[RASMB] Lamp Intensities on Analytical Ultracentrifuges

[John Philo]

John,
 
First, can you quantify what you mean by the noise is "quite bad". What is
the r.m.s. noise for a scan of an empty hole (not an empty cell) in the
rotor now, and what was it in the past?
 
These intensity readings are never absolute---20,000 counts on one
instrument might be 10,000 on one and 30,000 on another. The only thing that
counts is what is the ratio of the intensity when the lamp is clean versus
now. Even a 2-fold drop of intensity usually has a minimal impact on the
noise level, so the real source of the problem may be something else
altogether (perhaps a dirty slit assembly). 
 
John

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of John E Harlan
Sent: Friday, June 01, 2007 11:49 AM
To: rasmb at server1.bbri.org
Subject: [RASMB] Lamp Intensities on Analytical Ultracentrifuges



I am starting to have some problems with rapidly decreasing lamp intensities
on my analytical instruments.  Within about 1 month of moderate use after my
service people were in (they cleaned the optics while checking other
things), I find the noise in my velocity absorbance scans is quite bad.
When I check the intensities I find maxima at 230nm to be 8300 for an XLA
and 13000 for an XLI, well below the 20000 to 30000 I should find for a well
functioning instrument. 

I have two questions: 

1)  What could cause such a rapid decay of performance.  I suspect oil leaks
fouling the optics (I have observed droplets in the can on at least one
occasion).  I understand alignment can also cause problems.  Is there
something else to ask my service people to check? 

2)  I have heard that people that have upgraded to a turbo-molecular vacuum
pump have been quite pleased with performance.  Can this upgrade help keep
my optics clean, if indeed that is the problem? 

Thanks for your help in advance. 

John

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