ABSTRACT
A neutron detector, based on scintillator and Cherenkov detector, was designed to monitor the D-T neutron generator in a PGNAA online measurement system in our previous study. In this paper, the foil activation method was used to study the intrinsic detection efficiency of the detector to the D-T neutron generator. The Fe foil with 99.99% purity was selected as the activation foil. The experiments and the GEANT4 simulations were carried out to study the intrinsic detection efficiency of the monitor. The results show that the intrinsic detection efficiency of the monitor is 20.42% ± 0.76%. Then, the calibrated detector and Fe foils were simultaneously used to measure the neutron flux of D-T neutron generator. The relative deviation between the results of the two methods is 5.64%.
ABSTRACT
A new method is proposed to detect fast neutron flux: the neutron-induced X-ray fluorescence method. In this method, the neutrons are firstly converted to charged particles, and then the charged particles interact with the target to generate the characteristic X-ray fluorescence. Finally, the Kα X-ray emission from the target is detected for measurement of the neutron flux. On the basis of this method, the structure of the detection device is designed: it is composed mainly of a layer of a fast neutron converter and a layer of the target. The Geant4 Monte Carlo simulation toolkit is used to optimize the detection device. According to the simulation results, the detection device is manufactured so as to perform the feasibility verification experiments. In the experiments, a D-T neutron generator is used as the neutron source, and the number of neutrons is changed in two ways: by change of the working voltage of the neutron generator or by change of the measurement time. The experimental results show that there is a good linear relationship between the number of neutrons and the Kα X-ray counts when the measurement time is changed. When the working voltage of the neutron generator is changed, a 3He proportional counter is used as a reference detector. The results show that the trend of the Kα X-ray counts is in good agreement with the trend for the 3He proportional counter. It is proved that this method is feasible for fast neutron flux measurement.
ABSTRACT
Heavy metals in haze episode will continue to threaten the quality of public health around the world. In order to decrease the emission of heavy metals produced from coal burning, an online X-ray fluorescence (XRF) analyzer system, consisting of an XRF analyzer with data acquisition software and a laser rangefinder, was developed to carry out the measurement of heavy metals in pulverized coal. The XRF analyzer was mounted on a sled, which can effectively smooth the surface of pulverized coal and reduce the impact of surface roughness during online measurement. The laser rangefinder was mounted over the sled for measuring the distance between a pulverized coal sample and the analyzer. Several heavy metals and other elements in pulverized coal were online measured by the XRF analyzer directly above a conveyor belt. The limits of detection for Hg, Pb, Cr, Ti, Fe, and Ca by the analyzer were 44 ± 2, 34 ± 2, 17 ± 3, 41 ± 4, 19 ± 3, and 65 ± 2 mg·kg(-1), respectively. The relative standard deviation (%RSD) for the elements mentioned was less than 7.74%. By comparison with the results by inductively-coupled plasma mass spectrometry (ICP-MS), relative deviation (%D) of the online XRF analyzer was less than 10% for Cr, Ti, and Ca, in the range of 0.8-24.26% for Fe, and greater than 20% for Hg and Pb.
ABSTRACT
A new prompt-gamma neutron activation analysis (PGNAA) setup has been designed for element determination in aqueous solution with a 300 mCi 241Am-Be neutron source and a 4in.×3in. (diameter×height) BGO detector, uncooled. A polyethylene cylindrical sample container approximately 40cm in outer radius and 80cm in height was used. To reduce the neutron dose in the detector, a block of 5cm thickness Li2CO3 was placed between the source and the detector for separation, but no gamma-blocker was used. By adjusting the position of the detector and optimizing the geometrical conditions of the setup, the element detection limit with a low activity neutron source was further improved. This methodology was checked by simulations with chlorine, mercury and cadmium determination and by experiments with chlorine determination in aqueous samples. The results show a good linear relationship between chlorine concentration and the count of its characteristic peak, and the detection limit of chlorine can reach 41.7mg/L with a collection time of 3600s for each spectrum. Additionally, a linear relationship was identified between mercury concentration and the count of its characteristic peak, but for cadmium, a non-linear relationship was observed in the simulations.
