a design study for a cobra upgrade to - Institut für Kern- und ...

26 4 Scintillation detectors
spectrum, produced by monoenergetic photons of energy E > 2mec 2 .
For detectors, also backscattering peaks, escape peaks and multiple
Compton events can be seen in an energy spectrum.
Figure 4.2: Energy spectrum of the primary electrons produced by monoenergetic
photons of energy E > 2moc 2 in an absorber [27].
The residual energy of the scattered photons which is not transferred to
electrons or positrons at the primary interaction is present in the scintillator
as photons of reduced energy. These are X-rays of energy Be, photons
of energy E − Tcs and annihilation quanta of energy mec 2 . X-rays
are usually absorbed by the scintillator and the latter two have according
to their reduced energy a higher probability of being absorbed than
the primary photons. Consequently a high efficiency for full photon
energy detection can not be achieved with absorbers of slightly larger
dimensions than the range of the primary photon. This requires absorber
sizes were also secondary photons, electrons and positrons are
completely absorbed. Simulations considering the optimal absorber dimensions
are presented in chapter 5.1—“Monte Carlo studies for the
upgrade design”.
NEUTRONS interact mainly with the nuclei of the absorber material,
rather than with the atomic electrons. As uncharged massive particles
they penetrate the electron clouds of the atom and collide with the nucleus.
Scattering and absorption are the two possible types of interac-