Tube Tails and size/strain estimation
Since the time of our first usage of the fundamental parameters profile model,
our measurements are disturbed by so-called "tube tails". Tube tails mean:
A small part of the X-rays emitted by the tube originates not inside the
focus, but up to 1cm outside the focus. This means 1mm equatorial
broadening towards both sides of the optical focus. If not corrected,
this tube tails may totally disturb the profile shapes calculated by
fundamental parameters. See the following figure:
This figure shows tube tails of three different tubes operating with identic
current/voltage as measured with a 40µm slit at sample position plus
a 30µm receiving slit. All tubes were long fine focus types
(12x
0.04mm2 optical focus). The AEG FK61 tube was at
4500 hours life stage, the Thomson FK61/Siemens KFLCu2K tubes were new.
KFLCu2K is a brand new ceramic type. Maximum intensities are 5500...7000 cps.
Diffractometer was an XRD7 with 175mm radius.
Learnt profile shapes include this tube tails as part of the geometry
function.
This tube tails depend on
- Manufacturer
- Tube type/specimen
- Current/voltage
- Life stage
- Take-off angle of the X-rays (usually 6°)
of the tube.
Since version 2.4.3, you should use the switch
TubeTails=...
in the *.sav
file for the GEOMET run. Give a tube tails
measurement as shown above. You may use the same file formats as for the
VAL[x]
entry for measurement data input.
For explanation, we show the measurement of SRM 660 standard (LaB6)
without (a) and with (b) tube tails correction for the used AEG tube:
We have measured the SRM 660 standard with two different tubes using
identic slits. For demonstration of remaining errors, we give results using
two different Cu Kα spectrae as cited from
- H. Berger; X-ray Spectrom. 15 (1986) 241-243
- G. Hölzer, M. Fritsch, M. Deutsch, J. Härtwig, E. Förster;
Phys. Rev. A 56 (1997) 4554-4568
These are the results:
Cu Kα from Berger (1986)
Diffractometer: XRD3000TT |
Cu Kα from Hölzer et al.
(1997)
Diffractometer: XRD3000TT |
Co Kα from ibid.
Diffractometer: URD6 |
Tube type |
AEG |
Rudolstadt |
Without Tube Tails correction |
size/nm |
324(4) |
496(6) |
strain x 106 |
0 |
0 |
With Tube Tails correction |
size/nm |
1109(51) |
995(38) |
strain x 106 |
156(7) |
152(7) |
|
Tube type |
AEG |
Rudolstadt |
Without Tube Tails correction |
size/nm |
308(4) |
468(6) |
strain x 106 |
0 |
0 |
With Tube Tails correction |
size/nm |
884(31) |
793(23) |
strain x 106 |
115(8) |
105(8) |
|
Tube type |
Philips |
Without TT corr. |
size/nm |
610(10) |
strain x 106 |
0 |
With TT corr. |
size/nm |
944(34) |
strain x 106 |
96(10) |
|
Both tables greatly illustrate the success of the tube tails correction.
At our opinion, tube tails are the strongest fault of fundamental parameters
profiles. Obviously, the uncertainties of different
Cu Kα spectrae overdominate
the residual error of our fundamental
parameters approach. Otherwise, our measurements clearly shows the
imperfectness of line profile standards. The total error of our approach,
including Cu Kα uncertainty, is much less compared to line
standard imperfectness.
Obviously, the data given by Berger (1986) are somewhat to broad compared to
Hölzer et al. (1997). Data given by Hölzer et al. give comparable
results for different anodes. Therefore, we recommend using the data given
by Hölzer et al., which are available for Cr-, Fe-, Co- and Cu-anodes.
Using tube tails correction, one may think about
using BGMN for line profile analysis (size/strain analysis).