From: andekl_no@saaf_spam.se   
      
   Keith F. Lynch  wrote:   
      
   > Henry Spencer  wrote:   
   > > To stop X-rays, you basically need mass.  Most any kind of mass   
   > > is as good as any other kind; essentially nothing is transparent   
   > > to X-rays.   
   >   
   > No.  There's a strong dependency on atomic number.  Lead blocks x-rays   
   > much better than the same mass of water does.   
      
   There is also a strong dependancy on photon energy, especially for high   
   atomic numbers. What you say is true for x-ray tube x-rays, that are   
   usually in the 20-200 keV range. You possibly worked with even lower   
   energies if you used beryllium for windows.   
   Solar x-rays extend into the MeV range, and there the dependency on   
   atomic number is next to nothing (within a factor of 2).   
      
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