  A new method for the experimental study of ionization loss of relativistic
negatively charged particles moving in a crystal in the channeling regime using
a semiconductor surface-barrier detector with smoothly tunable thickness of the
depleted layer is proposed. The ionization loss can only be measured in the
depleted layer of the detector. The thickness of the depleted layer in a flat
semiconductor detector can be smoothly regulated by the value of the bias
voltage of the detector. Therefore, the energy distribution of the ionization
loss of relativistic particles which cross the detector and move in the
channeling regime in the detector crystal can be measured along the path of the
particles at variation of the bias voltage of the detector. Ionization loss
spectra should be different for channeling and nonchanneling particles, and
both fractions can be determined. The application of a Si surface-barrier
detector-target is considered. Measurements with such a detector would make it
possible to study: the energy distribution of ionization loss of channeling
negatively and positively charged particles; spatial distribution of ionization
loss as a function of the path length of channeling particles; the dechanneling
length of negatively charged particles; and to clear up the role of
rechanneling of the particles in the crystal. Comparison of experimental data
with calculations can help to develop a description of the dynamics of motion
of negatively charged particles channeling in a crystal. A better understanding
of the dechanneling length properties can be useful in the production of
positrons and other particles such as neutrons by an electron beam in crystals,
and in the development of crystalline undulators, and at a crystal-based
extraction of electron beams from a synchrotron.
