  Neutron energy spectrum from 120 GeV protons on a thick copper target was
measured at the Meson Test Beam Facility (MTBF) at Fermi National Accelerator
Laboratory. The data allows for evaluation of neutron production process
implemented in theoretical simulation codes. It also helps exploring the
reasons for some disagreement between calculation results and shielding
benchmark data taken at high energy accelerator facilities, since it is
evaluated separately from neutron transport. The experiment was carried out
using a 120 GeV proton beam of 3E5 protons/spill. Since the spill duration was
4 seconds, proton-induced events were counted pulse by pulse. The intensity was
maintained using diffusers and collimators installed in the beam line to MTBF.
The protons hit a copper block target the size of which is 5cm x 5cm x 60 cm
long. The neutrons produced in the target were measured using NE213 liquid
scintillator detectors, placed about 5.5 m away from the target at 30^{\circ}
and 5 m 90^{\circ} with respect to the proton beam axis. The neutron energy was
determined by time-of-flight technique using timing difference between the
NE213 and a plastic scintillator located just before the target. Neutron
detection efficiency of NE213 was determined on basis of experimental data from
the high energy neutron beam line at Los Alamos National Laboratory. The
neutron spectrum was compared with the results of multi-particle transport
codes to validate the implemented theoretical models. The apparatus would be
applied to future measurements to obtain a systematic data set for secondary
particle production on various target materials.
