Development of a silicon carbide radiation detection system and experimentation of the system performance.

Silicon carbide (SiC) detectors have excellent radiation detection capabilities for various radiation particles, including high energy resolution, fast response times, and good radiation resistance. A SiC radiation detection system was developed to measure the neutron fluence rate and the γ-ray dose rate in high intensity radiation fields. The system was composed of two SiC detectors, a temperature monitor, two preamplifiers for each SiC detector, a data acquisition unit with two signal channels, three pairs of communication devices, and an application software to analyze and visualize the measurement data. The two SiC detectors were fabricated based on two kinds of 4H-SiC diodes and used to respectively respond to neutrons and γ-rays. Repeated experiments showed that the two SiC detectors of the system can respond to α-particles, neutrons, and γ-rays. To verify the performance of the SiC detection system, including the response linearity of the neutron fluence rate, the measurement range of the γ-ray dose rate, and the radiation resistance of the SiC radiation detectors, the system was tested in multiple neutron and γ-ray fields. The tests results show the system can measure the neutron fluence rate from 5.64 × 10 2 cm-2 s-1 to 1.03 × 10 5 cm-2 s-1 with excellent linearity response, and the γ-ray dose rate from 0.005 Gy/h to 20 Gy/h. Furthermore, the SiC detectors demonstrated good radiation resistance. The neutron and γ-ray radiation field can still be measured stably by the system after exposure to neutron fluence of 1.07 × 10 14 cm-2 and γ-ray dose of 3.52 × 10 4 Gy. This work is the preliminary research to continue the exploration how to measure the n/γ hybrid fields accurately using SiC detectors considering the different energy of neutrons.

Unmanned stationary online monitoring system based on buoy for marine gamma radioactivity.

Research on unmanned online monitoring equipment for marine radioactivity surrounding nuclear power plants is of great significance. In this work, a small radioactivity monitoring system based on buoy was designed and manufactured for the emergency situation of nuclear accidents. The core of the radioactivity monitoring system is the underwater gamma spectrometer. The spectrometer can respond to gamma rays from 60 keV to 3 MeV, and can identify the nuclides whose characteristic rays belong to this energy range. The detection efficiency curve was calculated through Monte Carlo simulation and verified in a standard liquid source. A data acquisition processor was also designed to coordinate the detectors in the system and wirelessly transmit online monitoring data. Three experiments were carried out in the seawater around the Tianwan Nuclear Power Plant in Lianyungang, China using this online marine radioactivity monitoring system based on buoys. The stability and radioactivity monitoring capabilities of the system have been verified.

Design and optimization of an advanced time-of-flight neutron spectrometer for deuterium plasmas of the large helical device.

A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D-D neutrons (DDNs) from helical/stellarator plasmas. The main mission of the new TOFED is to study the supra-thermal deuterons generated from the auxiliary heating systems in helical plasmas by measuring the time-of-flight spectra of DDN. It will also measure the triton burnup neutrons (TBNs) from the d+t reactions, unlike the original TOFED in the EAST tokamak. Its capability of diagnosing the TBN ratios is evaluated in this work. This new TOFED is expected to be installed in the basement under the LHD hall and shares the collimator with one channel of the vertical neutron camera to define its line of sight. The distance from its primary scintillators to the equatorial plane of LHD plasmas is about 15.5 m. Based on Monte Carlo simulation by a GEANT4 model, the resolution of the DDN energy spectra is 6.6%. When projected onto the neutron rates that are typically obtained in LHD deuterium plasmas (an order of 1015 n/s with neutral beam injection), we expect to obtain the DDN and TBN counting rates of about 2.5 · 105 counts/s and 250 counts/s, respectively. This will allow us to analyze the DDN time-of-flight spectra on time scales of 0.1 s and diagnose the TBN emission rates in several seconds with one instrument, for the first time in helical/stellarator plasmas.

[Application of FTIR micro-spectroscopy in the tribology].

The wave number of characteristic absorption peak nu asC-O-C of the polyester formed on the frictional process were determined by Fourier Transform Infrared (FTIR) Micro-spectroscopy, and the wave number displacement of characteristic absorption peak nu asC-O-C was analyzed based on the conversion mass of polyester formed. The internal relations between anti-wear order rule of hydroxyl fatty acids and vibration absorption peak nu asC-O-C of polyester formed by hydroxyl fatty acids was deduced according to these results, and the anti-wear order of hydroxyl fatty acids was reasonably explained, that is 13, 14-di-hydroxydocosanoic acid > 13 (14)-monohydroxydocosanoic acid = 9,10-dihydroxyoctadecanoic acid > 9,10,12-trihydroxyoctadecanoic acid > 9(10)-monohydroxyoctadecanoic acid. A net polyester film is formed by 13, 14-dihydroxydocosanoic acid and a linear polyester film is formed by 9, (10)-monohydroxyoctadecanoic acid and 13(14)-monohydroxydocosanoic acid.

Neutron emission measurement at the HL-2A tokamak device with a liquid scintillation detector.

Neutron emission measurement at the HL-2A tokamak device with a liquid scintillation detector is described. The detector was placed at a location with little structure material in the field of view, and equipped with a gain monitoring system which could provide the possibility to evaluate the gain variation as well as to correct for the detector response. Time trace of the neutron emissivity was obtained and it was consistent with the result of a standard (235)U fission chamber. During the plasma discharge the neutron yield could vary by about four orders of magnitude and the fluctuation of the detector gain was up to about 6%. Pulse height spectrum of the liquid scintillation detector was constructed and corrected with the aid of the gain monitoring system, and the correction was found to be essential for the assessment of the neutron energy spectrum. This successful measurement offered experience and confidence for the application of liquid scintillation detectors in the upcoming neutron camera system.