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[en] This article mainly introduced the development and structure of canned motor pump and shaft seal pump at PWR. Especialy, the performance of canned motor pump for AP1000 and shaft seal pump was analyed and compared, their advantages and shortcomings were pointed out, which provided reference for the relevant nuclear power technical staff. (authors)
[en] Objective: Gastric emptying scintigraphy was performed with radionuclide-labeled liquid test meal to determine the best position and evaluation index for the clinical examination of gastric emptying. Subsequently, the incidence of gastroparesis in diabetic patients was evaluated, and the basis for its diagnosis and severity index was obtained. Methods: A total of 155 participants were divided into the control (n = 55) and experimental groups (n = 100). The volunteers were made to drink 99Tcm-DTPA radioactive nuclide liquid test meal and to lie down on an exam table. SPECT was utilized to dynamically and instantaneously image anterior and posterior gastric emptying in the lying position. After image acquisition, the stomach area was highlighted as the ROI. Through computer processing, the time-radioactive change curve was obtained, and then lying anterior and posterior gastric-half emptying time (GET1/2) and gastric emptying rate in 30 minutes (GER30min) were calculated. Three days later, the patients received the same amount of radionuclides in liquid test meal for the dynamic imaging of posterior gastric emptying in the sitting position. Data acquisition and processing were conducted using the previously described protocol for gastric emptying in the lying position. Imaging data from the normal control and experimental groups were compared by using t-test. Results: In the control group, the lying anterior GET1/2 was(12.76 ± 2.22) min with an upper limit of 95% confidence interval of 17.1 min. This parameter could be used as a criterion for the evaluation of gastric emptying function. The GET1/2 and GER30min of the lying anterior and posterior of the normal control group were significantly different (t = 5.35, 11.20, -6.37, -9.77, all P < 0.05). The lying anterior GER30min of experimental groups 1 (without digestive system symptom diabetes) and 2 (with digestive system symptom diabetes) were significantly different (t = 6.22, 3.01, both P < 0.05). The lying anterior GER30min of the experimental group was lower than that of the control group, and was lower in experimental group 2 than in experimental group 1. Based on the GET1/2 of the experimental group, 41% of the patients exhibited dysfunctional gastric emptying, whereas 9% of the patients suffered from severely impaired gastric emptying. Conclusion: Radionuclide-labeled liquid test meal gastric emptying imaging is a simple, accurate and reliable detection method. GET1/2 and GER30min can be used as gastric emptying function impairment degree index, and the lying anterior position was selected as a better method of radionuclide-labeled liquid test meal gastric emptying imaging which can be used in clinical extension. (authors)
[en] Objective: To verify the accuracy of the calculation of MCNP ray air kerma rate and ambient dose equivalent rate. Methods: The theoretical calculation of air kerma rates was compared with simulated values, and the actual measurement of ambient dose equivalent rate values and simulation values are compared. Results: Kerma rate theoretical values and simulation values are in good agreement. The maximum error of the measured value of ambient dose equivalent rate of the analog value of is less than 7.9% and inversely proportional to the square of the distance between the two present trends, error becomes smaller with increasing distance between the two points. Conclusion: MCNP program can accurately simulate the air kerma rate and ambient dose equivalent rate, The program can be applied to the development of radiation protection programs and computer room and other work. (authors)
[en] In the process of α-source spectrum measurement, influence factors of the detector efficiency of the PIPS-α spectrometer are the geometric factor, air layer absorption, dead layer absorption, the intrinsic detection efficiency, and so on. In order to calculate the activity of sources more accurately, to analyse the type and concentration of the parent nuclide, it is of great significance to explore the influence of these factors on the detection efficiency. Monte Carlo software was used to simulate the energy spectrum measurement of different source-detector distance and vacuum degree, SRIM was used to simulate the range and distribution of alpha particles in the air and dead layer with 5 MeV alpha particles, and PIPS-α spectrometer was used to measure the actual spectra of three standard radioactive sources 241Am, 238Pu, 239Pu. According to the results of experiments and simulation, the influence of various factors on the detection efficiency was analyzed, the intrinsic detection efficiency of spectrum of different α-sources was calculated. The results show that: in the PIPS-α spectrometer measurement process, the main factors affecting the detection efficiency of the spectrometer is geometric factor and intrinsic detection efficiency; the absorption of alpha particles by air and dead layer is negligible; the intrinsic detection efficiencies of the spectrometer for 241Am, 238Pu, 239Pu standard sources are 64.84%, 49.95%, 51.55% respectively. (authors)
[en] Highlights: • Rod-shaped BaCoxTixFe12-2xO19 is prepared by precipitation-topactic reaction method. • The synthesis process of rod-shaped BaCoxTixFe12-2xO19 is investigated. • The dependent morphology and phase component on the content of doping ions are analyzed. • The shape anisotropy and doping ions play important roles in the magnetic performances. - Abstract: Rod-shaped BaCoxTixFe12−2xO19 was prepared by precipitation-topactic reaction method with using needle-like α-FeOOH as a template, and its formation process, morphology, phase components and magnetic performances were investigated by XRD, FT-IR, SEM, EDS and VSM. The experimental results show that the prepared rod-shaped BaCoxTixFe12−2xO19 contains a small amount of middle phase α-Fe2O3, and with the content of (Co2+, Ti4+)-doping ions raising the contained middle phase increases. The dependence of the length-diameter ratio on the content of (Co2+, Ti4+)-doping ions is associated with the contained middle phase. With the content of (Co2+, Ti4+)-doping ions increasing, the prepared rod-shaped BaCoxTixFe12−2xO19 presents a slow reduction of coercivity, and the development of its saturation magnetization displays a drop followed by a slight increase. The shape anisotropy and occupancy of doping ions may play important role in the magnetic performance of prepared rod-shaped BaCoxTixFe12−2xO19.
[en] In the disposal of nuclear waste, regulation and classification of transuranium elements, alpha radioactivity monitoring work in special places such as nuclear arsenal, we usually use the alpha energy spectrum measuring technique. Alpha energy spectrum measurement is one of the key measurements of nuclear radiation, which occupies an important position in the field of nuclear radiation monitoring. In order to accurately analyze the impact of different source-detector distance, vacuum degree, placement angle and other factors on alpha energy spectrum measurement, we used Monte Carlo method to simulate α energy spectrum measurement, thus reduced experiment time and improved the accuracy. The Monte Carlo method was used to establish chamber model for the PIPS-alpha spectrometer, which, by changing the distance between a radiation source and detector, simulates the alpha energy spectrum. The simulation results are corrected according to the experimental results to improve the degree of agreement between experiment and simulation. Experiments show that the Monte Carlo model is accurate and can be used for simulating the impact of different source-detector-distance, vacuum degree, placement angle and other factors on alpha energy spectrum measurement. This method not can only be applied to other alpha energy spectrum measurement, but also be used in single energy spectrum research of alpha particles. The study is to provide a basis for the alpha spectrum measurement technology and data support for alpha spectrum technology. (authors)
[en] In nuclear waste drum inspection by Segmented Gramma Scanning(SGS), the detector counts are different with the point sources at different positions during the rotation process, and the attenuation distance needs to be calibrated. We used the Matlab's data fitting method and numerical calculation method to get the corrected attenuation distance. The Monte-Carlo code was used to simulate the radionuclide in a waste barrel uniformly filled with polyethylene material with density of 1.0 g/cm3. Then the count distributions of 137Cs point sources at seven different locations in the barrel were obtained. The detector counts were simulated every 30 degrees on seven different rotational circles, and the corrected average attenuation distance was given by calculating the partial area with high contribution rate. The relative error of the activity estimation obtained by this method is between 0.6% and 25.2%. Compared to traditional methods (the relative error of the activity estimation is between 11.8% and 209.9%), the error is decreased obviously. (authors)
[en] Highlights: • A facile approach is proposed to synthesize ultra-small Fe2N nanocrystals/MNGCS. • The Fe2N content and BET surface area of Fe2N/MNGCS can be adjusted by altering the acid etching time. • The optimized Fe2N/MNGCS catalyst demonstrates better ORR performance than 10 wt% Pt/C catalyst. • Such excellent performance is ascribed to the rational balance of the density of Fe–N/C active sites, and the transport of electron and electrolyte ion. A low-cost, highly active, stable, and methanol tolerant electrocatalyst towards the oxygen reduction reaction (ORR) is extremely desirable for promoting the commercialization of fuel cells. Herein, we reported a facile two-step pyrolysis and acid leaching process to synthesize a high performance ORR electrocatalyst, where ultra-small Fe2N nanocrystals were incorporated into mesoporous nitrogen-doped graphitic carbon spheres (MNGCS). The Fe2N/MNGCS electrocatalysts with difference Fe2N contents and BET surface areas were obtained via altering the acid leaching time, and all exhibited the apparent electrocatalytic activity. The optimized ORR activity was achieved over (Fe2N/MNGCS)4 with the positive half-wave potentials (0.881 V vs RHE), high selectivity (4 e− process), excellent long-term stability (95.2% of the initial current remaining after 60,000 s of continuous operation) and good tolerance against methanol-crossover effect (94.9% of the current retained prior to 4.0 M methanol injection) in alkaline media, which even was more superior to that of commercial Pt/C catalyst. The remarkable ORR activity was originated from the cooperative effect of ultra-small Fe2N nanocrystals and MNGCS, where the balance of catalytic active site density, mesoporous structure, BET specific surface area, and electron conductivity played a key role in determining the ORR performance.
[en] Large amounts of low and intermediate level radioactive waste (LILW) will be produced and piled up with the nuclear power industry development and the increasing widespread application of radioisotopes. The types of nuclides and the activity of the radioactive waste should be measured before the radioactive waste is disposed. Segmented gamma scanning (SGS) measure is an important technique of quantitative analysis for nuclear scrap and radioactive waste. However, when point source location changes, both the relative attenuation distance and scale efficiency are not corresponding, which causes errors of counts of detectors on activity estimation. This study is based on 12 different positions counts method and through Monte Carlo simulation methods, records waste barrels with uniform filling of polyethylene samples. It will find the max & min counts records with Beer-Lambert attenuation law to value the turning radius, so that it can determine the location of radioactive nuclides in the current segment. Thus, the problem of the attenuation distance, scale efficiency non-correspondence of the radionuclide in different location which lead to SGS estimate error of point source activity is solved. (authors)
[en] An algorithm based on moment estimation is presented to determine the initial parameters of the particle spectrum peak shape function for the iteration fitting procedure. The algorithm calculates the mean value, variance, and third-order central moment by using the spectrum peak data, solves the parameters of the fitting function, and then provides them as the initial values to the Levenberg–Marquardt algorithm to ensure convergence and optimized fitting. The effectiveness of the proposed algorithm was tested by gamma and alpha spectra. The algorithm can be used in automated peak curve fitting and spectral analysis. - Highlights: • The proposed algorithm was based on moment estimation. • Initial parameters of the particle spectrum peak shape function were estimated. • The Levenberg–Marquardt algorithm was used to fit the spectrum peak. • The proposed algorithm was applied to analyze gamma and alpha spectra.