NeuLAND - FAIR

events
800
600
400
200
0
0 200 400 600 800 1000
total light (a.u.)
events
600
400
200
0
0 50 100 150
multiplicity
Figure 4.14.: Left hand side: Total energy deposited in NeuLAND from 600 MeV neutrons
for multiplicities of 1 (black), 2 (green), 3 (red), 4 (blue), 5 (yellow)
and 6 (magenta). Right hand side: Multiplicity from number of submodules
with valid signals, again for 1 to 6 neutrons impinging with 600 MeV.
4.5.3. Neutron Tracking
For the final assignment of neutrons we now utilize the calorimetric information for
the neutron multiplicity. Typically, the number of clusters in the event is much larger
than the derived neutron multiplicity, as detailed before. We, therefore, have to select
from the list of clusters the ones that are most reliable, thus ensuring that also the
correct momenta of neutrons are reconstructed. The time-wise first cluster is taken as
the first neutron track. For the remaining clusters, a resorting procedure is performed.
An excellent criterion appears to be a combined requirement on the smallest difference
of velocity of the neutron βcluster (associated with the cluster), the beam velocity βbeam
and the largest energy deposit of the cluster Ecluster dep . The clusters are sorted according
to their values of
Rcluster = |βcluster − βbeam|
E cluster
dep
(4.2)
starting with the smallest value of Rcluster. Finally, clusters from this sorting are defined
as neutron tracks up to the maximum number of neutrons from the calorimetry
argument. The remaining clusters are eliminated from the further analysis.
The quality of the neutron detection and its separation into the various multiplicities can
be understood from the so-called neutron separation matrices, displayed in tables 4.5 for
200, 600 and 1000 MeV neutrons impinging on NeuLAND, at a distance of 15.5 m to
the origin of the neutrons. For multiplicities of up to 5 neutrons simulated (columns),
the percentage of detection in the various neutron channels derived from the tracking
algorithms is indicated, respectively (rows).
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