212
9.
X-RAYS
words, X-rays are of appreciably shorter wave—length than light
rays.
The elementary theory of Bohr may be modied by
'
‘
_
assuming that the effect of the charge on the nucleus, Ze,,is
reduced by the outer electrons by an amount ae. Thus, (Z — a)e
is the elïective nuclear charge.
.
In gure 9—16, no attempt has beenmade to show the actual
energies but only to indicate that the K, L, M, etc., levels are more
or less separate
each other and also to show the further, com—
plicating feature that each of these, except K, consists of several
adjacent levels of roughly the same energy. The transition of an
electron between the upper
L and the K level gives an X-ray whose
-
wave—length in the case of tungsten is 0.208 angstrom and is called
the
line.
The transition from middle L to K is of smaller
energy and hence longer wave-length (=0.213 angstrom, called
The wave-lengths of KBl and K62 are 0.195 and 0.179
angstrom, respectively. Transitions are not possible between all
levels:
certain “selection rules,” similar to those in optical
spectra, must be followed.
The relative intensities of the lines
in the K series are independent of the voltage on the tube;
tungsten Ka1,
K51 and Kæ, they are approximately 100, 50,
35 and 15, respectively. The ratios for the L series depend on;
the voltage.
.
_
«
…
9—15.
The Number of Extra—nuclear Electrons.—From the
of alpha particle scattering, it was established thatthe
charge on the nucleus of an atom was numerically equal t01ts
.
atomic number.
In order, therefore, that the complete atom
should be elëctrically neutral, the number of extra-nuclear elec—
‘
trons must be equal to the atomic number. Measurementson
the scattering of X—rays at various angles from different materials
—
has given'direct proof that this is true. For _elements‘oflow
.,
‘
‘
atomic
and for X—rays of moderate wave—lengths,the
-
classical theory of Thomson 14
may be used with condence
In_thiS theory, the electric vector of the X—ray wavecausesan
of the electrons in the scattering mater1aland,düe
.to the acceleration, a
waVe-is radiated.
The1ntegrated
'; }
electrons is»…calculated to obtain the total mten31tY
Ofthe
ed
from WhiCh‘ themass”
:
œngbevcomputed,__1ïiThis quantrtytheloga
9.
X-RAYS
words, X-rays are of appreciably shorter wave—length than light
rays.
The elementary theory of Bohr may be modied by
'
‘
_
assuming that the effect of the charge on the nucleus, Ze,,is
reduced by the outer electrons by an amount ae. Thus, (Z — a)e
is the elïective nuclear charge.
.
In gure 9—16, no attempt has beenmade to show the actual
energies but only to indicate that the K, L, M, etc., levels are more
or less separate
each other and also to show the further, com—
plicating feature that each of these, except K, consists of several
adjacent levels of roughly the same energy. The transition of an
electron between the upper
L and the K level gives an X-ray whose
-
wave—length in the case of tungsten is 0.208 angstrom and is called
the
line.
The transition from middle L to K is of smaller
energy and hence longer wave-length (=0.213 angstrom, called
The wave-lengths of KBl and K62 are 0.195 and 0.179
angstrom, respectively. Transitions are not possible between all
levels:
certain “selection rules,” similar to those in optical
spectra, must be followed.
The relative intensities of the lines
in the K series are independent of the voltage on the tube;
tungsten Ka1,
K51 and Kæ, they are approximately 100, 50,
35 and 15, respectively. The ratios for the L series depend on;
the voltage.
.
_
«
…
9—15.
The Number of Extra—nuclear Electrons.—From the
of alpha particle scattering, it was established thatthe
charge on the nucleus of an atom was numerically equal t01ts
.
atomic number.
In order, therefore, that the complete atom
should be elëctrically neutral, the number of extra-nuclear elec—
‘
trons must be equal to the atomic number. Measurementson
the scattering of X—rays at various angles from different materials
—
has given'direct proof that this is true. For _elements‘oflow
.,
‘
‘
atomic
and for X—rays of moderate wave—lengths,the
-
classical theory of Thomson 14
may be used with condence
In_thiS theory, the electric vector of the X—ray wavecausesan
of the electrons in the scattering mater1aland,düe
.to the acceleration, a
waVe-is radiated.
The1ntegrated
'; }
electrons is»…calculated to obtain the total mten31tY
Ofthe
ed
from WhiCh‘ themass”
:
œngbevcomputed,__1ïiThis quantrtytheloga