NeuLAND - FAIR

Counts
600
500
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300
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100
without light guide
light guide: pyramidal
light guide: spherical
light guide: parabolic
0
5 6 7 8 9 10 20
Time (ns)
Counts
900
800
700
600
500
400
300
200
100
without light guide
light guide: pyramidal
light guide: spherical
light guide: parabolic
0
5 6 7 8 9 10 20
Time (ns)
Figure 4.11.: Arrival time photons from simulations with different light guide shapes, displayed
on the left-hand side for an entrance window of the photomultiplier
of 1 inch, and of 1.5 inch in the figure at the right-hand side.
4.5. Scintillator Studies of Full-Size NeuLAND
The detailed simulations shown in the following subsections were performed using the
R 3 BRoot framework. As reference the most important parameters are again summarized
here. Within R 3 BRoot the TGEANT3 interface was selected, including the interaction
option GCalor for low-energy neutrons. The dimensions of the NeuLAND detector in
these simulations are defined very similar to the proposed final detector design, see section
5. Only the light guides are omitted within this study due to the high computational
effort of optical photon tracking, see section 4.4. The detector submodules are 250 cm
long and have a cross section of 5 × 5 cm 2 . Twenty submodules are grouped in planes
of 250 × 250 cm 2 and the detector depth of 3 m is built up from 60 planes, which are
stacked alternating with horizontal and vertical paddles. Light quenching for protons
was taken into account using Birk’s relation [Bir-64]. The transport of the resulting
light from the position of production to the readout positions of the scintillator bars
takes into account the scintillator time response and the light attenuation length of the
bar. Energy thresholds were set to approximately 160 keV for both read-out sides, including
a small variation to simulate typical behaviour of jitter in read-out electronics.
An integration time of approximately 200 ns is applied for the collection of the light
output. The time of each hit is derived from the mean time of the both readout times
of the bar. Unless specified differently a time resolution of 150 ps was assumed. The
adaption factor for the total energy deposit, obtained from the R 3 BRoot comparison to
the neutron calibration data of LAND, see section 4.1.2, was applied for the description
of energy loss in NeuLAND accordingly. 1 Figure 4.12 shows exemplarily a typical event,
displayed in a NeuLAND side view.
1 Although the mismatch in the total energy deposit spectra is most likely originating from a malfunctioning
absolute energy calibration in the experiment, we take the reduction of total energy loss for
further simulations as a safety margin into account.
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