Fibre optic detector for x-ray systems

Abstract

FIELD: nuclear engineering.SUBSTANCE: invention relates to the field of scintillation equipment intended for recording ionizing radiation. A fibre optic detector for radiographic units includes a scintillation crystal matrix, optical fibres, a photodetector, and electronics, wherein the scintillation crystal matrix consists of scintillation crystals with a cross-sectional area equal to 2.25 mm2 and a pitch between crystals of 1.55 mm; an optical light guide is attached to the scintillation crystal matrix, which consists of optical fibres; the centres of the scintillation crystals coincide with the centres of the optical fibres; the diameter of the optical fibre is less than the transverse size of the scintillation crystal; the sensitive area of each PIN photodiode attached to the optical fibre completely covers the end of the fibre; the length of the ring memory buffer in the reading electronics is 4096 words at a data arrival frequency of 50 MHz.EFFECT: increasing the coordinate resolution, light acquisition, the number of recorded frames and simplifying the assembly of the detector.1 cl, 1 dwg

Description

[0001] The invention relates to scintillation technology, specifically to high-speed scintillation detectors designed to detect ionizing radiation. Such scintillation detectors are intended for fundamental research in elementary particle physics and for solving applied problems. They can be used in radiography using bremsstrahlung of high-energy particles for research purposes to analyze the internal structure of objects with large optical thicknesses, and can also be used in radiography of large objects, such as during inspection of trucks, railway containers, and sea containers.

[0002] The discovery of X-ray imaging made it possible to study the internal structure of an object without destroying it. When passing through substances of varying density, X-rays are attenuated differently, allowing for a shadow image of the object to be obtained. There are applications requiring the study of objects with large optical thicknesses. For such objects, gamma rays with energies of several megaelectronvolts are used. Assemblies of heavy scintillator crystals are widely used for highly efficient gamma ray detection. The light signal from the interaction of gamma rays with the scintillator material is recorded by various photodetectors. In particle physics, photodetectors are typically placed on the end of the scintillator, while in applied applications, photodetectors are placed outside the ionizing radiation region using various optical or fiber-optic systems.

[0003] Public utility model RU 190405 U1 is known from the prior art. The system for recording shadow X-ray images comprises a matrix screen-converter consisting of scintillator crystals, adjacent at their sides and isolated from each other by a reflective material. Each scintillator crystal is equipped with its own wavelength-shifting optical fiber and photodetector. The number and relative positions of the scintillator crystals correspond to the number and relative positions of the photodetectors. The wavelength-shifting optical fiber of each scintillator crystal is connected by a transport optical fiber to a correspondingly located photodetector.

[0004] The disadvantages of this system include insufficient coordinate resolution for research purposes, allowing for a more detailed analysis of the internal structure of objects, and the technological complexity of manufacturing scintillator crystals. Each scintillator crystal has a groove into which a wavelength-shifting optical fiber is glued, but this technology is difficult for scintillator crystals with a cross-sectional area of ​​less than 2.25 mm. 2 , since the groove walls with such dimensions will be thin and fragile.

[0005] The closest solution is the "Highly Efficient Multi-Frame Registration System" presented in patent RU 2852198 C1. The multi-frame X-ray image registration system comprises a matrix screen converter, designed as a multi-element scintillation screen consisting of grooveless crystals. Nine optical fibers are bonded perpendicular to the end of each crystal and connected to image registration modules based on matrix photodetectors (hereinafter referred to as MPDs) configured for different response times, three for each MPD.

[0006] However, this solution has the following disadvantages: low light signal acquisition value, since the collected scintillation light from the crystals is divided into 9 optical fibers; the use of matrix photodetectors, in which the sensitive area consists of many pixels (cells).The size of a single cell is several micrometers, causing the optical fiber to illuminate several thousand cells, which leads to an increase in noise in direct proportion to the square root of the number of cells, consequently reducing the signal-to-noise ratio and decreasing the magnitude of the recorded signal; the number of recording frames is limited to three matrix photodetectors; the complexity of manufacturing a fiber-optic transmission line, since high precision positioning of the optical fibers in the fiber-optic transmission line is required to prevent light transfer between crystals, and aluminum sputtering on the optical fibers is necessary to transfer light from one optical channel to another.

[0007] The technical result of the proposed invention consists in increasing the coordinate resolution, light acquisition, the number of recorded frames and simplifying the technological assembly of the detector.

[0008] Improvement of coordinate resolution is achieved by using scintillation crystals with a small cross-sectional area of ​​2.25 mm 2, and a crystal pitch of 1.55 mm. The collected light signal is increased by individually reading the optical fiber channels, as well as by using a PIN photodiode for each optical fiber. An increase in the number of frames to ten is achieved by using individual PIN photodiodes and a circular memory buffer in the readout electronics with a length of 4096 words at a data receipt rate of 50 MHz (the number of frames can be increased by installing the required memory capacity or by reducing the data receipt rate). Simplification of the assembly process is achieved by eliminating wavelength-shifting fibers and using an optical fiber consisting of 1 mm diameter optical fibers assembled so that the centers of the scintillator crystals coincide with the centers of the optical fibers.Also, because the optical fiber diameter is smaller than the transverse dimension of the scintillation crystal, high precision connection positioning is not required (the optical fiber diameter is 1 mm, meaning the optical fiber is 0.5 mm smaller than the transverse dimension of the crystal). Furthermore, this optical fiber assembly allows for the fibers to be routed to the opposite side of the matrix, depending on the configuration of the optical fibers and photodetectors.

[0009] Fig. 1 shows the elements of the fiber optic detector, where 1 is the gamma-quantum flux, 2 is the object under study, 3 is the scintillation crystal matrix, 4 is the optical light guide; 5 are the optical fibers; 6 are the PIN photodiodes; 7 is the readout electronics.

[0010] The detector operates as follows. A stream of gamma quanta 1 passes through the object being studied 2 and strikes a scintillation crystal matrix 3, which consists of individual scintillation crystals. The side faces of the scintillation crystals are covered with a light-insulating aluminum coating to isolate the crystals from each other. To enhance the light signal, the end of the matrix where the gamma quanta fall is covered with a reflective aluminum layer. When gamma quanta interact with the scintillation material, scintillation light is generated. This light is transmitted via optical fiber 4 and optical fibers 5 to PIN photodiodes 6, the sensitive area of ​​which completely covers the end of the fiber. The PIN photodiodes convert the light signal into an electrical signal, which is processed and digitized by reading electronics 7.

[0011] Example of the invention. A gamma-ray beam 1 passes through the object under study 2 and hits a scintillation crystal matrix 3. The scintillation crystal matrix 3 consists of single scintillation crystals with a cross-sectional area of ​​2.25 mm 2, and 35 mm long, assembled in a 16x16 matrix with a pitch of 1.55 mm between the crystal centers. The interaction of gamma quanta with the scintillation substance produces scintillation light, which is collected using optical fiber 4, consisting of individual optical fibers with a fiber diameter of 1 mm and a length of 15 cm and optical fibers 5 with a diameter of 1 mm and a length of 4 m, which are arranged in such a way that the center of a single optical fiber coincides with the center of the end of the scintillation crystal. Then, the scintillation signal is transmitted to PIN photodiodes, the sensitive area of ​​​​them completely covers the end of the fiber, they convert it into an electrical signal. The electrical signal is processed and digitized by reading electronics 7. The length of the circular memory buffer in the reading electronics is 4096 words at a data receipt frequency of 50 MHz, which ensures the registration of up to ten frames.

Claims

A fiber optic detector for X-ray imaging systems, comprising a scintillation crystal matrix, optical fibers, a photodetector, and electronics, characterized in that the scintillation crystal matrix consists of scintillation crystals with a cross-sectional area equal to 2.25 mm 2 , and a pitch between crystals of 1.55 mm, an optical fiber is attached to the matrix of scintillation crystals, which consists of optical fibers, the centers of the scintillation crystals coincide with the centers of the optical fibers, the diameter of the optical fiber is less than the transverse size of the scintillation crystal, the sensitive area of ​​​​each PIN photodiode attached to the optical fiber completely covers the end of the fiber, while the length of the ring memory buffer in the reading electronics is 4096 words at a data receipt frequency of 50 MHz.

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