X-ray source

[Barry E. Burke]

Dear Nick (and all other CCD folks out there),

You might be interested to learn of a variable x-ray source produced by
Amersham International which can be used outside a dewar window.  It
consists of an Am-241 source which can be aimed at any of six targets.  The
emissions from the Am-241 cause x-ray fluorescence from the targets and are
a convenient source of variable x-ray energies.  The source is compact (37
mm diameter by 23 mm high), and the target wheel can be rotated to present
each target to the primary source.  The targets, their K-alpha energies,
and photoelectron count in silicon are:

1.Cu   8.04 keV   2203 e-
2.Rb  13.4          3663
3.Mo  17.4          4778
4.Ag   22.1         6055
5.Ba   32.1          8784
6.Tb   44.2          12,118

Of course, the higher energies interact less with the silicon, and so one
needs much longer integration times to collect enough events.  On the other
hand, the flux from this source increases as the energy goes up (30X more
at Tb than Cu).  Am-241 has a half-life of 433 years, so its output will be
quite stable in contrast to Cd-109.  I believe someone here at Lincoln
successfully used even the Cu line through the window of his dewar.

We purchased this item in 1991, and its product code then was AMC2084, but
can't recall the price.  I have a British phone number where you might
reach them: (0494) 544000.  There is an American office in Arlington
Heights, Illinois.

Barry Burke

Barry E. Burke
M.I.T Lincoln Laboratory, M.S. LI-127
244 Wood Street
Lexington, MA 02173-9108
bburke at ll.mit.edu
Phone: (617) 981-0680; FAX: (617) 981-5957