Measurement of the [Formula: see text]Ta([Formula: see text]) cross sections up to stellar s-process temperatures at the CSNS Back-n.

The neutron capture cross section of [Formula: see text]Ta is relevant to s-process of nuclear astrophysics, extraterrestrial samples analysis in planetary geology and new generation nuclear energy system design. The [Formula: see text]Ta([Formula: see text]) cross section had been measured between 1 eV and 800 keV at the back-streaming white neutron facility (Back-n) of China spallation neutron source(CSNS) using the time-of-flight (TOF) technique and [Formula: see text] liquid scintillator detectors. The experimental results are compared with the data of several evaluated libraries and previous experiments in the resolved and unresolved resonance region. Resonance parameters are extracted using the R-Matrix code SAMMY in the 1-700 eV region. The astrophysical Maxwell average cross section(MACS) from kT = 5 to 100 keV is calculated over a sufficiently wide range of neutron energies. For the characteristic thermal energy of an astrophysical site, at kT = 30keV the MACS value of [Formula: see text]Ta is 834 ± 75 mb, which shows an obvious discrepancy with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNiS) recommended value 766 ± 15 mb. The new measurements strongly constrain the MACS of [Formula: see text]Ta([Formula: see text]) reaction in the stellar s-process temperatures.

Imaging and reconstruction of high-energy proton beam spot before target based on secondary gamma rays.

The distribution and stability of the incident proton beam spot are critical for the stable operation of a high-power spallation target. This study proposes a method to capture images of the incident proton beam spot based on secondary gamma rays. The distribution of the backward secondary gamma rays irradiated by the primary proton beam on the incident surface of the target is close to the distribution of the protons and can be measured at a low-radiation position far from the target area. A relation of distributions between the incident protons and the secondary gammas is constructed by using the point response function of this pinhole imaging system. The proposed method of imaging is suitable for monitoring the distribution of the proton beam on the target in facilities that use a beam power of several megawatts or tens of megawatts, such as spallation neutron sources or accelerator-driven subcritical systems.

Feasibility of nuclide-identified imaging based on the back-streaming white neutron beam at the China Spallation Neutron Source.

Back-streaming neutrons through the incoming proton channel at the spallation target station of the China Spallation Neutron Source have been studied as a white neutron source (Back-n). We report a physical study on white neutron imaging based on the Back-n beamline. The wide neutron energy spectrum spanning from 1 eV to 100 MeV was very suitable for nuclide-identified imaging as well as measurements of nuclear data and other applications. We calculated the back-streaming white neutron energy spectrum using the Monte Carlo N-Particle code. A comparison of the results of calculation with those of the FLUktuierende KAskade code and experimental measurements were carried out. The energy resolution of the Back-n beam was close to 5% depending on the neutron energy and the modes of operation, and its spatial resolution could attain the order of tens of micrometers.

Iron-oxide-identifying imaging method based on a wide-energy neutron beam for corrosion inspection in reinforced concrete structures.

To prevent potential hazards caused by steel corrosion, there is an increase in demand for non-destructive inspection or monitoring of reinforcing steel corrosion in concrete structures. In this study, an iron-oxide-identifying imaging method is proposed that is based on a neutron resonance transmission imaging technique. According to the correlation analysis of the resonance characteristics of iron and oxygen and the elemental fractions, the iron oxides in the corroded reinforced concrete samples were accurately identified and mapped. The volume identification limit of the rust layer was further analyzed, and it is close to 0.1 mm. For the resonance energies of nuclides Fe-56 and O-16 in the tens and hundreds of keV range, the intensity of neutrons at the corresponding energy is only lower about three orders of magnitude after passing through a 40-cm-thick concrete block. The iron-oxide-identifying imaging method could also obtain a clear image of the iron-oxide distribution inside the 20-cm-thick corroded reinforced concrete sample.

RESEARCH ON DOSE MONITORING IN BACKSCATTERING NEUTRON HALL IN CHINA SPALLATION NEUTRON SOURCE.

The back-n project in China Spallation Neutron Source (CSNS) was launched primarily for nuclear data measurements. In the backscattering neutron hall, the neutron and gamma monitors were used for dose monitoring. Because of the dead time problem of monitors, performance of the monitors in such pulsed radiation field needs to be analyzed. In this research, experiments with dose monitors and personal dosemeters were conducted, and simulation by Monte Carlo code FLUKA was performed. Results showed that the values by monitors are smaller, and the larger the dose, the larger the difference. The reasons in term of energy response and dead time have been analyzed, and corrections were discussed. After corrections, the measured value can agree with the simulation results in the range of about a factor 3. Totally speaking, the values recorded by neutron and gamma monitors can be a reference for radiation safety management in CSNS.