Effect of multiple ionization on the radiolysis of liquid water irradiated with heavy ions a theoretical study using Monte-Carlo simulations

L'eau est un constituant majeur de la plupart des organismes vivants. Elle joue, à ce titre, un rôle central en radiobiologie, en introduisant une part d'effet indirect et/ou quasi direct résultant de sa radiolyse. Une large majorité d'études de chimie sous rayonnement des solutions aqueuses concernent les rayonnements à faible transfert d'énergie linéique (TEL) tels que les rayons y de 6°Co ou les électrons accélérés. Bien qu'elle soit encore incomplète à certains points de vue, un panorama de la radiolyse de l'eau pure ou contenant divers solutés à faible TEL peut être obtenu dans la plupart des cas. Il n'en est cependant pas ainsi pour les rayonnements à grand TEL où plusieurs aspects de cette radiolyse n'ont pas jusqu'ici été pleinement résolus. Parmi les points d'interrogation qui demeurent, citons : (1) le rendement primaire des radicaux hydroperoxyle/anion superoxyde (pKa = 4,8) augmente en fonction du TEL, et ceci même en l'absence d'oxygène. Un tel comportement est contraire à ce que l'on observe pour les autres rendements radicalaires. L'origine de ces radicaux n'est pas clairement établie, même s'ils constituent l'espèce radicalaire principale à haut TEL; (2) le rendement primaire en H20 2 croît avec le TEL jusqu'à un maximum, après lequel il décroît; aucune explication satisfaisante n'a été offerte quant à la présence d'une telle décroissance de ce produit moléculaire à haut TEL; (3) les détails précis du mécanisme par lequel les rayonnements à grand TEL sont très efficaces pour inactiver les cellules tumorales hypoxiques sont encore mal connus. Une interprétation possible de la réduction du facteur d'amplification de l'oxygène (FAO) à haut TEL est donnée par la génération in situ d'un microenvironnement oxygéné autour des trajectoires à grande densité d'ionisation (hypothèse de l'"oxygène à l'intérieur même des trajectoires").Abstract: Water makes up a predominant part of the milieu of living tissue, and, not surprisingly, plays a central role for understanding the interaction of ionizing radiation with biological systems. Most aqueous radiation chemistry studies have involved low-linear energy transfer (LET) radiation, such as [superscript 60]Co [gamma]-rays or fast electrons. A survey of the literature shows that the radiolysis of liquid water at low LET is generally well understood. However, at high LET, several reported data have not hitherto been quantitatively explained : (1) The primary yield of hydroperoxyl/superoxide anion (HO[subscript 2][superscript ¨]/O[subscript 2][superscript ¨-], p[kappa][subscript a] = 4.8) radicals increases with increasing LET, a behavior that is contrary to the other radical yields. As yet, the origin of these HO[subscript 2][superscript ¨]/O[subscript 2][superscript ¨-] radicals is not clearly established, even though they are the major radical species produced at high LET; (2) The primary yield of hydrogen peroxide rises with increasing LET to a maximum, after which it falls. No suitable explanation for the presence of such a decrease in H[subscript 2]O[subscript 2] yields at high LET has been offered; (3) The exact details of the mechanism by which high-LET radiations are very efficient for the inactivation of tumoral hypoxic cells, are still not well known. One possible explanation for the decreased radiobiological oxygen enhancement ratio (OER) at high LET is offered by the generation in situ of an oxygenated microenvironment around the tracks of more densely ionizing radiations (the so-called"oxygen-in-the-track" hypothesis). This work has been originally motivated by the hypothesis proposed by FERRADINI and JAY-GERIN (1998) that multiple ionization (MI) of water would be responsible for the large HO[subscript 2][superscript ¨]/O[subscript 2][superscript ¨-] yield produced in liquid water subject to heavy-ion irradiation. The purpose of this study is to test the validity of this hypothesis. To this aim, Monte Carlo track structure simulations are used to calculate the G-values of the various radiolytic species, including O[subscript 2], generated in the radiolysis of deaerated liquid water by several different types of radiation ([superscript 1]H[superscript +], [superscript 4]He[superscript 2+], [superscript 12]C[superscript 6+], and [superscript 20]Ne[superscript 9+] ions) over a wide range of LET up to [tilde] 900 keV/[micro]m, at neutral pH and in 0.4 M H[subscript 2]SO[subscript 4] (pH 0.46) solutions at 25ÀC. It is found that, upon incorporating the mechanisms of double, triple, and quadruple ionizations of water in the calculations, a quantitative agreement between theory and experiment can be obtained. In particular, in neutral (pH 7) solutions, our results reproduce very well the large increase observed in [Special characters omitted.] at high LET. Under the conditions of this study, the mechanisms of triple and quadruple ionizations make only a minor contribution to the yield of HO[subscript 2][superscript ¨]/O[subscript 2][superscript ¨-]. With the exception of protons, our calculations also simultaneously predict a maximum in [Special characters omitted.] around 100-200 keV/[micro]m in accord with experiment. For each irradiating ion considered, this maximum occurs precisely at the point where [Special characters omitted.] begins to rise sharply, suggesting, in agreement with experiments, that the yields of HO[subscript 2][superscript ¨]/O[subscript 2][superscript ¨-] and H[subscript 2]O[subscript 2] are closely linked. Moreover, the incorporation of MI in our simulations has only little effect on the variation of the computed [Special characters omitted.] and G[subscript ¨OH] values as a function of LET. In the case of acidic solutions irradiated by [superscript 12]C[superscript 6+] and [superscript 20]Ne[superscript 9+] ions, our results also predict a well-defined maximum in the curve of [Special characters omitted.] as a function of LET of [tilde] 1.4 molec./100 eV ([tilde] 45% greater in magnitude than that found in neutral water) around 180-200 keV/[micro]m, in good agreement with experiment. Finally, our simulation results show a steep increase in the initial and primary yields of O[subscript 2] with increasing LET. For example, for 24-MeV [superscript 12]C[superscript 6+] ions (LET [tilde] 500 keV/[micro]m), the initial in situ track concentration of oxygen is estimated to be about 3 orders of magnitude higher than the concentration of O[subscript 2] found in typical human cells. Such results, which largely plead in favor of the"oxygen in the heavy-ion track" hypothesis, could have profound consequences in radiobiology and in particular explain the observed reduction in the oxygen enhancement ratio (OER) with increasing LET. In conclusion, our results strongly support the importance of the role of MI in the heavy-ion radiolysis of water at high LET. They suggest that MI, although infrequent relative to single ionization events, is very efficient chemically

The cadmium electrode: Review of the status of research

Investigations characterizing the negative cadmium electrode used in a nickel cadmium battery cell are summarized with citations to references where more detailed information is available. Emphasis is placed on data pertinent to aerospace applications. An evaluation of some of the published results of cadmium electrode research is included

Institute for Transuranium Elements Activity Report 2002.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Manganese biogeochemistry in the sunlit ocean = Die Biogeochemie des Mangans in der euphotischen Zone

The trace metal manganese (Mn) plays a significant role in seawater as it is bio-essential for phytoplankton. Mn plays a critical role as a redox center in Photosystem II (PSII) during the conversion of water to oxygen in photosynthesis. It is also essential in other redox related enzymatic processes; in particular Mn is important as the active metal center in superoxide dismutase (SOD) which provides intracellular protection against oxidative stress due to photochemically produced superoxide (O2 ). Mn exists in seawater in three redox states: soluble and prevalent Mn(II), insoluble Mn(III) and Mn(IV)-oxides. In the euphotic zone the biogeochemical cycling of Mn is strongly influenced by reactive oxygen species (ROS). The highly reactive and short-lived superoxide (O2 ) and hydrogen peroxide (H2O2) can both act as oxidants and reductants, and they play a key role in the Mn processes in seawater. For example the dominant Mn sources to the open ocean are the Mn-oxides which are present in atmospheric dust which are reduced to soluble Mn(II) by photochemically produced H2O2. While these processes have been crudely identified, the dominant reactions and mechanisms of Mn and ROS in seawater are poorly understood. This lack of knowledge demands investigations into the in-situ dissolution processes of Mn from dust and into studying the exact reaction mechanisms between Mn and ROS in the euphotic zone. This thesis comprises four manuscripts. Manuscripts 1 and 2 (Wuttig et al., subm., 2013a; Wuttig et al., subm., 2013b) focus on the cycling and reaction mechanisms of Mn and ROS. Manuscript 3 (Wuttig et al., in prep., 2013) addresses differences in the input and distribution of cadmium (Cd), iron (Fe) and Mn in the Eastern Tropical Atlantic Ocean off Cape Verde, and manuscript 4 (Wuttig et al., 2013) describes Mn cycling after dust additions in a trace metal clean mesocosm experiment in the Mediterranean Sea. This study has conclusively shown that Mn and organic matter are the dominant sinks for O2 in the Eastern Tropical North Atlantic (manuscripts 1; Wuttig et al., subm., 2013a). Mn dominates this decay especially in the surface waters which are influenced by high atmospheric dust deposition and near the sediment/water interface due to Mn sediment resuspension. This contrasts with current knowledge based on findings from the Mn poor Southern Ocean where copper (Cu) was shown to be the major sink. In manuscript 2 it is demonstrated that O2 decays by reaction with inorganic Mn(II) in seawater following a first order loss rate which appears to involve a catalytic reaction involving the Mn(II)/MnO2+ couple, in which MnO2+ is a manganous superoxide complex (Wuttig et al., subm., 2013a). Thus in sunlit and oxygenated waters Mn(III) is unlikely to be found in significant concentrations when strong Mn(III) binding ligands are not present. In other studies Mn(III) was found under anoxic conditions in the presence of unknown strong Mn(III) binding ligands. Therefore, in contrast to the Mn(II)/MnO2+ pair, Mn(III) cannot act as a SOD in the oxygenated surface ocean. In the Eastern Tropical North Atlantic Ocean atmospheric dust is the main source of Mn to surface waters (manuscript 3; Wuttig et al., in prep., 2013). However this study provides clear evidence that equatorial upwelling and sediment resuspension are important Mn sources in this region. In contrast to findings from the Eastern Tropical Pacific, where unexpected high surface concentrations were observed, no secondary Mn(II) maximum was found in the Eastern Tropical North Atlantic Ocean. This could have been introduced by a combination of lateral transport of Mn rich waters from the coastal margins and reduction of Mn-oxides. While Aeolian sources were predominantly influencing Mn and also Fe cycling in the Eastern Tropical Atlantic, Cd was not controlled by dust deposition (manuscript 3; Wuttig et al., in prep., 2013). These biologically relevant elements exhibited contrasting distribution patterns. For Fe and Mn, atmospheric depositions masked a classical nutrient type profile, while Cd was very depleted at the surface and concentrations steadily increased with depth. Cd was highly correlated to Phosphate (hereafter referred to as P). The Cd/P ratio was mainly controlled by P with elevated concentrations at depth resulting in strongly differing ratios in surface and subsurface layers of 16.6 pmol / µmol and 237 pmol / µmol, respectively. The complex photochemical processes during the dissolution of Mn dust are also subject of manuscript 4. This paper describes a mesocosm project in the Mediterranean with two consecutive additions of evapocondensed dust conducted. The data also show that the dissolution and loss rates of Mn were comparable during both seedings. The calculated fractional solubilities for the first and the second dust addition were 41 ± 9 % and 27 ± 19 %, respectively. The results presented in this thesis have significantly improved our understanding of Mn distribution and especially cycling in the euphotic zone. An insight into the mechanisms between Mn and ROS and into the dissolution processes from dust is given

An Appreciation of the Scientific Researches of Dr Peter H. Dawson

Upon the death of Peter H. Dawson in 2015, mass spectrometry lost a major figure. Within the area of radiofrequency quadrupole electric fields applied to mass spectrometry, Dawson stands alongside its pioneers Wolfgang Paul, Nobelist and inventor of the technology, and Wilson Brubaker, who identified and overcame the deleterious effects of fringing electric fields on quadrupole mass filter performance. Seventy‐one of Dawson's 97 scientific publications are concerned with quadrupole mass analyzers, ion traps and monopole mass spectrometers. Of especial note are his book and review articles in which he disseminated information on the theoretical fundamentals and practicalities of these systems to a wider audience, thereby having a major impact on the development of this important field of endeavour. The scientific researches of Dr Dawson and his advice and counsel, influenced to a major degree, and to the better, the research careers, teachings and the lives of the authors of this piece. Their combined researches quadrupole devices led to the commercialization of the ion trap as a mass spectrometer by which mass spectral information became available at greatly reduced cost. Thus, the advent of commercial ion trapping instruments permitted a greater use of mass spectrometry in both technically advanced countries and those less well advanced. The greatest impact in health services was mass spectrometric analysis of environmental problems, well and stream water, food free of pesticides, etc., and forensic sciences. Our combined indebtedness to Dr Dawson is manifested by this appreciation of his scientific work, the highlighting of his main contributions, and creation of a substantive reference source to his work that can be used by other scientists. A comprehensive list of Dr Dawson's publications, including abstracts or summaries, has been arranged in chronological order of date of submission