Date: Fri, 11 Feb 94 11:46:08 EST
Subject: Microprobe standards
From: Nick.Ware@anu.edu.au

Jussi Liipo (10-Feb-94) wonders why he gets a 4wt% error when switching
from Cr2O3 to a pure Cr standard using EMPA/WDS. I suggest 3 possible
causes:

1) The conductive coating on the Cr2O3 is wearing thin. Collect an EDS
spectrum and check to see if the high energy cut-off is exactly at the
accelerating voltage.

2) The spectrometer deadtime correction may be at fault. Measure the
deadtime and check that it is the value used in the computer program. Even
if the deadtime is fixed electronically using a busy signal (eg CAMECA
instruments since 1979) errors can creep in. We operated happily for two
years with a deadtime of 3.5 microseconds thinking it was set at 2
microseconds.

3) The parameters in the matrix correction program are wrong. Sometimes
these are initialised from ASCII files on ancient floppy disks. Start by
checking the mass attenuation coefficient for Cr by O.

Kippis

Nick Ware

N.G.Ware Phone (06) 249 3429
Research School of Earth Sciences A.H. (06) 295 2219
Australian National University Fax (06) 249 5989
Canberra A.C.T. 0200