Fig. 2: MC simulation results for particles arriving at the diamond detector.

a The flux of neutrons as a function of neutron energy according to their origin. Forward-emitted protons (\({p}_{fwd}^{+}\)) dominate neutron production in the high-energy region. The non-continuous spectrum for neutrons generated by electrons is an artifact of insufficient statistics. The light blue dashed line corresponds to the sum of the individual neutron production channels. The shaded area represents the statistical uncertainty of the simulation results for a given energy bin. b Time of arrival of prompt photon radiation fields (predominantly from bremsstrahlung from the source and bremsstrahlung produced by electrons elsewhere) vs. time of arrival of neutrons. A shorter flight path would imply overlap between the arrival of photons and high-energy neutrons. The vertical dashed/dotted lines mark different neutron energies. c Correlation between the time-of-flight and energy of the neutrons. All events far from the red-dashed line, representing primary neutrons, correspond to neutrons scattered or produced elsewhere by secondary sources other than in the catcher target. The inset displays a histogram of the difference between the neutrons' arrival time at the detector and the expected arrival time for the direct path. The expected times were calculated from the neutrons' energies. Only the neutrons with differences of less than 3 ns (width of the initial ion pulse, shaded area. See inset in Fig. 5a) are considered primary neutrons produced in the catcher.