Neutron Yields from 155 MeV/Nucleon Carbon and Helium Stopping in Aluminum

Neutron fluences have been measured from 155 MeV/nucleon ⁴He and ¹²C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon ⁴He stopping in Al and 155 MeV/nucleon ¹²C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the ¹²C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 ± 0.03) as does the ⁴He + Al system (1.02 ± 0.04), despite the fact that ¹²C has three times as many neutrons as does ⁴He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the ⁴He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon ⁴He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.