Neutron collimator with a variable passage cross section

Dec. 30, 1969 κ. krebs etal 3,437,218

NEUTRON COLLIMATOR WITH A VARIABLE PASSAGE CROSS SECTION

Filed Feb. 18, 1966

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BY

INVENTORS

Karlheinz Krebs Rene Rochez

ATTORNEYS

United States Patent Office

3,487,218

Patented Dec. 30, 1969

3,487,218 NEUTRON COLLIMATOR WITH A VARIABLE PASSAGE CROSS SECTION

Karlheinz Krebs, Ispra, and Rene Rochez, Besozzo, Italy, assignors to European Atomic Energy Community 5 (Euratom), Brussels, Belgium

Filed Feb. 18, 1966, Ser. No. 528,646 Claims priority, application Germany, Mar. 25,1965, E 28 955

Int. Cl. HOlj 1/52, ’35/16; G21g 3/00

U.S. CI. 250—105 1 Claim ¹⁰

ABSTRACT OF THE DISCLOSURE

A neutron collimator with a variable passage cross-section and consisting of an open-ended, hollow lead through body penetrating the shielding of a nuclear reactor and two collimation blocks movably mounted therein characterized by the fact that the opposing surfaces of the 20 collimation blocks, defining the collimation channel, are oblique to the axis of the channel and that radiation inhibiting means are provided between the body and blocks the latter being capable of movement to a position wherein they effectively close the channel. 25

The invention relates to neutron collimators (e.g. stationary collimators used for experimental purposes in connection with nuclear reactors) of the kind having a 30 variable passage cross-section and comprising two opposed blocks in a throughway (e.g. formed in a reactor shield or in a tubular body provided in a shield) and providing by their opposed surface two walls of the collimation passage said blocks being movable towards and away 35 from one another to vary the passage cross-section.

In one known construction of such a collimator, the blocks are parallel and are moved towards and away from one another, in equidistant relationship to one another, by a parallel guide system. A disadvantage of this 40 known construction is that the neutron radiation intensity at the collimator exit decreases strongly as the passage cross-section decreases, and also the radiation source cannot be collimated sharply on to a particular spot or a defined surface.

The invention provides a neutron collimator of the above kind in which over at least a part of their movement, the surfaces are oblique to the axis of the passage whereby the passage tapers in the axial direction.

The arrangement may be that the said surfaces can be _gomoved into contact on the axis.

Preferably the passage tapers as aforesaid throughout its length. It is also preferred that the obliquity and hence the taper is adjustable or variable.

In one form of the invention the blocks have pin and _5gslot (or groove) connections with the walls of the throughway, the slots being oblique to the axis, whereby relative movement between the block and the walls of the throughway in the axial direction is accompanied by movement of the blocks towards or away from one an- ₆θ other as aforesaid.

It is preferred that the blocks and throughway mate with a saw-tooth configuration.

The movements of the blocks may be effected hydraulically.

A specific embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings wherein:

FIG. 1 is a vertical transverse sectional view of the neutron collimator taken along the line 1—1 of FIG. 3; γθ FIG. 2 is a horizontal sectional view of the neutron collimator taken along the line 2—2 of FIG. 1; and

FIG. 3 is a vertical longitudinal sectional view taken along line 3—3 of FIG. 1.

The neutron collimator mainly comprises four stationary shielding blocks 1-4 and two moving collimating blocks 5, and 6. All the blocks are made of stainless steel and have passages for cooling liquid (not shown). The four stationary blocks which form a tubular body, bound wall 7 of a rectangular cross-section throughway or channel 8 in which the blocks 5 and 6 are mounted. The free space between the blocks 5 and 6 is the actaual collimation passage, and the cross-section thereof can be varied by movement of the blocks 5 and 6. The rear exit orifice of the passage is at 9.

Those surfaces 10 and 11 of the collimating blocks which bound the collimating passage are oblique to the passage axis 13 from the entry 12 to the exit 9. As will be described hereinafter in greater detail, the surfaces 10 and 11 can be brought into contact with one another on the channel axis 13. A point of importance in this connection is that, unlike the prior art, the collimation channel has a tapering or pyramidal longitudinal cross-section with a definite opening angle, and a scissors-like adjustment of the blocks 5 and 6 makes it possible to adjust the opening angle to suit the particular experiment being performed. Consequently, if the block-guide mechanics are appropriately devised, the following can be provided:

(a) The entry and exit orifices of the collimation passage can be adjusted individually. For instance, the large neutron exit window of a nuclear reactor can be effectively collimated on to the small orifice of the control channels of a neutron chopper.

(b) The neutron radiation can be collimated on to the target at different distances thereof (the distance has the reference z in FIGURE 2); also, radiation intensity can be varied by altering the collimation.

As FIGURE 2 shows, the collimating blocks 5 and 6 are of sawtooth shape on the outside, and mate with the associated wall parts of the stationary blocks 3 and 4. The labyrinth gap 14 thus formed inhibits the passage of nuclear radiation. Similar means are provided in the horizontal gaps of the main channel 8 and associated walls of the blocks 1 and 2 and in the surfaces 10 and 11 of the blocks 5, 6. Thus the blocks 5, 6 are offset from one another at a place 15, to ensure that a straight gap is not left when the collimation passage is closed.

Also as can be seen in FIGURE 3, to make the horizontal gaps in the main channel proof to radiation, the stationary blocks 1 and 2 are formed with recesses 16 and 17, and the moving blocks 5 and 6 have corresponding top and bottom projections, such as shoulders 18 and 19.

The adjusting movements mentioned in (a) and (b) above are produced in the neutron collimator by cooperation between grooves and guiding pins or pegs. FIGURES 2 and 3 show the grooves 20 and 21 and the pins or pegs 22, 23. The grooves are contrived in the stationary block 2, and the pins or pegs take the form of anti-friction bearings mounted on short shafts on the bottom of the collimating blocks 5 and 6. Also visible in FIGURE 3 is the drive for the collimating blocks 5 and 6 which drive will be described hereinafter.

The scissors movement of the collimating blocks 5 and 6 is produced by the combination of lengthwise displacement of the blocks and the transverse movement produced by the grooves and pins. In this particular case, the grooves 20 and 21 are straight and extend oblique to the channel axis 13. All the grooves may be at the same angle thereto or the grooves 20 may be at an angle different from that of grooves 21. The collimation angle is the angle between the surfaces 10 and 11 of the blocks 5 and 6. This construction substantially covers case (b).

3,487,218

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Greater flexibility of the system can be obtained if, instead of the block 2 being formed with stationary grooves, it is provided with interchangeable or rotatable inserts formed with grooves. The inserts for instance in the form of plugs, have the grooves on their inner end faces.

Plugs are provided for any desired movement pattern of the collimating blocks. All the adjustments mentioned in (a) and (b) can be provided by insertion of the appropriate plugs or, if rotatable plugs are used, by rotation of the plugs. Plugs formed with grooves which curve towards the channel axis are required for one particular group of adjustmments.

The drive for the collimating blocks 5 and 6 is hydraulic and comprises actuating cylinders 24 and 25 screwed to the stationary block 1. The associated pistons operate a lever system whose construction is indicated in broken lines in FIGURES 2 and 3. Levers 26 and 27 pivoted to a spindle 28, are linked to the hydraulic pistons at 29 and are similarly connected to the collimating blocks at 30. Correspondingly, the collimating blocks have at their rear end pivot points 31 disposed in two downwardly extending projections 32 engaging in matching recesses 33 in the block 2.