Verlag des Forschungszentrums Jülich
JUEL-1932
Humm, John Laurence
The analysis of auger electrons released following the decay of radioisotopes and photoelectric interactions and their contribution to energy deposition
192 S., 1984
ABSTRACT
This work is a study of the microdosimetry of Auger
electrons resulting from inner shell ionization phenomena
in atoms of significance in radiation biology and medicine.
Inner shell atomic vacancies are produced in radionuclides
which decay by electron capture or internal conversion
or can be produced by the photoelectric effect.
The result of creating an inner shell vacancy in an atom
is a vacancy cascade process in which a large number of
low energy Auger electrons are released. Auger emitters
when present at the radiosensitive structures of biological
materials have been shown to be highly radiotoxic, although
little is known about the energy deposition around
such sites.
The theoretical part of this work includes the use
of a Monte-Carlo technique to calculate discrete Auger
electron spectra for the electron capture decaying radionuclides:
iOdine-125, iodine-12], iron-55 and copper-64
and following photoelectric interactions in phosphorus and
argon. The individual spectra for 10,000 photoelectric
interactions were used as the basis for local energy deposition
calculations. Not only the mean energy deposition
has been calculated but also its fluctuation around the
mean where it is shown that the mean energy deposited may
be quite untypical of the energy deposition from single
disintegrations.
~irther the possibility of selective photoelectric
absorption in phosphorus bound DNA and DNA labelled with
cold iodine is-investigated. Using argon as a substitute
for phosphorus to study this problem further, energy deposition
measurements have been performed to examine the
patt~rn of energy deposition and-the mean energy deposition~€
Fi at photon energies just above and below the K=9dge
of argon~ The problems encountered in such microdosimetric
measurements are discussed in detail and in particular an
anomalous double peak phenomenon observed in-proportional
counters employing a helix grid electrode is reported
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