[RASMB] Intensity of the Xenon flash lamp

[John Philo]

Karel,

There is no absolute scale for these lamp intensities---the readings for a
good, clean lamp will vary significantly from instrument to instrument both
because the lamp outputs vary somewhat and because the gain of the
photomultipliers varies. Thus a reading of 6000 may indeed be normal
(maximum possible) for your instrument.

I agree with Bo that the true test is what is the noise level, and more
importantly whether your data are noisier now than in the past. That test
should be done by scanning an empty hole and calculating the r.m.s.
deviation around the mean (the mean of course in principle should be zero).
By that test most instruments will give rms levels of 0.003-0.004 OD, but
again really only a history for your instrument will establish what is
normal.

Regarding the monochromator moving issue, there was a software problem in
certain older versions of the instrument firmware (the firmware was sending
a wavelength seek command when none was needed, which sometimes caused the
monochromator to move). But I don't think that problem exists in versions
newer than perhaps ~7 years old.

John Philo
Alliance Protein Laboratories

-----Original Message-----
From: rasmb-admin at server1.bbri.org [mailto:rasmb-admin at server1.bbri.org] On
Behalf Of Karel Planken
Sent: Monday, July 12, 2004 2:26 AM
To: 'rasmb at rasmb-email.bbri.org'
Subject: [RASMB] Intensity of the Xenon flash lamp


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Dear AUC user,
Because various people say different things about what the intensity of the
229/230 nm peak in the Xenon flash lamp emission spectrum should be: some
say it should be above 15.000, other say it should be above 4000 and the
Beckman instruction manual says above 6000 (a graph is shown with an
intensity of around 36.000), I would like to ask you what should it be and
how do I check my Signal to Noise ratio? Our intensity at 229 nm in the
emission spectrum of the Hamamatsu L 2435 '96-09 Xenon lamp is somewhat
below 6000, which was recorded at 5.9, 6.5, and 7.1 cm from the axis of
rotation through a windowless cell. The service engineer is not willing to
do anything about it because according to him (and others he got in contact
with) the intensity is within the machines limitation as long as it is above
4000 @ 229 nm! So what should I do (the lamp was cleaned over and over again
as well as the slit assembly)? Another problem we experience is that
sedimentation velocity profiles jump around despite that theyu are recorded
at the same wavelength! I would like to know if anyone has seen this before
and more important how can I solve my problem?

Thank you for your time and I will eagerly await your reply,

Karel Planken.
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