Key Technology Research Of Alpha Particle Inner Pollution Measuring Device

With the rapid development of industry, the demand for energy is growing, theexploration and development of energy moved from ordinary energy, such as coal,petroleum and gas to wind power, solar and nuclear energy. Nuclear energy quicklyoccupied the most proportion of new energy with its advantage of efficience andnon-polluting. While enjoyed the great benefits of nuclear energy, people took the riskof nuclear contamination and nuclear radiation. In2011, the nuclear radiation incidentof Japan’s Fukushima was happened, it striked the alarm to the world once again.People began to pay a hightly attention to nuclear contamination preventing, nuclearradiation monitoring and first aids about nuclear accident and so on.Since rays produced by the decay of radionuclides can not be detected byconventional methods, people need professional measuring instruments to keep abreastof nuclear contamination in personnel or the environment. The topic, which this paperwas subordinated, was funded by the project of "a rapid detection for a large quantitiesof nuclear radiation crowd with in vivo contamination ". It aimed to develop a portableand intelligent inner pollution alpha particle detection system, which combined existingtechnology with advanced scientific equipment. The project focused on the mechanicalstructure of the alpha particle pollution measuring device. It started with creatingdetection platform and improving the tightness of the vacuum container. The emphasisof the study was the structure design and size optimization of the vacuum vessel. And itmade the measuring devices to become convenient, functional and practical, beautifuland compact, with a wide scope of application.The paper investigated the function and scope of different types of nuclearradiation detectors and select the silicon surface barrier detector as the core of detectiondevice. Considering silicon surface barrier detector structural features, it improveddetector on the basis of the support program and designed suspended detect platform, sothat avoided secondary pollution outside of the detector surface and improved detectionefficiency. In addition, it designed a rotation device to control the radioactive sample,which made the cotton swab maintain axial rotation, so that not only improved theuniformity and activity accuracy of radioactive, but also shortened the sampling time and improve work efficiency.Experiments showed that there was a serious leak problem within a squaremeasuring pollution α particle measurement chamber device, because the anglebetween two sealing surfaces can not be eliminated as well as the machining accuracyof closed surfaces did not meet the sealing requirements. From these two reasons, itpresented the design of a cylindrical measuring chamber with separate closed surface.Firstly, separating features of the cavity was facilitate to machine the componentsseparately, because the surfaces formed sealing was continuous with no step andtransition surface. With Model CA6140lathe processing, the container closuresurface’s roughness was1.6. And with the way of line cutting processing, the roughnessof closure surfaces in square measurement chamber was3.2. In contrast, parts’ surfacesfrom lathe were smoother. The biggest advantage of separate closed surface was theangle caused by poorly design can be reduced and the closed surfaces tended to snappparallelly in symmetrical external force. Secondly, the design of dovetail slot onannular sealing surface could prevent the gasket from dislocation and loss whensuffered extrusion and deformation.Having a tightness test for a period of eight days in order to verify the vacuumcontainer improved--the measurement chamber that did not detect--could solve theinstability and leakage problems of the vacuum degree. Experimental results showedthat the cylindrical vacuum vessel’s maximum degree of vacuum was-78kpa (relativedegree of vacuum), and the maximum vacuum lasted1440min, which more than theworking time of the measuring. Therefore, the design of the vacuum vessel had good airtightness, and was able to provide a clean and low-loss environment for the detection.Upon solving the problem of leakage, it made a further optimization andimprovement of the quality and structure for the vacuum vessel on the basis of theprogram. ANSYS software’s core principle was finite element method, it used thecomputer as a tool to simulate the actual physical problem and solve the problem. Atfirst, it took advantage of the ANSYS software with its function of finite elementanalysis and operated on the graphical user interface (GUI). At second, completedoptimiztion for vacuum vessel according to the process of "build a mathematical model-define the finite element model-set and analyzed for optimization variables". At last,got the most appropriate set of thickness size: cylinder wall thickness was2.5mm, thefront cover thickness was5mm, post head thickness was5mm, preflange thickness was4mm, post flange thickness was4mm.Finally, it analysed the stress of the vacuum vessel structure. ANSYS software was able to not only complete the structural static analysis of the model but also displaystress cloud and make a classification of stress. Checked the stress cloud after modelstress analysis, selected high stress regions to define rating paths, output stress of eachnode on the path and extracted corresponding effective stress in accordance with thestress category. Based on pressure vessel design rules, completed strength assessmentin all high stress areas. The results proved the the vacuum vessel met the strengthconditions.According to the experimental results of stress analysis and vacuum sealing vesselmodel, it can be determined that the Alpha particle inner pollution measuring deviceowned advantages such as lighter, smaller size, easy operation and stability tightness.The research results had met design specifications and were worthy to furtherpromoting and applicating.