Radiation dose distribution inside interaction chamber in PW laser facilities during laser-plasma proton acceleration experiments and method to increase the proton energy spectrum measurement resolution

The map of the radiation dose distribution has been determined experimentally inside the interaction chamber during high-power laser - thin solid target experiments. In addition, the map also has been assessed theoretically by performing 3D simulations. Maximum values of the integrated doses of tens of mGy/shot are recorded in a direction normal to the target, at a distance of about 30 cm apart from the laser-target interaction point. Monte-Carlo simulation of the radiation doses map around the laser-foil interaction point is performed using Geant4 General Particle Source code and the particular geometry chosen for the experimental setup. The computed radiation dose distribution shows a good agreement with experimental results, and this represents the most important progress made within the contract. We introduce a new method to increase the measurement resolution of the proton energy spectrum, based on using a stack of thin solid detectors, preferably CR-39 [OSIM Patent Application, A/00337/05-06-19]. Each detector is thinner than the Bragg peak region that characterises the loss of kinetic energy as a function of the particle penetration depth in the detector material. The thickness of the Bragg peak region is defined as the full width at half maximum (FWHM) of the energy loss curve, that describes the specific energy deposition dE/dx of a heavy charged particle as a function of the penetration depth x.