From: '''newspam'''@nonad.co.uk   
      
   On 11/01/2021 19:49, RichD wrote:   
   > On December 20, 2020, Martin Brown wrote:   
   >>> Ever so slightly different values are quoted in various references.   
   >>> The value I use is one seen frequently, 6.02214076 E23 . Other   
   >>> perceptions ?   
   >>   
   >> Unless you are doing something very unusual it makes little difference   
   >> beyond 4 sig fig.   
   >> Physicists care about it when ... ion counting in mass spectrometry   
   >   
   > What exactly is ion counting, and how?   
      
   Imagine a photomultiplier tube but without the glass envelope and   
   already in a vacuum chamber. Hit it with an ion at 8kV acceleration and   
   it spalls a cascade of electrons. You don't need so many gain stages.   
      
   There is a limit to how quickly it can recover (dead time) - ours used   
   to max out at about 10MHz. They can also be run at a much lower gain in   
   a pseudo analogue sort of way as a current detector.   
      
   This lot claim to be up to 1GHz ion count rates now. No idea if it is   
   genuine and works as advertised. I don't work on that stuff any more.   
      
   http://www.cromlab.es/Articulos/SGE/ETP/TA/TA-0103-A.pdf   
      
   --   
   Regards,   
   Martin Brown   
      
   --- SoupGate-Win32 v1.05   
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