Performance Analysis And Structural Optimization Of CRT Concrete For Radiation

In the past decades,cathode ray tube（CRT）has widely existed in electronic products such as television,computer display screen and so on.Its main material is a kind of glass containing harmful heavy metal elements such as lead and barium.With the development of science and technology,CRT is gradually being eliminated.At present,these waste CRT have become an important factor endangering the environment.If they are not handled properly,the heavy metal elements contained in them will cause serious harm.It is necessary to find a suitable recycling way.Although the heavy metal elements contained in it are harmful to the environment and human body,it has good radiation shielding ability,which makes it a good raw material choice for anti radiation concrete.Researchers at home and abroad have preliminarily tried and verified the feasibility of preparing anti radiation concrete with waste CRT material as an additive.For the selection and use of shielding materials,the calculation of various shielding parameters must be considered,but at present,there is a lack of comprehensive calculation of relevant shielding parameters of CRT concrete,and the application is mostly concentrated in the field of photon shielding,and there is less research on the application of other types of ray shielding.The purpose of this study is to use the theoretical analysis method to calculate the shielding parameters commonly used in radiation shielding,build a practical database,establish a fast prediction model,evaluate the shielding performance,supplement,improve and optimize the current protection options.In this paper,the Monte Carlo software MCNP（Monte Carlo N-particle transport）is used to calculate the linear/mass attenuation coefficient,average range,accumulation factor and transmittance of concrete with different CRT content under different shielding thickness and energy in the application of photon shielding.Through the counting methods of F1 current counting card and F4 fluence counting card,combined with the counting energy card DEn,the transmitted photon fluence and air kinetic energy are calculated.At the same time,because the calculation of accumulation factor is cumbersome and there are many affected variables,this study proposes to use BP（back propagation）neural network to establish a prediction model for accumulation factor,which can accurately predict target parameters.In addition to photon shielding parameter calculation,for proton therapy protection,the instantaneous radiation dose rate outside the shield is mainly determined by secondary neutrons.Due to the high penetration and electrical neutrality of neutrons,high-energy neutrons will determine the shielding requirements of proton synchrotron.Therefore,the evaluation of proton protection performance is to evaluate its neutron protection ability.In this paper,Monte Carlo software is used to calculate the neutron fluence outside the wall after passing through the shielding body in the proton shielding,the ambient dose equivalent rate at 30cm around the machine room and the reflected neutron fluence received by the water model,so as to measure its shielding ability and the patient protection ability respectively;The radionuclide activity and photon fluence produced by decay of different shielding materials in proton shielding are considered.The above indexes are used as the standard to evaluate the performance and practicability of shielding materials in proton machine room,and the shielding optimization opinions are put forward.The main achievements of this subject include:The common parameters of CRT concrete used for photon shielding are obtained,the practical database of shielding protection is constructed,and the rapid prediction model of exposure buildup factor（EBF）based on BP（Back Propagation）neural network is established;The protective performance of CRT applied to proton therapy shielding is comprehensively evaluated,and the suggestions of structural optimization are put forward.For the calculation of shielding parameters,the photon energy range covers 0.015 MeV-15MeV and the shielding thickness is up to 20 mean free paths（MFP）.The parameters include the mass attenuation coefficient,linear attenuation coefficient,average free path,EBF and transmittance of concrete mixed with different proportions of CRT fragments under different energy;BP（back propagation）neural network is proposed to predict EBF,and its prediction effect is evaluated.The average error is 3.364%,which verifies the reliability of the neural network prediction method.For proton therapy,with the increase of CRT content（10%-90%）,the transmitted neutron fluence continues to decrease(5.06×10-10-1.77×10-10 cm^-2/particle),and the reflection of neutrons will gradually increase(2.64×10-9-3.20×10-9 cm^-2/particle),resulting in increased harm to patients.When 50%CRT concrete is used to reach the proton therapy room model,the maximum ambient dose equivalent is lower than 3.80 μSv/h/nA,the value of 90%CRT concrete less than 3.11 μSv/h/nA.The activity variation range of radionuclides produced by induced radioactivity in CRT concrete with different content is 2.74×10-3-5.38×10-3 Bq·cm^-3 0-60 minutes after irradiation,and the maximum photon fluence is 8.13 ×102 cm^-2;At the same time,based on the above calculation results,the optimization model of three-layer shielding structure of ordinary concrete,high CRT content concrete and boron containing concrete is proposed,and the surrounding dose equivalent rate is less than 1.88 μSv/h/nA.Through comparison,it is found that CRT concrete has excellent radiation shielding performance,which can be used for photon,proton and neutron shielding,and can protect the environment and save resources.