Neutron Scattering

into two ionic particles with kinetic energies of 0.573Mev and 0.191Mev for the proton and
the 3 H (tritium), respectively . As shown in Figure 8 .17, both ions cause a "primary"
ionization cloud within the suiroundings where the neutron was absorbed. These ions are
accelerated by an electric field and produce by a so-called "secondaly" ionization process an
avalanche of ions . Only the electrons give a signal at the anode because they achieve a much
larger acceleration according to their small mass. The size of the voltage pulse at both ends of
the anode is used for determination the position of absorption and thereby the scattering
angle . In a two-dimensional detector there are two perpendicularly arranged wire lattices,
from which by coincidence measurements the position ofthe absorbed neutron is determined .
8 .5 .3 .2. Scintillation Detector
Another type of detector are solid state detectors using the principle of scintillation.
reaction equation is the following :
6 Li+n 4He+ 3H+4.79MeV (8 .13)
The
A Li glass with 6.6% 6 Li is mixed with Cerium (Ce) . By absorbing a neutron in 6Li two
ionic products of reaction are formed, which interacting with Cerium produce about 4000
photons of 400nm wave length per neutron. In the disperser the photons form a light cone of
90° as depicted in Figure 8 .18 . The light cone is adjusted by the thickness of the disperser and
by the slit between scintillator and disperser (total reflection) so that the light overshadows
two photo multiplier . The photo multiplier have a diameter of 8cm and in total 8x8 photo
Neutron capture event
Reflector
Scin tillator
Air Gap
Light Disperser
Light Cone
Figure 8 .18 : Process of detection ofa 6 Li scintillation detector
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