Real-time monitoring of the Bragg peak location of carbon ions is urgently required for the quality control of hadron therapy. In this study, we design an annular detector to monitor the Bragg peak location of carbon ...Real-time monitoring of the Bragg peak location of carbon ions is urgently required for the quality control of hadron therapy. In this study, we design an annular detector to monitor the Bragg peak location of carbon ions with Geant4 simulation. This 360° surrounding structure has a high detection efficiency for the small-dose situation. The detector consists of a multilayered collimator system and an Na I scintillator for prompt gamma counting. The multilayered collimator includes a lead layer to prevent unwanted gammas and the paraffin and boron carbide layers to moderate and capture fast neutrons. An inclination of the detector further diminishes the background signal caused by neutrons. The detector, with optimized parameters, is applicable to carbon ions of different energies. In addition, the scintillator is replaced by an improved EJ301 organic liquid scintillator to discriminate gammas and neutrons. Inserting thin Fe slices into the liquid scintillator improves the energy deposition efficiency. The Bragg peak location of 200 Me V/u carbon ions can be monitored by prompt gamma detection with the improved liquid scintillator.展开更多
The popular methods to estimate wave height with high-frequency（HF） radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improv...The popular methods to estimate wave height with high-frequency（HF） radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improve the accuracy and increase the valid detection range of the wave height measurement, particularly by the smallaperture radar, it is turned to singular peaks which often exceed the power of other frequency components. The power of three kinds of singular peaks, i.e., those around ±1,±√2 and ±1√2 times the Bragg frequency, are retrieved from a one-month-long radar data set collected by an ocean state monitoring and analyzing radar,model S（OSMAR-S）, and in situ buoy records are used to make some comparisons. The power response to a wave height is found to be described with a new model quite well, by which obvious improvement on the wave height estimation is achieved. With the buoy measurements as reference, a correlation coefficient is increased to 0.90 and a root mean square error（RMSE） is decreased to 0.35 m at the range of 7.5 km compared with the results by the second-order method. The further analysis of the fitting performance across range suggests that the peak has the best fit and maintains a good performance as far as 40 km. The correlation coefficient is 0.78 and the RMSE is 0.62 m at 40 km. These results show the effectiveness of the new empirical method, which opens a new way for the wave height estimation with the HF radar.展开更多
Mapping wind with high-frequency(HF)radar is still a challenge.The existing second-order spectrum based wind speed extraction method has the problems of short detection distances and low angular resolution for broadbe...Mapping wind with high-frequency(HF)radar is still a challenge.The existing second-order spectrum based wind speed extraction method has the problems of short detection distances and low angular resolution for broadbeam HF radar.To solve these problems,we turn to the first-order Bragg spectrum power and propose a space recursion method to map surface wind.One month of radar and buoy data are processed to build a wind spreading function model and a first-order spectrum power model describing the relationship between the maximum of first-order spectrum power and wind speed in different sea states.Based on the theoretical propagation attenuation model,the propagation attenuation is calculated approximately by the wind speed in the previous range cell to compensate for the first-order spectrum in the current range-azimuth cell.By using the compensated first-order spectrum,the final wind speed is extracted in each cell.The first-order spectrum and wind spreading function models are tested using one month of buoy data,which illustrates the applicability of the two models.The final wind vector map demonstrates the potential of the method.展开更多
Currently, large-scale equipment is essential for heating plasma. In this study, based on the theoretical investigation of high-current electron beam applications, a new method for heating plasma is proposed. If this ...Currently, large-scale equipment is essential for heating plasma. In this study, based on the theoretical investigation of high-current electron beam applications, a new method for heating plasma is proposed. If this method is successful, fusion power can be generated much more easily and inexpensively than using conventional methods. This study considered the theoretical possibility of generating ultrahigh-temperature plasma by confining plasma particles between the anode (positive potential) and electric fields using Rutherford scattering of particles forming a heavy-mass-positive-ion layer. In order to form this deuteron-positive ion layer, hydrogen gas is encapsulated in a closed container and applied to a negative with an insulator film on the inner surface. Next, the gas is ionized by irradiating a high-current electron.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11375073 and U1232206)
文摘Real-time monitoring of the Bragg peak location of carbon ions is urgently required for the quality control of hadron therapy. In this study, we design an annular detector to monitor the Bragg peak location of carbon ions with Geant4 simulation. This 360° surrounding structure has a high detection efficiency for the small-dose situation. The detector consists of a multilayered collimator system and an Na I scintillator for prompt gamma counting. The multilayered collimator includes a lead layer to prevent unwanted gammas and the paraffin and boron carbide layers to moderate and capture fast neutrons. An inclination of the detector further diminishes the background signal caused by neutrons. The detector, with optimized parameters, is applicable to carbon ions of different energies. In addition, the scintillator is replaced by an improved EJ301 organic liquid scintillator to discriminate gammas and neutrons. Inserting thin Fe slices into the liquid scintillator improves the energy deposition efficiency. The Bragg peak location of 200 Me V/u carbon ions can be monitored by prompt gamma detection with the improved liquid scintillator.
基金The National Natural Science Foundation of China under contract No.61371198the National Special Program for Key Scientific Instrument and Equipment Development of China under contract No.2013YQ160793
文摘The popular methods to estimate wave height with high-frequency（HF） radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improve the accuracy and increase the valid detection range of the wave height measurement, particularly by the smallaperture radar, it is turned to singular peaks which often exceed the power of other frequency components. The power of three kinds of singular peaks, i.e., those around ±1,±√2 and ±1√2 times the Bragg frequency, are retrieved from a one-month-long radar data set collected by an ocean state monitoring and analyzing radar,model S（OSMAR-S）, and in situ buoy records are used to make some comparisons. The power response to a wave height is found to be described with a new model quite well, by which obvious improvement on the wave height estimation is achieved. With the buoy measurements as reference, a correlation coefficient is increased to 0.90 and a root mean square error（RMSE） is decreased to 0.35 m at the range of 7.5 km compared with the results by the second-order method. The further analysis of the fitting performance across range suggests that the peak has the best fit and maintains a good performance as far as 40 km. The correlation coefficient is 0.78 and the RMSE is 0.62 m at 40 km. These results show the effectiveness of the new empirical method, which opens a new way for the wave height estimation with the HF radar.
基金The National Natural Science Foundation of China under contract Nos 61371198 and 62001426.
文摘Mapping wind with high-frequency(HF)radar is still a challenge.The existing second-order spectrum based wind speed extraction method has the problems of short detection distances and low angular resolution for broadbeam HF radar.To solve these problems,we turn to the first-order Bragg spectrum power and propose a space recursion method to map surface wind.One month of radar and buoy data are processed to build a wind spreading function model and a first-order spectrum power model describing the relationship between the maximum of first-order spectrum power and wind speed in different sea states.Based on the theoretical propagation attenuation model,the propagation attenuation is calculated approximately by the wind speed in the previous range cell to compensate for the first-order spectrum in the current range-azimuth cell.By using the compensated first-order spectrum,the final wind speed is extracted in each cell.The first-order spectrum and wind spreading function models are tested using one month of buoy data,which illustrates the applicability of the two models.The final wind vector map demonstrates the potential of the method.
文摘Currently, large-scale equipment is essential for heating plasma. In this study, based on the theoretical investigation of high-current electron beam applications, a new method for heating plasma is proposed. If this method is successful, fusion power can be generated much more easily and inexpensively than using conventional methods. This study considered the theoretical possibility of generating ultrahigh-temperature plasma by confining plasma particles between the anode (positive potential) and electric fields using Rutherford scattering of particles forming a heavy-mass-positive-ion layer. In order to form this deuteron-positive ion layer, hydrogen gas is encapsulated in a closed container and applied to a negative with an insulator film on the inner surface. Next, the gas is ionized by irradiating a high-current electron.
