RU59268U1 - MULTI-LAYER RADIATION DETECTOR - Google Patents

Abstract

The utility model relates to the field of analysis of materials, specifically to the study or analysis of objects by radiation methods for the detection of radioactive materials and sources. The technical result of the utility model is to expand the energy range for detecting penetrating radiations and their types, determine the location and direction of movement of the radiation source, identify it or determine the type of radiation, identify camouflaged in neutron-slowing media of nuclear substances and products from them, the possibility of a hidden express analysis. The technical result is achieved in that the multilayer detector contains at least one layer containing elements that detect fast neutrons, one layer that records thermal neutrons, one layer contains elements that register gamma radiation, one layer made of polyethylene, one layer made of lead foil. The layers are made autonomously in the form of flat geometric shapes with the ability to move them. At least on one face of each polystyrene rod there is a groove in which a spectroscopic scintillating fiber is placed, photodiodes are located at the ends of the fibers. 1 n.p.f. 4 ill.

Description

The utility model relates to the field of analysis of materials, specifically to the study or analysis of objects by radiation methods for the detection of radioactive materials and sources.

Known multilayer detector containing an optical transducer for detecting penetrating radiation in the form of a neutron flux, made in the form of a block of layers of polymer scintillating optical elements, stacked alternately in two mutually perpendicular directions. The operation of the unit is based on the production of recoil protons in the element material, the conversion of recoil proton energy into light radiation, and the detection of radiation by a position-sensitive photodetector.

Patent of the Russian Federation No. 2119178, IPC: G 01 T 3/06, Bull. No. 26, 1998

A multilayer detector allows you to register only fast neutrons and does not allow you to identify radiation and determine the direction of radiation. The sizes of the elements are limited and are fibers with a transverse size of not more than 1 mm.

Known multilayer detector, made in the form of a block of layers of polymer scintillating optical elements made of a set of materials, the density of which increases monotonically from the first row to the last layer and photodetectors.

A handout of the Institute of Solid State Physics of the Russian Academy of Sciences, Chernogolovka, Moscow Region. 2005 "Anti-terrorism translucent installations for the rapid detection of explosives." Prototype.

The disadvantage of such a detector and the installation as a whole is the need to obtain images of hidden objects when x-rayed by radiation of specific objects in an explicit manner. It makes it impossible to conduct a hidden process of research and measurement.

The detector is designed to detect only one type of radiation, namely, x-ray and cannot detect neutron radiation. The utility model eliminates the disadvantages of analogues and prototype.

The technical result of the utility model is to expand the energy range for detecting penetrating radiations and their types, determine the location and direction of movement of the radiation source, identify it or determine the type of radiation, identify camouflaged in neutron-slowing media of nuclear substances and products from them, the possibility of a hidden express analysis.

The technical result is achieved in that a multilayer radiation detector containing layers of hydrogen-containing scintillating optical elements stacked in rows and photodetectors contains at least one layer containing elements detecting fast neutrons, one layer recording thermal neutrons, one layer containing elements registering gamma radiation, one layer made of polyethylene, one layer made of lead foil, the layers are made autonomously in the form of a flat geometer physical figures with the possibility of their movement with the formation of volumetric figures, and changes in their location, electrical connections are made in the form of loop connections, scintillating optical elements are made in the form of polystyrene rods, the rods are connected with the possibility of changing the distance between them, at least on one face of each rod, a groove is made in which a spectroscopic scintillating fiber is placed at the ends of the fibers

photodiodes are located, provided with leads for connection with scintillation burst registration circuits.

The invention is illustrated in figures 1-4.

Figure 1 schematically shows a device of five layers, where: 1 - a layer containing elements detecting fast neutrons (a layer of type BN), 2 - a layer containing elements that register thermal neutrons (a layer of type TH), 3 - a layer containing elements registering gamma radiation (layer like GI). 4 - a layer made of polyethylene (a layer of type PE) and serves, depending on its location, to slow down fast neutrons or reflect fast and thermal neutrons. 5 - the layer is made of lead foil (layer type CB), serves to enhance the signal from gamma radiation. 6 - spectroscopic fibers of the layer, 7 - photodiodes, 8 - spectroscopic fibers of the layer 2.

Figure 2 shows the dependence of the frequency of the generation of intrinsic electronic noise at the output of a layer consisting of 96 elements, both with discrimination of the signal in amplitude and without it (zero threshold). The repetition rate of the generation (intrinsic) noise of each of the photodiodes is 1 MHz. The time gates of the coincidence scheme in this case are 10 ns.

For comparison, Fig. 3 shows the dependence of the signal frequency caused by natural background neutron radiation, taking into account the intensity and spectral composition of neutron radiation in Moscow for a type-BN layer 1 with a volume of 9.6 dm ³ containing the same 96 elements.

Figure 4 shows the dependence of the signal-to-noise ratio on the discrimination threshold of the photodiode signals for two types of fast neutron sources Pu-Be and ²⁵² Cf at a recording time of 1 s.

Flexible loop electric connections allow you to move each of the layers in the plane and / or in parallel planes, as well as change the sequence of layers.

This makes it possible to carry out various combinations for detecting radiation from moving and stationary objects and to register radiation in the mode of covert express analysis.

The detector may contain the following combinations of layers of various types: PE-BN-TH-SV-GI; PE-BN-TN-GI; BN-TH-SV-GI; PE-BN-TN; TN-SV-GI; BN-TN; SV-GI; PE-BN; TH-PE-TH; BN; VT; GI.

The thickness of type-4 layer 4 is determined by the slow neutron moderation length and, depending on the type of the proposed source, may be 3-5 cm. Type 1-BN layer 1 contains luminescent polystyrene rods equipped with spectroscopic fibers 6 and photodiodes 7 and is used to register fast neutrons . The use of spectroscopic fibers allows you to collect light from rods with a volume of at least 10 ² cm ³ and use photodiodes 7 of small (about 1 mm) diameter to record scintillation flares. A multilayer detector may instead of layer 4 type-PE contain several layers 1 type-BN. This increases the cost of the detector, but at the same time increases its effectiveness. The next layer 2 consists of lithium-containing luminescent fibers that serve to detect thermal neutrons. Under the influence of thermal neutrons, a nuclear reaction ⁶ Li (n, α) T occurs in the fiber. Charged particles (alpha and newt) cause scintillation flashes, part of the light of which propagates through the fiber to its ends. The ends of the fibers 8 in the layer are adjacent with a gap of 0.1-0.3 mm to the spectroscopic fiber (Fig. 1), at the ends of which photodiodes 7 are also installed. To increase the detection efficiency, the detector may contain several such layers. Detector efficiency

of the number of layers for fiber with a diameter of 1 mm, taking into account the composition of the fiber manufactured by NucSafe, is presented in table 1.

Table 1. Number of layers one 2 3 four 5 Efficiency 0.51 0.76 0.87 0.93 0.97

Layer 5 type-SV serves to convert gamma radiation into charged particles and increase the efficiency of registration of gamma radiation.

Layer 3 of type-GI contains rods that luminesce under the action of gamma radiation and are equipped, similarly to layer 1 of type-BN, with spectroscopic fibers 6 and photodiodes 7.

The elements of layers 1 and 2, and layer 3 of the GI type, used to register fast and thermal neurons, and gamma radiation are equipped with two photodiodes 6 included in the coincidence circuit, which ensures a decrease in the pulse repetition rate due to the intrinsic noise of the photodiodes.

The total number of recording elements of the detector layer is selected from the condition that the pulse repetition rate caused by background radiation exceeds the repetition rate of the intrinsic noise pulses from all elements.

From the graphs presented in figures 2 and 3 it is seen that the frequency of the noise of the signal from 96 recording elements coincides with the pulse repetition rate caused by background neutron radiation, at a threshold corresponding to the generation of six photoelectrons in the photodiode.

The possibility of detecting a fast neutron source using a layer consisting of 96 elements of the same volume (9.6 dm ³ ) is shown in Fig. 4 for Pu-Be and ²⁵² Cf sources at a fast neutron flux density to the detector of 3 × 10 ^-2 n / cm ² s during 1 s. The figure shows the dependence of the ratio of the useful signal to the standard error, taking into account the presence of a background signal.

It can be seen that the optimal threshold value is 7-8 photoelectrons.

Spectroscopic fibers 2 are used to collect light from luminescent flashes and to output light to photodetectors (photodiodes), which are located at the ends of the spectroscopic fibers 6, 8. In the case of remote photodetectors, the spectroscopic fibers 2 are joined to the light guide fiber to avoid large light losses.

The signal from the photodiodes 7 when the detector is turned on to the measuring structures enters the coincidence circuit and then to the electronic device for collecting and analyzing information.

The scintillating optical rods of layer 1 are made of a hydrogen-containing substance and simultaneously serve as both a fast neutron moderator and their detector. Fast neutrons (ionizing radiation flux) slow down in scintillating optical rods and lose elastic energy during the elastic scattering of neutrons by hydrogen nuclei, giving rise to recoil protons, which cause scintillations.

Light from scintillation flashes propagates through the scintillating optical rods of layer 1, is collected by spectroscopic fibers 6 and transmitted to the ends of spectroscopic fibers 6, where photodiodes 7 are located.

Photodiodes 7, layer 2 for thermal neutrons, layer 3 for recording gamma radiation and x-ray radiation are provided with conclusions for connection with coincidence schemes.

The coincidence scheme, in particular, includes a two-channel amplifier, two resistive voltage dividers for selecting a supply voltage in the range of 50-60 volts independently for each of the two photodetectors and a temporary gate. The use of temporary gates reduces the number of false events.

The signals from the matching circuits are fed to the controller input, and after processing to the computer. The controller polls the output registers of coincidence schemes, carries out the primary processing of the received information and transfers it to the computer. Matching schemes, controllers, and an information processing center are not the subject of this invention.

Depending on the type of radiation source, as well as the chemical composition of objects located between the radiation source and the detector, the detector can receive: only fast neutrons; thermal neutrons only; only gamma radiation; various combinations of the first three types of emissions. When only fast neutrons are emitted, they cause scintillation bursts in the elements of the layer. In addition, slowing down in layer 1, these neutrons cause scintillation bursts in the elements of layer 2.

To increase the efficiency of the production of thermal neutrons, several layers can be used 1. Moreover, they can be located both one after another and around layer 2. In the latter case, instead of an additional layer 1 of type-BN, layer 4 can be installed, providing reflection to the detector both fast and thermal neutrons.

Identification of the source of fast neutrons is made by: the maximum amplitude of the pulses received from layer 1; the ratio of the number of pulses from layers 1 and 2; temporal correlations between pulses coming from layer 1; temporal correlations between pulses coming from the elements of layer 1, with pulses coming from layer 2.

When the distance between the source and the detector is less than or of the order of the size of the detector, the direction of motion of the source is determined by the sequence of operation of the recording elements (rods) of layer 1.

With a flux of only thermal neutrons (a fast neutron source is in a hydrogen-containing substance), pulses come only from layer 2. With a flux of only gamma radiation, pulses come only from layer 3 of the GI type.

When the distance between the source and the detector is less than or on the order of the size of the detector, the direction of movement of the source is determined by the sequence of operation of the recording elements (rods) of layer 3 of the type-GI.

Layer 5 type-SV is used to convert x-ray and gamma radiation into charged particles in order to increase the efficiency of registration of these emissions. Identification of the source is carried out by the amplitude spectrum of pulses from the elements of the layer. In mixed flows of various types of radiation, pulses come from different types of layers.

Information about the source is obtained on the basis of a joint analysis of all available information:

the amplitude of the signals from layer 1; the amplitudes of the signals from layer 3, the time correlations between the pulses received from the individual elements of layer 1; time correlations between the pulses received from the elements of layer 1 and from layer 2; time correlations between pulses received from elements of layers 1 and 3; time correlations between pulses received from elements of layers 1, 2, 3; the ratio of the number of pulses received from different layers,

the effect caused by the use of layers 4 and 5.

Claims (1)

A multilayer radiation detector containing layers of hydrogen-containing scintillating optical elements arranged in rows and photodetectors, characterized in that the detector contains at least one layer containing elements detecting fast neutrons, one layer recording thermal neutrons, one layer containing elements registering gamma radiation, one layer made of polyethylene, one layer made of lead foil, the layers are made autonomously in the form of flat geometric igurs with the possibility of their movement with the formation of volumetric figures, and changes in their location, electrical connections are made in the form of loop connections, scintillating optical elements are made in the form of polystyrene rods, the rods are connected with the possibility of changing the distance between them, at least on one face of each a groove is made in the rod, in which a spectroscopic scintillating fiber is placed, photodiodes are located at the ends of the fibers, provided with leads for connection with scintillation registration schemes s outbreaks.