Tubetails

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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:

tube tails

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 (12x0.04mm2 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

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:

srm660a

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

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 x106 0 0
With Tube Tails correction
size/nm 1109(51) 995(38)
strain x106 156(7) 152(7)
Tube type AEG Rudolstadt
Without Tube Tails correction
size/nm 308(4) 468(6)
strain x106 0 0
With Tube Tails correction
size/nm 884(31) 793(23)
strain x106 115(8) 105(8)
Tube type Philips
Without TT corr.
size/nm 610(10)
strain x106 0
With TT corr.
size/nm 944(34)
strain x106 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).