Wenbao Jia

The background influence of cadmium detection in saline water using PGNAA technique

In order to solve the background influence of cadmium detection in saline water using prompt gamma neutron activation analysis (PGNAA) technique, a series experiments have been designed and carried out. Furthermore, a method based on internal standard was used to correct the neutron self-shielding effect, and the background influence has been decreased sequentially. The results showed a good linear relationship between the characteristic peak counts and the concentrations of cadmium after the neutron self-shielding correction. And in the detection of saline water by PGNAA technique, the proposed methodology can be used to reduce the influence of background with the self-shielding effect correction.

Study on the PGNAA measurement of heavy metals in aqueous solution by the Monte Carlo–Library Least-Squares (MCLLS) approach

In the present work, a prompt gamma neutron activation analysis (PGNAA) setup, which consists of a 300mCi 241Americium-Beryllium (Am-Be) neutron source and a 4 × 4-in. Bismuth germanium oxide (BGO) detector, was developed for heavy metal detection in aqueous solutions. A series of standard samples with analytical purity were prepared by dissolving heavy metals in deionized water. Quantitative spectrum analysis was performed by the Monte Carlo-Least-Squares (MCLLS) approach to measure the standard samples. The detector response functions of 4 × 4-in. BGO detector were generated by using the CEARDRF code. The element libraries were simulated in silico by the CEARCPG code, which was developed by Dr. Gardner. The simulation results presented were in very good agreement with the experimental results. The correlation coefficients were very close to 1 when the fitted spectrum was compared with the experimental spectrum. By applying the MCLLS approach, the relative deviation of the measurement accuracy was less than 2.27% for Ni, Mn, and Cu and up to 69.33% for Pb.

Compact Shielding Design of a Portable 241Am–Be Source

A compact shielding tank for portable 241Am-Be neutron source, which is used in nuclear well logging, was designed according to the Monte Carlo simulation. From inner to outer, the proposed tank has two shielding layers to shield the high- and low-energy neutrons. In this study, the shielding properties of several materials were evaluated. Tungsten was selected as the neutron moderator to build the inner layer. The thermal neutron absorber in the outer layer was made of polyethylene containing 1.2% boron carbide. The volume and weight of the new tank reduced by 86% and 54%, respectively, by using this dual-layer shielding model, when compared with those of the old shielding tank. Moreover, the simulation results indicated that the total dose rate anywhere outside the tank is less than 0.025mSv/h and that the intensity of gamma flux at the tank surface becomes lower.

Designing a new type of neutron detector for neutron and gamma-ray discrimination via GEANT4

Design of a new type of neutron detector, consisting of a fast neutron converter, plastic scintillator, and Cherenkov detector, to discriminate 14-MeV fast neutrons and gamma rays in a pulsed n-γ mixed field and monitor their neutron fluxes is reported in this study. Both neutrons and gamma rays can produce fluorescence in the scintillator when they are incident on the detector. However, only the secondary charged particles of the gamma rays can produce Cherenkov light in the Cherenkov detector. The neutron and gamma-ray fluxes can be calculated by measuring the fluorescence and Cherenkov light. The GEANT4 Monte Carlo simulation toolkit is used to simulate the whole process occurring in the detector, whose optimum parameters are known. Analysis of the simulation results leads to a calculation method of neutron flux. This method is verified by calculating the neutron fluxes using pulsed n-γ mixed fields with different n/γ ratios, and the results show that the relative errors of all calculations are <5%.

Radiation-induced changes in electrical conductivity and structure of BaPbO3 after γ-irradiation

Several barium plumbate (BaPbO3) solid samples, made from PbO and BaCO3 powder by chemistry liquid-phase coprecipitation, were investigated before and after γ-irradiation. The solid samples were irradiated by a 60Co γ-irradiation source whose dose rate is about 0.7 kGy per hour. The irradiation times were 0, 72, 144, 216, 288 and 360 h. Then, the four-probe method, X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to indicate the changes in electrical conductivity and microstructure of BaPbO3 after γ-irradiation. The XRD results indicated that the content of PbO was reduced as the irradiation dose was increased and eventually vanished from the surface of samples. However, there was no new obvious substance phase found from the XRD atlas. It seems that the PbO transformed into nearly amorphous Pb5O8. The conjecture could be proved by the results of annealing experiment and SEM. The XPS results seem to show that the microstructure of BaPbO3 was slightly changed.

Degradation mechanism of p-cresol in aqueous solutions by gamma-ray irradiation

Degradation mechanism of p-cresol in aqueous solutions by gamma-ray irradiation was investigated at various initial p-cresol concentrations with different absorbed doses. The results show that p-cresol in aqueous solutions can effectively be degraded by gamma-ray irradiation. Chemical oxygen demand was used to assess the degree of mineralization of p-cresol. The degradation can be enhanced by the additions of free Radical Scavengers. The degradation products were identified by high-performance liquid chromatography with tandem mass spectrometric. Degradation mechanism of p-cresol in aqueous solutions were proposed according to the products analysis.

Catalytic Effect of a Semiconductor on the Removal of Hexavalent Chromium from Aqueous Solution by γ-Ray Irradiation

Hexavalent chromium is a type of toxic chemical, it may cause allergies, hereditary genetic defects and cancer in humans by inhalation, and it is also a persistent danger to the environment. However, chromium metal, trivalent chromium and tetravalent chromium have low toxicities. In this study, semiconductor materials (quartz fibre and TiO2) were added to a hexavalent chromium solution and the removal efficiency of hexavalent chromium as a function of the γ-ray irradiation dose, as well as the catalytic mechanism, was investigated. It was observed that the reduction of hexavalent chromium by γ-ray irradiation was largely promoted in the presence of semiconductor materials; the semiconductor materials act as catalysts under the gamma-ray irradiation. The hexavalent chromium in the solution can be converted to an insoluble precipitate by gamma-ray irradiation. These results are highly beneficial to apply semiconductor materials as catalysts for the removal of contaminants by radiation.

Feasibility study for wax deposition imaging in oil pipelines by PGNAA technique

Wax deposition in pipelines is a crucial problem in the oil industry. A method based on the prompt gamma-ray neutron activation analysis technique was applied to reconstruct the image of wax deposition in oil pipelines. The 2.223MeV hydrogen capture gamma rays were used to reconstruct the wax deposition image. To validate the method, both MCNP simulation and experiments were performed for wax deposited with a maximum thickness of 20cm. The performance of the method was simulated using the MCNP code. The experiment was conducted with a 252Cf neutron source and a LaBr3: Ce detector. A good correspondence between the simulations and the experiments was observed. The results obtained indicate that the present approach is efficient for wax deposition imaging in oil pipelines.

A method to describe inelastic gamma field distribution in neutron gamma density logging

Pulsed neutron gamma density logging (NGD) is of great significance for radioprotection and density measurement in LWD, however, the current methods have difficulty in quantitative calculation and single factor analysis for the inelastic gamma field distribution. In order to clarify the NGD mechanism, a new method is developed to describe the inelastic gamma field distribution. Based on the fast-neutron scattering and gamma attenuation, the inelastic gamma field distribution is characterized by the inelastic scattering cross section, fast-neutron scattering free path, formation density and other parameters. And the contribution of formation parameters on the field distribution is quantitatively analyzed. The results shows the contribution of density attenuation is opposite to that of inelastic scattering cross section and fast-neutron scattering free path. And as the detector-spacing increases, the density attenuation gradually plays a dominant role in the gamma field distribution, which means large detector-spacing is more favorable for the density measurement. Besides, the relationship of density sensitivity and detector spacing was studied according to this gamma field distribution, therefore, the spacing of near and far gamma ray detector is determined. The research provides theoretical guidance for the tool parameter design and density determination of pulsed neutron gamma density logging technique.