Disribute particles uniformly inside a sphere with huge radius (10^9) - Matlab

I would like some help with the following:

   L2=10^9;
   nP=10^6;

   x(:,1)=L2.*rand(nP,1);
   y(:,1)=L2.*rand(nP,1);   % Select  initial partice position randomly (only positive values) NS
   z(:,1)= L2.*rand(nP,1);


   for ip=1:nP
      r1(ip,1)= sqrt(x(ip,1)^2 + y(ip,1)^2 + z(ip,1)^2);   % distance from (0,0,0) for each iteration

      while r1(ip,1)>=L2

         x(ip,1)=L2.*rand(1,1);
         y(ip,1)=L2.*rand(1,1);     % Select  initial partice position randomly (only positive values) NS
         z(ip,1)=L2.*rand(1,1);
         r1(ip,1)= sqrt(x(ip,1)^2 + y(ip,1)^2 + z(ip,1)^2);
      end
   end

The problems I face are:

1) Since the radius L2 is very big, when I multiply with L2 with rand I get values very close to the boundaries of the box (10^8 for example) and I want the particles uniformly distributed all around the sphere.

2) Also after I run the while command the resulting distributions are no more uniform.