LiF(200), LiF(220), LiF(420)

LiF crystal types exist in a variety of lattice planes (200, 220, 420, etc.). In the sequence (200) --> (220) --

> (420), resolution increases and reflectivity decreases (Fig. 17).

Fig. 17: Intensities of the crystals LiF(220) and LiF(420) in relation to LiF(200). (Intensity LiF(200) =

1)

LiF(200):

A universally usable crystal for the element range atomic number 19 (K) onwards; high reflectivity, high

sensitivity.

LiF(220):

Lower reflectivity than LiF(200) but higher resolution; can be used for the element range atomic number

23 (V) onwards; particularly suitable for better peak separation where peaks overlap.

Examples of the application of the LiF(220) for reducing peak overlaps:

Cr Ka1,2 - V Kb1

Mn Ka1,2 - Cr Kb1

U La1 - Rb Ka1,2

LiF(420):

One of the special crystals; can be used for the element range atomic number 28 (Ni or Co Kb1) onwards;

best resolution but low reflectivity.

Figure 17 shows a reflectivity of only 10% of that of LiF(200) for LiF(420) in the energy range around 10

keV.

PET:

A universal crystal for the elements Al to Ti (K-peaks), Kr to Xe (L-peaks) and Hf to Bi (M-peaks).

ATTENTION

The PET is the crystal with the greatest heat-expansion coefficients, i.e. temperature fluctuations are

most noticeable here.

Fundamental Principles Introduction to X-Ray Fluorescence (XRF)