Research On Detecting Device Of Heavy Metal Elements In Rice By EDXRF Analysis

Supported by National High Technology Research and Development Program of China: high precision spectrum detection instrument development.(No.2012AA061803).With the increasingly serious environmental pollution, agricultural ecosystem is polluted by the industrial emissions heavy metals, and many crops have been polluted to varying degrees. Rice has a strong adsorption capacity about Cd, As, Pb and other heavy metals in the growth process, so it could be very to be contaminated. Rice is the main food source for nearly half of population of the world. In order to avoid the rice which polluted by the heavy metals gets into the market and folks' dining-table, the heavy metals detection in rice has become very urgent, especially for the Cd. The traditional detecting technology for the heavy metals in food almost has many shortcomings such as long term, complicated operation, cannot meet the requirement of rapid detection on the spot and so on. In recent years, energy dispersive X-ray fluorescence technology is used for the rapid detection of heavy metals in food because of its rapid, non-destructive testing, simple sample preparation and other advantages. At present, energy dispersive X-ray fluorescence analysis is mostly used in alloys and mineral elements while less used in the trace heavy metals detection which in rice and other light matrix. In this paper, using the Monte Carlo method to simulate the establishment of optimal detection means of trace metals elemental which for the EDXRF analysis of the heavy metals in rice.First, determining the conditions of the various parameters by theoretical analysis on the detection device, and then simulating the conditions of detection device in each department. The main achievements and innovative of this paper are as follows:(1)Through the different angle combinations between “source–sample” angle ? and“sample–detector” angle ?, and according to CdK? normalized count and peak tobackground ratio to determine the best “source – sample” angle ? is 25°, the best“sample – detector” angle ? is 25° too;(2)At the best “source–sample–detector” distance conditions, simulate the different distance combinations about “source–sample” distance and “sample–detector”distance. According to CdK? normalized count and peak to background ratio to determine the best “source – sample” distance is 0.25 cm, the best “sample – detector”distance is 0.55cm;(3)Simulating the three kinds of external shape of the sample(planar,wedge-shaped, and flake) by MCNP5, the results show that the best shape is the wedge shaped, and its best angle is 80°;(4)Through the Monte Carlo simulation of primary filter, obtained that the optimal thickness of filter Al, Fe, Cu, is 330?m, 18?m, 12?m, and the best element for primary filter is Cu;(5)The secondary filter is a pair of balanced filter which composed by Ru and Rh.According to the theoretical formula to calculate the thickness of Ru and Rh, the result show that the Rh thickness is 25.21?m and the Ru thickness is 26.47?m. The simulation result shows that using balance filter can improve the peak to background ratio;(6)According to the simulation results, when the X-ray tube voltage up to the 60 kV,the detection of Cd in the rice has a best measurement results;(7)Use the La as the second target materials, designe two kinds of second target device which are transmission type and reflection type. Transmission type secondary target device use the optimum geometric structure of the first target device. The reflection type secondary target device uses the normal polarization three dimensional optical paths. The simulation results show that transmission type secondary target optimum thickness is 30?m, at the same time, and the effect of transmission type secondary target is far better for reflective.By the theory research and Monte Carlo simulation determine the best conditions for X-ray fluorescence analyzer detecting device, and proposed a transmission type secondary target device and it has showed a better result. The results provide guidance for the practical application and detecting device design which used in detecting heavy metals in rice by EDXRF method.