[en] For preparation of the decommissioning of VVER type reactors a method has been developed by example of the Rheinsberg VVER-70 reactor, leasing to the calculation of radioactivity in the construction components of the reactor as well as in the surrounding materials of the reactor. The method comprises and evaluation of the data available, calculation of the neutron flux density, generation of cross-sectional data for activation calculation, programmes for activation calculation as well as calculation of resulting dose capacity. The effect of different modellings of radiation history and other influence factors on the result of the calculation was examined. (orig.)

No abstract available

No abstract available

[en] The most complex molecule detected unambiguously in the gas phase of dense interstellar clouds possesses thirteen atoms. How are this and other complex molecules synthesized? Under the low temperature conditions of the normal interstellar medium (10-70 K), only exothermic chemical reactions without activation energy are of importance. These include reactions involving neutral radicals and, more importantly, ion-molecule reaction. Ion-molecule reactions can synthesize complex molecules under two conditions: (1) there must be a large amount of molecular hydrogen, and (2) some carbon must be in a reactive form such as C or C⁺ rather than in an inert form such as CO. Under these conditions it will be shown that some but not all of the observed gaseous complex molecules can be produced in the gas phase

[en] A mechanism by which competitive binary and ternary ion-molecule reactions can occur is proposed. Calculations are undertaken for the specific system CH3(+) + NH3 + He which has been studied in the laboratory by Smith and Adams (1978), and the potential surface of which has been studied theoretically by Nobes and Radom (1983). It is shown that a potential-energy barrier in the exit channel prevents the rapid dissociation of collision complexes with large amounts of angular momentum and thereby allows collisional stabilization of the complexes. The calculated ternary-reaction rate coefficient is in good agreement with the experimental value, but a plot of the effective two-body rate coefficient of the ternary channel vs helium density does not quite show the observed saturation. 21 references

[en] A theory of radiative association reaction rates for systems in which one or more competitive exothermic binary channels exist has been developed. The theory is utilized to calculate the rate of the radiative association reaction between CH3(+) and NH3, which is important in the synthesis of CH3NH2 in dense interstellar clouds. This reaction is calculated to have a large rate coefficient despite the existence of two competitive exothermic channels. The cause of the large radiative association rate coefficient is an activation energy barrier of 2.3 eV in the dominant binary exit channel. It is suggested that a variety of other radiative association reactions, of importance to interstellar chemistry, can also occur with large rate coefficients at low temperature despite the presence of competitive exothermic channels if similar activation energy barriers are present. 18 references

[en] A sizable number of radiative association reaction rate coefficients involving polyatomic molecular ions have now been calculated and utilized in ion-molecule models of the chemistry of dense interstellar clouds. Recent evidence suggests that these calculated rate coefficients may be an order of magnitude too low in many cases. The evidence is reviewed and developed and calculated rate coefficients are updated. In addition, the temperature dependence of each reaction rate coefficient in the 10--50 K range is estimated if this information has not previously appeared in the literature

No abstract available

[en] The possibility that complex hydrocarbons can be produced in dense interstellar clouds by ion-molecule gas phase reactions is considered in detail. Steady-state calculations indicate that the observed abundances of species such as C₄H cannot be reproduced via gas phase models unless a large amount of atomic carbon (CI) is present. With an assumed CI fractional abundance of 10^-5, our calculations can reproduce the fractional abundance of C₄H observed in TMC 1. Thus, in our view, the presence of CI, itself not readily explicable via standard ion-molecule treatments, appears to be necessary to explain the abundances of complex hydrocarbon species

[en] A simple model has been developed to estimate the abundances of large hydrocarbon molecules produced by gas-phase, ion-molecule reactions in dense interstellar clouds. Hydrocarbons through 30 carbon atoms in size are considered in the model. Molecular complexity is built up via synthetic reactions involving smaller hydrocarbon neutral and ions. A quasi-time-dependent model has been utilized in which the abundances of hydrocarbons with fewer than 10 carbon atoms are fixed at values calculated in a previous model. The time dependence of the abundances of the more complex hydrocarbons is then followed. The results show that, with favorable values for important rate coefficients, it is possible to produce sizeable abundances of hydrocarbon molecules exceeding about 20 carbon atoms in size an in a time scale of not greater than 10 to the 6th yr. 31 refs