RU2593433C1 - Method and device for measurement of neutron beam(s) profile - Google Patents

Abstract

FIELD: radiation technology.

SUBSTANCE: invention relates to radiation technologies, as well as to research, development, and operation of nuclear installations and accelerators. Method for measurement of neutron beam(s) profile in plane perpendicular to its / their dedicated direction consists in that fast neutron beam(s) are directed to detection plane of profile meter located perpendicular to its / their direction(s), surface of which plane is set of parallel isolated strips; signals from each strip, generated as result of interaction between neutron and strip substance, are transmitted to recording electronic unit, executing reception and analysis of detected events using software for determination of neutron beam(s); detection plane of profile meter is double-sided strip silicon detector, one side therein is set of X strips, and second side is set of Y strips perpendicular to the X strips; at that, charged particles are recorded formed in each specific strip as result of reactions with emission of protons and alpha-particles in neutron capture on silicon nuclei ²⁸Si(n,p)²⁸Al, ²⁸Si(n,α)²⁵Mg; at that, by receiving electric signals from corresponding X and Y strips, coordinates X and Y of interaction points of neutrons with substance of any strip in profile meter, at that, on basis of unique communication numbers of simultaneously actuated X and Y strips, connected to match; at that, based on set of events on each of X and Y strips in profile meter, time and amplitude analysis of detected events is automatically executed.

EFFECT: technical result is increased accuracy of determining axes directions of labelled beams, simplified procedure of measuring characteristics of beams, as well as faster measurement.

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Description

The invention relates to the field of radiation technology, as well as to the research, development and operation of nuclear facilities and accelerators and can be used to measure the spatial distribution of neutron fluxes, as well as to measure the profile of the beam (s) of tagged neutrons.

A known method for determining the X and Y coordinates of the intersection points of the axes of each of the labeled neutron beams at certain distances from the neutron source with a plane perpendicular to the direction of the labeled neutron beams (prototype) using the device [1, 2] for measuring the distribution of labeled neutrons in the plane perpendicular to the direction propagation of a neutron flux comprising: scintillation strip profilometer; recording electronics for collecting and preliminary analysis of signals from strips of a scintillation profilometer and from pixels of an alpha detector installed near a neutron source; power units of the profilometer and recording electronics, while a portable neutron generator of NG is used as a source of labeled neutrons (neutrons are tagged using a multi-pixel silicon alpha detector that detects alpha particles generated in the dt-alpha + n reaction (14.1 MeV) from the tritium target in the direction opposite to the neutron emission direction and located inside the NG). In this case, the angular distribution of neutrons is almost isotropic in a solid angle of 4π; therefore, the number of labeled neutron beams is determined by the number of pixels of the alpha detector located inside the NG. Using the coincidence of signals from a specific pixel of the NG alpha detector and from one of the strips of the scintillation profilometer (if the strips of the profilometer are located along the X and Y axes of the plane perpendicular to the direction of the neutron beam, then they will be called X- and Y-strips, respectively) , we obtain information on the profile of each of the labeled neutron beams along the X and Y axes (information on the distribution of labeled neutron beams along the X and Y axes is extracted from the analysis of data obtained in measurements with a profilometer in two mutually perpendicular positions of scintillation strips relative to the direction of the labeled neutron beam). Carrying out measurements at two different distances from the neutron source, the X and Y coordinates of the intersection points of the axes of each of the labeled neutron beams are measured at given distances with a plane perpendicular to the direction of the labeled neutron beams.

The method for measuring the profile of a neutron beam can be described, referring to the principle of operation of the prototype profilometer, which consists of a multi-anode photomultiplier tube (PMT), square-shaped strips of plastic scintillator, light-guiding fibers (fibers) that are isolated from each other by means of which a light flash arises in any resulting strip profilometer neutron elastic scattering with hydrogen nuclei constituting the plastic scintillator (C ₁₄ H ₁₂₎ is transmitted to the corresponding anode mnogoanodnog PMT.

The signals from the output of the PMT with a certain amplitude corresponding to a certain number of firing strips in which the neutron interacted with the scintillator substance are fed to the recording electronics block for analysis in order to determine the numbers of fired X- and separately Y-strips, and therefore, X and Y coordinates of the intersection points of the axes of each of the labeled neutron beams with the XY plane of the profilometer.

The disadvantages of the prototype method are as follows:

1. To measure the distribution of neutron beams along the X and Y axes in a plane perpendicular to the direction of the labeled neutron beams incident on this plane, it is necessary to perform two consecutive measurements with horizontal and vertical arrangement of scintillation strips of the profilometer, and a device is needed to rotate it plane scintillation strips profilometer 90 ° relative to each other.

2. Obtaining a recorded electrical signal from each strip during neutron interaction occurs in two stages: energy is converted into light (scintillator), then light is converted into an electric signal (PMT), and at each stage of conversion there is an inaccuracy.

3. The use of multi-anode PMTs leads to the presence of a “crosstalk” (the effect of crosstalk in two adjacent X- (or Y-) strips), which in turn leads to the appearance of additional uncertainty in the measurement of neutron coordinates.

4. A rather sophisticated technology for the light insulation of strips from each other, as well as the transmission of a light flash from each strip to the anode of a multi-channel photoelectronic multiplier.

5. A complex procedure of amplitude calibration of a scintillation spectrometer with the use of standard gamma sources Cs-137, Co-60 and cosmic radiation is required to determine the coefficients with the help of which the conversion to equal detection efficiency for each of the 16 strips is made.

6. Limitation by the coordinate of the accuracy of the profilometer due to the large width of the scintillation strips (7.5 mm).

7. The use of scintillation strips with a thickness of 5 mm leads to a high level of background due to their random loading due to cosmic radiation and the rescattering of neutrons in the material of the strips with their subsequent registration by adjacent strips.

The present invention is intended to solve the following technical problems:

- determination of the spatial distribution of the neutron flux density within the dimensions of the X-Y plane of the profilometer;

- increasing the coordinate accuracy of measuring the spatial distribution of the neutron flux density within the dimensions of the X-Y plane of the profilometer;

- determination of the profile and direction of the axes of the labeled neutron beams;

- reduction of measurement time.

The tasks are solved as follows:

A beam (beams) of fast neutrons falls on the detecting plane of the profilometer perpendicular to its direction (s), and a two-sided silicon strip detector is used as the detecting plane of the profilometer, one side of which is a set of X-strips, and the other is a set of Y -strips perpendicular to the X-strips and register charged particles formed in the detector volume as a result of reactions with emission of protons and alpha particles during neutron capture on ²⁸ Si (n, p) ² silicon nuclei ⁸ Al, ²⁸ Si (n, α) ²⁵ Mg; in this case, by removing electrical signals from the corresponding X- and Y-strips, the X and Y coordinates of the neutron interaction points with the silicon of the detector are determined based on the unique relationship of the numbers of simultaneously triggered X- and Y -strips included in coincidences, then, after a set of events for each of the X- and Y-strips of the profilometer, the spatial distribution of neutrons incident in the plane of the profilometer is measured.

In the case of using labeled neutrons, the method consists in sending beams of labeled neutrons formed in a neutron generator with a multi-element (multi-pixel) alpha detector located perpendicularly to the detection plane of a double-sided silicon strip detector (neutron tagging is carried out by detecting alpha particles one of the elements (pixel) of the alpha detector, which is formed in the binary nuclear deuterium-tritium reaction), analyze events, simultaneously for egistrirovannyh respective X- and Y-strips bilateral silicon profilometer, in coincidence with the signal from the corresponding pixel alpha detector.

A device for measuring the profile of a neutron beam (s) contains a detecting plane, which may consist of one or more detecting elements, a high-voltage power supply for the detecting plane, a power supply for recording equipment, a data acquisition and analysis electronics block, where the detector is used as a detecting element a double-sided strip silicon detector, which is a silicon crystal with p + and n + strips located on opposite sides, while m X-strips on one side of the crystal are parallel to each other and perpendicular to the direction of Y-strips on the other side of the crystal.

The detecting plane of the profilometer can also consist of a group of separate identical detecting planes (detecting elements), each of which is a two-sided strip silicon detector, while the number of detecting elements that make up the detecting plane is determined from the condition ΣS (el) ≥S (beam), where ΣS (el) is the total area of all detecting elements making up the detecting plane, S (beam) is the surface area limited by the dimensions of the measured neutron flux (fluxes) in the plane of the profilometer located at a certain distance from the neutron source.

In the case of measuring the profile of labeled neutron beams generated by a neutron generator with an alpha detector, a device that implements the proposed method contains a profilometer based on a double-sided silicon strip detector with recording electronics for receiving and analyzing signals from X- and Y-strips, organizing data matching signals with signals from the corresponding pixels of the alpha detector NG, as well as the power system of the profilometer.

Distinctive features of the proposed method from the well-known adopted for the prototype are:

The neutron beam is directed perpendicular to the detecting plane, a two-sided silicon strip detector is used as the detecting plane of the profilometer, one side of which is a set of X-strips, and the other is a set of Y-strips perpendicular to X-strips, while charged particles resulting from this are recorded reactions with the emission of protons and alpha particles during neutron capture on silicon nuclei ²⁸ Si (n, p) ²⁸ Al, ²⁸ Si (n, α) ²⁵ Mg, while removing electrical signals from the corresponding X- and Y-strips determine the coordinates X and Y of the points of interaction of neutrons with the substance of a given strip of the profilometer, while on the basis of an unambiguous relationship between the numbers of simultaneously triggered X- and Y-strips included in coincidence, moreover, after a set of events for each of the X- and Y-strips of the profilometer time and amplitude analysis of recorded events is performed.

Beams of labeled fast neutrons are formed perpendicularly to the detecting plane of the silicon profilometer, formed by a neutron generator with a multi-element (multi-pixel) alpha detector located inside it (neutron tagging is carried out by registering an alpha particle with one of the elements (pixel) of an alpha detector, generated in a binary nuclear deuterium-tritium reaction, the emission of which from the target is practically opposite to the direction of neutron emission), an analysis of events is performed, simultaneously aregistrirovannyh respective X- and Y-strips bilateral silicon profilometer, in coincidence with the signal from the corresponding pixel alpha detector, wherein the measured spatial distribution of neutrons in detecting X-Y plane corresponding to each of the tagged neutron beams.

Let us explain that in a device that implements the claimed method, a two-sided silicon strip detector is used as a detecting plane, which is two identical in shape and content detecting X and Y planes located on both sides of a semiconductor silicon crystal with pn junctions, while X -strips on one side of the crystal are parallel to each other and perpendicular to the direction of the Y-strips on the other side of the detector, each X- and Y-strips are directly electrically connected through amplifiers with latter is present with the readout electronics block collection and event analysis, the reverse bias is applied to the detector from the HVPS for the detection plane.

Using the invention provides the opportunity:

- reduce the time of measuring the spatial distribution of neutrons in the plane of X- and Y-coordinates due to the use of a double-sided strip silicon detector, which allows you to immediately determine the two coordinates of the neutron interaction point in the detector volume;

- increase the accuracy of the spatial distribution of the neutron flux in the plane of the X- and Y-coordinates by reducing the step of the strips of the silicon detector and by directly converting the ionization energy into an electrical signal in a silicon detector;

- significantly reduce the background level, determined by the small thickness of the silicon detector (300-500 μm), by reducing the neutron rescattering in the detector material, which reduces the likelihood of signals from one scattered neutron immediately on two adjacent strips.

Due to the presence of these distinctive features in comparison with the prototype, the following technical results are achieved:

- The proposed method is intended to obtain information about the spatial distribution of labeled neutron beams in the XY plane of the profilometer and to determine the size of the interaction region of labeled neutron beams with a silicon detecting plane of the profilometer. This is achieved by using a double-sided silicon strip detector, consisting of X- and Y-strips located orthogonally on different sides of the detector. In the interaction of fast neutrons with the substance of a crystal of a silicon detector as a result of reactions with the emission of protons and alpha particles during neutron capture on silicon nuclei ²⁸ Si (n, p) ²⁸ Al, ²⁸ Si (n, α) ²⁵ Mg, silicon is ionized by the charged particles (p and α). As a result of the collection (drift) of the ionization charge in the electric field created in the detector volume, electrical signals are simultaneously induced on the corresponding X- and Y-strips, which are fed to the inputs of the readout electronics.

- The ability to simultaneously obtain the X- and Y-coordinates of neutrons, which as a result of a nuclear reaction with silicon give an electrical signal simultaneously in the X- and Y-strips of the detector.

- A simpler and more reliable removal of electrical signals from the X- and Y-strips of a silicon profilometer in comparison with the optical removal of a scintillation profilometer.

- The absence of practically the effect of crosstalk ("crosstalk") in two adjacent X- (or Y-) strips increases the accuracy of determining the coordinates of neutrons.

The list of drawings:

1. In FIG. 1 (Appendix 1) shows a variant of the General scheme of the device.

2. In FIG. 2 (Appendix 1) one of the variants of the fast neutron profilometer circuitry based on double-sided strip silicon detectors is shown.

3. In FIG. Figure 3 (Appendix 2) shows the spectrum of energy losses of charged particles resulting from the reactions of the interaction of fast neutrons with silicon nuclei, measured using a prototype profilometer based on a silicon detector.

In FIG. 1 shows a General diagram of a device that implements the proposed method.

The device comprises a detecting plane 1 intended for measuring the spatial distribution of labeled neutron beams and consisting of 4 identical double-sided strip silicon detectors 2; block recording electronics 3; power supply 4 of the detecting plane 1 and the recording electronics 3. The same drawing shows: a neutron generator 5 with a multi-pixel alpha detector 6 located inside it, forming labeled neutron beams; tritium target 7; neutron generator control unit 8.

In FIG. Figure 2 shows an example of the inclusion of a double-sided silicon strip detector with amplifiers for reading signals from strips. The pitch of the X- and Y-strips of the profilometer is 2 mm, the length of the strips is 60 mm, the thickness of the detector is 0.3 mm.

In FIG. Figure 3 shows the energy loss spectrum of charged particles resulting from neutron interaction reactions (E _n = 14.1 MeV) with silicon nuclei in the volume of a silicon detector. This spectrum was obtained by passing neutrons through a silicon detector with a sensitive area of 0.64 cm ² and a thickness of the sensitive region of 300 μm. The number of neutrons passing through the detector is 2.62 × 10 ⁷ , the number of recorded signals (neutrons) by a silicon detector with an area of 0.64 cm ² and a thickness of 300 μm is 5.2 × 10 ³ at a detection threshold of 1 MeV. From the obtained experimental results, the detection efficiency of fast neutrons (E _n = 14.1 MeV) by a silicon detector was determined, which is 3.1 × 10 ^-4 cm ^-2 / 300 μm / 1 MeV. The obtained value of the neutron detection efficiency has the physical meaning of the following: silicon detector with an active area of 1 cm ² and 300 microns thick while passing therethrough April ¹⁰ fast neutron (E _n = 14.1 MeV) neutron signal register 3.1 at an energy threshold in the electronics 1 MeV.

The proposed method can be effectively used to solve neutron diffraction problems in the study of the internal structure of an object located between a neutron source and a profilometer. The substances that make up the object under study have a different degree of attenuation of the neutron flux when passing through them (different degrees of neutron absorption), which, in turn, leads to a decrease in the number of neutrons recorded by strips X and Y that are “obscured” by a region in the object occupied by substances with a large neutron absorption cross section, compared with all other areas of the object filled with other substances that make up the irradiated object.

Literature

1. V.M. Bystritsky, N.I. Zamyatin et al., Collection of reports of the International scientific and technical conference "Portable neutron generators and technologies based on them", p. 547, VNIIA, Moscow, 2013.

2. V.M. Bystritsky, N.I. Zamyatin et al., Collection of reports of the International scientific and technical conference "Portable neutron generators and technologies based on them", p. 572, VNIIA, Moscow, 2013.

Claims (2)

1. The method of measuring the profile of a neutron beam (beams) in a plane perpendicular to the direction selected (their) direction, namely, that the beam (beams) of fast neutrons are sent to the detecting plane of the profilometer perpendicular to its (their) direction (directions), the surface of which is a collection of parallel isolated strips, the signals from each of the strips, resulting from the interaction of a neutron with the substance of the strip, are fed to the recording electronics unit and, receiving and analyzing recorded events using software for determining the profile of a neutron beam (beams), characterized in that a two-sided strip silicon detector is used as the detecting plane of the profilometer, one side of which is a set of X-strips, and the other is a set of Y -strips perpendicular to the X-strips, in this case, charged particles formed in each specific strip are recorded as a result of reactions with the emission of protons and alpha particles during ahvate neutrons by nuclei of silicon ²⁸ Si (n, p) ²⁸ Al, ²⁸ Si (n, α) ²⁵ Mg, wherein by removing electrical signals from the respective X- and Y-coordinates of the strips define X and Y points of neutron interactions with the substance of the profiler strip, in this case, based on the unambiguous relationship of the numbers of simultaneously triggered X- and Y-strips included in coincidence, in this case, after a set of events for each of the X- and Y-stripes of the profilometer, time and amplitude analysis of the recorded events is automatically performed. 2. The method according to claim 1, characterized in that beams of labeled fast neutrons are formed perpendicularly to the detecting plane of the profilometer from silicon. They are formed using a neutron generator with a multi-element (multi-pixel) alpha detector located inside it (neutron tagging is carried out by detecting alpha particles by one of the elements (pixel) of the alpha detector, which is formed in the binary nuclear deuterium-tritium reaction, the emission of which from the target is practically opposite to the direction of neutron emission), analysis of events that lead simultaneously registered corresponding X- and Y-strips bilateral silicon profilometer, in coincidence with the signal from the corresponding pixel alpha detector, wherein the measured spatial distribution of neutrons in detecting X-Y plane corresponding to each of the tagged neutron beams.

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