High energy (greater than or equal to 50 MeV) protons can be considered, wh
en their ionization losses stopping power is taken into account, as the rad
iation with low (< 5 keV/mum) linear energy transfer (LET). However, their
energy is already sufficient to create, through the nuclear reactions in ir
radiated matter, secondary particles with much higher LET. This phenomenon
can modify the characteristics of the energy transfer process due to these
particles, which should be taken into account when such particles are used
for radiobiology studies and/or for radiotherapy.
The importance of these secondary particles was studied experimentally by m
eans of the LET spectrometer based on a chemically etched track detector, i
n which the tracks of primary protons are not revealed. The studies were pe
rformed in proton beams available at the Joint Institute of Nuclear Researc
h (JINR) at Dubna, Russia, with protons of primary energies of about 200 Me
V and 1 GeV. The microdosimetric distribution of secondary particles mentio
ned are presented and compared and their contribution to primary proton ion
ization losses absorbed dose is estimated. This contribution increases rela
tively with the proton energy, and also changes with the depth of penetrate
d material. The importance of this phenomenon to some applications is discu
ssed. (C) 2001 Elsevier Science Ltd. All rights reserved.