210
9.
X_RAYS
\
forms Which the crystal might have. They show, in a beautiful
,,
manner, the symmetry
of crystalline formations.
9—12.
Other Forms of X—ray Spectrometers.”—The powder
method of Debye and Sherrer has been discussed briey in the
chapter dealing With the wave-length of electrons.
The rotating or oscillating crystal method is of great practical
importance in the analysis of crystals. The crystal is oscillated
or rotated slowly about one of its axes, perpendicular to the X-ray
beam.
At certain positions of the crystal, a given set of planes
Will make the correct Bragg angle for the reection of x-rays of a
given wave-length. Each spot on a photographic plate, located
as in the Laue apparatus, Will correspond to the reection of a ..
given wave-length from a given plane, or one of the higher orders.
.
X-rays are reected in succession from two crystals in‘the '
dauäle crystal spectrometer.
This instrument is used for precision
measurements of wave—length or of the distribution of energy [
around any one wave-length.
.
A curved sheet of crystal (mica for example) may be used instead
of a plane crystal in such a manner as to focus a given x-ray
and decrease the required exposure time.
9—13.
Moseley’s Law.—In 1913—14, Moseley13 made the rst
systematic study of the X—ray spectra (see gure 9—12) of different
elements used as targets in X-ray tubes.
He found two distinct
series of lines, identical With the K and L uorescent lines of
_
'Barkla and _Sadler. Moseley also
dlS.
K,3
La
covered an -1mportant relationshlp
beJÎ
tween
the frequency 11 of the X—rays
.
/
/
and the atomic number Z of the
‘
.
ting element. Moseley’s laW states that
FIG.9—IS.
diagram.
_
'\/V : C(Z _ a)’
(9—14)
.
_Where _C and 0 are constants. The Value of C' differ$ fdrtheK
_
"
and“
but -isï“thè “same- for lines in the same ser1esforall
'
À ’
,
Value
the ‘.‘ screening constant,” also dfers
(
Ÿ
fis nearly constant“for different elementsln
_
any
Moseley’s law mgraphical
,
…
.Ï"Ïf_ 'iS. indicated
thé” Ka)Kp
cinÏt'the K
as wellasby
.
;.
.
...
.
.
.
.
.
.
...
......
......…m.…uuu.iwuumuri
9.
X_RAYS
\
forms Which the crystal might have. They show, in a beautiful
,,
manner, the symmetry
of crystalline formations.
9—12.
Other Forms of X—ray Spectrometers.”—The powder
method of Debye and Sherrer has been discussed briey in the
chapter dealing With the wave-length of electrons.
The rotating or oscillating crystal method is of great practical
importance in the analysis of crystals. The crystal is oscillated
or rotated slowly about one of its axes, perpendicular to the X-ray
beam.
At certain positions of the crystal, a given set of planes
Will make the correct Bragg angle for the reection of x-rays of a
given wave-length. Each spot on a photographic plate, located
as in the Laue apparatus, Will correspond to the reection of a ..
given wave-length from a given plane, or one of the higher orders.
.
X-rays are reected in succession from two crystals in‘the '
dauäle crystal spectrometer.
This instrument is used for precision
measurements of wave—length or of the distribution of energy [
around any one wave-length.
.
A curved sheet of crystal (mica for example) may be used instead
of a plane crystal in such a manner as to focus a given x-ray
and decrease the required exposure time.
9—13.
Moseley’s Law.—In 1913—14, Moseley13 made the rst
systematic study of the X—ray spectra (see gure 9—12) of different
elements used as targets in X-ray tubes.
He found two distinct
series of lines, identical With the K and L uorescent lines of
_
'Barkla and _Sadler. Moseley also
dlS.
K,3
La
covered an -1mportant relationshlp
beJÎ
tween
the frequency 11 of the X—rays
.
/
/
and the atomic number Z of the
‘
.
ting element. Moseley’s laW states that
FIG.9—IS.
diagram.
_
'\/V : C(Z _ a)’
(9—14)
.
_Where _C and 0 are constants. The Value of C' differ$ fdrtheK
_
"
and“
but -isï“thè “same- for lines in the same ser1esforall
'
À ’
,
Value
the ‘.‘ screening constant,” also dfers
(
Ÿ
fis nearly constant“for different elementsln
_
any
Moseley’s law mgraphical
,
…
.Ï"Ïf_ 'iS. indicated
thé” Ka)Kp
cinÏt'the K
as wellasby
.
;.
.
...
.
.
.
.
.
.
...
......
......…m.…uuu.iwuumuri