Biomedical Engineering Reference
In-Depth Information
Fig. 16.2
DDCS for
0.5 MeV protons ejecting
an electron of E
e
D
10
-3
250 eV
in water vapor. CB1 results
performed by describing
the water molecule with a
MO-LCAO-SCF wave
function and by taking into
account the Salin's factor
(dashed line) or not (solid
line). The experimental data
(circles) are taken from
Toburen and Wilson [
31
]
10
-4
10
-5
10
-6
0
30
60
90
120
150
180
θ
e
(deg)
previously described CB1 model (see 16.2.1). Thus, the mechanism of electron
transfer to the continuum is introduced through this multiplicative factor. Under
these conditions, the obtained DDCS (see Fig.
16.2
) present the ECC peak and
clearly improve the agreement with the experimental observations at small ejected
angles. Let us note nevertheless that the agreement remains quite unsatisfactory at
large angles as already reported by Madison [
62
] for helium targets impacted by
100 keV and 200 keV protons.
Similarly, we compare in Fig.
16.3
a the CB1 and CDW-EIS DDCS (solid
and dashed line, respectively) for a water molecule (described within the CNDO
approach) impacted by 6 MeV/u C
6
C
ions and for ejected electron energies ranging
from 19.2 eV to 384 eV. The recent experimental measurements taken from [
39
]are
also reported for comparison. For this system, the ejection energies are relatively
low considering that the ECC mechanism must be preferably present at much higher
electron energies (approximately 3300 eV). The qualitative behavior of CB1 and
CDW-EIS is similar to that of Fig.
16.1
a, showing in general that CDW-EIS provides
a better description of experiments in the binary encounter peak region. At higher
ejection energies considered experimental data present an unexpected behavior in
this angular domain. In Fig.
16.3
b, CB1 DDCS obtained by using the Bragg's
rule, the CNDO and the Moccia's molecular representations are shown. It can be
observed again that the best agreement with experimental data is found when the
more complete Moccia's description is employed.
