No abstract

A theoretical description of multiple ionization of atoms and molecules produced by an energetic ion impact is developed. It is based on the statistical energy-deposition model of Russek and Meli ͓Physica ͑Amsterdam͒ 46, 222 ͑1970͔͒. In this model the probability for the formation of a collision-induced final state with n electrons in the continuum is obtained, assuming that its value is proportional to the volume of phase space available at that ionization state for a certain value of statistically distributed deposited energy. The model is extended in two respects. First, the deposited energy for each trajectory is considered as a fluctuating quantity with a certain distribution and the ionization probability is calculated as a weighted average over the distribution. Second, the mean value and straggling of the deposited energy are calculated within the Lindhard-Scharff local plasma approximation ͓Mat. Fys. Medd. K. Dan. Vidensk. Selsk. 27, No. 15 ͑1953͔͒. Sample calculations for collisions of protons and F 4ϩ ions with neon atoms at an energy of 1 Mev/amu are presented and compared with calculations within the independent-electron approximation and with experimental data.

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002-2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ(13)C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ(13)C(DIC) values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO(3) (I (sat) values 4-10) and with δ(13)C(DIC) values between-11.5 and-8.5 ‰. In spring waters, the δ(13)C(DIC) values were more negative, from-14 to-12 ‰, and I (sat) values of 1-2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ(13)C(DIC) correlated with the increase in the δ(13)C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.

An extended version of the statistical energy-deposition model is used for a description of multiple ionization of molecules by energetic ion impact. The energy transferred to the molecule during the collision is calculated as a function of the impact parameter within the local-electron-density approximation for a fixed molecular orientation. The fluctuating character of the deposited energy is taken into account by introducing a straggling of the energy transfer. For a given deposited energy the probability of multiple ionization of the molecule is assumed to be proportional to the volume of phase space available at the considered ionization state. The total ionization cross section is obtained by integrating over impact parameters and averaging over all orientations of the molecule. Sample calculations for collisions of He and F ions with N 2 and CO molecules are presented and compared with experimental data. A dependence of the multiple ionization cross section on the molecular orientation is considered. A strong molecule alignment effect has been obtained in agreement with recent experimental findings. ͓S1050-2947͑98͒00702-1͔

We present the first results of a study of the Gacka River spring area, an important Croatian drinking water resource. Stable isotope data (obtained at the Stable Isotope Laboratory SILab in Rijeka) are used in combination with hydrological and meteorological data. The delta18O values give information on the mean catchment altitudes of the three main springs of Gacka River (Majerovo vrelo, Tonkovica vrelo and Pecina). Hydrological, meteorological and stable isotope data indicate good mixing of infiltrated and ground waters. The precipitation d-excess shows a seasonally varying influence of continental and maritime air masses.