Column
KP
fil
ter
The
characteristic X-rays used for X-ray diffractometry generally contain
Ka
and
KP
X-rays. A substance that
passes
Ka X-rays while absorbing
most
KP
X-rays to monochromatize the beam is called a
KP
filter.
The mass absorption coefficient (hereinafter referred
to
as "absorption coefficient")
of
an
element becomes smaller
as wavelengths become shorter, and vice versa. However, when X
-r
ays with energy greater than the binding energy
between the nucleus and electrons
of
an element, strike the element, the absorption coefficient suddenly increases
due
to
the photoelectric effect. This discontinuous point in the absorption coefficient is called an absorption edge.
c
·~
200
I
ls
e-
0 100
.l'l
..
"'
"'
.,
::;:
0
K absorption
edge
o~
L,
absorption
edge
i...
absorption edge
L11
abso,pti
edge
I
O Wavelength
(A)
Change in mass absorption coefficie
nt
in accordance with wavelength (platinum)
For efficient absorption
of
KP
X-rays only, select an element as a KP
fi
lter with its absorption edge wavelength
located between the
Ka
X-ray and
KP
X-ray wavelengths. Those elements will have an atomic number one or two
less than that
of
the target element. The
fo
llowing table shows the target elements commonly used for X-ray
diffractometry and their corresponding
fi
lters. I
KO.
/ l
Ka.
= I I I
00
Table
KfJ
fil
ter
s
Wavelength (A)
Meta
ls used as a filter
Wavelength
of
When I
KB>IIKw
= 1/100
Target
Ka
1
KfJ,
Substa
absorption
Mass
per
-nces edge
Thickness
unit area
Ka
1
(A)
(mm)
(l!lcm2)
transmissi vity
Cr
2.290 2.085 v 2.269
0.0ll
0.007
63
Fe
1.9
36
1.757 Mo
1.896
0.011 0.008
62
Co
J.
789
1.621
Fe
1.
743 0.012
0.009
61
Cu 1.541 1.392 Ni 1.488
0.015 0.013
55
Mo 0.7093 0.6323
Zr
0.689 0.081 0.053
43
Ag
0.5594 0.4970
Rh
0.534
0.062 0.0
77
4 1
Wavelength
(A) Metals u
se
d
as
a filter
Wavelength
of
When l
x@llx,,
, = 1/500
Target
Ka
1
KfJ,
Substa
absorption
Mass
per
-nc
es edge
Thickness
unit area
Ka
1
(A)
(mm)
(l!/cm
2
)
transmissivity
Cr
2.290 2.085 v 2.269 0.017
0.0
10
49
Fe
1.
9
36
1.757
Mo
1.896
0.018
0.013
47
Co
1.789 1.62 1
Fe
1.
743
0.019 0.015
46
Cu
1.541 1.392
Ni
1.
488
0.023 0.020
40
Mo 0.7093 0.6323
Zr
0.689 0.120
O.o78 29
Ag
0.5594 0.4970
Rh
0.534 0.092 0.
114
27
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