Calculation of Spallation Neutron Spectra Induced by 256 MeV Protons with GEANT4 and FLUKA

Neutron spectra produced through spallation reaction are key parameters in the design of Accelerator Driven Subcritical Systems. Since the energy span is large and reaction channels are complicated, no complete evaluated nuclear data library is ready for use. Suitable theoretical models are required to calculate the data. The CiADS (China initiative Accelerator Driven System) is going to be constructed in China. At the first stage, the adopted proton energy is about 250 MeV. FLUKA and GEANT4 are used to calculate the double differential cross sections at 7.5°, 30°, 60° and 150° induced by 256 MeV protons bombarding on thin aluminum, iron, lead and uranium targets, respectively. The double differential neutron yields at 30°, 60°, 120° and 150° are also calculated for 256 MeV protons bombarding on thick aluminum, iron and uranium targets, respectively. Three model lists INCLXX_HP, BIC_HP and BERT_HP implemented in GEANT4 are used separately. The calculation results are compared with corresponding experimental data. It is shown that results calculated with FLUKA and INCLXX_HP in GEANT4 fit the corresponding experimental data much better. The calculation results with BIC_HP overestimate the experimental data for thin targets in 5~30 MeV for more than 100%, except for aluminum at 150° and lead at 30°. For uranium target, the results calculated with BIC_HP is greater than the experimental results by more than 70% in the energy range 5~30 MeV at 30° and 60° and by more than 100% in the energy range above 5 MeV at 120° and 150°. In 20~100 MeV for aluminum, iron and lead targets, calculation results at 7.5° and 30° with BERT_HP underestimate the experimental data by more than 40%. And for uranium target, the experimental data up to 20 MeV are overestimated by more than 100%.