The effects of Fe concentrations in the pretreatment solution on the induction of plaque and the differences between genotypes on arsenate uptake by and translocation within rice seedlings grown in nutrient solution in the greenhouse were investigated. After iron plaque on rice roots was induced in solutions containing 20, 40, 60, 80, and 100 mg Fe2+ l(-1), seedlings were transplanted into nutrient solution with 0.5 mg As l(-1). The formation of iron plaque was clearly visible as a reddish coating on the root surface after 12 h induction. Fe2+ concentrations in the pretreatment solution and 0.5 mg As l(-1) in the treatment solutions did not significantly affect rice growth. There was a significant correlation between the concentrations of Fe and As in iron plaque on the root surface for the three genotypes. About 75-89% of total As was concentrated in iron plaque (DCB-extracts). There were no significant differences in As concentrations in the roots between the three genotypes; however, As concentrations in shoots differed significantly between them. Arsenic concentrations in shoots were positively correlated with iron concentrations in the shoots. The results suggest that iron plaque may act as a 'buffer' for As in the rhizosphere.
For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0 × 10 6 n/cm 2 /s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.
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