The irradiation of biomolecular nanosystems in the gas phase represents a major current research field in radiation science. From an experimental standpoint, it has great potential for new applications in analytical sciences and for the development of new synthesis techniques. Concurrent theoretical progress can provide new descriptions of radiative energy transfer in terms of molecular processes, opening new perspectives for the elucidation of the radiation dose in living systems and for the investigation of molecules which inhibit or counter the effects of irradiation. The key idea of the COLDIRR project is to deposit an investigated nanosystem onto a cold rare gas droplet prior irradiation. As the irradiation dynamics are complex processes involving several competing microscopic mechanisms, better controlled conditions can be advantageous for a detailed analysis of elementary mechanisms. Rare gas droplets (Argon, Helium) offer a remarkable opportunity to control the external conditions (temperature, orientation) under which irradiation takes place. The idea of depositing a system inside a rare gas droplet has been used for the analysis of molecular properties, which can particularly benefit from a well controlled temperature. To the best of our knowledge, advancing here to the case of more dynamical situations such as a non-linear irradiation process by high energy protons and electrons is a new step in the analysis of dynamical scenarios. The aim is a detailed analysis of mechanisms and extremely accurate description of the processes at strong excitations. This requires a high-degree of control of the working conditions expected which is after depositing the molecular systems onto rare gas droplets. The scientific objective is then to observe and characterize the interaction between molecules after irradiation. The whole experimental project will be accompanied by theoretical modelling relying on state of the art calculations of embedded molecular species submitted to non linear electromagnetic perturbations. Emerging from the results obtained in the frame of the MIRRAMO ANR programme, the COLDIRR project relies on the longstanding and fruitful collaboration between the Institut Physique Nucléaire, Université de Lyon, France and the Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Austria. The collaboration has been reinforced by the theoretical group from the Laboratoire de Physique Théorique IRSAMC, University of Toulouse, France. This consortium is a real opportunity to reach a high level of synergy of the experimental development, a mutually complementary measurement strategy for irradiation with electrons and protons and a joint strategy for theoretical developments and measurements. Technical developments will be based on the know-how of the two involved experimental groups (e.g., development of a new nanodroplet set-up and a sophisticated detection system). This will allow a detailed analysis of fragmentation processes of (cold) biomolecular cluster ions after collisions with protons. The theory group will develop a new model/method (based on time-dependent density functional theory in the Local-Density Approximation) for the description of irradiation of biomolecular nanosystems with protons. Effects of solvatation by water and embedment in Argon nanodroplets will be of particular interest in these theoretical investigations. The concept of the project allows technical developments in parallel to experimental measurements. The latter will start with collision studies of mass-selected protonated molecular clusters with monokinetic protons, as a function of the increase in the complexity of the systems studied (hydration, embedment in Ar/He nanodroplet). Fragmentation patterns and cross section functions for different protonated clusters as a function of degree of complexity will yield valuable and unique information elucidating the basic reactions underlying irradiation damage.