  The ratio of the fluxes of secondary and primary nuclei in cosmic rays has
long been used as an indicator of the grammage traversed in the journey of
cosmic ray particles throughout the Galaxy. The basic idea is that primary
particles are accelerated in astrophysical sources, such as supernova remnant
shocks and eventually propagate in the Galactic volume, occasionally
interacting with gas, mainly in the disc of the Galaxy, and there they produce
secondary nuclei through spallation. At sufficiently high energy, typically
$\gtrsim 100$ GeV/n, the ratio of fluxes of the secondary nucleus to that of
the main primary nucleus is found to scale as $E_{k}^{-\delta}$, where $E_{k}$
is the energy per nucleon (a conserved quantity in spallation reactions) and
$\delta$ identifies the energy dependence of the diffusion coefficient. The
same shock waves that may be responsible for cosmic ray acceleration in the
first place also pick up any other charged particle in the upstream, provided
being above threshold for injection. The secondary nuclei produced by
spallation in the interstellar medium are no exception, hence they also get
accelerated. This effect is unavoidable, only its strength may be subject of
debate. We compute the spectrum of secondary elements such as boron and lithium
taking into account shock reacceleration and compare our predictions with the
recent observations of the B/C ratio and preliminary measurements of the boron
and lithium flux. Both these sets of data seem to confirm that reacceleration
of secondary nuclei indeed plays an important role, thereby affecting the
validity of those scaling rules that are often used in cosmic ray physics.
