Ionizing radiation experiences

This means that the rate constants derived from ionizing radiation experiments with bulk monomers are not the second-order k+p given by (2.5), but first-order rate constants, pj, given by (3.1). A comparison of these equations shows that the putative k+p reported... 

The quantity k3 may be considered as an instrumental constant to be determined in a blank experiment—that is, without added solute. In this case, the current is given by I(t)/I(0) = (1 - vt/d) exp( - k3 t), from which k can be determined. With the solute added, the current initially decays exponentially (fast decay) from which is determined h + k2 + k3, while the ratio of the initial plateau to the initial current gives k2/(k] + k2 + k ). The detachment rate k2 is now obtained from the last two numbers, and then the attachment rate fe, is also obtained since k3 is already predetermined. In short, both attachment (kj and detachment (k2) rates are obtainable from the time dependence of the cell current following a brief pulse of ionizing radiation. 

Lastly, we mention one more excitation mechanism that has been observed in molecules. It is well-established that following strong field ionization in atoms and molecules, under certain conditions, the ionized electron can be driven back to the ion core where it can recombine to produce high-harmonic radiation, induce further ionization, or experience inelastic scattering. However, there is also the possibility of collisional excitation. Such excitation was observed in [43] in N2 and O2. In both molecules, one electron is tunnel ionized by the strong laser field. When the electron rescatters with the ion core, it can collisionally ionize and excite the molecular ion, creating either N + or Ol+ in an excited state. When the double ion dissociates, its initial state can... 

Initial experiments have shown that gemcitabine has a potent enhancing effect on the cellular effects of ionizing radiation reports with rodent EMT6 (26) cells and with HT-29 human colon carcinoma cell lines (27) showed that noncytotoxic concentrations of the drug lead to significant enrichment of radiation-induced cell lethality (Fig. 3). In the latter study it was found that the noncytotoxic concentrations of the drug (10 nM... 

The presence of ionizing radiation in the upper regions of the earth s atmosphere and the realization that atmospheric chemistry can occur on the surface of ice and dust particles have lead many authors to study on the interaction of LEE with molecular solids of ozone [203], HCl [236], and halogen-containing organic compounds [176,177,195-197,199-202,205,214,217,224-234] in an effort to shed new light on the problem of ozone depletion. In a recent series of experiments, Lu and Madey [297,298] found that the and CG yields... 

This review has looked at the direct effects of ionizing radiation on nucleic acids. The first step was to review detailed EPR/ENDOR experiments on irradiated model compounds at low temperatures in order to study the primary radiation-induced defects. Next, it was shown how these EPR spectra are used to simulate the EPR spectra of the DNA polymer. 

For an un-cross-linked material that undergoes predominantly cross-linking when exposed to ionizing radiation, solvent extraction experiments reveal that at certain absorbed dose (the critical dose), a percentage of the material, is converted into insoluble gel. Beyond that point, the percentage of gel increases as a function of irradiation dose. In general, both the degrees of... 

In addition to ESR spectroscopy, which is a general method for detecting radicals, Dole et al. (9, 10, 11, 12) have developed a method of ultraviolet spectroscopy at low temperatures, which is specific for allylic and polyenylic radicals. Numerous papers have dealt with changes in polymers on irradiation, and all of these conclude that the reactions, in one way or another, arise from the formation of free radicals. Only a few papers describe experiments in which the radicals have been observed directly by ESR or ultraviolet spectroscopy at low temperatures. This article merely summarizes the present knowledge of the nature of radicals formed in polyolefins by irradiation in vacuum (ionizing radiation and ultraviolet light) and discusses some new trends in studying these radicals. 

It is evident from the data presented that ultraviolet light has different and more specific effects on forming radicals in polyolefins than those previously found for ionizing radiation. Furthermore, hydrogen atoms have been observed in the ESR spectra from ultraviolet experiments (6, 24). The hydrogen radicals, however, are not believed to be located in the polymer matrix but to be formed in the glass or adsorbed on the glass surface of the sample cell (6). 

HPhe Fricke dosimeter (ferrous sulfate solutions) has been used to measure A the radiation intensity of various types of ionizing radiation sources since its development by Fricke and Morse in 1927 (2). It is widely accepted because it yields accurate and reproducible results with a minimum of care. This system meets many of the requirements specified for an ideal dosimeter (5, 9) however, it has a limited dose range, and for our applications it has been necessary to develop a dosimeter covering larger doses. Of the systems reviewed (6, 7), two (ferrous sulfate-cupric sulfate and ceric sulfate) showed the most promise for use with the radiation sources at the U. S. Army Natick Laboratories (8). Of these, the ferrous-cupric system has received the most use, and this paper describes our experience in using this system and suggests procedures by which it may be used by others with equal success. 

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