I have incorporated a 5cm diameter aluminum disk below a modified magnetic
mount on a regular Supper goniometer head. The arc adjustments are removed
and the disk attached above the translation adjustment. This disk is in
fact two disks (each 2.5mm thick) sandwiching a small disk heater and a
thermocouple embedded in thermally conductive paste. The two disks are
attached together by epoxy around the edge. Leads from the thermocouple
and the heater exit together from the side of the disk and are routed down
(with plenty of slack to allow the goniometer to turn freely) and run to a
thermostatic controller to keep the disks above freezing (also prevents
burnout if the N2 stream gets interrupted). All electrical components are
available from Orion. On my markI version both disks are flat, although a
a markII version produced with a colleague has the upper side of the top
disk somewhat conical, nominally to reduce turbulence in the N2 flow. So
far (about 1.5 years) I have found the markI causes no significant
turbulence problems and completely eliminates icing on the goniometer. We
do still occasionally suffer from some icing on the end of the nozzle
which can eventually hang down far enough to get x-rays. This can be
carefully removed by scraping; however, sometimes the falling frost ice
can finish up on the crystal. I gather nozzle icing may be preventable
with a heater wire on the edge of the nozzle, but haven't gotten to it
yet.
Jim Head
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James F. Head, PhD e'mail jfh at medxtal.bu.edu
Professor of Physiology tel # (617) 638-4396
Structural Biology Group fax # (617) 638-4273
Department of Physiology
Boston University School of Medicine
