| Alpha particle, which has short range, weak penetrating power and strongionizing power, is one kind of highly ionized particles. In spite of the maturetechnologies of measuring alpha radiation level in a short distance, the measurers’health may be affected because of the absorption of alpha particles. Therefore, it isnecessary to develop one kind of technology of Long Range Alpha Detection(LRAD).This kind of technology has a broad prospect and it can solve the detectionproblem of internal surfaces of pipes and irregular-shaped radiation sources. By theapplication of LRAD technology, a safe, direct, rapid, real-time and nondestructivemeasurement can be achieved.The method of LRAD is first put forward by researchers in Los Alamos NationalLaboratory (LANL), and then they made big progress in1990s.The LRAD devicewhich was developed in1999has a great application effect. In China, the study ofLRAD starts later. In recent years, study on performance and calibrating of LRADdevice, the measuring and locating method of alpha radiation source, has been done.However, the measuring method of LRAD device is still immature and needs furtherresearch. In the previous research of our group, there are still some problems asfollows:There are many factors which can affect the measuring results of LRAD devices.For example, the internal radius and length of pipes, speed of airflow, temperature,humidity, radiation level of the source and source-detector distance and so on, all ofthese factors have a complicated non-linear relation with the measuring results. Thusit is necessary to study the non-linear relation in order to optimize the LRAD device.In this paper, the influence characteristics of temperature, humidity andmulti-source have been studied. And a mathematical expression of factors andmeasuring results has also been obtained by using Nonlinear Fitting Method andMultiple Regression Method. The research is conducted by support of NationalNatural Science Foundation of China (NSFC) of the program named “The Study andApplication of Nonlinear Calibration Method of Influence Factors of Radiation LevelMeasuring in Irregular-shaped Pipes (41274108)”.1. The influence characteristics of temperature and humidityIn order to definitize the influence of temperature and humidity on measuring results, a vast experimental analysis has been done. The changing pattern oftemperature, humidity and measuring results has been obtained. And the reason ofmeasuring results changing with temperature and humidity has been analyzed basedon theory of recombination of ionized gases and surface adsorption. By combiningexperimental research and mathematical analyze and using Boltzmann Model, it canbe concluded that temperature and humidity have negative correlation with themeasuring results. By randomly choosing20groups of experimental data andapplying multiple regression method, an analytic expression of the three has beenformed as Z=30549.7640-362.6630x-184.1760y. In the analytic expression, themultiple correlation coefficient is0.756and the determination coefficient is0.5720. Itcan be concluded that F=11.3530(F-Inspection)，P=0.001(P-Significance level) andthe analytic expression is effective.2. The influence characteristics of multiple source in irregular-shaped pipes inLRAD measurementAiming at the problem of measuring the radiation level of multiple radiationsources or large area of contamination, an experiment which consists of3differentradiation sources241Am (3772.2Bq),239Pu(224.4Bq) and239Pu(65.8Bq) has beendone. In the experiment, different two-source combinations are chosen to bemeasured, the relevant distance of the two radiation sources varies in0cm,10cm,20cm and40cm. Then the distance between detector and source combinationincreases by the step of20cm. In that way, the influence characteristics of categoriesand activities of radiation sources on measuring results is obtained. By combining theexisting theories, an explorative explanation of the influence characteristics has beenworked out. This explorative experimental research may be beneficial for furtherresearch on measurement of large-scale contamination of pipe internal surface. Aboveall, experiments on influence characteristics of temperature, humidity and multipleradiation sources on LRAD measuring results has been conducted and theircomplicated relations has been concluded. It is worthy of mention that an analyticexpression of temperature, humidity and measuring results has been obtained. What ismore, these conclusions could be applied to optimize the LRAD devices, increasingthe measuring accuracy of the devices. Meanwhile, the research of influencecharacteristic of multiple sources still need more basic data, and this research issignificant for measurement of alpha radiation level of large-scale contamination.Therefore, relevant research of LRAD has a high application value and a broadpromotion prospect. |
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