Re: pulse width

Alice L. Givan (Alice.L.Givan@Dartmouth.EDU)
30 Jul 96 17:33:37 EDT

Lots of questions about a tricky subject. I'll start by telling you the bits
that I think I know --- and hope that others will correct me/and or contribute
their two cents to the discussion. Pulse width should be fairly
straightforward -- and be related to the diameter of the particle (or clump of
particles), as long as the diameter of the particle is significantly larger
than the laser beam. However, since much of flow analysis (eg pulse height
measurements) assumes that the particles are smaller than the laser beam (and
many particles are smaller than the laser beam) this could be an initial
problem .....

Forward scatter, however, is even more complex. It's related to refractive
index as well as to size of the particle. And, of more relevance, it is
proportional to cross-sectional area of the particle (NOT to diameter). The
larger the cross-sectional area of the particle, the more light passes through
it and gets refracted around the obscuration bar to reach the photodector. So,
even if refractive indices are constant from particle to particle and even if
the particles are larger than the laser beam (both highly questionable), you
would not expect a straight line relationship between FSC and pulse width, but
rather a curve.

Let someone else take over from here!

Alice L. Givan
Englert Cell Analysis Laboratory
Dartmouth Medical School
Lebanon, New Hampshire
NH 03756 USA
tel 603-650-7661
fax 603-650-6130
e-mail givan@dartmouth.edu