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Dear Bernd,

We use a O2-CO2 converter of a type slightly different from that   
described by  Kim Baublys. It consists of a pyrex tube containing a   
graphite disk suspended in a platinum wire basket. The graphite disk is   
about 1 cm in diameter and is not conditioned in any particular way. When   
a brand new disk is placed in the system, it must be outgassed for a   
while (typically 20 to 30 minutes is enough, sometimes it takes more).   
 The graphite disk is heated by halogen lamps (150 watts - 24 volts,   
manufactured by OSRAM) placed on either side of the pyrex tube and   
equipped with semi-spherical reflectors set so as to concentrate the   
emitted heat onto the graphite disk.  With this set up there is no need   
for a high frequency generator. Another advantage is that none of the   
internal metallic parts (Pt basket), with which O2 gas is in contact, is   
submitted to electrical voltage.

This system works beautifully well, is very simple to operate and   
inexpensive to build and maintain.  It is illustrated and described in   
some details in a publication that will be coming out within a month or   
two in Chemical Geology (Isotope Geoscience Section). The title is:   
 Fouillac A-M. and Girard J.-P., 1996,  Laser oxygen isotope analysis of   
silicate/oxide grain separates: evidence for a grain size effect ?

Hope this helps

Jean-Pierre

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Jean-Pierre GIRARD
BRGM
DR/PCI                                   phone :       (33) 38-64-32-15
Ave. C. Guillemin                       fax  :       (33) 38-64-37-11
B.P. 6009                      e-mail :        [log in to unmask]
45060 Orleans                           web :        www.brgm.fr/
France