A method based on the cross-sectional relationship between^(10)B(n,α)^(7)Li and^(1)H(n,γ)^(2)H was proposed to detect and reconstruct the three-dimensional boron concentration/dose distribution in vivo during boron ...A method based on the cross-sectional relationship between^(10)B(n,α)^(7)Li and^(1)H(n,γ)^(2)H was proposed to detect and reconstruct the three-dimensional boron concentration/dose distribution in vivo during boron neutron capture therapy(BNCT).Factors such as the neutron energy,fluence rate,and degree of non-uniform distribution of the boron concentration in a voxel may affect the results of this method.A theoretical analysis of the accuracy of the method using a Monte Carlo simulation shows that the determining error is generally less than 1%under different tumor locations and neutron source configurations.When the voxel size is larger than 0.4 cm,the determining error might be higher for a non-uniformly distributed boron concentration in the voxel because of the changes in the neutron energy and fluence rate.In conclusion,the proposed method enables an accurate threedimensional boron determination in vivo during BNCT.展开更多
In this paper,computational methods are used to optimize the design of a prompt-gamma neutron activation analysis(PGNAA) system on China Advanced Research Reactor(CARR).Approaches are adopted for obtaining accurate ne...In this paper,computational methods are used to optimize the design of a prompt-gamma neutron activation analysis(PGNAA) system on China Advanced Research Reactor(CARR).Approaches are adopted for obtaining accurate neutron beam parameter and saving the computing time.For the radiation shielding design,the optimizing factors include the cost,weight,volume,machining convenience and background radiation at the detector position.Low background spectrum and high sensitivity are expected.The simulation results,and experiences from international PGNAA community,were used in the design of the CARR PGNAA system.展开更多
基于Ru(Z=44)丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh(Z=45),Pd(Z=46),Ag(Z=47),Cd(Z=48)(质子数Z位于Ru,Z=44之上)及Zr(Z=40),Nb(Z=41),Mo(Z=42),Tc(Z=43)(质子数Z位于Ru,Z=44之下)的A～(100～126)丰中子...基于Ru(Z=44)丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh(Z=45),Pd(Z=46),Ag(Z=47),Cd(Z=48)(质子数Z位于Ru,Z=44之上)及Zr(Z=40),Nb(Z=41),Mo(Z=42),Tc(Z=43)(质子数Z位于Ru,Z=44之下)的A～(100～126)丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf自发裂变瞬发γ射线γ-γ-γ三重符合、特别是新建立的γ-γ-γ-γ四重符合数据的系统观测和研究,在Ru,Pd,Cd和Nb丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES,TRS,PSM,CCCSM和SCTAC理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru及其上的Rh(Z=45),Pd(Z=46),Ag(Z=47)和Cd(Z=48)丰中子同位素的研究表明:Rh丰中子核具有比最大值稍小的三轴形变,γ=-28°,并在103–106Rh同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N=68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru(N=70)中存在;观察到了从具有最大三轴形变的110,112Ru中手征破缺到稍小三轴形变的112,114,116Pd中扰动的手征破缺的过渡;在较软的Ag核中观察到了丰富的谱学结构,在104,105Ag中鉴别出了可能的手征对称破缺,在较重的115,117Ag中提出了趋于三轴形变的γ软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z=50,N=82满壳附近122,124,126Cd核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=-30°,三轴形变极小增益为0.67 Me V),经具有大三轴形变的Rh核(γ=-28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ～-41°,三轴形变极小增益为0.32 Me V),再经Ag核中的γ软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh11/2)2中子转动顺排的上行γ驱动,和第二带交叉(πg9/2)2质子转动顺排的下行γ驱动效应,成功地解释了114Pd中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd,两者均为N=68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N=68同中素中鉴别出最大三轴形变,均比理论预言的108Ru和110Pd多4个中子。在Z值位于Ru(Z=44)之下的Zr(Z=40),Nb(Z=41),Mo(Z=42)and Tc(Z=43)丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了γ自由度;较重的Nb核(A=104～106)基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A 103)基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N=59),在100–106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了γ振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=-26°,并观察到了手征对称破缺。质子数Z从41到48的A～(100～126)丰中子同位素,特别是Pd和Nb同位素,呈现出关于三轴形变的过渡特征。展开更多
基金This work was supported by the National Natural Science Foundation of China(Nos.11805100 and 11905106)the Fundamental Research Funds for the Central Universities(No.NG2020003).
文摘A method based on the cross-sectional relationship between^(10)B(n,α)^(7)Li and^(1)H(n,γ)^(2)H was proposed to detect and reconstruct the three-dimensional boron concentration/dose distribution in vivo during boron neutron capture therapy(BNCT).Factors such as the neutron energy,fluence rate,and degree of non-uniform distribution of the boron concentration in a voxel may affect the results of this method.A theoretical analysis of the accuracy of the method using a Monte Carlo simulation shows that the determining error is generally less than 1%under different tumor locations and neutron source configurations.When the voxel size is larger than 0.4 cm,the determining error might be higher for a non-uniformly distributed boron concentration in the voxel because of the changes in the neutron energy and fluence rate.In conclusion,the proposed method enables an accurate threedimensional boron determination in vivo during BNCT.
基金Supported by National Natural Science Foundation of China(No.10805077)
文摘In this paper,computational methods are used to optimize the design of a prompt-gamma neutron activation analysis(PGNAA) system on China Advanced Research Reactor(CARR).Approaches are adopted for obtaining accurate neutron beam parameter and saving the computing time.For the radiation shielding design,the optimizing factors include the cost,weight,volume,machining convenience and background radiation at the detector position.Low background spectrum and high sensitivity are expected.The simulation results,and experiences from international PGNAA community,were used in the design of the CARR PGNAA system.
基金US Department of Energy(DE-FG-05-88ER40407,DE-AC02-05CH11231,DE-FG02-95ER40934,DE-AC05-00OR22725,DE-AC52-07NA27344,DE-FG02-95ER40939)National Natural Science Foundation of China(11175095,10975082,11235001,11320101004,11305059,11275063,11275068,11135005,11075103)+2 种基金Special Program of Higher Education Science Foundation(2010000211007)National Basic Research Program of China(973 Program)(2013CB834401)Russian Foundation for Basic Research(11-02-12050,11-02-12066)~~
文摘基于Ru(Z=44)丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh(Z=45),Pd(Z=46),Ag(Z=47),Cd(Z=48)(质子数Z位于Ru,Z=44之上)及Zr(Z=40),Nb(Z=41),Mo(Z=42),Tc(Z=43)(质子数Z位于Ru,Z=44之下)的A～(100～126)丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf自发裂变瞬发γ射线γ-γ-γ三重符合、特别是新建立的γ-γ-γ-γ四重符合数据的系统观测和研究,在Ru,Pd,Cd和Nb丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES,TRS,PSM,CCCSM和SCTAC理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru及其上的Rh(Z=45),Pd(Z=46),Ag(Z=47)和Cd(Z=48)丰中子同位素的研究表明:Rh丰中子核具有比最大值稍小的三轴形变,γ=-28°,并在103–106Rh同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N=68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru(N=70)中存在;观察到了从具有最大三轴形变的110,112Ru中手征破缺到稍小三轴形变的112,114,116Pd中扰动的手征破缺的过渡;在较软的Ag核中观察到了丰富的谱学结构,在104,105Ag中鉴别出了可能的手征对称破缺,在较重的115,117Ag中提出了趋于三轴形变的γ软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z=50,N=82满壳附近122,124,126Cd核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=-30°,三轴形变极小增益为0.67 Me V),经具有大三轴形变的Rh核(γ=-28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ～-41°,三轴形变极小增益为0.32 Me V),再经Ag核中的γ软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh11/2)2中子转动顺排的上行γ驱动,和第二带交叉(πg9/2)2质子转动顺排的下行γ驱动效应,成功地解释了114Pd中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd,两者均为N=68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N=68同中素中鉴别出最大三轴形变,均比理论预言的108Ru和110Pd多4个中子。在Z值位于Ru(Z=44)之下的Zr(Z=40),Nb(Z=41),Mo(Z=42)and Tc(Z=43)丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了γ自由度;较重的Nb核(A=104～106)基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A 103)基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N=59),在100–106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了γ振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=-26°,并观察到了手征对称破缺。质子数Z从41到48的A～(100～126)丰中子同位素,特别是Pd和Nb同位素,呈现出关于三轴形变的过渡特征。
