vided the average charge does not deviate from by
3% at the most [9]. Using (3), we then obtain the fol
lowing expression:
(4)
This approximation is valid for describing the pro
cesses that occur in gaseous targets. In solid targets,
the time between two successive collisions becomes
less than the lifetime of the excited states of an inci
dent particle, and a considerable portion of the inci
dent ions, having electrons in excited states, is
involved in chargeexchange processes. In a solid tar
get, chargeexchange cross sections are thus averaged
over the exited states of an incident ion. This leads to a
change in the electron capture and loss cross sections,
all other conditions being equal. These changes are
sensitive to the velocity of the colliding particles, V,
the nuclear charge of ions, Z, and the atoms of the
medium, Zt
, as well as to the initial charge of the ions,
i0. Closer studies of the differences between the charge
fractions of ions in gases and solid targets were per
formed by Bohr and Lindhard [10] and Betz and
Grodzins [11].
Studying the phenomena of charge exchange with
ions in solids is generally a very difficult task from the
point of view of both experimental research and theo
retical description. The use of a twocomponent
approximation is considered to be justified for light
ions (e.g., He) or for fastmoving and heavier ions with
energies of several MeV/nucleon at sufficiently high
energies where only two charge components, FZ and
FZ–1, play important roles.
RESULTS AND DISCUSSION
In this work, approximation (3) is used to calculate
the average charges of He and N ions passing through
celluloid films. Figure 1 shows the experimental data for
the average charges of He ions in dependence on the
thickness of the celluloid target for different values of the
initial charge of the ions [5]. The velocity values for the
ions are 12 × 108
cm/s—E = 0.75 MeV/nucleon—and
18.7 × 108
cm/s—E = 1.8 MeV/nucleon. In this case,
only charge components FZ and FZ – 1 can be consid
ered in the beam, and the calculations performed
according to formula (3) describe the experimental
results for the values of the coefficients α = 0.5 at V =
12 × 108
cm/s and α = 0.2 at V = 18.7 × 108
cm/s.
The formation of the equilibrium state of N ions in
the considered range of velocities (4–12) × 108
cm/s
cannot be described by a twocomponent approxima
tion. Expression (3), however, can be used to calculate
the average charge for the varying coefficient α, taking
into account the dependence of α on the initial charge
of the incident ion, as
(5)
eq i
1 0 ln