Emergency Dose Assessment Method Based On Alumina Devices

Nuclear wars,serious nuclear and radiation accidents,nuclear and radiological terrorist events are characterized by suddenness,uncertainty,and the source items are complex.In such mass-casualty disasters,a large numbers of public,emergency responders and some combatants could be exposed to significant doses of penetrating radiation,who may not be equipped with individual radiation dose monitors or dosimeters.The scientific assessment of the dose received by individuals is essential for effective response.In addition,the distribution and characteristics of the initial radiation field change rapidly over time.At the same time,most of the accumulated dose for individuals were obtained in the initial period of the events.During the whole event,with the uncertainty of personnel behaviors and range of activities,these factors bring more challenges to the assessment of emergency dose.Focusing on the practical needs and difficulties of scientifically evaluating the emergency dose of individuals without dose measurement equipments in the above scenarios,and based on the research progress of emergency dose assessment techniques,this work made a comprehensive screening of various materials and devices with luminescence characteristics,found that alumina devices widely used in various electronic devices shown excellent application potential.When the above scenarios occur,the alumina devices in various electronic equipments carried by the irradiated personnel are collected on the spot,and the absorbed dose of the devices obtained by measuring its luminescence signal,then the emergency dose of the personnel could obtained by appropriate conversion of the cumulated dose of the device.According to the relationships between the luminescent response of alumina devices,cumulated dose of devices and personal emergency dose,there are five relevant aspects of research carried out in this work.The main research contents and conclusions are summarized as follows:?1?The research of luminescence mechanism and characteristics of alumina devices.The kinetics order of the alumina substrates were investigated by three different methods:peak shift method,peak shape and isothermal decay method,and compared with alumina crystals for differences.The activation energy and frequency factor of the surface mount resistance were calculated by variable heating rate method,initial rising and peak shape methods respectively.The experimental data of the relevant luminescence characteristics of such devices were obtained,and the possible luminescence mechanism was discussed.So it was confirmed that the possibility of its application in emergency dose measurement.?2?The study on the dosimetry properties of alumina devices.The carbon-doped alumina crystals were prepared by VGF method,which significantly improved the dosimetry properties of TL and OSL.The mean TL sensitivity per unit mass of the VGF?-Al₂O₃:C is 152 times higher than that of the TLD-100.The TL detection threshold of VGF?-Al₂O₃:C is 0.12?Gy.And the mean OSL sensitivity per unit mass of the VGF?-Al₂O₃:C is 1.6 times higher than that of the TLD-500K.The OSL detection threshold of VGF?-Al₂O₃:C is 0.21?Gy.It was then used as reference to establish a comparative study on the relevant properties of various alumina devices.A series of systematic experiments were conducted to study the characteristics of dose response,photon energy dependence,minimum detection limit,measurement repeatability,sensitivity and consistency of the alumina device.Detailed measurement data were obtained,analyzed and compared with the corresponding characteristics of carbon-doped alumina crystals.The experimental results indicated that the performance of alumina devices met the requirements for emergency dosimetry,it was a feasible technical approach.?3?The emergency dose assessment method based on alumina devices.According to the basic principle of emergency dose assessment based on luminescence materials and standard curve method,the complete measurement procedures of TL and OSL were proposed.Tthe determination,influencing factors and main parameters of each step were presented and discussed.The multi-component single-aliquot regenerative dose assessment method for alumina devices was designed to effectively solve the standardized measurement problems in emergency dose assessment applications.The method also could been extended to the dose assessment of other luminescence materials.?4?The influence factors and correction methods.The influencing factors of different states,working temperature,illumination time and sampling temperature were studied in detail through series of simulation experiments.The results show that the different states had limited influence on the surface mount resistance of TL and OSL luminescence signals,relative changes were within 10%.Higher temperature would result in lower level of signal,the maximum relative strength loss was about 25%.Light and temperature will significantly reduce the intensity of the luminescence signal in the alumina device,after exposured 2 hours in natural light,the maximum attenuation was53%.Neutron and beta have little effect on the luminescence signal of the alumina device inside the electronic device.Through the experimental study on the fading of the luminescence signal in the alumina device at room temperature,it was found that the relative intensity of TL was linear with the logarithm of elapsed time,and the relative intensity of OSL was exponentially decayed with time.?5?The effects of photon energy,irradiation mode and relative position on the dose of radiation absorbed by alumina devices were determined by combining Monte Carlo simulation with experiments.The Monte Carlo calculation model of alumina device was established and placed in different positions of the male voxel phantom.The absorbed dose per unit fluence of alumina device under different energy and different irradiation modes was calculated by simulation.Then the scale coefficient corresponding to the reference value of the red bone marrow absorbed dose conversion coefficient in the publication of ICRP No.116 had been obtained.Also the relationship between the emergency dose of the individuals and the irradiated dose of the device was established.Through above research,the scientific evaluation of the emergency dose of the individuals who were not be equipped with dosimeters under special circumstances had been effectively solved,which complements the existing personal dose measuring equipment system,and provide practical and reliable technical means for meeting the needs of various scenarios in the future.The preliminary results and academic contributions of this dissertation summarized as follows:1)proposed a new way to use personnel alumina devices for emergency dose assessment,parameters such as trap depth,frequency factor were obtained by various methods;2)prepared carbon-doped alumina crystals by vertical gradient condensation method for the first time,which significantly improved the related dosimetry properties of the crystals compared with others;3)proposed multi-components single-aliquot regenerative dose method for emergency dose assessment,which established a suitable solution for large-scale personnel emergency dose estimation;4)given conversion coefficients between the absorbed doses of devices and the RBE weighted averaged absorbed dose in red bone marrow by simulation calculation,which established a correlation between the luminescence signal of the alumina devices and the dose received by individuals.