Research On Radiation Dosimetry Problems Caused By Beam-Loss In Intermediate-Energy High Intensity Proton Linacs

The prompt and residual dose, which induced by beam losses in high power proton accelerators, are significantly important to be considered in constructing and operating a high power proton accelerator. Many researches on these issues have been done in the accelerator projects under constructing and planning in the world. The researches on these problems are also required by ADS research and CSNS project in our country.The purposes of this thesis are to develop the studies on radiation dosimetry problems induced by beam losses in high intensity proton linacs, to establish the methodologies of research, and to deal with the related problems in China ADS research and CSNS project. The main difficultes in these researches are that there are no general accelerator beam-loss models and special calculating codes besides of lacking of nuclear reaction data in intermediate and high energy range. Semi-empirical methods and the Monte-carlo method are widely adopted in these research works in the world. The semi-empirical methods are the general ones to estimate dose outside the shielding and so to estimate the shielding thickness, thus these methods can be used to verify the Monte-carlo calculations; however the There are many kinds of Monte-carlo codes using on these problems, each research group has been establishing its own set of models, codes and methodologies.In this thesis semi-empirical methods have been first analyzed,studied and summarized, then the Monte-carlo techniques have been applied to construct the accelerator beam-loss research model, to programme the dosimetry softwares, to establish the models, parameters and methodologies on various dosimetry problems on research;finally this two methodologies have been used to calculate the concerned radiation dosimetry problems in high intensity proton linac conceived by China ADS research and in RCS of CSNS project, the results have been compared. these researches are as follows:(1) semi-empirical methods studyWhen proton in GeV energy range, The mathematical expression of "Moyer" model is expatiated on the basis of the characteristics of radiation field outside the shielding and the related theories of the hadron cascade shower at GeV energy range; in 50～1000 MeV energy range, the Tesch's formula is given based on the point-source sight-in-line. After analyzing on the using conditions and the application range, a set of practical formulas and parameters in calculating the dose outside the intense beam proton linac shielding and the shielding thickness are submitted. Point-source model can be used to deal with the maximum dose circumstances outside the shielding when beam is full loss, it also calcultates the dose outside the shielding and the shielding thickness in the case of uniform beam loss after multiplying by suitable coefficient;when using line-model, the simplified formulas are usually adoped. The result given by semi-empirical methods can act as reference to the relevant computition results of Monte-carlo method.(2) The research on Monte-carlo methodology for radiation dosimetry problems induced by beam loss(SHIPLIFE method)1)model construct and model parameters research:SHIPLIFE modelThis thesis creatively conceives a model called SHIPLIFE model (shielding and pipe model with line-source fixed-angle emitting), that is: beam pipe is cylindrical shell, filled with air;shielding is consisted of coaxial cylindrical ordinary concrete layers, the layers number varies with proton energy;tunnel is filled with air; cylindrical air layer is filled around the shielding;protons are uniformly on one distance along the beam axis, the lost protons departures the axis with very small angle and hits the pipe. The parameters of SHIPLIFE model are also confirmed.2) development of special software on radiation dosimetry problems induced by beamlossThis thesis develops a set of special softwares handling the radiation dosimetry problems induced by beamloss on the basis of basic principles of calculating ambient dose equivalent or equivalent dose and the character -istics of radiation field outside the shielding of the intense beam proton linac:rearrange code is appled to files convert;dosicalc code is appled to calculating fluence distribution, ambient dose equivalent, etc. ; formatbin and ambbin are appled to calculating dose distribution in tunnel space. As the dosicalc code can handle simultaneously a batch of same kind of detectors, it is suitable for calculations of ambient dose equivalent distribution research, also suitable for calculations of residual dose research, together with other softwares, it consists the special software of research on radiation dosimetry problems in intense beam proton linac.3) methodology of research on radiation dosimetry problems induced by beamloss, SHIPLIFE methodsBy the space, the radiation dosimetry problems can be divided to three region,out the shielding, in shielding, inside the shielding(accelerator tunnel) ;by the time, it can be divided to two stages, running (prompt radiation) and stop (residual radiation). According this circumstance and the actual problems, this thesis, based on the SHIPLIFE model, establish the SHIPLIFE methods of researching on radiation dosimetry problems induced by beamloss through four aspects:SHIPLIFE-OUT model and research methodology for out -shielding dosimetry research;SHIPLIFE-IN model and research methodology for in-shielding dosimetry research;SHIPLIFE-TUNBIN model and research method -ology for tunnel spatial dose distribution research;SHIPLIFE-REPH model and research methodology for tunnel residual dose distribution research.(3) Research on the radiation dosimetry problems which ADS and CSNS relate toUsing semi-empirical methods and SHIPLIFE methods, calculations are made on radiation dosimetry problems which the intense beam proton linac conceived by ADS research and RCS accelerator of CSNS project relate to. For the intense beam proton linac conceived by ADS research, SHIPLIFE methods are applied to all the calculations of the out-shielding, in-shielding, tunnel spatial dosedistribution and residual dose. Theλ_eff, H_π/2 values obtained by SHIPLIFE-OUTmethod are complied with the ones by semi-empirical methods;calculations show that SHIPLIFE-IN method can also be used to abtain approximately theλ_eff, H_π/2 values and shielding thickness as SHIPLIFE-OUT method does. ForCSNS, only the SHIPLIFE-IN method is used and attenuation length in shielding is calculating which are compliant with the results calculated by semi-empirical methods.This thesis has established rudimentarily the methodology based on semi-empirical methods and monte-carlo methods for researching radiation dosimetry problems induced by beamloss in intermediate energy high intensity proton linac. SHIPLIFE methods are presented, it has been applied to calculating radiation dosimetry problems induced by prompt and residual radiations in proton linac conceived by China ADS research and shielding thickness in CSNS, respectively, the relevant results are consistent with that semi-empirical methods do, that proves that SHIPLIFE methods are credible. The SHIPLIFE model which presented in this thesis makes a further step than simplified model and has the basic characteristics of accelerator, the line-source model is closed to real things, this SHIPLIFE model is suitable to methodology research on the radiation dosimetry problems.The innovations in this thesis are that after investigating and analyzing the researches on radiation dosimetry problems induced by beamloss in median energy intense beam proton linac in the world, firstly construct the SHIPLIFE model;divides dosimetry problems researches into out-shielding dose research, in-shielding dose research, tunnel dose research, tunnel residual dose research, and establishes each calculation model and method;programmes codes used to calculating ambient dose equivalent and other physical quantities and some auxiliary codes are also programmed;firstly make researches on dose distributions and residual dose problems in ADS and CSNS proton accelerators and compares with semi-empirical methods, the consistent results are obtained.The research of this thesis has important meaning of developing the research on radiation dosimetry problems induced by beamloss in intense beam proton linac in our country,it not only gives a method for the research on dosimetry problems in median energy intense beam proton linac and offers some data as reference for the project design;but also makes a foundation and a platform for further research.