Adsorbed radiation dose

Irradiation techniques are more and more widely utilized for industrial applications for instance, for food preservation, medical sterilization, and polymer processing. Such techniques require specific rules of control by means of accurate dosimetry [89]. In this context, new promising dosimeters based on resistance measurements of organic conducting crystals have been reviewed by Zuppiroli et al. [89]. The crystals utilized as dosimeters are either small needles (0.01 x 0.01 x 3 mm3) or larger plates (0.1 x 0.5 x 3 mm3), and their electrical resistances ( 1 kfl in the first case, 1 H in the second) increase exponentially with the adsorbed radiation dose, up to quite high doses. 

DEPENDENCE OF THERMAL CONDUCTIVITY OF POLYETHYLENE ON THE ADSORBED RADIATION DOSE. 

Analysis of the change in the mechanical properties of high-density polyethylene submitted to gamma irradiation shows that a 5% offset affects yield stress, and yield stress obtained from compression tests increased as the adsorbed radiation dose... 

A.S.T.M., Standard Method of Test for Adsorbed Gamma Radiation Dose in the Fricke Dosimeter, D 1671-63. 

It is important to note that radon per se is not the direct radiation hazard, but rather it is certain daughters (radioactive-decay products of the radon—mainly isotopes of polonium) that contribute the major radiation dose to lung tissue. These isotopes are chemically reactive. They can stick, either in elemental form or adsorbed onto minute airborne particles, to the lining of the bronchial passageways, whence they eradicate the surrounding tissue. 

To obtain the adsorbed amount as a function of pressure and temperature different variables can be measured adsorbed mass by means of a bedance, consumption of the sorptive gas by means of calibrated volumes, concentration changes in a carrier gas by means of gas chromatography, changes of the dielectric constant, heat of adsorption, nuclear magnetic resonance of special adsorptives, radiation dose of radioactive labelled gas. 

PAN-KCoFC and PAN-4A composite adsorbents were prepared for the removal of cesium and strontium ions from acidic nuclear waste solutions. High porous spheri( composite adsorbents could be prepared using a dual nozzle technique. The acid and radiation stability tests showed that the both composite adsorbents were stable against acid solutions higher than pH - 2 and radiation dose less than 1.89 MGy, respectively. Adsorption tests showed that the PAN-KCoFC was selective for cesium ion and the PAN-zeolite 4A was for strontium ions, respectively. The ion exchange equilibrium isotherms were obtained and evaluated for the binary systems. 

These radicals have extremely high potenliul energy and are able to react non-selectively with absorbed species. Large radiation doses (>I0 kGy) produce atom displacements in the crystal lattice, whereas at lower doses (<100 Gy) adsorbed species are degraded by transfer of the energy initially absorbed by the solid to the... 

Fig. 15. Radiolysis of methane adsorbed on 7-alumina expressed in terms of total product carbon (TPC, = chemisorbed CH4 + 2 (C2H4 + C2H6) + 3(C3H6 + C3H8)]. (a) Variation in TPC yield with radiation dose delivered to the CH3/AI2O3 system for samples previously outgassed at V, 623 K o, 673 K A, 723 K or 0, 923 K. (b) Variation in TPC yield with coverage by physisorbed methane on similarly pretreated A1203 samples dosed with methane and then 7-irradiated at two different dose rates of o, 1.1 and a, 0.29 M h 1. (c) Comparison of TPC desorption curves for 3 equivalently pretreated A12C>3 samples to which methane was added , before 7-irradiation at 77 K o, after 7-irradiation at 77 K but before warm-up A, after 7-irradiation at 77 K and warm-up to 300 K for 1 h.

The third correction factor, which is the ratio of the adsorbed dose buildup factors in the sample and the dosimeter, is usually ignored, but is shown in this paper to be very important. The absorbed dose buildup factor is defined in this paper analogous to the dose buildup factor, a notation used when the unit roentgen was still the unit of radiation dose. This paper shows the magnitude of this third correction factor, which is caused by differences in gamma-ray attenuation coefficients and softening of the gamma-ray spectrum. As an illustrative example, the dose in different dosimeters is calculated as a function of the distance from a point isotropic cobalt-60 source in water. 

Generation of acidity in silica gel by ionizing radiation was reported by Barter and Wagner (274). p-Dimethylaminoazobenzene was adsorbed out of anhydrous solution in CCI4 in the red, acid form. About 3 /aeq/gm of acid sites were generated by a dose of 3 10 rad, as determined by titration with butylamine. 

Knowing the deleterious effects of ionising radiations on PTFE, much attention was paid on their effects on PVDF although the latter had been told to behave well under irradiation. As an example, PVDF multifilament yarns can be y irradiated up to the absorption of 80 kGy without any effect on their Young s modulus [38], However, the structure of the polymer was somewhat modified as its energy to break kept constant and even increased by about 50% while the adsorbed dose was less than 8 kGy but decreased for higher adsorbed doses, down to 1/3 of its maximum value (1/2 of its initial value) when the adsorbed dose reached 81 kGy. To avoid these bulky effects, the interest of... 

Experiments using no emulsifier were conducted in tbe same stainless steel autoclave equipment described above (Machi et nf.. 1975). Stable latices were obtained, believed to be achieved by hydroxyl end groups and adsorbed hydroxyl ions. As with a number of the experiments with emulsifiers the polyethylene had a considerable cross-linked gel content. Finally, the same group of workers studied tbe radiation-induced emulsion polymerization of ethylene in a flow system (Kodama et al, 1974). Both potassium inyristate and ammonium perfluorooctanoate were used as emulsifiers. At longer residence times (above 0.2 hr) the rate of polymerization was essentially constant. As with the batch system it was assumed that the number of particles remained constant. In this region the rate was found to be proportional to tbe 0.3 power of the potassium myristate concentration and the 0.5 power of the dose rate, not too different from the batch systems. The kinetics was developed and estimates of tbe propagation rate constants obtained. Despite other similarities between the two systems, these were quite different, however, from those extracted from the batch experiment. 

These results serve to outline possible mechanisms for desorption as a complicating factor under radiation and give some idea as to the energies and efficiencies involved. It is clear that irradiation with heavy particles to modest doses is certain to remove adsorbed molecules as well as the outer layers of the solid itself. The effect of electrons. X-rays and y-rays will be less marked, and probably more variable, but one could expect desorption of an appreciable fraction of a monolayer for integrated electron fluxes of the order of lO i cm-. This is a reasonable bombardment to achieve directly with electrons, but an equivalent dose from X- or y-rays would require 10 to 10 minutes at usual intensities (10 to 10 r/min). One would not expect much desorption from the doses ordinarily used in catalytic studies, 10 to 10 minutes at 10 to 10 r/min, except for cases in which energy absorbed in the solid was effective for the process at the surface. On the other hand, fragments produced on the surface by radiation may account for effects on activity at fairly low doses. 

In radiation-induced initiation, irradiation plays the role of initiator. The intensity of radiation, i.e. its rate, or, still more precisely, the rate of the adsorbed dose Pd, is an equivalent of the initiator concentration. Hence, the dependence of the overall polymerization rate v on the dose rate will be considered. In the initiation stage, when irradiation affects the monomer, free-radical initiation centres R are formed. By analogy with conventional initiation we have... 

Fig. 6. Evidence from ESR for the growth of oxygen anion radicals at gas/solid interfaces exposed to various radiations, (a) (i) Kinetic curves for chemisorption of oxygen (1) and the formation of ion radicals 02 (2) on A1203 under the action of 7-irradiation. T = 25°C, dose rate = 0.5 X 1017 eV g-i min (ii) ESR spectrum of 02 adsorbed on 7-Al203. Reproduced with permission and minor adaptation from ref. 81. (b) Changes in intensity of ESR signal of 02 at g 2.0, /2 0, and in oxygen pressure on illumination of an 02/Zr02 sample. Reproduced with permission and minor adaptation from ref. 82. (c)(i) ESR spectrum of O and (ii) its growth at an N20/ZnO interface on exposure to UV illumination. Reproduced with permission from ref. 85.

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