Tuo Xianguo

Environmental geochemistry of heavy metal contaminants in soil and stream sediment in Panzhihua mining and smelting area, Southwestern China

Mining and smelting activities are the main causes for the increasing pollution of heavy metals in soil, water body and stream sediment. An environmental geochemical investigation was carried out in and around the Panzhihua mining and smelting area to determine the extent of chemical contamination in soil and sediment. The main objective of this study was to investigate the environmental geochemistry of Ti, V, Cr, Mn, Cu, Pb, Zn and As in soil and sediment and to assess the degree of pollution in the study area. The data of heavy metal concentrations reveal that soils and sediments in the area have been slightly contaminated. Geochemical maps of Igeo of each heavy metal show that the contaminated sites are located in V-Timagnetite sloping and smelting, gangues dam. The pollution sources of the selected elements come mainly from dusts resultant from mining activities and other three-waste-effluents. The area needs to be monitored regularly for trace metal, especially heavy metal enrichment.

Geochemical baseline and trace metal pollution of soil in Panzhihua mining area

A total of 31 topsoil samples were systematically collected from the Panzhihua mining area including steel smelting, coal mining, urban and rural districts. A normalization procedure was adopted to establish the environmental geochemical baseline models for this area. By using the above baseline models, the regional geochemical baseline values of As, Cr, Cu, Ni, Pb and Zn were determined. On the basis of the baselines, the enrichment factors were used to analyze the mechanism of trace metal pollution in topsoil from anthropogenic sources, and the results showed that the serious trace metal pollution is caused by human activities in coal mine, iron mine, smelting factory, tailing dam and other industrial districts in the Panzhihua area.

A Monte Carlo simulation and setup optimization of output efficiency to PGNAA thermal neutron using 252Cf neutrons

We present the design and optimization of a prompt γ-ray neutron activation analysis (PGNAA) thermal neutron output setup based on Monte Carlo simulations using MCNP5 computer code. In these simulations, the moderator materials, reflective materials, and structure of the PGNAA 252Cf neutrons of thermal neutron output setup are optimized. The simulation results reveal that the thin layer paraffin and the thick layer of heavy water moderating effect work best for the 252Cf neutron spectrum. Our new design shows a significantly improved performance of the thermal neutron flux and flux rate, that are increased by 3.02 times and 3.27 times, respectively, compared with the conventional neutron source design.

A Random Pulse Generator for Simulating Nuclear Radiation Signals

According to the statistical properties of the nuclear signal pulse on the amplitude and time, a random pulse generator for simulating nuclear radiation signals is designed in this paper. The noise of the ADC acquisition circuit is used to obtain two-way seeds of random number. The obtained seeds of random number are processed by linear feedback shift register (LFSR) to generate high-speed and uniformly distributed random number continuously, then random numbers of Gaussian distribution are produced based on lookup table method and random numbers of exponential distribution are produced by setting the threshold value. Random numbers of Gaussian distribution are sent to the D/A converter to convert digital signal to analog signal, and random numbers of exponential distribution are sent to control time interval between two pulse signals. Eventually the random pulse that follows the gauss distribution on the amplitude and the exponential distribution on the time interval between two adjacent pulse signals is shaped by pulse shaped circuit. The practical test results show that the random pulse follows the gauss distribution on the amplitude and the exponential distribution on the time interval between two adjacent pulse signals, meeting statistical regularity of nuclear signal.

Geometric matrix research for nuclear waste drum tomographic gamma scanning transmission image reconstruction

A geometric matrix model of nuclear waste drums is proposed for transmission image reconstruction from tomographic gamma scans (TGS). The model assumes that rays are conical, with intensity uniformly distributed within the cone. The attenuation coefficients are centered on the voxel (cube) of the geometric center. The proposed model is verified using the EM algorithm and compared to previously reported models. The calculated results show that the model can obtain good reconstruction results even when the sample models are highly heterogeneous.

Effect of temperature on MRPC with pad read-outs

To obtain a quantitative understanding of the influence of temperature on the performance of multi-gap resistive plate chambers (MRPCs), we have tested the performance of a 10-gap, 12-pad, 2×2×12 cm2 active area MRPC at different temperatures with cosmic rays. Presented are results from measurements of high-voltage scans, noise rate, dark current, streamer, time resolution, count rate, charge spectrum, and detection efficiency. The test results show that the MRPC performance is significantly affected by temperature arising from the temperature-dependence of the glass resistivity.

An Algorithm of Reduction Salt-Pepper Noise in TGS Images

Noise is an important factor in image quality of TGS In according to the Neighborhood Homogeneous Measurement (NHM) was proposed to process the salt-pepper noise of TGS image system which avoided the shortcomings of traditional median filtering algorithm and improved median filtering algorithm. A cross noise measurement window was designed in adaptive median filtering algorithm to adjust the domain of image pixel, which divided image pixel into noise and signal point through the calculation results of NHM. The iteration method was introduced to inhibit noise signal. The results showed that adaptive median filtering algorithm could effectively reduce the salt-pepper noise of TGS image system.