GB1597077A

GB1597077A - Tube for irradiation equipment

Info

Publication number: GB1597077A
Application number: GB1292878A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1977-04-04
Filing date: 1978-04-03
Publication date: 1981-09-03
Also published as: FR2386891A1; FR2386891B1; DE7714834U1; JPS6128120B2; CA1097436A; JPS53123691A; CH614549A5; DE2721043A1; NL7803554A; DE2721043C2

Abstract

Irradiation devices contain in the region of the emerging radiation a device which limits the cross-section of said radiation. As a matter of simplicity, said device is constructed as a tube, whereas it was previously necessary to provide a set of tubes of different cross-sections when the device was provided for the purpose of irradiating surfaces having different cross-sections. The novel tube contains four backing plates (32, 33, 34, 35) which bound the exit opening (47) of the device and can be displaced symmetrically relative to the centre of said opening. Mounted on each backing plate is a vertical side wall (53, 54, 55, 56) in the lateral extension of which there are arranged lamellae (65, 66, 67, 68) which can be erected parallel to the side wall or can be folded back onto the backing plate. It is possible in this way to vary the cross-section of the tube over a wide range by displacing the backing plates and erecting the lamellae required for the purpose of forming a closed tube. <IMAGE>

Description

(54) TUBE FOR IRRADIATION EQUIPMENT (71) We, BBC BROWN, BOVERI & BR< COMPANY LIMITED, a Company organised under the laws of Switzerland, of CH-5401, Baden, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The present invention relates to a tube for irradiation equipment for stopping down an emergent beam, comprising a base-plate with a central aperture, and intended for attaching to the irradiation equipment, as well as four carrier plates, each of which possesses a limiting edge and a sliding edge located at right angles to each other, which carrier plates are located parallel to the baseplate, the limiting edge of each carrier plate resting against the sliding edge of an adjacent carrier plate, and each of the two mutually opposite pairs of carrier plates being displaceable, parallel to the direction of their sliding edges and symmetrically with respect to the centre of the transmission aperture defined by the limiting edges, for the purpose of continuously varying that transmission aperture, during which displacement each of the displaced carrier plates carries with it the carrier plate, resting against the limiting edge of the former plate, parallel to the direction of the limiting edge of the latter plate.

The term irradiation equipment is in particular applied, in the text which follows, to particle accelerators, electron accelerators, gamma irradiation equipment and X-ray equipment. For therapeutic and diagnostic use it is essential to limit the cross-section of the beam emerging from the irradiation equipment to the requisite minimum and to screen off the radiation effectively. at the sides, between the outlet aperture of the irradiation equipment and the surface of the article to be irradiated. At the same time, when using an electron accelerator the proportion of the secondary X-rays and scattered electrons produced by the high speed electrons in the diaphragm system, and manifesting itself outside the actual field of irradiation, should be kept as low as possible in order to reduce the side-effect of the irradiation.

As a further condition, it should be possible to choose as many variations of field dimensions as possible, within the range of field sizes imposed by the irradiation equipment. For this reason, a variety of devices have also already been disclosed, and are used, with which the cross-section of the radiation can be stopped down, and the beam can be screened off laterally.

A first known device consists of a set of diaphragms, of which each is firmly fixed to a tube. The diaphragm and tube can be fixed detachably to the casing of the electron accelerator. For example, the diaphragms are in the form of thick lead sheets which have a central aperture which limits the cross-section of the emergent electron beam. The tube serves to stop down the electron beam, and screen it off laterally. This relatively simple device suffers from several disadvantages. It is only possible to adjust the beam to fixedly predetermined cross-sections, and the exchangeable diaphragms, with attached tube, require a great deal of storage space, are expensive, are difficult to handle because of their weight, and must, whenever a change in beam cross-section is necessary, be exchanged, thereby consuming a relatively large amount of time.

Another known device comprises a baseplate on which several diaphragms are located in succession in the direction of the beam. Each of these diaphragms has several diaphragm blocks continuously displaceable at right angles to the direction of the beam.

This device permits continuous variation of the diaphragm cross-section and hence of the effective electron beam and does not require an additional tube. A disadvantage of this device is that because of the diaphragms being arranged in succession, a part of the fast electrons is screened off near the object to be irradiated, as a result of which a relatively high proportion of gamma radiation and secondary electrons is liberated, which must be avoided particularly in the case of radiation therapy, and that if the diaphragm aperture is small the diaphragm blocks project beyond the cross-section of the useful electron beam, which makes it difficult, or even impossible, to introduce the device into recesses and, for example, to irradiate the armpits or the throat.

Further, a device is already known which possesses a variable diaphragm built into the accelerator casing. and corresponding tubes of different cross-section which can be attached to the accelerator housing. In this device. the advantages of the variable diaphragm can only be utilised partially because the diaphragm must necessarily be set to the dimensions of the available tubes. Furthermore, this device suffers from all disadvantages already mentioned above for exchangeable tubes.

Accordingly. it is the object of the present invention to provide a tube for irradiation equipment, which tube is of continuously variable cross-section, and in which the external dimensions of the free end are only slightly greater than the dimensions of the free aperture at the end of the tube, in order to permit, as far as possible, unhindered approach to the object to be irradiated.

According to the invention, this object is achieved by means of a tube of the initially described type, which is characterised in that on each carrier plate there are provided a side wall and at least one lamella, which side wall projects, at the side of the limiting edge which abuts the sliding edge, at right angles from the carrier plate and which lamella or lamellae is or are pivotably fastened in the region of the limiting edge and can be laid down on the carrier plate or be erected, as an extension of the side wall, in order to form a side wall of a tube of variable cross-section, this side wall being of uniform height when formed by two or more lamellae.

The new tube can be adjusted to any quadrangular cross-section with dimensions between a minimum square, the side length of which corresponds to the length of one side wall, and a maximum square, the side length of which corresponds to the length of one side wall and of the corresponding lamellae. Because the lamellae not required to form the tube side walls are laid down on the carrier plates, the external cross-section of the tube is only slightly greater than the internal cross-section, thereby permitting unhindered introduction of the tube into recesses.

For simpler manual adaptation ofthe tube walls to the selected cross-section, a plurality of magnets can be fixed to each carrier plate, which magnets hold the lamellae laid down on the carrier plate, and a spring engages at the base of each lamella, in order to urge the lamellae, if released from the holding magnets, into the vertical position.

In a preferred embodiment, further measures are provided which, on adjusting the tube cross-section, automatically raise the lamellae or lay them down on the carrier plate. For this purpose there is, in the first place, fixed to each carrier plate, along the extension of the limiting edge, a tongue.

which carries on its end projecting onto the adjacent carrier plate, a stop of which one side face rests against the adjacent erect lamella and prevents its pivoting into the laid-down position, whilst its other side face has a wedge-shaped chamfer and is pushed under the adjacent laid-down lamella and, on displacing the carrier plate in order to increase the transmission aperture, lifts this next lamella off the holding magnet. Furthermore, an electromagnetic device (referred to in the description below as an electromagnetic switch device) may be located on each side wall, which device possesses a lever which, after the carrier plate has been displaced in order to reduce the transmission aperture, lays down the lamella adjoining the side wall, on the adjoining carrier plate, against that carrier plate, i.e.

into the laid-down position.

A preferred embodiment of the tube according to the invention is described below with reference to the accompanying drawings.

In these: Figure 1 shows the schematic representation of an accelerator window with diaphragms and a tube of the hitherto conventional type, Figure 2 shows the plan view of an embodiment of the new tube, Figure 3 shows the section along line Ill-Ill through the tube according to Figure 2, Figure 4 shows the side view, partially in section, of the tube according to Figure 2, viewed in the direction of the arrow IV, and Figure 5 shows the schematic representation of a contact switch in the tube baseplate.

Figure 1 shows schematically the aperture of an electron accelerator with diaphragms for the electron beam, and a tube. Accelerator 10 possesses a window 11 which is intended to transmit a narrow electron beam.

At a distance from the window, in the direction of the emergent electron beam, are located a first scatterer 12 and a main scatterer 13, which broaden the narrow electron beam. In order to limit the maximum diameter of the electron beam issuing from the accelerator casing 14, a first diaphragm 16 is fixed within the casing. Furthermore, a screen 17 is provided, which screens off an anterior diaphragm 18, located in the region of the aperture of the casing, and possesses a central aperture 19 through which the electron beam emerges from the accelerator casing. This central aperture is framed by a holder device 21, into which an exchangeable tube 22 is inserted.

In order to adapt the cross-section of the electron bcam emerging from the tube to the intended use it is possible to use, in this arrangement, anterior diaphragms 18 of different free internal cross-sections or a fixedly built-in anterior diaphragm with a variable free internal cross-section, as well as to use exchangeable tubes matching these crosssections.

The embodiment of the tube of variable cross-section, according to the invention, shown in Figures 2 and 3 is built up on a baseplate 30. The baseplate is intended for fixing to the screen 17 and has a large central aperture 31. Four carrier plates 32, 33, 34 and 35 are located on the baseplate. Each carrier plate has at least two edges located at right angles to one another, namely a limiting edge 37, 38, 39 or 40 and a sliding edge 42, 43, 44 or 45. The carrier plates are so located relative to one another that the parts of the limiting edges which adjoin the sliding edges form the framing of a transmission aperture 47 and the remaining part of each limiting edge rests against the sliding edge of an adjacent carrier plate.The carrier plates can be displaced parallel to the plane of the baseplate by means of a displacement device customary for adjustable anterior diaphragms, which device is known to those skilled in the art and is therefore only indicated with broken lines 50, 51. This displacement device permits each of the two pairs of carrier plates, formed by mutually opposite carrier plates, 32, 34 or 33, 35, to be displaced symmetrically to the centre of the transmission aperture 47, independently of the other pair of carrier plates, and in the direction of its sliding edge. During this displacement, the two carrier plates of the other pair of carrier plates are carried with the first pair so that the contact between adjacent carrier plates and the framing of the transmission aperture always remains preserved.If, for example, the carrier plates 33, 35 are pushed apart, the carrier plate 34 follows the displacement of the carrier plate 33 and the carrier plate 32 follows the carrier plate 35. In this way, the square transmission aperture 47 shown in Figure 2 can be reduced and enlarged or be reshaped into an upright or horizontal rectangle of any desired dilnellsions.

As can be seen most clearly in Figure 2, a side wall 53, 54, 55 or 56 projects from each carrier plate. Each side wall is located along the limiting edge and one of its lateral edges terminates in the corresponding sliding edge of the carrier plate. Each side wall stands at right angles to the carrier plate and the four side walls form a closed tube if the four carrier plates are pushed together sufficiently far so that their limiting edges frame the smallest envisaged transmission aperture. In the lateral extension of each side wall, and above the limiting edge, there is additionally fixed a thin shaft 60, 61, 62 or 63. On this shaft a plurality of lamellae are pivotably mounted, of which for clarity, only lamellae 69 to 71 on the shaft 60 of the carrier plate 32 are identified by reference numbers.All the lamellae can be pivoted between a laid-down position in which they are located virtually parallel to the surface of the carrier plate, and an erect position, in which they are located parallel to the side wall. In Figures 2 and 3, the lamellae 65 to 68 on the carrier plate 32 (and the corresponding lamellae of the other carrier plates) are drawn in the erect position, and the lamellae 69, 70 and 71 on the carrier plate 32 (as well as the corresponding lamellae of the other carrier plates) are drawn in the laid-down position.

As will be immediately obvious to anyone skilled in the art, it is possible, by erecting those lamellae which are located along the parts of the limiting edges which form the framing of the transmission aperture, to form a tube the internal cross-section of which is virtually of the same size and the same shape as the cross-section of the transmission aperture. Because the lamellae not required for broadening the tube walls remain in their laid-down position, the external cross-section of the free end of the tube is not much larger than its internal cross-section, that is to say the cross-section of the electron beam which emerges through the tube. This construction makes it possible to introduce the free end of the tube, without hindrance by projecting side pieces, even into recesses.As has already been described above, this is particularly important when using irradiation equipment in medicinal diagnostics and therapy, for example if the tube is to be brought into an armpit or against the neck of a patient.

If the transmission aperture is set to a dimension which does not correspond to the grid predetermined by the lateral length of the lamellae, the last erect lamella of each side wall projects partially beyond the corner of the tube. This apparent disadvantage is virtually of no importance if the lateral length of the lamellae is not great.

As can be seen best in Figure 4, each lamella consists of a steel strip 75, at one lengthwise end of which is located a lamella base 76, i.e. a base member or "foot" of the lamella, whilst in the region of its other lengthwise end there are located several absorption pieces 77, 78 and 79. The lamella base preferably consists of bearing metal and has a bore 81, by means of which the lamella is pushed onto the shaft 60. The absorption pieces are in particular intended to absorb secondary X-rays and stray electrons. In a combination which is particularly suitable for this purpose, the absorption pieces 77, 78 and 79 consist of light metal, steel or Antikorrodal.

In the embodiment of the new tube shown in the figures, a plurality of small permanent magnets is located on each carrier plate, amongst which. for clarity. only magnets 83 to 89 on carrier plate 32 are identified by reference numbers. These permanent magnets are provided in order to hold the lamellae which have been laid down on the carrier plate.

As may be seen from Figure 2, the lamellae overlap in cross-section. The result of this is that the tube wall composed of adjacently located lamellae is "tight" and that none of the erect lamella can be laid down as long as the last erect lamella is locked in its position. For this purpose, a thin tongue 92 is fixed to each carrier plate (Figure 4) which tongue projects, in the extension of' the limiting edge 38, beyond the adjacent carrier plate 32, and carries a stop 90. This stop rests, with one of its sides, against the particular last lamella 68 of a tube wall, and thereby prevents this lamella from being pivoted from the erect position into the laid-down position. Preferably, this stop is wedge-shaped in the direction of the sliding edge.This makes it possible. when displacing a pair of carrier plates in order to enlarge the cross-section of the framed transmission aperture 47, to slide the stops, fixed to the two displaced carrier plates, with their wedge-shaped surfaces under the lamellae 69 of the adjacent carrier plates 32 and to lift these lamellae off the permanent magnets 87.

To each lamella there is allotted a spring 91 which engages in the region of the base of the lamella (Figure 4) and pivots it into the erect position as soon as it has been released from the holding magnet.

In the shown embodiment of the tube there is furthermore located, on the outside of each side wall 54, an electromagnetic switch device 93 which comprises a lever 94 which has a virtually vertical rest position and can be pivoted through about 90 into the working position shown with broken lines in Figure 4. After displacing one pair of carrier plates in order to reduce the crosssection of the transmission aperture, the switch devices on the side walls of the displaced carrier plates are actuated, whereupon in each case the last lamella of the adjacent tube wall is pivoted into its laiddown position and is held by the corresponding permanent magnet.Because of the mutual overlap of the lamellae. which has already been mentioned above. laying down one lamella results in all further lamellae autc,rnatically being laid down in the direction facing away from the corresponding side wall. This ensures that on reducing the crosssection of the transmission aperture all lamellae no longer required to form the tube have been laid down on the corresponding carrier plate.

As has already been described above, it is necessary, when using irradiation equipment for diagnostics and therapy, to bring the free end of the tube as close as possible to the object or to the patient. Because of the large weight of the entire installation, special drive motors are used for the required displacement motions or rotary motions of individual parts of the equipment. In order to ensure that these drive motors are switched off as soon as the tube has been brought to a minimum distance from the patient, special proximity switches are used. In a first embodiment of such a safety device, an insulated electrode 100 is fixed to the free end of each side wall. The electrodes, numbering four in total, are preferably wired electrically in parallel, and form a capacitor with the tube.

This capacitor is connected, in a known manner, to an HF measuring bridge which is put out of balance as the tube approaches a patient and switches off the feed voltage for the drive motors, via a comparator/trigger circuit, when a presettable unbalance has been reached.

In another embodiment of this safety device, the baseplate of the tube is fixed in an insulated manner to the accelerator casing, and the entire tube is used as a capacitor electrode.

In yet another embodiment, the safety device is actuated not on approaching. but only on touching, the object to be irradiated.

As is shown schematically in Figure 5, this embodiment uses an insert 102 which is located parallel to the baseplate 30 and can be inserted into the holding device 21. A stud bolt 103, which passes through a corresponding bore in the baseplate 30, is fixed to each of the four corners of this insert. In addition, an electrical switch is provided, of which one contact 104 is fixed by means of an insulating disc 105 to the baseplate, whilst its other contact 106 is fixed by means of an insulating disc 107 to the free end of the stud bolt.

Around each stud bolt is inserted, between the insert 102 and the baseplate 30, a spring 108 which presses the baseplate away from the insert and presses the contact 104 onto the contact 106. The four switches are preferably wired electrically in series. When, on moving or turning the installation or the patient, the tube is touched and compressed or tipped against the force of one or more springs, the contacts of the corresponding switches are separated from one another and a safety circuit is broken and switches off the feed voltage for the drive motors.

In an embodiment of the new tube used in practice the side length of each side wall is 4 cm. which makes it possible to telescope the carrier plate sufficiently that the minimum tranmission aperture 47 corresponds to a square with sides 4 cm long. Furthermore, with this embodiment 16 lamellae are located on each carrier plate, the side length of each lamella being I cm. Accordingly, the maximum transmission aperture can be set to correspond to a square with sides 20 cm long.

As has already been described in detail above, any quadrangular transmission aperture with dimensions lying between the two stated extreme values can be set up with the new tube. In this embodiment, the height of the side walls and lamellae is 17 cm.

It has already been mentioned that the preliminary diaphragm 18 must be set to the cross-section of the tube. Since the object to be irradiated determines the cross-section of the tube, this tube cross-section is first set up.

This setting can be effected manually or by means of servo-motors. Preferably, an adjustable anterior diaphragm is used, and the cross-section of the tube as well as the aperture of the preliminary diaphragm are picked up by actual value indicators, for example potentiometers. The actual values are then compared in comparators and the resulting error signal is used to control the diaphragm servo-motors until the actual values for the diaphragm aperture correspond to the actual values of the tube crosssection. It will be understood that in this way it is possible to set up various predetermined or even arbitrary relations of tube crosssection to diaphragm aperture.

In a further embodiment of the new tube, an anterior diaphragm 18, forming part of the accelerator, is rendered unnecessary. In this embodiment, an increased distance is provided for between the baseplate and the carrier plates, and diaphragm blocks are mounted on those surfaces of each carrier plate which face the baseplate; alternatively, the carrier plates are constructed so as to incorporate diaphragm blocks. It will be appreciated that, with this embodiment, whenever there is an adjustment of the tube cross-section, there is also an adjustment of the effective diaphragm aperture.

Finally. it is also possible to adjust the tube cross-section and the diaphragm aperture by means of remote control from an operating panel or from a data store. Appropriate circuits are known to all those skilled in the art and will therefore not be described in detail.

WHAT WE CLAIM IS: 1. A tube for irradiation equipment for stopping down an emergent beam, comprising a baseplate with a central aperture, and intended for attaching to the irradiation equipment. as well as four carrier plates, eacfl ot which possesses a limiting edge and a sliding edge located at right angles to each other, which carrier plates are located parallel to the baseplate, the limiting edge of each carrier plate resting against the sliding edge of an adjacent carrier plate, and each of the two mutually opposite pairs of carrier plates being displaceable, parallel to the direction of their sliding edges and symmetrically with respect to the centre of the transmission aperture defined by the limiting edges, for the purpose of continuously varying that transmission aperture, during which displacement each of the displaced carrier plates carries with it the carrier plate, resting against the limiting edge of the former plate, parallel to the direction of the limiting edge of the latter plate, wherein, on each carrier plate there are provided a side wall and at least one lamella, and each side wall projects, at the side of the limiting edge which abuts the sliding edge, at right angles from the carrier plate, and which lamella or lamellas is or are pivotably fastened in the region of the limiting edge and can be laid down on the carrier plate or be erected, as an extension of the side wall, in order to form a side wall of a tube of variable cross-section, this side wall being of uniform height when formed by two or more lamellae.

2. A tube according to claim 1, wherein each lamella comprises a a steel strip at one end of which is fixed a lamellar base member, which has a bore, by means of which the lamella may be pushed onto a shaft, whilst in the region of its other end are fixed several absorption pieces for secondary X-rays and stray electrons.

3. A tube according to claim 1, wherein a plurality of magnets intended for holding the lamellae laid down on the carrier plate is fixed to each carrier plate and a spring engages at each lamella base in order to urge the lamella, if released from the holding magnets, into the vertical position.

4. A tube according to claim 1, wherein a tongue is fixed to each carrier plate, along the extension of the limiting edge, which tongue carries, on its end projecting onto the adjacent carrier plate, a stop, of which one side face rests against the adjacent erect lamella to prevent it from being laid down unintentionally, whilst its other side face has a wedge-shaped chamfer and is pushed under the next lamella so that, when the carrier plate is displaced in order to enlarge the transmission aperture, the wedge serves to lift this next lamella off the holding magnet.

5. A tube according to claim 1, wherein an electromagnetic device is located on each side wall, which device possesses a lever which, after a displacement of the carrier plate in order to reduce the transmission aperture lays down the lamella, present on the adjacent carrier plate and adjacent to the side wall, against the carrier plate.

6. A tube according to claim 1. wherein an insulated electrode for a capacitive proximity switch is fixed to the free end of each side wall, which electrode forms, with the side wall, a capacitor which is connected to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. on each carrier plate, the side length of each lamella being I cm. Accordingly, the maximum transmission aperture can be set to correspond to a square with sides 20 cm long. As has already been described in detail above, any quadrangular transmission aperture with dimensions lying between the two stated extreme values can be set up with the new tube. In this embodiment, the height of the side walls and lamellae is 17 cm. It has already been mentioned that the preliminary diaphragm 18 must be set to the cross-section of the tube. Since the object to be irradiated determines the cross-section of the tube, this tube cross-section is first set up. This setting can be effected manually or by means of servo-motors. Preferably, an adjustable anterior diaphragm is used, and the cross-section of the tube as well as the aperture of the preliminary diaphragm are picked up by actual value indicators, for example potentiometers. The actual values are then compared in comparators and the resulting error signal is used to control the diaphragm servo-motors until the actual values for the diaphragm aperture correspond to the actual values of the tube crosssection. It will be understood that in this way it is possible to set up various predetermined or even arbitrary relations of tube crosssection to diaphragm aperture. In a further embodiment of the new tube, an anterior diaphragm 18, forming part of the accelerator, is rendered unnecessary. In this embodiment, an increased distance is provided for between the baseplate and the carrier plates, and diaphragm blocks are mounted on those surfaces of each carrier plate which face the baseplate; alternatively, the carrier plates are constructed so as to incorporate diaphragm blocks. It will be appreciated that, with this embodiment, whenever there is an adjustment of the tube cross-section, there is also an adjustment of the effective diaphragm aperture. Finally. it is also possible to adjust the tube cross-section and the diaphragm aperture by means of remote control from an operating panel or from a data store. Appropriate circuits are known to all those skilled in the art and will therefore not be described in detail. WHAT WE CLAIM IS:

1. A tube for irradiation equipment for stopping down an emergent beam, comprising a baseplate with a central aperture, and intended for attaching to the irradiation equipment. as well as four carrier plates, eacfl ot which possesses a limiting edge and a sliding edge located at right angles to each other, which carrier plates are located parallel to the baseplate, the limiting edge of each carrier plate resting against the sliding edge of an adjacent carrier plate, and each of the two mutually opposite pairs of carrier plates being displaceable, parallel to the direction of their sliding edges and symmetrically with respect to the centre of the transmission aperture defined by the limiting edges, for the purpose of continuously varying that transmission aperture, during which displacement each of the displaced carrier plates carries with it the carrier plate, resting against the limiting edge of the former plate, parallel to the direction of the limiting edge of the latter plate, wherein, on each carrier plate there are provided a side wall and at least one lamella, and each side wall projects, at the side of the limiting edge which abuts the sliding edge, at right angles from the carrier plate, and which lamella or lamellas is or are pivotably fastened in the region of the limiting edge and can be laid down on the carrier plate or be erected, as an extension of the side wall, in order to form a side wall of a tube of variable cross-section, this side wall being of uniform height when formed by two or more lamellae.

an HF measuring bridge.

7. A tube according to claim 1, wherein, to form a capacitive proximity switch, the entire tube is fixed in an insulated manner to the housing of the irradiation equipment and is connected to an HF measuring bridge.

8. A tube according to claim 1, wherein, to form a contact switch. the tube is additionally provided with a plate-like insert which is attachable to the casing, from which insert there project at least three stud bolts, the baseplate having bores for these stud bolts to pass through and, in the region of these bores. contacts located on insulating discs which contacts co-operate with contacts which are fixed by means of insulating discs to the free ends of the stud bolts, and wherein there are provided springs, located between the plate-like insert and the baseplate, which press the baseplate away from the plate-like insert and, in order to close the contact switch, press the contacts fixed to the baseplate onto the contacts fixed to the stud bolts.

9. A tube for irradiation equipment for stopping down an emergent beam, substantially as hereinbefore described with reference to and as shown in Figures 2 to 5 of the accompanying drawings.