The small angle neutron scattering （SANS） instrument is presently being constructed at Chinese Spal- lation Neutron Source （CSNS） in China, and the biological shielding design is needed to prevent the instrument from causing excessive dose rates in accessible locations. In this paper, the study of shielding design for SANS that relies on Monte Carlo simulation is introduced. Beam line shielding calculations are performed considering both scenarios of closed versus open TO chopper. The basic design scheme of the beam stop is discussed. The size of the TO chopper rotor is also estimated.
The spallation reaction was studied with 250 MeV proton beam and 400 MeV/u carbon beam at the HIRFL-CSRin Lanzhou. The neutron and residual radionuclide production were measured by using the off-line -spectroscopymethod. The radiation dose induced in spallation reaction was studied by using the thermoluminescent detectors.Moreover, an on-line neutron measurement method was developed by using a digital pulse shape discriminationsystem. All of the experimental method will be used to study the neurotics of the ADS system.
Irradiation experiment was performed at the HIRFL-CSR in Lanzhou. A Pb foil with 100 mm diameter and0.15 mm thickness was used to measure the mass-yield distributions of induced radionuclides. A natural Pb cylinderwith 100 mm diameter and 250 mm length was used as the beam dump behind the Pb foil. An ionization chamberwas placed in front of the Pb foil to monitor the beam current. The carbon beam with an energy of 400 MeV/uwas stopped in the Pb cylinder after through the Pb foil. The irradiation was lasted about 20 h to make the beamfluence enough. After irradiation, the gamma spectra of Pb foil were measured by a off-line -spectrometry method.The measurements were performed by using a high-purity germanium (HPGe) detector.
Ge HonglinZhang XueyingMa FeiChen liangZhang HongbinJu YongqinZhang YanbinLi YanyanWang Bo
The neutron yield from thick target of Pb irradiated with 250 MeV protons has been studied experimentally.The Pb target was surrounded by a water bath, where this size effectively contained most of the neutrons emittedfrom the target. The moderated neutrons were measured by the activity induced in an array of Au activation foils(with or without Cd cover). The axial coordinates of the foils without Cd cover were Z = -15, -10, -5, 0, 5, 10, 15,20 cm along the target axial, and the radial coordinates of the foils were R = 7.5, 12.5, 17.5, 22.5 and 27.5 cm abovethe target axial. The Au-foil activities were determined by measuring the peak intensities of the 412 keV line from198Au[1], and the results are shown in Fig. 1.
Ma FeiZhang XueyingJu YongqinZhang HongbinChen LiangGe Honglin
Spallation neutrons were produced by the irradiation of Pb with 250 MeV protons. The Pb target was surrounded by water which was used to slow down the emitted neutrons. The moderated neutrons in the water bath were measured by using the resonance detectors of Au, Mn and In with a cadmium （Cd） cover. According to the measured activities of the foils, the neutron flux at different resonance energies were deduced and the epithermal neutron spectra were proposed. Corresponding results calculated with the Monte Carlo code MCNPX were compared with the experimental data to check the validity of the code. The comparison showed that the simulation could give a good prediction for the neutron spectra above 50 eV, while the finite thickness of the foils greatly effected the experimental data in low energy. It was also found that the resonance detectors themselves had great impact on the simulated energy spectra.
