Stable Isotope Geochemistry


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"Robert D. Stickrod II" <[log in to unmask]>
Reply To:
Fri, 20 Feb 2004 13:22:33 -0800
text/plain (102 lines)

Of course make sure the SOURCE is off if you decide to try the filament lead
switch.  if the vacuum chamber is sealed up now, that's a good first try if
the filament position is close.  If you have the source out already, remove
the trap on the opposite side so you can see the position of the filament by
looking through the hole where the trap was situated.  By trial and error
you can check this alignment; remove the filament if the actual tungsten
wire is not almost perfectly bisecting the small hole, adjust its position
and reinstall to have another look through the trap hole, looking for an
improved position.  I've had to very carefully, and very slightly, change
the filament-head position, not the tunsten wire itself.  The head will move
a bit but a slip of the hand could ruin the soldered connections to the
post.  The way I did it was to slightly change the angle of the bend in the
strips of metal that attach the filament head to the post.  Use very little
pressure and achieve minimal movement to the head's position and recheck
until it's lined up properly.


Bob Stickrod, Lab Manager
Idaho Stable Isotopes Laboratory
Department of Forest Resources
College of Natural Resources, Room 214
P.O. Box 441133, University of Idaho
Moscow, ID 83844-1133, U.S.A.
[log in to unmask]
lab: (208) 885-6512
fax: (208) 885-6226
cell: (509) 338-2814

>From: "Chenery, Carolyn A" <[log in to unmask]>
>Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
>To: [log in to unmask]
>Subject: [ISOGEOCHEM] Low signal intensity after replacing filament on
>Delta XL
>Date: Mon, 16 Feb 2004 13:29:21 -0000
>We recently replaced the filament and cleaned the source on our Delta Plus
>XL continuous flow mass spec (with ConFlo III, a TC/EA and a Flash EA).
>The sensitivity is now less than 1/2 of what we had before.  Previously we
>had a signal on mass 45 of  5.06V for 1 bar CO2 now it is only 2.1V
>During tuning I noticed the signal does not alter when the trap voltage is
>changed and to get maximum intensity the X deflection, Electron energy, X
>focusing voltage and Y1 are at maximum.  All the other settings are in the
>middle range.
>I have had the source out again and checked all the component positioning,
>orientations and pin connections.  The relative intensities for mass 44, 45
>and 46 are normal and peak shapes aren't bad.  The mass calibration has and
>the HV DAC have not changed significantly.  The Ion gauge reading is 4.4e-6
>as it always has with the needle valve open.  As far as I can tell there is
>no problem with the gas inlet.
>Has any one had similar problems and can you suggest the cause (and a
>Many thanks,
>Carolyn A. Chenery
>NERC Isotope Geoscience Laboratory
>British Geological Survey
>Kingsley Dunham Centre
>Keyworth, Nottingham
>U.K. NG12 5GG
>e-mail:  [log in to unmask]
>Phone: (+44) 01159 363406 (office)
>            (+44) 01159 363119 (laser laboratory)
>            (+44) 01159 363302 (fax)
>            (+44) 01159 363100 (switchboard)
>The NIGL Web Site is:
>The BGS Main Web Site is:
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