Dale Callaham recently asked for information regarding our enhanced
     PMT's.

     These enhanced PMT's are offered as an upgrade to MRC-600 owners and
     are fitted as standard to the MRC-1000 & MRC-1024.

     Dale understands correctly that incident photons undergo multiple
     internal reflections, hence increasing their probability of electron
     generation.  This probability of electron generation is known as the
     Quantum Efficiency (QE) and is increased by at least a factor of 1.7
     from 490nm through to >800nm.  Indeed, the improvement factor reaches
     a value of approximately 2.5 at 800nm.

     The gain and dark current characteristics for both types of tube are
     similar.

     If anyone else would like the QE comparison curves (or the data) then
     please contact me directly and I will forward them to you.

     Best regards

     Duncan McMillan
     Senior Product Manager
     Bio-Rad Microscopy Division
     UK

     Tel        (44) 1442-232552 xt 300
     e-mail     [log in to unmask]