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Патент USA US2119679

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June 7, 1938.
c. v. LlTTON
Q 2,119,679
X-RAY TUBE
Filed May 29., 1936
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June 7, 1938.
2,119,679
C. V. LITTON '
X-RAY TUBE
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June 7, 1938.
c. v. LITTION
2,119,679
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X-RAY TUBE
Filed May 29, 1936
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Patented June 7, 1938
* '
2,119,679
UNITED STATES PATENT or'rlcs
2,119,010
x-nsr runs
Charles V. Litton, San Mateo County, Calif.
Application my 29, ms, Serial No. cam
‘
15 Claims.
(onto-s5)
This invention relates to x-ray tubes and has
to do more particularly with tubes designed for
use in the making of x-ray pictures.
For radiographic purposes it is desirable always
5 to use a tube with a very small focal spot be
anode heat than one in which the anode is ro
tatable.
In order to achieve the above-stated objective
it is essential that the cathode beam be move
able laterally of its direction of propagation dur
ing operation of the tube; and to eifect such a
lateral movement of the beam I prefer to make
cause by so doing the maximum de?nition is ob
tainable‘.
possible to use a very small spot where a_ consid
erable thickness must be penetrated because the
10 target would not withstand the great tempera
ture which would result from concentrating the
necessarily high milliamperage on such a small
area for the time required to e?ect a suiiicient
exposure. Therefore it is necessary with ordinary
use of what may be termed electrical de?ecting
means-operating upon the beam either electro
statically or electromagnetically. But I do not 10'
consider that the scope of my invention is limited,
in all of its aspects, to any particular mode or
means by which the lateral movement of the
15 tubes to use larger focal-spots on heavy work“ beam is accomplished.
and to accept as inevitable the concomitant sac
ri?ce of de?nition.
‘
The hypothetically possible methods of meet
ing the aforementioned de?ciency are:
20
(1) To discover a satisfactory target metal
that will withstand much higher temperatures
than any metal now known;
(2) To discover much more e?'icient means
than is now known for dissipating the generated
heat and:
(3) To eii'ect a continuous movement of the
- focal-spot over the
face of the target so that no
one portion of the target is exposed to bombard
ment for a suiiicient length of time to permit of
30 an excessive temperature rise.
The present invention falls within the third
mentioned classi?cation.
-
For radiographic purposes it is usually neces
sary, or at least preferable, that the focal spot be 15
substantially stationary in space-that is, from
the viewpoint of the object being radiographed
and, likewise, from the viewpoint of the photo
graphic ?lm or plate.
In one of its principal aspects, my invention is
characterized by the fact that the focal spot is
caused to traverse (scan) the face of the target
(during operation of the tube) while at the same
time the tube as a whole is moved more or less
bodily in directional opposition to the target 26
traversing movement of the focal spot-the focal
spot being thereby maintained substantially ?xed
in space.
There are two known electrical methods by 80
which a cathode beam, 1. e: a beam of electrons,
It has been proposed heretofore to provide ro
tating or otherwise continuously moving targets
35 and it is believed that such tubes have been de~
veloped commercially; but there are inherent and
seemingly unavoidable di?iculties standing in the
way of commercial production and use of x-ray
tubes of that character—which dimculties arise
40 out of the fact that there are moving parts inside
the tube which cannot be lubricated, yet must be >
closely ?tted in order to
maintain a proper de
gree of precision.
One of the principal objects of the present in
45 vention is to devise an x-ray tube of the type
wherein the focal spot continuously traverses the
face of the target during operation of the tube,
but in which the anode, including the target, is
?xed-that is, not rotatable or otherwise move
able with respect to the envelope of the tube-the
ultimate objective being an x-ray tube of the
class referred to which is free from internal me
and moving electrical contactsand which, in ad
for the dissipation of
A cathode beam traversing a magnetic field in
space, more‘ or less normally to the magnetic lines
of force, will be deflected laterally, crosswise of 45
the magnetic lines of force, just as a metallic
conductor passing through a magnetic ?eld and
carrying a'current (as in an electric motor) will
be caused to move transversely of‘ the
lines of force; and, if the magnetic ?eld is .al
beam will be reciprocated
‘ ternating the cathode
laterally.
The two aforementioned methods of de?ecting
the cathode beam may be employed individually
55
2,119,079
2
or jointly.
That is to say, the beam may be os
cillated and thus caused to scan the target in
two directions simultaneously by means either‘of
anode and wholly or to a large extent prevents
the electrons of the cathode beam being in?u
enced by the anode until they have passed beyond
two sets of electrostatic de?ectors or two de?ect
ing magnets or by means of one set of electro
static de?ectors and one de?ecting magnet. The
two scanning movements of the cathode beam are
preferably approximately at right angles to each
the point or points where they are laterally de
?ected. The electrons, instead of being accel
erated initially by the anode ?eld, are,‘ instead,
in?uenced wholly or mainly by the ?eld set up by
the shield potential-the shield, itself, being, in
other-one occurring preferably at a fairly high
frequency such as sixty cycles per second while
the other occurs at a relatively low frequency, say
one to ?ve cycles per second. The low frequency
a sense, a sort of intermediate anode.
At the
same time, the constricted portion of the shield 10
having the opening through which the beam
passes is, in effect, a virtual cathode-that is,
scanning of the target is in synchronism with
the oscillatory physical movement of the tube as
a whole and is in a plane such that, from the
viewpoint of the object being radiographed, the
focal-spot is substantially stationary.
To bring about a predetermined lateral de
?ection of a cathode beam either electrostatically
or electromagnetically, the required electrostatic
deflecting potential or magnetic ?eld intensity, as
from the viewpoint of the anode.
It is contemplated that the cathode beam may be
in the form of a pencil having a more or less circu 15
lar cross-section as in a conventional round-focus
X-ray tube or that it may have a more or less
rectangular cross-section as in a conventional
line-focus tube. With a cathode beam of the last
mentioned form the scanning of the target need 20
be only in one direction, that is laterally of the
linear focal-spot. The scanning in that case
the case may be, is more or less proportional to would be at a low frequency only, isochronously
the anode potential. By this I mean that the with the reciprocatory movement of the tube.
25
electrical potential or magnetic force required to
Referring to the drawings:
de?ect the cathode beam in an ordinary X-ray
Fig. 1 is a side elevational view of an X-ray
tube to any given extent is more or less directly’ tube mounted on a support which is adapted to
proportional to the voltage across the anode
be reciprocated, together with the tube. This
cathode terminals. With a tube operating at, view also depicts a driving motor and speed reduc
let us say, one hundred k. v., the necessary de
tion gear together with a low frequencyalter 30
?ecting potential would be quite high. Similarly, nating current generator or magneto which serves
a magnetic ?eld of very considerable strength to provide alternating de?ecting voltage in syn
would be needed to e?ect a like de?ection of the chronism with the reciprocatory movement of
beam.
tube;
It is very desirable to be able to bring about the theFig.
2 is an endwise view of the tube and other 35
requisite deflection of the beam without having to
resort to excessively high potentials on the elec
trostatic de?ecting electrodes and, similarly, to
avoid the necessity for a very powerful magnetic
?eld where the de?ecting is accomplished mag-'
netically. I have discovered a method and means
whereby the de?ecting of the beam can be brought
about with relatively small de?ecting potentials
or a relatively weak magnetic ?eld, as the case
may be. This I accomplish through an arrange
parts shown in Fig. 1;
Fig. 3 is a circuit diagram of an arrangement
for providing low frequency alternating potential
from a source of direct current.
tube and also illustrating diagrammatically the
electrical connections;
45 ment which operates to shield the cathode beam
from the in?uence of the high anode potential
until after the electrons which constitute the
beam have traveled past the point or points in
their space path at which they are laterally de
electrons being caused to move at
50 ?ected-the
relatively low velocity through the initial por
tion of their space path (during which period
they are laterally de?ected) and thereafter at a
greatly increased velocity.
The velocity of electrons in a highly evacuated
55
space path is a function of the space potential
which in an ordinary x-ray tube is the potential
difference across the anode-cathode terminals.
If the space potential actually operating upon the
60 electrons emitted by the cathode can be made
materially less than the anode-cathode potential
difference, during an initial portion of the elec
tron movement from cathode to anode, the ve
locity of the electrons through such initial por
tion of the space path becomes correspondingly
less.
-
Fig. 4 is a view, mostly in longitudinal section,
showing the interior construction of the X-ray
-
In the X-ray tubes illustrated in the accom
Fig. 5 is a cross-sectional view of the tube
.45
taken along the line 5-5 of Fig. 4;
Fig. 6 is a cross-sectional view taken along the
line 6—6 of Fig. 4;
Fig. 7 is a face view of the target showing the
focal-spot and illustrating the movement of the
focal-spot back and forth across the face of the
target;
Fig. 8 is also a view of the face of the target
with the path of the focal-spot depicted there
on. This view illustrates the result of a pencil
like cathode beam scanning the target in one di 66
rection (vertically) at a relatively high frequency,
say sixty cycles per second, and in the other di
rection at a relatively low frequency, say from
one to ?ve cycles per second;
Fig 9 is an external elevational view of an
X-ray tube which is much the same as those il
lustrated in the preceding figures but differing
therefrom in that an external de?ecting magnet
is employed to take the place of one of the two
sets of electrostatic de?ector plates;
0
Fig. 10 is an elevational view of the de?ecting ,
magnet shown in Fig. 8 and a cross-sectional view
through the tube illustrating more especially the
space relation between the pole pieces of the
there is included a shield on which is impressed magnet and the electrostatic de?ector plates in- '1
a suitable intermediate positive potential. The side the tube;
shield has a somewhat constricted opening
Fig. 11 is a view of the cathode end of an al
through which the cathode beam passes to the ternative tube structure in which the projected
target without physical obstruction; but, at the beam is of rectangular cross-section, that is to
panying drawings and hereinafter described,
same time, the shield operates as a barrier to the . say. a line-focus beam; and
7i electrostatic lines of force emanating from the
9,110,079
Fig. 12 is a cross-sectional view taken along
the line l2-l2 of Fig.
In Figures 1 and 2, reference numeral I des
11.
-
.
ignates, as an entirety, an X-ray tube in accord
ance with this invention comprising an evacu
ated glass envelope of cylindrical form in which
are enclosed all the usual elements including the
anode with its target and a thermionic cathode‘
together with other parts shownin Fig. 4. At
10 the anode end of the tube is an air-cooling radi
ator 2 of conventional form. The left hand or
cathode end of the tube is provided ‘with a con
ventional screw plug 3 which is shown inserted
in a screw socket 4. Heating current is supplied
15 to the cathode of the tube through the screw
plug 3 and socket 4. The whole tube together
3
desired low frequency alternating potential can
be produced across the terminals 31 and 38.
Figs. 4, 5 and 6 illustrate somewhat in detail
an x-ray tube wherein‘ the cathode beam is in
the form of a pencil of small diameter and more
or less circular cross-section. The cathode beam
1
is reciprocated at a fairly high frequency, say
sixty cycles per second, in directions toward and
away from the object to be radiographed-thus
producing, in effect, a linear focai-spot-and at
the same time the cathode beam is reciprocated 10
slowly at right angles to the '- previously men
tioned plane of reciprocation-thus, in‘ effect,
causing the linear focal-spot to move laterally
back and forth across the face of the target. Fig.
with the radiator 2 and socket 4 are mounted on
7 illustrates, approximately, how the focal-spot 15
and supported by a pair of uprights 5 and 6,
respectively, which, in turn, are mounted on and
cillatory transverse movement of the target. Fig.
would appear to an observer and depicts the os
20 carried by a cross member ‘I of insulating ma
terial. Cross member 1 is provided with an
8 illustrates the path of the focal-spot when re
ciprocating in one direction at say sixty cycles
opening 3 through which X-rays are emitted. To
per second and in the other direction at say one
the lower side of cross member ‘I and at either
end is attached a pair of channel-shaped mem
25 bers 9 and- HJ respectively. These latter are seat
ed in guides II and I2 in which they are free to
ray tube which is designated as a whole by ref
erence numeral i comprises a glass envelope 20
slide reciprocably as indicated by the double
headed arrow in Fig. 2.
'
to ?ve cycles per second.v ,
Referring more particuarly to Fig. 4, the X
of generally cylindrical form, the interior of
which is‘ highly evacuated. Inside the ‘envelope
are shown an anode 2i which is usually of cop
per, a thermionic cathode 22, a "gun” or accel-i
Guides II and I2 are secured to and carried
.30 on the top of a table or base plate l3, of insu
latin material, which would generally form a
erator 23, a pair of electrostatic de?ector plates
24 and 25 and a second pair of similar electro 30
static de?ector plates 26 and 21. Inserted in the
anode 2| is a circular tungsten button
part %of or be carried by the adjustable arm of
an X-ray machine.
Mounted upon base plate I3 is an'electric mo
35 tor l4 having a speed reduction gear enclosed
within a housing i 5. A drive-shaft projecting
from the speed reduction gear housing has an
o?-set crank pin it, to which is journaled a con
necting rod I], one end of which is pivotally con
nected at l8 to the cross member 'I. With the
motor in operation the cross member ‘I to
gether with the X-ray tube and other parts
carried by the cross member are reciprocated
In addition to the‘elements already mentioned
it is desirable to provide a cylindrical shield 29
and a focusing coil 30.
The thermionic cathode is provided‘ with a
suitable focusing shield 3| having a circular
opening 32 throughwhich a stream of electrons 40
known as the cathode ‘beam is 'emitted—this
beam being projected toward the target 28 as in
slow1y—-the length of the stroke being madeto
all conventional X-ray tubes. The accelerator
equal the distance spanned by the cathode beam
or gun 23 is provided with a central opening large
in its travel across the face of the target in the
same direction as that in which the tube is re
enough to permit passage of the cathode beam 45
ciprocated. The scanning of the target andv the
physical reciprocatory movement of the tube are
isochronized so that from the viewpoint of the
upon it a suitable predetermined positive poten
tial. The function of the gun is to form the
object being X-rayed the focal-spot remains sta
tionary. As a matter of fact the focal-spot is
stationary in space but there is a relative movement between the focal-spot and the surface of
55 the target.
Also shown mounted on the table I3 is an electric generator or magneto l9. This is driven
through the speed reduction gear l5’ and it is
designed to produce an alternating voltage of
the same frequency as that at which the X-ray
tube is physically oscillated. The voltage from
this generator is isochronous with the oscillatory
movement of the tube .and is of a magnitude
such as to be suitable for application to the low
65 frequency electrostatic de?ector plates which will
be described later.
'
As an alternative to the low frequency gen
erator l9 there may be provided an arrangement
such as shown in Fig. 3 which comprises a direct
70 current source 33 across the terminals of which
is connected a potentiometer 34 having two slid
ing contacts 35 and 36. By moving these con
tacts continuously, in opposite directions, at the
desired low frequency and isochronously with the
75 oscillatory movement of the X-ray tube, the
'
electronic discharge into a concentrated beam
and propel the beam toward the target. The
use of such guns in oscillograph machines is well
known.
.
The electrostatic de?ectors 24, 25, 26 and 21
consist each of a small metal plate which may be 55
rectangular in form as shown. Across the de
?ector plates 24 and 25 is applied
suitable magnitude. This low frequency poten
tial is the one which may be supplied by the
generator I 9 or the arrangement of Fig. 3. It
must be isochronous with the reciprocatory 65
movement of the tube in order that the focal
spot may remain stationary in space.
The cylindrical shield 29 has a constricted neck
portion at the end thereof adjacent the target,
which neck portion de?nes an opening through
which the cathode beam must pass to reach the
Shield 29 operates as a barrier to the
electrostatic lines of force emanating from the
anode, wherefore the electrons forming the cath
2,119,079
4
ode beam are not in?uenced by the target until
they have entered and at least partially passed
through the opening in the shield-at which
point the electrons are quickly accelerated by
the high anode potential and thus caused to
strike the target at a suitable velocity for the
production of X-rays. A positive potential of
some suitable intermediate value is impressed
?ected transversely of the magnetic lines of force
passing between the pole pieces. 0n the con
trary, the cathode beam is not de?ected trans
versely of the electrostatic lines of force between
the de?ector plates but, instead, it is de?ected
toward the positive plate. This accounts for the
space relationship between the de?ector plates
28, 21 and the pole pieces of magnet 41 as illus
trated in Fig. 10.
It is possible‘to use two sets of de?ecting mag
nets and thus eliminate both sets of electrostatic
de?ector plates, but it is thought that it would
upon shield 29 and, as a consequence, the shield
performs the function of an anode in that it im
parts a propulsive force to the electrons, caus
ing them to move toward the target-but at a
lower velocity than that at which they would be
be necessary to provide considerable separation
between the two magnets in order to keep their
space fields sumciently isolated.
Figs. 11 and 12 illustrate the construction of
the cathode end portion of a tube similar to that
of Figs. 4, 5 and 6, except that a cathode beam
of linear form (rectangular cross-section) is pro
jected. In this case the thermionic cathode 4l
instead of being in the form of a conical spiral
is of linear form; the aperture 49 in the focusing
shield and likewise the passageway 50 through
propelled if under the in?uence of the high
anode potential. Thus the electrons are caused
to move at a relatively low velocity through that
part of their space path in which they are acted
upon by the de?ector plates and, resultantly,
a relatively low potential on those plates will
answer the purpose. Were it not for the shield
29, the de?ecting, potentials would necessarily
be quite large in X-ray tubes operating at high
anode voltages-a condition which it is highly
desirable to avoid. What has been said with
95
the gun 23 are rectangular in form. Only one
set of de?ector plates 26 and 21 is required be- _
cause the linear beam scans the target only in
one plane, i. e. laterally of the linear focal-spot.
respect to the effect of the shield upon the de
?ecting potentials applies also to its effect upon
the requirements as to the intensity of the mag
netic ?eld which may be employed to de?ect the
beam as a substitute for electrostatic de?ection.
The function of the focusing coil 30 is to con
centrate or reconcentrate the cathode beam. It
is well known that the effect of a magnetic ?eld
upon a cathode beam passing axially’ there
through is to concentrate the beam. Thus, if
the beam shows any tendency to spread out this
may be cured by means of a focusing coil Ill.
The focusing coil should not be confused with the
A de?ecting magnet may be used with the tube
structure of Figs. 11 and 12 to take the place of
the electrostatic de?ector plates 28 and 21.
What is claimed is:
1. The combination in an X-ray tube compris
ing a target, a cathode and focusing means, of
means for cyclically de?ecting the cathode beam
thereby causing the focal-spot cyclically to scan
the target, and means for cyclically moving the
target isochronously with the cyclical scanning
movement of the focal-spot whereby to maintain
the focal-spot substantially stationary in space.
magnetic de?ecting coil which presently will be
described. They perform entirely different func
2. The combination in an X-ray tube compris
ing a target, a cathode and focusing means, of
40 tions.
In addition to physical structure, Fig. 4 in
means for cyclically de?ecting the cathode beam
thereby causing the focal-spot cyclically to scan
the target, and means for cyclically reciprocat
ing the target isochronously with the cyclical
cludes a diagrammatic showing of electrical con
nections.
There is depicted _a transformer 39
having a primary winding 40,, a secondary wind
ing 4i, which supplies heating current to the
45 cathode and a secondary winding 42 which sup
scanning movement of the focal-spot whereby‘
to maintain the focal-spot substantially station
plies sixty cycle potential to the electrostatic
ary in space.
de?ector plates 24 and 25. The low frequency
generator 19 shown in Fig. 1 is also illustrated
diagrammatically in Fig. 4. A source of direct
current 43 supplies biasing potential to the focus
ing shield ll; another direct current source 44
supplies a positive potential to the gun 23 and
the cylindrical shield 29 has impressed upon it
a still higher positive potential by .virtue of the
55 inclusion in its circuit of the additional direct
current source 45. The maximum positive poten
tial is of course applied to the anode 2! as is indi
cated by the inclusion of still another direct
source 46. In practice the several D. C. poten
tials would generally be derived from recti?ed
and ?ltered alternating current.
.
_
In Figs. 9 and 10 are illustrated a combination
which includes a de?ecting magnet 41 between
the pole pieces of which the X-ray tube I is
85 mounted.
The de?ecting magnet 41 takes the
place of one of the two pairs of electrostatic de
?cctor plates. It may be substituted for either
pair. If substituted for plates 24 and 25 the
winding of magnet 41 would be supplied with
70 sixty cycle current; but if the magnet is used
as a substitute for de?ector plates 26 and 21 its
winding would be supplied with low frequency
current.
As previously stated, the cathode beam is de
3. The combination in an X-ray tube compris
ing a target, a cathode and focusing means, of
electrical means for cyc'lically de?ecting the
cathode beam thereby causing the focal-spot cy
clically to scan the target, and means for cycli
cally reciprocating the tube together with said
target isochronously with the cyclical scanning
movement of the focal-spot whereby to maintain
the focal-spot substantially stationary in space.
4. In combination, an X-ray tube comprising
an evacuated envelope, a target and a cathode
within said envelope, focusing means for con
centrating electrons propagated by said cathode
into a beam and directing said beam toward said
target, two sets of electrical de?ecting means
operable individually to de?ect said beam later
ally in different directions respectively, one of 65
said sets of electrical de?ecting means being con
nected to a source of relatively high frequency
alternating potential, the other of said sets of
electrical de?ecting means being connected to a
source of relatively low frequency alternating
potential whereby the focal-spot projected upon 70
said target is caused to scan said target cycli
cally in two directions substantially at right
angles and means for reciprocating said tube
cyclically in the same plane as that in which
the focal-spot scans the target at low frequency“
2, 1 19,679
5
the reciprocatory movement of said tube being
isochronous with the low frequency scanning ments of both the x-ray tube and the focal-spot
movement of the focal- t.
5. The combination with an X-ray tube com
prising a target and means for projecting a 'cath-'
ode beam at said target, of means for causing the
focal-spot produced thereby to scan said target
reciprocably and means for reciprocating said
10 tube isochronously with the scanning movement
of said focal-spot,‘ the reciprocatory movement of
said tube and the reciprocatory movement of said
focal spot being at all times in mutual directional
opposition so that said focal spot remains sub
16
20
stantially stationary in space.
6. The combination in an X-ray tube compris
ing an envelope, a target, a cathode and focusing
means within said envelope; of means for de
?ecting the cathode beam whereby to cause the‘
occuring in the same plane, said plane of oscilla- -
tion being such that the focal-spot is maintained
substantially stationary relatively to the subject
being radiographed.
10. The combination in an x-ray tube of -an
evacuated envelope, an electronic-emissive cath
ode and an anode in spaced relation within said
envelope, means for concentrating the electronic
emission from said cathode into a beam and di 10
recting said beam toward said anode, a shield
forming a space within said envelope which is
isolated to a substantial degree from the in?uence
_of said anode so that the electrons emitted by
said cathode are not greatly accelerated by the
anode field,- at leastvuntil they have traversed‘
a substantial portion of the space path between'
focal-spot to traverse the face of the target, and , said cathode and said anode, said cathode being
mechanism for moving the x-ray tube bodily in situated within said isolated space, said shield
having an opening to permit . passage there 20
unison with the aforementioned traversing move
ment of the focal-spot but oppositely in direction through of the cathode beam, and electrical
whereby to maintain the focal-spot substantially
?xed
relatively to the subject being radiographed,
25
said last-mentioned means and said mechanism
being so interassociated as to operate in timed
relation one to the other.
‘
_
7. The combination with, an X-ray. tube com
30 prising an envelope, a target, a cathode and fo
cusing-means within said envelope, of means for
means operative upon said beam within said iso
lated space for de?ecting said beam laterally of
its direction of propagation.
-
11. The combination in‘an X-ray tube of an 25
evacuated envelope, an electronic-emissive cath
ode and an anode in spaced relation within said
envelope, means for concentrating the electronic
emission from said cathode into a beam and di
recting said beam toward said anode, a tubular 30
shield within said
, a chamber which
to maintain the focal-spot ‘substantially ?xed
envelope, said shield forming
is largely isolated, by virtue of
the shield, from the in?uence of the anode elec
trostatic ?eld, said cathode being situated in said
chamber, said shield having an opening for the 35
passage therethrough of the cathode beam, means
relatively to the subject being radiographed, said - for impressing a positive high potential on said
last-mentioned means and said mechanism being
40 so interconnected as to operate in timed relation
one to the other.
'
'
lower than that of the anode, upon said shield,
and electrical means operative within said cham 40
ber to deflect said beam laterally of its direction
8. The improved method of operating a radio-,
of propagation.
,
graphic X-ray tube of thetype comprising a. tar
12.
The
combination
in
an
X-ray
tube
of
an
get, a cathode and cathode-beam focusing means
45 within an envelope and wherein the cathode beam evacuated envelope, an electronic-emissive cath
is caused to impinge upon the face of the target ode and an anode in spaced relation within said
and produce thereon a focal-spot, said improved envelope, means for concentrating the electronic 45
method comprising: moving the cathode beam
laterally of its direction of propagation so as to
cause the focal-spot to traverse the face of the
target and, at the same time, moving the X-ray
tube bodily in a direction opposite to the lateral
movement of the cathode beam at substantially
50
the same speed as that at which the focal-spot
55 traverses the face of the target so that the focal
spot remains substantially stationary relatively to
the subject being radlographed notwithstanding
55
its movement relatively to the face of the target.
9. The improved method of operating a radio
graphic X-ray tube of the type comprising a tar
get, a cathode and cathode-beam focusing means
within an envelope and wherein the cathode beam
is caused to impinge upon the face of the target
and produce thereon a focal-spot, said improved
65
60
method comprising: oscillating the cathode beam
laterally of its direction of propagation so as to
that of the anode, upon said shield, and means
cause the focal-spot oscillatorily to traverse the
face of the target and, at the same time, oscil
lating the X-ray tube bodily so that the face of
70 the target moves always in directional opposition
to the movement of the focal-spot thereacross,
the oscillatory movement of the face of the target
for impressing potentials of opposing polarities
upon said de?ecting electrodes.
'13. The combination in an X-ray tube of an
evacuated envelope, an electronic-emissive cath
ode and an anode in spaced relation within said
envelope, means for‘ concentrating the electronic 70
being maintained always at substantially the
emission from said cathode into a beam and di
same speed as that at which the focal-spot trav
recting said beam toward said anode, shielding
erses the face of the target, the oscillatory move
means dividing the space path between said cath
ode and anode into at least two successive parts, 75
8,110,079
at least one of said parts being electrically iso
lated, at least to a substantial degree, from the
in?uence oi’ said anode, said shielding means
having an opening to permit passage of said
beam to said anode, the arrangement being such
that the electrons constituting said beam move
toward said anode through an initial portion of
the space path at a relatively low velocity and,
thereafter, at a relatively high velocity, electri
10 cal beam de?ecting means adiacent a portion of
the space path wherein the electrons move at rel
atively low velocity, means for‘ impressing a rela
tively high positive potential on said anode with
respect to said cathode, and means for impress
ing a lower positive potential on said shielding
means with respect to said cathode.
on said anode, means ior impressing a positive
potential, lower than that of the anode, upon
said shield, means for impressing a potential
upon said gun and means for impressing a vary
ing potential across said de?ecting electrodes.
15. The combination in an electrical discharge
device of an evacuated envelope, an ion-emitting
electrode and a second electrode in spaced rela
tion within said envelope,'means for concentrat
ing the ionic emission from said first-mentioned
electrode into a beam and directing said beam
toward said second electrode, a shield forming a
space within said envelope which is isolated to a
substantial degree from the in?uence of said sec
ond electrode so that the ions emitted by said ll
?rst electrode are not greatly accelerated by the
ileld or said second electrode, at least until they
l4. Thecombination in an x-ray tube of an have traversed a substantial portion oi’ the space
evacuated envelope, an electronic-emissive cath
path between said electrodes, said ?rst electrode
ode and an anode in spaced relation within said being situated within said isolated space, said
envelope, a gun adjacent said cathode, an elon
shield having an opening to permit passage~ there
gated tubular shield enveloping said cathode and through of said beam, and electrical means oper
gun, and at least one pair of electrostatic de
?ecting electrodes within said tubular shield, said
electrodes being arranged in mutual opposition
and operative to effect lateral de?ection of the
beam of electrons propagated from said cathode,
means for impressing a positive high potential
ative upon said beam within said isolated space
for de?ecting said beam laterally of its direction
oi propagation.
,
CHARLES V. LI'I'I'ON.
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