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Note 2. Model III for L = 4 kpc. For all settings, we keep fixed 〈 n$_{e}$ − 〉 = 0 . 033 and T$_{e}$ ∼ 10 $^{4}$K. The reference parameters for the sur- face density Σ ref and the hydrogen fraction f ref H are given in Table 1. 

The last parameter is the Alfv´ enic speed, for which we need to consider the whole transport equation. The speed V$_{a}$ is used to define K$_{pp}$ [see Eq. (6)], which appears in the terms b and c [Eqs. (3) and (4)] of Eq. (1). If we consider the latter equation and the transport operator L in Eq. (2), the rescaling Σ new = x × Σ ref leads to L new = x ×L $^{ref}$. This implies b new = x × b $^{ref}$, c new = x × c $^{ref}$, and S new = x ×S $^{ref}$. Let us consider the three terms each in turn. For b , if we look at Eq. (3), this x factor is automatically ensured for the Coulomb and ionisation losses (they depend on the gas surface density), and also for adiabatic losses (as V new c = x × V ref c ). This implies K new pp = x × K ref pp . From Eq. (6), we have K$_{pp}$ ∝ V 2 a /K$_{0}$ , such that the previous equality yields 

This gives V new a = x × V ref a (the same information is given by the c term), in agreement with the results of Table 2. 

## 4.3. Summary for the gas surface density 

An uncertainty of x % on the gas surface density leads to SystUnc of x % on K$_{0}$ , V$_{c}$ and V$_{a}$ , but it leaves the diffusion slope δ unchanged. This is true, whatever the value for the halo size L . For the sake of completeness, we should note that this also affects the source term: the source abundances are now q new = x × q $^{ref}$. 

## 5. Influence of the source spectrum 

In Paper I, we showed that some correlations exist between the source spectra and the transport parameters. Below, we investigate in more detail how the transport parameters are changed if we assume different input for α (spectral index of the sources) and η$_{S}$ (related to the spectral shape at low energy: − 

## 5.1. Influence of the source slope α 

It is usually said that the source spectrum energy depen- dence Q ( E ) factors out of the secondary-to-primary ratio. This agrees with the results gathered in Table 3, which shows the effect of varying the source slope α (or equiva- lently the slope of the measured fluxes γ = α + δ ). This is especially true for Model I (no reacceleration), whereas if reacceleration is included (Models II and III), a few % 

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Note 3. Models 0, I, II, and III for L = 4 kpc. The parameter γ is the slope of the propagated fluxes ( γ = α + δ ). The source spectrum is Q ( E ) ∝ β $^{η$_{S}$}$R − $^{α}$, and η$_{S}$ = − 1. 

change on the parameter γ leads to a few % change on V$_{a}$ , K$_{0}$ , and δ . 

From the last column of the same table, we see that on a statistical basis, the best model is Model III, then Model II, Model I, and finally Model 0. The relative merit (goodness-of-fit) of each class of models (III, II, I, and 0) remains unchanged when α is changed. 

## 5.2. Influence of the low-energy source spectrum through 

The second parameter that can be varied in the source term is the low-energy shape β η$_{S}$ [see Eq. (9)], which is a priori not very well constrained, both from observational and the- oretical points of view. The evolution of the best-fit trans- port parameters as a function of η$_{S}$ is shown in Fig. 1, for Model 0 (dash-dotted lines/stars), I (dotted lines/plusses), II (dashed lines/crosses), and III (solid lines/open circles). 

The three configurations have marked minima in their χ 2 min (bottom panel), but not at the same η$_{S}$ . Models 0 and I have a similar χ 2 dependence (weak impact of the presence of the wind), as have Models II and III (both af- fected by reacceleration). Understanding the exact depen- dence of the transport parameters with η$_{S}$ is not the goal of the analysis. The important point to underline is that changing η$_{S}$ does not allow reconciling convection Models I and III with smaller δ . As δ varies only in the range 0 . 3 − 0 . 5 for Model 0 (pure diffusion), we conclude that for present B/C data, large δ are associated to the constant Galactic wind. The largest variation is observed for Model II (reac- celeration only), for which δ is allowed to be either smaller or larger than δ best II = 0 . 33 (associated with η best S ≈ 1) for a smaller or a larger η$_{S}$ . For any η$_{S}$ , Model III always per- forms better than the other two models. 

