RU2290665C1 - Screen for transforming penetrating radiations - Google Patents

Abstract

FIELD: engineering of constructive elements of devices for non-destructive control of materials and goods by radiation methods, possible use for detection of flaws in same in industrial and field situations, and also for detecting hazardous substances at control posts, railroad stations, in airports, customs.

SUBSTANCE: in the screen for transforming penetrating radiation, radiation transportation channels are made in form of fiber-optic scintillator units, channels are connected to form a packet in form of truncated cone or truncated pyramid, and transformer screen is made extensive along radiation expansion direction.

EFFECT: increased efficiency and spatial resolution not only in parallel, but also in conic beam, possible radiography by means of conic beam of objects of various dimensions, expanded functional capabilities of detector, registration of various types of penetrating radiation: fast neutrons, thermal neutrons, x-ray and gamma beams.

2 cl, 2 dwg

Description

The invention relates to the field of non-destructive testing of materials and products by radiation methods and can be used for their flaw detection in production and field conditions, as well as for the detection of hazardous materials at checkpoints, railway stations, airports, customs services.

Known fiber module, assembled from layers of polymer scintillating optical fibers, stacked alternately in two mutually perpendicular directions.

U.S. Patent No. 4,942,302, IPC G 01 T 3/06, 1990

The specified device has low efficiency, because does not provide two-coordinate registration of recoil protons with a range less than the cross section of a single fiber; and also has restrictions on the number of fibers in the layer and the number of layers imposed by the number of photodetectors used. The device has a limited spatial resolution, determined by the cross-section of the fiber.

Known fiber module, assembled from layers of polymer scintillating optical fibers, stacked alternately in two mutually perpendicular directions. The ends of the fibers are located in the planes of the faces of the fiber parallelepiped formed by layers of fibers. The diameter of the fibers is equal to half the mean free path of the recoil proton in the fiber material. Patent of the Russian Federation No. 2119178, IPC G 01 T 3/06, bull. No. 26, 1998

This module is difficult to implement, has a relatively low efficiency, low spatial resolution, and is designed to detect only fast neutrons.

In a portable installation for non-destructive testing of materials and products using radiation sources, characterized by a small size of the emitting region. Moreover, the radiation density of the source decreases with distance in inverse proportion to the square of the distance to the source. When the size of the investigated object, comparable with the distance to the source of radiation, the object is irradiated with a conical beam.

In this case, these analogues do not provide spatial resolution for the peripheral areas of the object.

Known detectors should be located at sufficiently large distances from the source at which the beam can be considered parallel. This decreases the performance of the control.

To make fuller use of radiation, reduce monitoring time, and reduce the activity induced in the object, the object under study and the radiation detector are located at the smallest possible distance, while the object is irradiated with a conical radiation beam.

To ensure high detection efficiency of radiation in the detector, it is necessary to use transducer screens extended along the beam.

When using known detectors, the increase in efficiency due to the thickness of the screen converter is limited by the occurring loss of spatial resolution: the higher the efficiency, the lower the spatial resolution. To achieve the highest possible detection efficiency, for example, fast 14 MeV neutrons, the screen thickness should be 10-12 cm.

When the distance between the neutron source and the screen is 0.5 m, for a detector with a screen 10 cm thick and 20 cm in diameter, the spatial resolution at the periphery of the detector will deteriorate to a value of about 1.8 cm.

Known screen transducer of penetrating radiation, made in the form of a truncated cone or a truncated pyramid with diverging capillary channels for transporting radiation, the walls of which have the shape of the side surface of a truncated cone or pyramid, or cylinder, or prism, at one end of which is located a means that is sensitive to radiation. Patent of the Russian Federation No. 2239822, IPC G 01 N 23/04, bull. No. 31, dated December 10, 2004. Prototype.

The prototype is difficult to manufacture, designed to work with an extended radiation source, in essence it is only a radiation collimator and only a radiation sensitive tool allows it to be considered a screen-converter. The prototype allows you to identify and convert only one type of radiation.

The technical result of the invention is to increase the efficiency and spatial resolution not only in parallel but also in a conical beam, the possibility of radiography with a conical beam of objects of various sizes, expanding the detector's functionality, recording various types of penetrating radiation: fast neutrons, thermal neutrons, x-rays and gamma rays .

The technical result is achieved by the fact that in the screen transducer of penetrating radiation, made in the form of a truncated cone or a truncated pyramid with diverging channels for transporting radiation, the walls of which are in the form of a lateral surface of a truncated cone or pyramid, or cylinder, or prism, on one end of which there is a means sensitive to radiation, radiation transport channels are made in the form of fiber optic scintillators, channels are arranged in a package in the form of a truncated cone or a truncated iramidy.

A means for detecting radiation with a different spectrum is located on the smaller end of the arranged packet in the form of a phosphor layer.

The invention is illustrated in figure 1 and figure 2.

Figure 1 presents the optical diagram of a radiographic detector for a conical neutron beam, where: 1 is a source of fast neutrons, 2 is a screen transformer made in the form of a fiber-optic truncated cone or a truncated pyramid, 3 is a deflecting mirror, 4 is a projection lens, 5 - image intensifier, 6 - zoom lens, 7 - CCD.

Figure 2 presents a cross section of the screen of the transducer 2, where: 8 - fiber, 9 - phosphor layer.

In order for the screen-converter 2 to be as efficient as possible, the axial lines of the fibers 8 must intersect at one point, namely in the center where the radiation source will be located, and each fiber should be in the form of a truncated cone or a truncated straight pyramid. In the latter case, the packing density of the fibers 8 in the screen-converter 2 will be 90%. When the output cross-section of the fiber is 1 × 1 mm ^{2, the} input cross-section of the fiber should be 0.8 × 0.8 mm ² .

The rectangular cross-section (about 1 × 1 mm) of the fibers 8 also provides a high (approximately 90%) packing density in the transducer screen 2. In the case of cylindrical and conical fibers, their packing density in the transformer screen 2 is lower. Below is the effectiveness of registration.

The fibers 8 of the screen transducer 2 are made of polystyrene and have a reflective sheath. The prototype model of a neutron detector has a screen with a cross section of 150 × 150 mm.

The length of the screen along the neutron beam is 100 mm. The optical image that occurs in the transducer screen 2 as a result of irradiation is transferred through the fibers 8 to the surface of the transducer screen 2, facing the deflecting mirror 3, which is transmitted to the projection lens 4, and then with its help to the image amplifier 5 and further using a zoom lens 6 on the CCD matrix 7.

Unlike other types of known receivers, a device with a fiber-optic screen-converter 2 is more universal, since its design makes it possible to use other types of screens instead of it: dispersed screens for detecting fast neutrons, as well as luminescent screens for thermal neutrons and x-ray radiation. These screens have a thickness of several tens of microns to several millimeters. They are installed in the focal plane of the projection lens 4, which coincides with the large end face of the conical screen of the transducer 2.

When radiography, the source of fast neutrons 1 is located at the point of intersection of the axes of all fibers 8. The test sample (not shown) is installed between the source 1 and the screen transducer 2.

When registering fast neutrons, the fibers 8 of the screen-converter 2 are made of luminescent polystyrene. When registering thermal neutrons - from luminescent polystyrene with boron additives. When registering x-ray and gamma radiation, fibers 8 are made of transparent scintillators designed to detect these types of radiation: germanium tungstate, yttrium garnet, etc.

To ensure a tight packing of the fibers in the screen transducer 2, the cross section of the fiber 8 should be square. The size of the cross section is determined taking into account the screen size (150 × 150), the number of elements of the CCD matrix 7 (560 × 768), as well as the spatial resolution of the detector (approximately 1.5 fiber thickness). For these sizes, the fiber cross-section should be about 1 × 1 mm ² .

The fibers 8 of the screen transducer 2 are made of polystyrene and can have a reflective sheath. Reflective sheath can be made in the form of a thin layer of silver paint. The presence of the shell provides a complete internal reflection of the light flash when it propagates along the fiber 8.

The prototype model of the neutron detector has a screen transducer 2 with an input section of 150 × 150 mm and an output section of about 200 × 200 mm. The length of the screen Converter 2 is 100 mm The optical image that arises in the transducer screen 2 as a result of irradiation with fast neutrons is transferred through the fibers 8 to the surface facing the projection lens 4, and then with its help - to the image intensifier 5 and then using the scaling lens 6 to the CCD 7.

To detect fast neutrons, polymer optical fibers 8 are usually used, in particular from luminescent polystyrene.

When registering thermal neutrons - from luminescent polystyrene with boron additives. When registering x-ray and gamma radiation, optical fibers are made of transparent scintillators designed to detect these types of radiation: bismuth germanate, yttrium garnet, etc.

A means for detecting radiation located on the smaller end of the arranged packet in the form of a phosphor layer 9 is made of known luminescent materials that are sensitive to various types of radiation.

To detect thermal neutrons, the phosphor layer 9 is made of light compositions: ⁶ LiF ZnS: Ag or Gd ₂ O ₂ S: Tb, or ¹⁵⁷ Gd ₂ O ₂ S: Tb, or ¹⁰ BZnS: Ag.

In the case of using light composition ⁶ LiF ZnS: Ag, the nucleus of the lithium isotope captures the thermal neutron and emits triton, and alpha particles, which cause the scintillation glow of zinc sulfide.

In the case of using the light composition Gd ₂ O ₂ S: Tb or ¹⁵⁷ Gd ₂ O ₂ S: Tb, the ¹⁵⁷ Gd nucleus captures a neutron and emits a conversion electron, which excites scintillation emission in the light composition. To record x-ray and gamma rays, the light composition of Gd ₂ O ₂ S: Tb was used. In such a light composition, under the influence of x-ray and gamma rays, charged particles arise: electrons and positrons, which cause the scintillation glow of Gd ₂ O ₂ S: Tb. The resulting glow through the fibers 8 is transmitted to the larger end of the screen transducer 2, facing the projection lens 4, and then with its help - to the image intensifier 5 and then using the scaling lens 6 to the CCD matrix 7.

The registration efficiency is provided by the length of the screen transducer 2 along the direction of radiation propagation.

To register objects with different dimensions, it is necessary to manufacture several transformer screens 2 with different angles between the generators. In this case, the distance from the radiation source 1 to the end of the screen-converter 2 also changes.

When changing the distance between the radiation source 1 and the sample, it is necessary to use a screen-converter 2 with an angle between the generators φ, which is determined by the transverse size of the screen end S and the distance from it to the source L: φ = S / L. This provides the opportunity to explore objects of various sizes.

Claims (2)

1. The screen transducer of penetrating radiation, made in the form of a truncated cone or a truncated pyramid with diverging channels for transporting radiation, the walls of which are in the form of a side surface of a truncated cone, or a pyramid, or a cylinder, or a prism, on one end of which there is a radiation sensitive tool characterized in that the radiation transportation channels are made in the form of fiber-optic scintillators, the channels are arranged in a package in the form of a truncated cone or a truncated pyramid, and the screen verters made extended along the direction of propagation. 2. The penetrating radiation transducer screen according to claim 1, characterized in that the means sensitive to radiation with a different spectrum is located on the smaller end of the arranged packet in the form of a phosphor layer.

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