NeuLAND - FAIR

8. Calibration
8.1. Calibration with Fast Neutrons
8.1.1. Calibration of a Subset of NeuLAND Modules
The calibration of a fast-timing neutron detector for high-energy neutrons is a difficult
task, since tagged neutron beams are rarely available. The experimental scheme, which
we elaborated in order to measure time resolution, efficiencies and data patterns at high
neutron energies, is detailed in the accepted GSI beam time proposal S406 [Bor-10].
The most important points are summarized in the following. The demands are precise
determinations of angle and energy of impinging neutrons on an event-by-event basis for
high-energy neutrons.
We will utilize neutrons stemming from a quasifree-scattering reaction of a deuteron
beam on protons. The deuteron beam is delivered from SIS18 at GSI with energies
between 200-1500 AMeV to the LAND reaction setup at Cave C, where the beam is
impinging on a CH2 target. Quasifree-scattering reactions are selected by detection of
both protons from the (p,2p) reaction in a wide angular range from 10 to 80 degrees. The
two protons stemming from the quasi-free p knockout reaction exhibit typical angular
correlations resulting in an opening angle ∆θ ∼ 90 ◦ and ∆Φ ∼ 180 ◦ . The angles are
measured with Si-strip detectors. The energy of the protons is measured with the Crystal
Ball detector. The transverse momentum of the spectator neutron is fixed by proton
kinematics, thus we know where the neutron detector is hit. Figure 8.1 shows the
angular distribution of protons for two incident beam energies. While for lower energies
a symmetric distribution in the proton polar angles peaking around 43 ◦ is observed,
an asymmetric distribution of angles is favored for beam energies above 500 AMeV,
resulting, e.g., in two strong peaks at around 15 ◦ and 70 ◦ for a reaction at 1000 AMeV.
Figure 8.2 shows exemplarily the spatial neutron distribution in 10 m distance from the
target for the neutrons stemming from the quasifree scattering reaction at 250 AMeV
deuterons on protons. In the following we detail how time resolution and efficiency of
a subset of NeuLAND submodules will be determined in an experiment scheduled for
the first half of 2012. Note, that the same beam time will be utilized as a calibration
experiment for the existing LAND detector for characterization of event patterns.
1. Time resolution:
Since the detection of a neutron is mostly of destructive character, at least with
respect to its momentum, studying the time resolution of neutron detectors is a
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