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In a previous study (Maurin et al., 2001), we explored the set of parametersdescribing diffusive propagation of cosmic rays (galactic convection,reacceleration, halo thickness, spectral index and normalization of thediffusion coefficient), and we identified those giving a good fit to themeasured B/C ratio. This study is now extended to take into account a sixthfree parameter, namely the spectral index of sources. We use an updated versionof our code where the reacceleration term comes from standard minimalreacceleration models. The goal of this paper is to present a general view ofthe evolution of the goodness of fit to B/C data with the propagationparameters. In particular, we find that, unlike the well accepted picture, andin accordance with our previous study, a Kolmogorov-like power spectrum fordiffusion is strongly disfavored. Rather, the $\chi^2$ analysis points towards$\delta\gtrsim 0.7$ along with source spectra index $\lesssim 2.0$. Twodistinct energy dependences are used for the source spectra: the usualpower-law in rigidity and a law modified at low energy, the second choice beingonly slightly preferred. We also show that the results are not much affected bya different choice for the diffusion scheme. Finally, we compare our findingsto recent works, using other propagation models. This study will be furtherrefined in a companion paper, focusing on the fluxes of cosmic ray nuclei.Comment: 32 pages, 13 figures, accepted in A&

New results on source and diffusion spectral features of Galactic cosmic rays: I $\vec{B/C}$ ratio