Study On The Shielding Effect And Background At The Experiment Hall Of Neutron Generator

A D-T neutron source model, based on the neutron energy spectrum, the neutron angular distribution, the source configuration and the target materials, was developed. The neutron/gamma energy spectrums outside the shield wall of neutron generator experimental hall at China Institute of Atomic Energy were simulated using MCNP code. The flux ration of neutron and gamma in different energy regions were presented. Then, the neutron flux and the associated y-ray flux in the generator experimental hall were measured. The time-of-flight spectrum and the y-ray energy spectrum were also measured for the Fe(n, xny) reaction. The results showed that theγ-ray background peaks were obvious in two spectrums. At last, combined with simulation data and experimental data, the main reasons for high background peak in the experiment hall were analysed.To reduce background of the experimental hall, an improving plan for the shield and the shield wall was proposed through the MCNP simulation to the transportion of neutron/gamma as well as referring to the experimental data of the background of the experimental hall. The plan can also be concluded as following, based on the original plan,54cm-weighted cement and 2cm-Pb were increased on the original shield wall,30cm-(C2H4)n and 11cm-Pb were added on the original shield, and the original collimator was replaced by the symmetrical-biconical collimator. Then, the neutron flux and the associatedγ-ray flux in experiment hall were measured. The results show that the background of the neutron flux and theγ-ray flux in the generator experimental hall have been lower about an order of magnitude than the former without improvement; theγ-ray background peak also disappears in the time-of-flight spectrum and theγ-ray energy spectrum for the new Fe(n, xny) reaction compared to the former.In addition, the parameters of neutron capture were given, as well as the optimal design for it have been completed by the MCNP code and the theoretical calculation. These works provide the reliable theoretical references to the neutron capturer for the further improvement.