一份蒙特卡洛程序 count=input('input the count:');%输入模拟粒子数 sigmaedata=[28370,13845,6908,2555,1223,2602,1925,905.3,479.7,164.5,74.24,23.86,66.60,36. 62,22.29,9.978,5.298,1.668,0.7378,0.2361,0.1099,0.06211,0.03939,0.02030]; sigmacdata=[0.0220,0.0393,0.0568,0.0904,0.1209,0.1479,0.1722,0.2136,0.2480,0.3092,0.348 6,0.3932,0.4153,0.4268,0.4319,0.4291,0.4215,0.3969,0.3691,0.3269,0.2944,0.2709,0.2512,0. 2209]; Edata=[1,1.5,2,3,4,5,6,8,10,15,20,30,40,50,60,80,100,150,200,300,400,500,600,800];%截面 数据 channel=zeros(1,ceil(662/5)+10);%多道数组 nget=0;%探测到的总计数 ntotal=0;%进入探测器的总计数 for ii=1:count%count 个粒子循环 collidetime=0;%当前粒子碰撞次数 %粒子状态初始化 E0=622; E=E0; z=-2; r=0; theta=2*pi*rand(1);% 源抽样，z,r,theta 坐标 miu=2*rand(1)-1; fai=2*pi*rand(1);%方向角抽样 if miu1%一个粒子在闪烁体中的输运过程 sigmae=interp1(Edata,sigmaedata,E,'linear'); sigmac=interp1(Edata,sigmacdata,E,'linear'); sigmat=sigmae+sigmac;%线性插值得到截面数据 L=-log(rand(1))/sigmat;%下次碰撞的距离 %计算下次碰撞位置坐标 rnew=sqrt(r^2+L^2*(1-miu^2)+2*r*L*sqrt(1-miu^2)*cos(fai-theta)); z=z+L*miu; cdth=(rnew^2+r^2-L^2*(1-miu^2))/2/r/rnew; sdth=L*sqrt(1-miu^2)*sin(fai-theta)/rnew; dtheta=asin(sdth); if cdth<0 dtheta=pi-dtheta; end theta=theta+dtheta; 

r=rnew; if(r>2)|(z>=4)|(z<0)%判断是否在闪烁体内 break; else end collidetime=collidetime+1; if rand(1)<(sigmae/sigmat) %光电效应 E=0; else%康普顿散射 alpha=E/511; flag=0; while flag==0 if rand(1)<=27/(4*alpha+29) x=(1+2*alpha)/(1+2*alpha*rand(1)); if rand(1)<=0.5*((alpha+1-x/alpha)^2+1) flag=1; end else x=1+2*alpha*rand(1); if rand(1)<=27/4*((x-1)^2)/x^3 flag=1; end end end E=E/x; alphat=alpha/x; miuL=1-1/alphat+1/alpha;%散射后的方向 a=miuL; b=sqrt(1-a^2); randangle=2*pi*rand(1); miunew=a*miu+b*sqrt(1-miu^2)*cos(randangle); sdf=b*sin(randangle)/sqrt(1-miunew^2); cdf=(a-miu*miunew)/sqrt(1-miu^2)/sqrt(1-miunew^2); sfn=sdf*cos(fai)+cdf*sin(fai); cfn=cdf*cos(fai)-sdf*sin(fai); fainew=asin(sfn); if(cfn<0) fainew=pi-fainew; end fai=fainew; miu=miunew; end%conputon/electtron %记录结果 end%while 

ntotal=ntotal+1;%进入探测器的总计数 if collidetime>0 nget=nget+1;%探测到的计数 Edown=E0-E;%沉积能量 FWHM=0.01+0.05*sqrt(Edown+0.4*Edown^2); delta=0.4247*FWHM; Eget=Edown+delta*randn(1);%记录能量 num=ceil(Eget/5); %寻道址 if num~=0 channel(num)=channel(num)+1; end end end%for count plot(channel); fprintf(1,'探测效率为%1.5f',nget/ntotal);