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On-going measurements of the cosmic radiation (nuclear, electronic, andgamma-ray) are shedding new light on cosmic-ray physics. A comprehensivepicture of these data relies on an accurate determination of the transport andsource parameters of propagation models. A Markov Chain Monte Carlo is used toobtain these parameters in a diffusion model. From the measurement of the B/Cratio and radioactive cosmic-ray clocks, we calculate their probability densityfunctions, with a special emphasis on the halo size L of the Galaxy and thelocal underdense bubble of size r_h. The analysis relies on the USINE code forpropagation and on a Markov Chain Monte Carlo technique (Putze et al. 2009,paper I of this series) for the parameter determination. As found in previousstudies, the B/C best-fit model favours diffusion/convection/reacceleration(Model III) over diffusion/reacceleration (Model II). A combined fit on B/C andthe isotopic ratios (10Be/9Be, 26Al/27Al, 36Cl/Cl) leads to L ~ 8 kpc and r_h ~120 pc for the best-fit Model III. This value for r_h is consistent with directmeasurements of the local interstallar medium. For Model II, L ~ 4 kpc and r_his consistent with zero. We showed the potential and usefulness of the MarkovChain Monte Carlo technique in the analysis of cosmic-ray measurements indiffusion models. The size of the diffusive halo depends crucially on the valueof the diffusion slope delta, and also on the presence/absence of the localunderdensity damping effect on radioactive nuclei. More precise data fromon-going experiments are expected to clarify this issue.

astronomy and astrophysics

A Markov Chain Monte Carlo technique to sample transport and source  parameters of Galactic cosmic rays: II. Results for the diffusion model  combining B/C and radioactive nuclei