Hi Carl,
I'm not sure what exactly you are asking. If you mean that if you change
the anode voltage from 400V to 500V and the gain goes from 2Alm to
10A/lm, will changing it from 500 to 600V give a gain of 50A/lm then the
answer is no the gain will be 30A/lm, you'd need to go to 700V to get
50A/lm. The graph "Anode Luminous Sensitivity and Gain Characteristics"
on the data sheet (fig 2 on my copy) shows this. It unfortunately a very
cluttered graph with non linear axes.
The other important question is what "mode" the PMT is being used in,
I.E single photon or current mode. If the light level is so low that you
are getting individual pulses (one for each photon) from the PMT then
adjusting the gain will not affect the number of pulses, just their
amplitude. If you are in current mode then the gain will directly affect
the signal level.
I do not know how the PCM2000 operates, but may instruments use a
current amplifier with a relatively long time constant. This when
individual pulses are present it integrates them and changes to current
mode when the out put becomes continuous. Have you tried imaging a
dilution series at different gain settings. Again I don't know the
PCM2000 but normally the "gain" control just adjusts the PMT anode
voltage. The other unknown is whether the ratio between the gain
"control" and the voltage is linear. Some instruments scale the voltage
change so that 10% change in the control really is 10% change in gain. A
dilution series check should show this.

HTH,
Robert.  

-----Original Message-----
From: Confocal Microscopy List [mailto:[log in to unmask]] On
Behalf Of carl
Sent: 09 November 2004 00:04
To: [log in to unmask]
Subject: PMT sensitivity

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Hi All,
Does anyone have info on the linearity of the sensitivity of the
Hamamatsu
R928 PMT  that we have in our Nikon PCM2000 confocal?  Does it change
with
gain settings?  I have a 4-page spec sheet on this thing but I can't
decipher what it is telling me.
Thanks very much,
Carl

Carl A. Boswell, Ph.D.
Molecular and Cellular Biology
University of Arizona
520-626-8469
FAX 520-621-3709
 
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