model is developed for the transport of 222Rn in a porous bed of activated charcoal. These processes can be described by parabolic second order differential equation. The equation is numerically solved using the finite differences method. With this model, the 222Rn activity adsorbed in the detector is calculated for diverse situations.
Irradiation of α-Al2O3 (Corundum) was carried out in contact with acidic media and with different doses (100-to-2500 kGy) and dose-rates (0.9, 2.6
and 6.1 kGy·h−1) of γ-rays. Simultaneously parallel experiments were carried out using the same procedure, but preheated at 150°C for two
days and then irradiated without acidic media. The solid thus obtained was used to determine the effect of γ-irradiation on
the sorption capacities of microamounts of fission products from strongly alkaline aqueous solutions of uranium. The results
revealed that the effect of γ-irradiation of α-Al2O3 and the acidic media in which it is immersed, is associated with a stable matrix resistant to significant changes in the
composition of the surface layer; whilst it seems that the effect of γ-irradiation of preheated α-Al2O3, is connected with changes of surface-OH groups strongly affected by heat treatment and irradiation dose.
The use of ionizing radiation to achieve some desired effect on silica gel, applicable to the adsorption of radionuclides
has been investigated as a function of the dose-rate over a wide range of doses, in experiments with strongly alkaline aqueous
solutions containing an excess of UO
relative to trace concentrations of88Y,103Ru,134Cs and141Ce. The results obtained revealed that γ-irradiation of silica gel was reproduced with an uptake comparable to that measured
for the unirradiated-silica gel. Radiation resistance is strongly influenced by the basic macromolecular structure, the presence
of water, and the particular environmental exposure conditions.
This work describes a method which was developed to determine the concentration of 222Rn gas and the equilibrium factor F between the concentration of the gas and its progeny by means of a single device that uses two Makrofol passive track detectors. The device is completely passive and time integrated. Conditions make it very appropriate to be used in any atmospheres in which human activity takes place, such as houses, schools, works and underground mines. A series of measurements of 222Rn gas concentration and equilibrium factor F were made in different cities of the Argentine Republic and the corresponding levels of doses were estimated.
A method for the measurement of the unattached radon progeny based on the electrostatic deposition on wire screens has been implemented and calibrated, using only one sampling pump. The importance of being able to measure the short-lived radon progeny resides in the special radiological significance that the unattached fraction has. It was possible to apply this measurement method to several dwellings of Argentina and then, have an estimated value of the unattached fraction under different aerosol source conditions. The remarkable aspect of this method is its simplicity, not only in the sample collection equipment used, but also in the measurement instruments, as well as the counting protocols that are simple and fast.
We obtain inequalities for the weighted approximation error of Baskakov type operators and their derivatives. Such inequalities
are valid for functions of polynomial growth and are expressed in terms of weighted moduli of continuity.
Authors:F. López, A. Mercê, F. Alguacil, and A. López-Delgado
The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic
parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal
conditions, at several heating rates, between 5 and 30°C min−1. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy
and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained
by applying different conventional calculating methods is also shown.
A passive diffusion method for the determination of radon concentration has been optimised and calibrated. The device consists
of a scintillation vial containing activated charcoal, a diffusion barrier and a desiccant agent. The response to diverse
atmospheric humidity and variable exposure intervals was studied. The result is a detector independent of atmospheric humidity
till 7 days of exposure. The method was compared with electret detectors (US EPA) with very satisfactory results. The advantages
of this method are its simplicity, low cost, low detection limit, the total automatization of the measurement and its total
independence of humidity to measure in a wide range of radon concentrations.