Irradiation adsorbed dose

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... 

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... 

Thermal and thermooxidative behavior were studied by Ihermogravimetric analysis in oxygen and nitrogen. Polyimide resins were irradiated with a 500 kGy total adsorbed dose of gamma radiation. 

Experiments were conducted in our laboratory to evaluate many of the dynamical expectations for rapid laser heating of metals. One of the aims of this work was to identify those population distributions which were characteristic of thermally activated desorption processes as opposed to desorption processes which were driven by nontbennal energy sources. Visible and near-infrared laser pulses of nominally 10 ns duration were used to heat the substrate in a nonspecific fashion. Initial experiments were performed by Burgess etal. for the laser-induced desorption of NO from Pt(foil). Operating with a chamber base pressure 2 x 10 torr and with the sample at 200 K, initial irradiation of a freshly cleaned and dosed sample resulted in a short time transient (i.e. heightened desorption yield) followed by nearly steady state LID signals. The desorption yields slowly decreased with time due to depletion of the adsorbate layer at the rate of ca. 10 monolayer... 

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. 

After irradiation (Fig. 7), the negative-going band exhibits a broad feature with a minimum near 3450 cm This represents the loss of adsorbed water, while the components at 3500-3800 cm represent the consumption of H-bonded silanols. This consumption can be attributed to condensation processes, leading to the formation of Si-O-Si, namely siloxane-bridge sites. Irradiation corresponds mainly to a dehydration of the system, essentially of water adsorbed on silica. This dehydration increases with the dose. Water adsorbed on silica is consumed, leading to the formation of Hj and H2O2. These observations are consistent with our previous results obtained with Controlled Pore Glasses. 

In the final paper of this important series (Machi et al., 1979d) the effect of tbe reaction conditions on the stability of the tetraBuoroethylene latices was studied. The stabilization was believed to be due to either carboxyl and groups or to the adsorbed hydrofluoric acid formed hy radiolysis of the monomer or to both. The surface charge densities, electrophoretic mobilities, and infrared spectra were all measured. The storage stability of tbe latices, measured by the appearance of coagulum, was found to be proportional to the total dose and the polymer concentration and not to depend on the dose rate. Since the stabilization results from the radiolysis of the monomer and wat this is quite reasonable as is the effect of concentration. The presence of monomer was necessary in the sense that irradiation of the latex in the absence of monomer did not improve the storage stability. 

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. 

Figure 1. (a) Schematic of the apparatus which may be employed in a surface photochemistry experiment. The Sample (S) is mounted on a temperature controlled block in UHV. It may be cleaned by argon ion bombardment. The adsorbate is dosed onto the surface (D). Its dark state is determined by TPD (as measured by mass spectrometry, MS), EELS, UPS etc. Irradiation is by an arc lamp via a monochromator or filters. Products arc detected by the same analysis tools. 

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.

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.

By contrast, a slower irradiation favors adsorption of ions not yet reduced onto atoms or small clusters formed at the start of irradiation and this process is not prevented by the polymer nor is the reduction in situ of the ions by electron transfer from the reducing radicals. Likewise, electrons from small clusters can be transferred to larger ones coated with adsorbed ions and polymer. The final size may thus be much higher than the above limit imposed by the polymer when just coalescence occurs and the size increases with the irradiation time required for the reduction (therefore at decreasing dose rate) (Figure 11b). 

This is likely to be due to a much higher concentration of single atoms suddenly produced in the solution these atoms act as many individual centers of nucleation and further coalescence (in contrast with low dose rate irradiation conditions under which fewer nuclei adsorb excess ions which are then reduced in situ)f" The same evolution of the absorption spectrum with the dose has been found at high dose rate for various values of the Ag and Au ion fraction in the initial solution. Clusters Ag,.,(Au are alloyed with the same composition. The maximum wavelength and the extinction coefficient of the alloy depend on x. The experimental spectra are in good agreement with... 

Radioactive products are present in decay storage tanks for gases extracted from the primary water before their release to the atmosphere. Not aU the plants use these tanks since the decay of waste gases is frequently obtained by delay lines that temporarily adsorb the gases on activated carbon. Where decay tanks are used, a rupture of one of them is serious. The total inventory of the stored gases is subdivided in several (typically eight) tanks. The most relevant external doses are those connected with the irradiation from the cloud of noble gases, whose total inventory may be of the order of 10 TBq. 

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