Secondary neutron-production cross sections from heavy-ion interactions in composite targets

Secondary neutron-production cross sections have been measured from interactions of 290 MeV/nucleon C and 600 MeV/nucleon Ne in a target composed of simulated Martian regolith and polyethylene, and from 400 MeV/nucleon Ne interactions in wall material from the International Space Station. The data were measured between 5° and 80° in the laboratory. We report the double-differential cross sections, angular distributions, and total neutron-production cross sections from all three systems. The spectra from all three systems exhibit behavior previously reported in other heavy-ion neutron-production experiments, namely, a peak at forward angles near the energy corresponding to the beam velocity, with the remaining spectra generated by pre-equilibrium and equilibrium processes. The double-differential cross sections are fitted with a moving-source parametrization. Also reported are the data without corrections for neutron flux attenuation in the target and other intervening materials and for neutron production in nontarget materials near the target position. These uncorrected spectra are compared with SHIELD-HIT and PHITS transport model calculations. The transport model calculations reproduce the spectral shapes well but, on average, underestimate the magnitudes of the cross sections.

Figure 1

(Color online) A schematic diagram of the experimental setup on the SB3 beam course at HIMAC. The quadrupole magnets are positioned at a concrete shielding wall separating the target hall from the shield room where the beam dump was located.

Figure 2

Pulse-height-to-energy calibration of the charge-integrating analog-to-digital converter. The open, square symbols show the fit to the Compton-edge data, and the closed, diamond-shaped symbols show the data from the maximum-recoil method.

Figure 3

Plot of neutron-detection efficiency (in percent) as a function of neutron energy. Efficiencies are shown for thresholds of 3 MeV (0.92 electron-equivalent MeV), 5 MeV (1.90 electron-equivalent MeV), and 20 MeV (11.5 electron-equivalent MeV) in neutron energy.

Figure 4

An estimation of the fraction of neutron flux that does not make it to the neutron detector owing to absorption and out-scattering in the marsbar target and other intervening materials between the target and detector. The open, square symbols show the fraction lost from the detector at 5°, and the closed, diamond-shaped symbols show the fraction lost from the detector at 80°.

Figure 5

(Color online) Double-differential neutron spectra from 290 MeV/nucleon C + marsbar, at the indicated laboratory angles. The error bars represent the statistical uncertainties. The symbols show the data after all of corrections described in Secs. 3d and 3e. The dashed (red) line shows the data before the corrections for attenuation and production from nontarget materials. The solid (black) lines show the fit to the data using a moving-source parametrization. The (green) dashed histograms show the results from a SHIELD-HIT calculation. Results from PHITS calculations are shown with the solid (blue) histograms. The spectra and fits are offset by successive factors of 10, as indicated in the legend.

Figure 6

(Color online) Double-differential neutron spectra from 400 MeV/nucleon Ne + ISS wall, at the indicated laboratory angles. The error bars represent the statistical uncertainties. The symbols show the data after all of corrections described in Secs. 3d and 3e. The dashed (red) line shows the data before the corrections for attenuation and production from nontarget materials. The solid (black) lines show the fit to the data using a moving-source parametrization. The (green) dashed histograms show the results from a SHIELD-HIT calculation. Results from PHITS calculations are shown with the solid (blue) histograms. The spectra and fits are offset by successive factors of 10, as indicated in the legend.

Figure 7

(Color online) Double-differential neutron spectra from 600 MeV/nucleon Ne + marsbar, at the indicated laboratory angles. The error bars represent the statistical uncertainties. The symbols show the data after all of corrections described in Secs. 3d and 3e. The dashed (red) line shows the data before the corrections for attenuation and production from nontarget materials. The solid (black) lines show the fit to the data using a moving-source parametrization. The (green) dashed histograms show the results from a SHIELD-HIT calculation. Results from PHITS calculations are shown with the solid (blue) histograms. The spectra and fits are offset by successive factors of 10, as indicated in the legend.

Figure 8

(Color online) Angular distribution for the 290 MeV/ nucleon C + marsbar system. The data are shown with the symbols. The error bars include both systematic and statistical uncertainties. The dashed (red) line shows the data without corrections for attenuation and for production from nontarget materials. Results from PHITS and SHIELD-HIT calculations are shown with the dotted (blue) and dot-dashed (green) lines, respectively. The solid line comes from a fit explained in the text.

Figure 9

(Color online) Angular distribution for the 400 MeV/ nucleon Ne + ISS wall system. The data are shown with the symbols. The error bars include both systematic and statistical uncertainties. The dashed (red) line shows the data without corrections for attenuation and for production from nontarget materials. Results from PHITS and SHIELD-HIT calculations are shown with the dotted (blue) and dot-dashed (green) lines, respectively. The solid line comes from a fit explained in the text.

Figure 10

(Color online) Angular distribution for the 600 MeV/ nucleon Ne + marsbar system. The data are shown with the symbols. The error bars include both systematic and statistical uncertainties. The dashed (red) line shows the data without corrections for attenuation and for production from nontarget materials. Results from PHITS and SHIELD-HIT calculations are shown with the dotted (blue) and dot-dashed (green) lines, respectively. The solid line comes from a fit explained in the text.