Scientific Programme

The main scientific tasks of the project can be summarised as follows:

A. To perform a detailed authoritative experimental investigation of plasmid DNA damage (induced on lyophilised monomolecular monolayers) by irradiation with electrons, protons, ultra-violet photons and ions by measuring single strand, double strand and base damage (using quantitative gel electrophoresis techniques). These experiments will allow fluence-effect relationships and spectral efficiency for fully hydrated and fully dehydrated conditions to be derived.

B. A joint experimental/theoretical investigation to determine the role played by excited electronic states and non-adiabatic couplings on the dynamics of biomolecules interacting with ionizing radiation. This will involve the calculation of potential energy surfaces and of the coupling between electronic states, the analysis of the coordination space and the study of quantum dynamics using wave packet propagation methods. The first molecules to be investigated will be H2O, uracil and its halogenated substituents. The effect of the solvents will also be evaluated.

C. (i) To review the experimental and theoretical cross section data available for mutual consistency. (ii) To compile a complete set of elastic and inelastic interaction cross sections and subsequent chemical reaction rates for the projectiles used with bio-molecular targets such that they may be used in other fields of radiation sciences (e.g., radiation protection, radiation medicine, etc.). This work to be integrated with the US DOE database for radiological protection and to form part of a developing EU strategy for database accumulation and multi-user access through E-grid technology.

To fulfill these objectives the research programme is organised through a series of research projects. COST action partners may be members of one or more of these actions. Five projects have been identified.

1. Determination of the cross section for ionization of the selected bio-molecules by photons, electrons, protons and ions as a function of energy including total and partial cross section functions. These studies will be carried out not only for neutral targets but also for charged bio-molecules (anions and (protonated) cations). Where possible, absolute experimental cross sections will be determined (also supported by calculations) and, in the case of protons, also direct and charge transfer cross sections will be measured as their interplay plays an important role in the energy degradation in biological material. The emphasis at the beginning of the programme will be on simple target systems like water, benzene (as a test bed) , and DNA bases. These investigations will then be extended to more complex systems like nucleotides and composite clusters in particular mixed clusters consisting of bio-molecules with varying numbers of waters molecules.

2. Determination of the kinetic energy release distribution of fragment ions produced in prompt and delayed (metastable) electron and photon induced dissociations of neutral and charged bio-molecules involving also laser time-resolved photoionization. In conjunction with theoretical modelling this will allow insight into the energy deposition and energy storage, and the binding energy situation of the precursor ions.

3. Determination of the molecular fragmentation pattern and the de-excitation processes in the interaction of singly- and multiply-charged ions with neutral and charged bio-molecules using projectile ions with charge states from 1 to 28 and with typical energies between the sub keV up to a few 100 keV range. Initially these experiments will be carried out in the gas phase under single collision conditions, it is however also planned to study in a complementary fashion such interactions with bio-molecules deposited in a surface matrix consisting for instance of water molecules.

4. Determination of site-specific rate constants for the reactions of singly and multiply protonated bio-molecules with various neutral molecules employing electrospray ionisation in conjunction with flow tube studies in order to answer the questions how do different conformers react with neutral reagents. This investigation will be supported by multiple-collision activation studies.

5. Development of models of track structure caused by the passage of ionizing radiation through matter. Reliable empirical or mechanistic models are needed in order to allow the types and magnitude of radiation risk and their prevention and/or limitation. The primary scientific goal of these models is to develop an understanding of the chemical changes that are consequent on the action of ionizing radiation on a target medium. Central to this are detailed, reliable and predictive theoretical model for the tracks left behind in matter after irradiation. Using data collected in other research projects such models will be developed and compared with observation.

The direction of these five research projects and their research portfolio will be critically evaluated at the mid way point of the Action such that these programmes may be redefined and/or other projects established, this is particularly likely when other research teams join the COST action.