United States Patent
`
`[19]
`
`[11] Patent Number:
`
`4,463,266
`
`Brahme
`Jul. 31, 1984
`[45] Date of Patent:
`
`[54] NEUTRON COLLIMATOR
`
`[75]
`
`Inventor:
`
`Anders Brahme, Bromma, Sweden
`
`[73] Assignee:
`
`Instrument AB Scanditronix, Sweden
`
`[21] Appl. No.: 236,199
`
`[22] Filed:
`
`Feb. 20, 1981
`
`Int.Cl.3
`[51]
`[52] U.S.Cl. .....
`
`.............................. G21K1/04
`
`...250/505.1;378/150;
`378/153; 378/206
`[58] Field of Search ............... 250/505, 511, 512, 251,
`250/492.1, 513, 514, 515, 509; 378/206, 150,
`153
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`1,484,663 2/ 1924 Mutscheller ........................ 250/509
`
`1,976,179 10/1934 Mannl
`.............
`378/206
`2,844,736 7/1958 Johns et al.
`250/512
`
`.........
`3,487,218 12/1969 Krebs et a].
`378/153
`
`3,715,597
`2/1973 Hofmann et al.
`. 250/513.1
`3,805,081
`4/1974 Barthel et a1.
`......
`378/150
`
`3,995,163 11/1970 Colditz ................
`. 250/518.1
`..........; ........... 250/505
`4,324,979 4/1982 Bowley et al.
`. FOREIGN PATENT DOCUMENTS
`
`. 192300 12/1906 Fed. Rep. of Germany ...... 250/514
`
`OTHER PUBLICATIONS
`
`tive Bucky Movement", Radiology, 135, Jun. 1980, pp.
`765467.
`
`Primary Examiner—Alfred E. Smith
`Assistant Examiner—~Carolyn E. Fields
`Attorney, Agent, or Firm———Lewis H. Eslinger
`
`[57]
`
`ABSTRACT
`
`A neutron collimator with an adjustable irradiation field
`for an effective neutron radiation source includes a
`protective radiation casing; a frame surrounded by the
`casing; a plurality of individual carrier arms mounted on
`the frame; a plurality of pairs of opposite elongated
`wedge-shaped slabs arranged side by side such that
`respective ones of the opposite wedge-shaped slabs
`form a fan~shaped configuration which converges
`toward an apex at the neutron radiation source, each
`wedge-shaped slab being mounted for rotational and
`translational movement on a respective carrier arm such
`that the wedge-shaped slabs of each pair are mounted
`for motion towards and away from each other along a
`path which intersects the irradiation field for the neu-
`tron radiation source and such that the inner side sur—
`face of each wedge-shaped slab is always directed gen—
`erally towards the neutron radiation source; and at least
`one bearing provided between each wedge-shaped slab
`and the respective carrier arm on which it is movably
`mounted.
`
`Barnes et a1., “The Scanning Grid: A Novel and Effec-
`
`13 Claims, 5 Drawing Figures
`
`
`
`ViewRay Exhibit 1007
`Page 1 of 9
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`ViewRay Exhibit 1007
`Page 1 of 9
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`

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`US. Patent
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`Jul. 31,1
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`4,463,266
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`Page 2 of 9
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`ViewRay Exhibit 1007
`Page 3 of 9
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`US. Patent
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`Jul. 31, 1984
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`Sheet 3 of4
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`4,463,266
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`ViewRay Exhibit 1007
`Page 4 of 9
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`ViewRay Exhibit 1007
`Page 4 of 9
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`U.S. Patent
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`Jul. 31, 1984
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`Sheet 4 of4
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`4,463,266
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`ViewRay Exhibit 1007
`Page 5 of 9
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`ViewRay Exhibit 1007
`Page 5 of 9
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`

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`1
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`NEUTRON COLLIMATOR
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`4,463,266
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`The present invention relates to a neutron collimator
`with adjustable irradiation field. A neutron collimator
`of this kind is disclosed in our Swedish patent applica-
`tion No. 79.05167-8. Said patent application discloses
`neutron absorbing blocks which may be shaped as a
`number of separate wedge-like slabs. The present inven-
`tion is an improvement of this previously known colli-
`mator and relates particularly to the orientation and
`motion of the slabs. In accordance with the present
`invention the wedge-like slabs are arranged side by side
`to form a fan-like configuration the (imagined) apex of
`which generally is at the effective neutron radiation
`source. Separate carrier means are provided which
`upon motion of the slabs impart the latter a transitional
`as well as a rotational movement of the kind that the
`inner side surface of each slab is pointing generally at
`said effective neutron radiation source for each setting
`of the slabs. Thanks to this “double focusing” of the
`slabs on the effective neutron radiation source an opti-
`mum, that is as sharp as possible, penumbra is obtained
`along the irradiation field rand.
`In accordance with the invention individual carrier
`means are provided for each slab thereby allowing indi-
`vidual setting of each slab.
`In accordance with another aspect of the invention
`each pair of opposite slabs can be closed together not
`only in the plane which contains the central beam from
`the effective neutron radiation source and which is
`perpendicular to all slab motion directions but also in
`planes which are parallel with said plane and which are
`displaced sideways in relation thereto. Non-centered
`dose distributions may therefore be Obtained. Moreover
`it is possible to prevent therapy radiation from reaching
`areas, the spine for example, which should not be irradi—
`ated when the effective neutron radiation source is
`rotated around the patient because the center of rotation
`of the effective neutron radiation source will be blocked
`by the collimator in accordance with the invention.
`An embodiment of the invention will be described in ‘
`detail below the reference to the accompanying draw-
`ings in which
`FIG. 1 is a cross—sectional view of the neutron colli-
`mator in accordance with the invention,
`FIG. 2 is a front view, partially a broken way, of the
`collimator shown in FIG. 1, said front view being taken
`along lines 11—11 in FIG. 1,
`FIG. 3 is cross-sectional view along line III—III in
`FIG. 1,
`FIG. 4 is a detailed view, shown in enlarged scale, of
`the carrier means for the left slab shown in FIG. 1 and
`FIG. 5 is a partial plane view and a partial section
`view of the device shown in FIG. 4.
`The general construction of the neutron collimator in
`accordance with the invention will now be described
`with reference to FIGS. 1—3. The collimator comprises
`a stationary collimator l and a continuously variable
`collimator 2. A bearing 3 rotatably connects units 1 and
`2 to each other. The stationary collimator is enclosing
`an effective neutron radiation source 4 from which high
`energy neutrons are emitted. The neutrons will hit a
`filter 5 increasing the average energy of the neutron
`beam and a flattening filter 6 in the indicated order
`before they pass a ionisation chamber 7 in which the
`intensity of the beam is measured. From this chamber
`the neutrons will enter the continuously variable colli-
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`mator 2 in which they pass a wedge filter 8 (compare
`FIG. 3), an inclined mirror 9 and finally a number of
`settable collimator slabs 10 of neutron absorbing mate-
`rial. The slabs 10 are supported on carrier means, not
`shown in FIGS. 1-3, mounted in a frame 11. Frame 11
`is surrounded by a casing 12 of a low density, high
`hydrogen atom content material, for example polyeth-
`ylene. Said casing 12 is surrounded by a thin layer of
`lead, not shown in detail, or of some other high atomar
`material
`serving as gamma
`radiation protection.
`Gamma radiation is generated when neutrons are ab-
`sorbed in casing 12. A similar protection against gamma
`radiation is provided by a lead glass slab 13 arranged in
`the bottom section of frame 11. The therapy neutron
`radiation is leaving the collimator through a protective
`window 14 attached to a frame 15.
`
`The irradiation field leaving the collimator is adjust-
`able and continuously variable with collimator slabs 10.
`An example of the collimator slab setting producing an
`irradiation field formed as. a kidney is shown in FIG. 2.
`FIG. 2 is also disclosing that the collimator. slabs 10 are
`arranged in pairs of opposite slabs, slab 10a opposite
`slab 10b, 10c opposite 10d etc. The collimator slabs are
`mounted for motion towards and from each other. Each
`slab can be set separately. In FIG. 2 slabs 10a and 10b
`are in abutting relationship, that is they are closed to-
`gether, while the pair of slabs 10c-10d has been set with
`little space therebetween through which space the neu-
`tron radiation may pass unobstructed. FIG. 2 is also
`disclosing that the central neutron beam from the effec-
`tive neutron radiation source as well as beams close to
`the central beam may be blocked, that is absorbed, by
`slab lflq and slabs adjacent thereto. This is advanta-
`geous when a patient is subjected to are therapy i.e. the
`collimator is rotated around the patient, because a vol-
`ume, e.g. the spine, which should not be subjected to the
`central beam is, in accordance with the invention posi-
`tibned at the centre of rotation of the effective neutron
`radiation source 4. This centre of rotation has been
`marked with A in FIG. 3.
`In FIG. 2 it is also shown that slabs 10 have different
`thickness, Central slabs qu—lOr and slabs adjacent
`thereto are thinner than the outer slabs 1011—1017. In
`accordance with an embodiment of the present inven-
`tion all slabs may be of the same thickness and in an
`alternate embodiment the thickness of the slabs may be
`further differentiated.
`,
`In FIG. 3 it is clearly shown that the slabs have the
`form of a‘wedge and that they are arranged side by side
`to form a fan-like configuration the imagined apex of
`which is positioned generally at the effective neutron
`radiation source 4.
`In FIG. 3 it is also shown that the irradiation field can
`be made visible on the patient by using a lamp 160 the
`light of which is reflected by an inclined mirror 9 from
`which the light is passing down through the collimator
`opening as set in order to strike the area to be subjected
`to the neutron radiation. The mirror image of lamp 16a
`is positioned at a point which generally corresponds to
`the position of the effective neutron radiation source 4.
`In FIGS. 4 and 5 the detailed construction of a pre‘
`ferred embodiment of the slab carrier means comprises
`an arm 17 extending into an aperture 18 provided in one
`of the side surfaces of each slab 10. Aperture 18 is ex-
`tending a small distance into the mid-section of the slab
`and is opening into a through opening 19. Through
`opening 19 is extending between the two main surfaces
`of each slab. In through opening 19 bearing means 20
`
`ViewRay Exhibit 1007
`Page 6 of 9
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`ViewRay Exhibit 1007
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`

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`3
`are provided, one bearing means on each side of the
`arm. Accordingly, the slab can be moved along the arm.
`In the shown embodiment said bearing means comprise
`rolls and the slab may therefore be rolled with low
`friction along a path which intersects the irradiation
`filed from the effective neutron radiation source 4.
`In FIG. 4 dash dotted line 21 represents the central
`beam from the radiation source. As is apparent from this
`Figure the inner side surface 22 of slab 10 can be moved
`towards and beyond the central beam 21.
`Aperture 18 and arm 17 are so positioned that the arm
`is supporting the slab in the vicinity of the centre of
`gravity of the slab. In doing so the weight of the slab is
`counterbalanced and only a small force is required in
`order to move the slab along the arm.
`As is apparent from FIG. 4 arm 17 is curved up-
`wardly. Bearing means 20 and through opening 19 have
`a corresponding curvature. The curvature is so selected
`that when moving the slab along the arm the slab will
`also rotate around a centre of rotation positioned at or
`in the vicinity of the effective neutron radiation source
`4. The inner side surface 22 of the slab will therefore
`always be directed generally toward or in-line with the
`effective neutron radiation source. The last-mentioned
`feature in combination with the fan-like configuration
`of the slab assembly indicates that the slabs are twice or
`double focused generally at the effective neutron radia-
`tion source. This double focusing brings about an opti-
`mum, that is as sharp as possible, penumbra along the
`band regions of the irradiation field.
`In order to ensure a mechanically rigid construction
`the outer free ends of each arm 17 are interconnected
`with the aid of rods 23 and distance means 24. Rods 23
`are extending through said through openings 19 of each
`slab 10.
`
`In the embodiment shown bearing means 20 comprise
`roller ways which are curved in accordance with the
`curvature of the arm. Each roller way includes two
`opposite slots having a square cross section. One of the
`slots is provided in the arm, the other in a mounting
`bracket 25 which is attached to a lip provided in the
`through opening 19. In the roller ways a number of
`cylindrical rollers are provided the central axes thereof
`lying in parallel planes but rotated 90° to each other.
`Instead of roller ways other friction reducing bearing
`means may be used, for example ball bearing ways,
`rollers provided in slots with trapezoidal cross section
`etc. In FIG. 5 the cross sections of arms 17 extending
`into slabs 10 are taken at different locations along the
`am. In the third slab from the right in FIG. 5 aperture
`18 and the web portionsof the slab surrounding this
`aperture are clearly shown. The cross section has been
`taken along lines A—A in FIG. 4. The cross section
`shown in the fourth slab from the left in FIG. 5 has been
`taken along lines B—B in FIG. 4.
`The position of the slabs along the arms are individu-
`ally settable with a setting device. In the embodiment
`shown this device comprises an electrical motor 26
`which when energized rotates a screwed rod 27 on
`which a nut 28 is screwed. Said nut is ball-shaped and is
`rotatably journalled in the bottom portion of slab 10.
`The motor 26 is'hinged in a pivot 29 attached to frame
`11. An inductive pick-up device 30 is surrounding the
`screwed rod and is transmitting a predetermined num-
`ber of electrical pulses for each revolution of the rod. A
`counter is counting said pulses and the count thereof is
`converted into a measure representing the distance be-
`tween the central beam 21 and a predetermined point
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`4,463,266
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`4
`provided on the slab. Instead of the setting device as
`shown a wire and pulley system may be used. Also
`pneumatic or hydraulic setting devices may be used
`instead of the electrical motor.
`To prevent adjacent main surface of the slabs from
`jamming when a slab is moved along the arm the upper
`and bottom section of each slab is provided with a num-
`ber of friction reducing means in the form of rollers 31
`extending only a small distance above only one main
`surface of each slab. In FIGS. 4 and 5 the bottom sec-
`tion rollers are shown and in FIG. 1 the positions of the
`corresponding upper section rollers are illustrated.
`Slabs 10 are manufactured from neutron absorbing
`material. The upper section of the slabs are manufac-
`tured from tungsten and the bottom section comprises
`low carbon soft iron, for example Armco-steel or steel.
`The slabs are provided with a number of through open-
`ings 32 generally completely filled with a material hav-
`ing low density but high hydrogen atom content, for
`example polyethylene. Two objects are achieved there-
`with, namely reducing the weight of the slabs and ther-
`malizing (retarding) the neutrons.
`Several measures have been taken to prevent neu-
`trons from escaping the collimator. In order to prevent
`a direct stray flux between the slabs stacked together
`side by side the top and bottom sections of the main
`surfaces of the slabs are provided with steps 33. In
`FIGS. 4 and 5 only the bottom steps are shown. The
`steps provided in one main surface of a slab are match-
`ing corresponding complementary steps provided in the
`main surface of an adjacent slab. In order to prevent
`stray neutron flux between two closed (abutting) slabs,
`for example slabs 10a and 10b in FIG. 2, the inner sur-
`face 22 of each slab is likewise provided with steps 34.
`The steps 34 provided on the inner side surface of one
`slab are matching complementary shaped steps 34 pro-
`vided in the side surface of the opposite slab. To prevent
`stray neutron flux in the region above the upper surface
`of the slabs said upper surface 35, shown in FIG. 1, has
`been curved and in the adjacent bottom section of colli-
`mator 2 a body 36 of neutron absorbing material has
`been provided, said body having a shape which is
`matched to the shape of the curved surface 35. The
`body 36 is of the same material as the casing 12.
`During the neutron radiation therapy treatment lead
`glass slab 13 must be moved away from the window 14
`and to this end it is movably supported on rollers 37
`supported in guides 38 which are attached to the bottom
`section of frame 11. The position of lead glass slab 16 is
`set with for example a chain and sprocket wheel system
`39 (compare FIG. 4).
`In accordance with another embodiment of the in-
`vention each arm 17 is omitted and instead bearing
`means, for example rollers, are provided below the
`bottom surface of each slab. In this embodiment the
`bottom surface of each slab is curved and is provided
`with a longitudinal, in cross section trapezoidal, slot in
`which the rollers are running. The rollers are resting
`against a curved surface provided on a support attached
`to the bottom section of the frame. The centre of curva-
`ture of the bottom surface of the slabs and of the curved
`surface of the opposite supports are at or in the vicinity
`of the effective neutron radiation source 4. When a slab
`is moved it is imparted a translational as well as rota-
`tional motion.
`
`The various embodiments described above may be
`modified and varied within the scope of the accompa-
`nying claims.
`
`ViewRay Exhibit 1007
`Page 7 of 9
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`4,463,266
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`5
`
`I claim:
`1. A neutron collimator with an adjustable irradiation
`field for an effective neutron radiation source, compris-
`mg:
`support means including a plurality of individual
`carrier means;
`frame means in which said support means is mounted;
`protective radiation casing means surrounding said
`frame means;
`a plurality of pairs of opposite elongated wedge-
`shaped slabs arranged side by side such that respec-
`tive ones of said opposite wedge-shaped slabs form
`a
`fan-shaped configuration which converges
`toward an apex at said neutron radiation source,
`each wedge-shaped slab having an inner side sur-
`face and being mounted for rotational and transla-
`tional movement on a respective one of said indi-
`vidual carrier means such that the wedge-shaped
`slabs of each pair are mounted for motion towards
`and away from each other along a path which
`intersects said irradiation field for said neutron
`radiation source and such that the inner side sur-
`face of each wedge-shaped slab is always directed
`generally towards said neutron radiation source;
`and
`at least one bearing means provided between each
`wedge-shaped slab and the respective individual
`carrier means on which it is movably mounted.
`2. A neutron collimator in accordance with claim 1,
`in which each slab includes a bottom surface which is
`curved towards the effective neutron radiation source
`and further including bearing means including rollers
`housed in opposite slots, one slot being provided in said
`curved bottom surface of each slab, the other slot being
`provided in a complementary curved mounting bracket
`attached to said frame means.
`3. A neutron collimator in accordance with claim 1,
`in which each slab is provided with a setting device for
`moving the slab along said respective carrier means.
`4. A neutron collimator in accordance with claim 1 in
`which each slab includes a curved top surface, and in
`which a portion of the casing means faces the top
`curved surface of the slabs and has a complementary
`curved form.
`5. A neutron collimator in accordance with claim 1,
`further including a lead glass slab movably mounted on
`guides provided in a bottom section of the frame means.
`6. A neutron collimator in accordance with claim 1,
`in which said neutron radiation source includes a cen-
`tral beam directed along a plane, and the inner side
`surface of each slab is movable beyond the plane which
`contains the central beam of the effective neutron radia-
`tion source and which is perpendicular to all slab mo-
`tion directions.
`7. A neutron collimator in accordance with claim 1,
`and further including a mirror arranged in the beam
`path of said neutron radiation source and an illumina-
`tion source positioned so that a bundle of light issued
`from the illumination source is reflected down through
`an opening confined by the inner side surfaces of the
`slabs as if the bundle of light virtually issued from the
`effective neutron radiation source.
`8. A neutron collimator in accordance with claim 1,
`in which each wedge-shaped slab includes a mid-sec-
`tion, an outer side surface opposite to the respective
`inner side surface, opposite main surfaces, an opening
`extending between the opposite main surfaces of the
`respective slab and an aperture positioned near the cen-
`
`6
`ter of gravity of the respective slab and extending
`through said outer side surface at the mid-section of the
`slab into said opening of the respective slab, and in
`which each individual carrier means includes an arm
`curved upwardly in the direction towards said neutron
`radiation source and extending into the aperture of the .
`respective wedge-shaped slab which is mounted
`thereon.
`9. A neutron collimator in accordance with claim 8,
`in which said at least one bearing means is provided at
`a top and bottom surface of each said arm, each bearing
`means associated with an arm and comprising a number
`of cylindrical rollers housed in opposite slots, one of
`said slots extending along a respective said arm and the
`other extending along a mounting bracket provided in
`said opening of a respective slab, said slots each having
`a square cross section and a curvature corresponding to
`that of the respective arm, the central axes of two adja-
`cent rollers lying in spaced parallel planes and being
`perpendicular to each other.
`10. A neutron collimator in accordance with claim 9,
`in which a plurality of said arms are connected to each
`other by rods extending through said openings in said
`slabs.
`11. A neutron collimator in accordance with claim 8,
`in which the main surfaces of each slab are provided
`with first steps, the first steps on one main surface of
`each slab being complementary shaped to those of the
`other main surface, and in which opposite inner side
`surfaces of opposite slabs of a pair are provided with
`second steps, the second steps of one slab being comple-
`mentary formed to that of the opposite slab in the pair.
`12. A neutron collimator in accordance with claim 8,
`in which each slab includes second bearing means pro-
`vided in and extending a small distance out from at least
`one main surface of the respective slab at top and bot-
`tom sections thereof.
`‘13. A neutron collimator with an adjustable irradia-
`tion field for an effective neutron radiation source, com-
`prising:
`support means including a plurality of individual
`carrier means;
`frame means in which said support means is mounted;
`protective radiation casing means surrounding said
`frame means;
`_
`a plurality of pairs of opposite elongated wedge-
`shaped slabs arranged side by side such that respec-
`tive ones of said opposite wedge-shaped slabs form
`a
`fan-shaped configuration which converges
`. toward an apex at said neutron radiation source,
`each wedge-shaped slab having an inner side sur-
`face and being mounted for rotational and transla-
`tional movement on a respective one of said indi-
`vidual carrier means such that the wedge-shaped
`slabs of each pair are mOunted for motion towards
`and away from each other along a path which
`intersects said irradiation field for said neutron
`radiation source and such that the inner side sur-
`face of each wedge-shaped slab is always directed
`generally towards said neutron radiation source,
`and each wedge-shaped slab including a mid-sec-
`tion, an outer side surface opposite to the respec-
`tive inner side surface, opposite main surfaces, an
`opening extending between the opposite main sur-
`faces of the respective slab and an aperture posi-
`tioned near the center of gravity of the respective
`slab and extending through said outer side surface
`at the mid-section of the slab into said opening of
`
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`4,463,266
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`7
`the respective slab, and in which each individual
`carrier means includes an arm curved upwardly in
`the direction towards said neutron radiation source
`and extending into the aperture of the respective
`wedge-shaped slab which is mounted thereon, the
`two main surfaces of each slab further being pro-
`vided with second openings generally completely
`filled with a low density, high hydrogen atom con-
`
`8
`tent material, each slab having a top portion com-
`prised at least of tungsten and the material in the
`remainder of the slab comprising at least one of
`steel and low carbon soft iron; and
`at least one bearing means provided between each
`wedge-shaped slab and the respective individual
`Carrier means on which it is movably mounted.
`I!
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