The Research Of Estimating Neutron Dose By The Activation Of Sodium In Human Blood

Assessing neutron dose by utilizing activated Na within human blood is Biophysics method. It can rapidly and accurately calculate the victim's neutron absorbed dose. Therefore,it can provide basis for clinical treatment, and also can provide reference for the future risk assessment of health consequences. Compared with the traditional measuring method of neutron dose, it has higher technical advantages and economic advantages, and has become an important technology of evaluating neutron dose after nuclear accidents.Foreign countries have carried out the research in the 1950s, In 1952, L.H.Hempelmann and his partner calculated the victim's neutron absorbed dose firstly with the method of neutron activation effect. In 1960s and 1970s, many scientific research institutions including the Los Alamos laboratory, the Oak ridge lab in America, the Atomic Energy lab of Britain and the International Atomic Energy lab had carried out much research respectively on this issue. In the late 20th century, China had taken action to utilize the technology of Na activation in human blood to evaluate the neutron dose. Due to the lack of basic and systematic research, the basic data is very scarce. It's unable to get the relation between ²⁴Na's activity and the absorbed dose of neutron because there's no research of impact characteristics of estimating neutron dose system such as the sample shape information, position information, detect distance ,detect time, and the neutron source's exposure time, irradiation distance and so on.The paper at the aim of bottleneck problem of estimating neutron dose by utilizing the principle of Na activation in human blood that mentioned above; on the basis of surveying the current situation both home and broad, supported by the Sichuan's science and technology project "The research and manufacture of neutron irradiating human blood detector (No.: 07GG010-010)" and the Ministry of Science Innovative Method "RBF-based algorithm for low bacKground radiation monitoring technology and equipment research (No.: 2008IM040500)" ,we launched out a systematic research on effect parameters of estimating neutron dose. Basing on the self-research of low background gamma detection system, we gained some precious experiment data as the comprehensive and basic work done .In order to get impact characteristics to the results that affected by the irradiation time, irradiation distance,detection time and other key points, the method of detecting different NaCl solution with ²⁵²Cf neutron resource radiation was taken. Thus, the best measuring condition under different measurement environment could be determined and the activity-to-dose conversion coefficients were calculated on the basis of Monte Carlo simulation. All of these have great reference value in evaluating the accuracy of the technology of estimating neutron dose.The main research contents and results in this paper are as follows:(1) The theory and method research of estimating human body's neutron absorbed dose by utilizing the method of measuring ²⁴Na's activity in blood.On the basis of analyzing the research achievements home and abroad, a series of experiment was carried out. Thus, we got a systematic method of estimating human body's neutron absorbed dose with the method of measuring blood ²⁴Na's activity.(2) The Optimal design for experimental facility by applying Monte Carlo method.Through Monte Carlo simulation of the low background gamma measurement system, the same samples, the closer detection, the higher detection efficiency; The samples of the same volume, the detection efficiency increases first, then reduces with the height increasing. It is not the undersurface radius greater ,the detection efficiency is higher. When the undersurface radius is greater than the detector's radius, the detection efficiency declines. So when measuring ²⁴Na's activity, the 10ml sample should be placed in plastic culture dish of 5cm diameter and placed on the detector directly; At the same time, simulating the influence of neutron absorbed dose caused by different irradiation distance, the volume and the shape of the sample, so provide preliminary theoretical basis for the experiment.(3) Calculated a series of activity-to-dose conversion coefficient by experiment combined with Monte Carlo simulation.Irradiating the sample by ²⁵²Cf neutron source, we get the relation between ²⁴Na activity and absorbed dose by changing the irradiation time, the irradiation distance and detection time and so on. Under Irradiating by bare ²⁵²Cf source,the Samples' activity-to-dose conversion coefficients have index degressive tendency with irradiation distance increasing ; Under Irradiating by D2O-moderated ²⁵²Cf source, the samples' activity-to-dose conversion coefficients change a little with distance increasing,the mean is 1.956728E-02(Gy·ml/Bq), and the activity-to-dose conversion coefficient of the samples irradiated by bare ²⁵²Cf source are higher than irradiated by D2O-moderated ²⁵²Cf source. The samples' activity-to-dose conversion coefficients don't change with irradiation time increasing.When the source is bare ²⁵²Cf and the irradiation distance is 10cm, the mean of The samples' activity-to-dose conversion coefficients is 2.09576E-02(Gy·ml/Bq);When the source is D2O-moderated ²⁵²Cf and the irradiation distance is 20cm, the mean of The samples' activity-to-dose conversion coefficients is 1.616497E-02(Gy·ml/Bq).And all of these have great reference value in evaluating the accuracy of the technology of estimating neutron dose.The innovations of this paper are mainly the following three aspects:(1) Utilizing the Monte Carlo method to optimize the facility of the experiment.(2) A series of systematic and basic experiment was carried out by utilizing the technology of Na activation in human blood to evaluate the neutron dose, simultaneously, we also got the impact characteristics with multiple factors affected. Thus, the measurement condition could be optimized naturally.(3) We evaluated body neutron dose by the Biophysics method, when got theγnet count, we calculated the radioactivity, then rectify the activity. Combining experiment with Monte Carlo simulation, deduced relationship between ²⁴Na activity and absorbed dose, then we formed a integrate system of evaluating body radiation dose from neutron by measuring the ²⁴Na's activity in the human blood.In conclusion, this paper started from evaluating human body absorbed dose by measuring the ²⁴Na's activity in human blood, utilized the Monte Carlo simulation to get the most optimal parameters from the low backgroundγmeasurement equipment. In order to get impact characteristics to the results that affected by the irradiation time, irradiation distance,detection time and other key points, the method of detecting different NaCl solution with ²⁵²Cf neutron resource radiation was taken. Thus, the best measuring condition under different measurement environment could be determined and the activity-to-dose conversion factors were calculated on the basis of Monte Carlo simulation. All of these have great reference value in evaluating the accuracy of the technology of estimating neutron dose.