RU2395103C1 - Device for measuring signal spectra of response of atomic elements to penetrating radiation - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: device for measuring signal spectra of the response of atomic elements to penetrating radiation has an assembly of scintillation plates, fibres which are laid in profiled grooves in the plates, where a light gathering lens is attached to the end of the fibres which forms a light beam for inlet into an acousto-optical filter with linear variation of tuning frequency from the pumping oscillator filter, with the following connected in series to the output of the filter: avalanche photodiode, analogue-to-digital converter, buffer memory and a computer which displays the detected signal spectra, as well as synchronisation of operation of elements of the device and control of pulse duration for linear adjustment of the acousto-optical filter from the pumping oscillator through telecommunication software installed on the computer. ^ EFFECT: more accurate measurement of the form of response signal spectra for reliable identification of atomic elements. ^ 4 dwg, 1 tbl

Description

The invention relates to nuclear physics and can be used in scientific measuring equipment, as well as in the development of tools for the rapid detection and identification of contraband materials during customs inspection, patrolling state borders.

Currently, for the rapid analysis of contraband materials, methods are being developed for their active exposure in order to increase the rate of division and subsequent recording of response signals of either instant or delayed response of substances to penetrating radiation. In this case, the identification of signature features of contraband material is based on measuring the amplitude-time dependencies between the instantaneous and delayed response of the substance to radiation. To identify atomic elements, a correlation analysis of amplitude-time signals is used. The conversion of penetrating radiation into an electrical signal is carried out by means of discriminating detectors.

It is known "Device for detecting gamma-neutron radiation" - Patent RU No. 2264674, H01J, 47/02, G01T, 1/185, 2003 - analogue. A device for detecting gamma-neutron radiation includes a cylindrical ionization chamber with a shielding grid, a high-voltage power supply, a charge-sensitive amplifier, the detector case with an external insulating coating is used as a cathode, and ultrapure xenon is used as a working medium at a pressure of 40-50 atm and respectively, with a density of 0.3-0.6 g / cm ³ with the addition of hydrogen in an amount of 0.2-0.3% of the total xenon content, in addition, a metal shielding mesh inside ionization chamber, has a degree of screening inefficiency σ≈ (3 ÷ 5)%.

The signal at the output of the analog device is proportional to the total power of the gamma-neutron radiation flux, which does not allow, in subsequent paths, to divide this flux into components according to the energy spectrum of individual gamma-rays.

Known industrial developments of detectors-measuring spectra of gamma radiation power levels: BDS detection units, BDEG-19P, CsJ (TI) gamma-detector-scintillator - FD1001 photodiode (http://www.detector.org.ua/detectors.html) - analogues.

The disadvantages of analogues are:

- the impossibility of unambiguous measurement of the shape of the energy spectrum of the response signal;

- small effective cross-section (aperture size) of the transducer-sensor and, as a result, - insufficient sensitivity of the meters.

The closest analogue to the claimed technical solution is the “Scintillation detector with fiber optic information retrieval” developed by SSC IHEP (Protvino and LPI RAS), commercially produced by SSC IHEP [see materials of the 30th VKCL, St. Petersburg, 2008] (http://theory.asu.ru/~raikin/Physics/PCR/2008_StPetersberg/RCRC2008/PROC/E AS / EAS_20.pdf). It is a two-layer assembly of scintillation plates with a total area of 1 m ² . Each layer is assembled from plates of 20 × 20 × 0.5 cm ³ . Light collection is carried out using spectroscopic fibers - fibers. Each plate has 4 grooves with a pitch of 3.6 cm and a depth of 2.2 mm at a distance of 4.6 cm from the edges. Fiber 1 mm in diameter is glued into these grooves. The ends of the fibers are assembled into a bundle, glued and polished. The end of the bundle is fixed close to the photocathode of the photomultiplier tube.

The disadvantage of the closest analogue is the inability to select the energy spectrum of the original signal at the output of the counter after amplification of the total light flux by a photoelectronic multiplier.

The problem solved by the claimed meter consists in reliable recording of the energy spectrum of the initial signal of the response of the atomic element to probing irradiation by successive proportional conversion of the radiation flux into the ultraviolet spectrum, and the ultraviolet spectrum into the visible light flux, followed by measuring the amplitude of the spectral components by transmitting the light flux through a linear tunable acousto-optic filter with adjustable sawtooth pulse width scan voltage.

The technical solution of the problem is carried out by the fact that the measuring instrument for the spectra of the responses of atomic elements to penetrating radiation, containing an assembly of scintillation plates, converting the response radiation flux into the ultraviolet radiation spectrum, fiber fibers laid in profile grooves of the plates, spectrally displacing ultraviolet radiation into the visible spectrum, end a fiber bundle, a light flux to electric signal converter, in addition to a fiber end, a light-collecting lens is glued, forming the diameter of the light beam for entering it into an acousto-optic filter, a filter pump generator with a reactive element and a sawtooth voltage generator for linearly changing the filter tuning frequency, an avalanche photodiode, an analog-to-digital converter, a buffer memory and a computer, connected in series to the output of the filter visualizing the recorded spectra of signals, as well as synchronizing the operation of the elements of the device and controlling the pulse duration of the generator sawtooth voltage by inserting a telecommunication program into the computer.

The invention is illustrated by drawings, where:

figure 1 - functional diagram of the meter;

figure 2 is a sequence of signal spectra: 1) the energy spectrum of the response radiation, 2) the ultraviolet conversion spectrum of the energy spectrum with scintillation plates, 3) the spectrum of the visible range at the output of the fibers;

figure 3 - dynamics of the tuning of the acousto-optical filter by the pump generator;

figure 4 - implementation of the recorded spectra of atomic elements.

The meter of the spectra of the signals of the responses of atomic elements to penetrating radiation, Fig. 1, contains an assembly of scintillation plates 1, fiber-fibers 2, laid in profile grooves of the plates, assembled in a bundle 3 of the optical fiber taps from the fibers, a light-collecting lens 4 for inputting the light flux into the acousto-optical filter 5, pump generator 6 for tuning the filter frequency, reactive element 7 of pump generator 6, sawtooth voltage generator 8 for linear deviation of the frequency of the pump generator, avalanche photodiode 9, analog-to-digital A new converter 10, a buffer memory 11, a personal computer 12 consisting of elements: a processor 13, random access memory 14, a hard drive 15, a display 16, a printer 17, a keyboard 18. The meter elements are synchronized by a telecommunication program recorded in the hard drive 15. Telecommunication The program implements the following functions: launching a probe beam generator with an adjustable duration and duty cycle of a packet of probe pulses, regulation of the sawtooth pulse width voltage depending on the duration of the probe pulse train, transfer of the digitized measurements from the ADC 10 and the buffer memory 11 to the RAM 14 for processing the recorded signal spectra on the computer 12.

The dynamics of the interaction of the elements of the meter is as follows. Atomic elements are distinguished by the binding energy of the nucleus released during nuclear reactions. The energy range of emitted gamma rays and particles occupies the interval from 1.1 MeV to 8.8 MeV. The binding energy of the nuclei of atomic elements and their isotopes is illustrated in table 1.

Table 1 Core Binding energy E _sv , MeV The ratio of E _SV to the mass number, MeV ₁ H ² 2.2 1.1 ₁ H ³ 8.5 2.83 ₂ not ³ 7.7 2.57 ₂ not ⁴ 28.3 7.075 ₈ Li ⁶ 32 5.33 ₈ Li ⁷ 39.2 5.6 ₄ ve ⁹ 58.2 6.47 ₄ Be ¹¹ 76.2 6.93 ₇ N ¹⁴ 104.7 7.48 ₆ C ¹² 92.2 7.68 ₈ O ¹⁶ 127.6 7.975 ₁₃ Al ²⁷ 225.0 8.33 ₂₆ Fe ⁵⁶ 492.2 8.79 ₈₆ Ru ²²² 1708.2 7.69 ₉₂ U ²³⁵ 1783.8 7.59 ₉₄ Pu ²³⁹ 1806.9 7.56

Selectable features in the identification of atomic elements can be:

- the energy spectrum of particles and quanta in the decay of the nucleus;

- the ratio between the spectra of instantaneous and delayed radiation;

- waveform of the recorded spectrum, i.e. amplitude relationships between spectral lines.

In the inventive meter to measure the shape of the spectrum of the signals of the responses of atomic elements using sequential proportional spectral displacement (figure 2):

- the energy spectrum of the response signal to the ultraviolet radiation spectrum by assembling (1) scintillation plates from anthracene solid solution (C ₁₄ H ₁₀ ) in polystyrene, giving the maximum light output. Since the intensity of the light flash is proportional to the energy lost by the particle, this assembly is used as a primary spectrometer;

- the spectrum of ultraviolet radiation in the spectrum of the visible range by means of an optical fiber-fiber 2.

The surface of the fibers is covered with a thin layer of lumogen substance that converts UV radiation into the visible range. Types of fibers (converters) that convert UV light (13-350 nm) into the visible range (405-610 nm) (see http://www.metrolux.de/contenido/cms/uv-and-ir-converter/)

The spectrum of the visible range by means of a light-collecting lens 4 is converted into a light beam with a diameter of about 5 mm for input into a tunable acousto-optic filter of type 5 (industrial developments) CB FOTF (Aurora), LAOTF (Bellcore) with a passband level of 3 dB (1 ... 1.6 nm) [see, for example, Ivanov A.B. Fiber optics: transmission system components, measurements. - M: Company Cyrus Systems, 1999, S. 180-182].

An acousto-optic filter is a crystal (piezoelectric) in which anisotropic Bragg diffraction is observed under the influence of a microwave pump generator in the range of 60-70 MHz, i.e. a diffraction grating is formed with a variable refractive index, due to which tunable filtration is achieved.

The linear frequency deviation of microwave generators of the meter wavelength range (60 ... 70 MHz) is carried out by connecting a reactive element (such as a reactive lamp) according to the scheme [see "Handbook of Radio Electronics" edited by A.A. Kulikovsky, Moscow: Energia, 1968. - p.50, Fig. 12-78, Reactive lamp]. Frequency deviation is achieved by applying an additional bias to the grid in the form of a sawtooth sweep voltage.

A ramp voltage generator with the possibility of applying synchronizing pulses to its input [see ibid., “Handbook of Radio Electronics”, p.238, Fig. 15-52].

The dynamics of the tuning of the acousto-optical filter by pumping it with a microwave generator with frequency deviation by sawtooth sweep pulses is illustrated by the diagrams of Fig. 3.

Other elements of the device were made on serial industrial developments: an avalanche photodiode of the APD type (sensitivity ~ 10 ^-15 relative to the dark current), analog-to-digital converter, P-267 microassembly, buffer storage device, LA-20 microassembly [see Yakubovsky B. et al. Digital and analog integrated circuits. Directory. M .: Radio and communications, 1990].

Since the accuracy of synchronization of the elements of the device should be ns, the telecommunication program is implemented on a special high-speed computer such as the Sun Microsystems Ultra family of computers (Scientific Research Institute for System Studies of the Russian Academy of Sciences) [see http://www.solariscentral.org].

The implementation of the recorded spectra of response signals in the form of amplitude-frequency characteristics of the visible range is illustrated by the graphs of Fig. 4.

The effectiveness of the meter is determined by the reliability of the identification of the atomic element. There is the possibility of collecting statistical data on the forms of frequency response spectra to create a base of reference signals. In the presence of a reference base, reliable identification of atomic elements is carried out by amplitude, duration and shape, which exceeds the known analogues.

Claims (1)

A spectral measuring instrument for the response of atomic elements to penetrating radiation, containing an assembly of scintillation plates that convert the response radiation flux to the ultraviolet radiation spectrum, fiber fibers laid in profile grooves of the plates, which absorb ultraviolet radiation into the visible spectrum, the end of the fiber bundle into the light flux converter an electric signal, characterized in that a light-collecting lens is glued to the end of the fibers, forming a diameter of the light beam for input into ustooptic filter, filter pump generator with a reactive element and a sawtooth voltage generator for linearly changing the filter tuning frequency, an avalanche photodiode, an analog-to-digital converter, a buffer storage device, and a computer visualizing the recorded signal spectra, as well as synchronization of the operation of the device elements and regulation of the pulse duration of the sawtooth voltage generator by laying computer telecommunications program.

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