RU103189U1 - PHOTO NUCLEAR - Google Patents

Abstract

 A photonuclear device including a pulsed electron beam accelerator, converter, electron filter, collimator, neutron detectors, electronic equipment for registering signals from neutron detectors, characterized in that the electron filter is made in the form of a set of galvanically isolated metal plates, the device is additionally equipped with a charge measurement device induced on each of the galvanically isolated metal plates, made in the form of a multi-channel recorder, and a follower interdependently connected to means for determining the energy deviation and the electron beam current from the nominal value, means for calculating the relative change in the neutron yield, means for normalizing the detected neutrons number by the relative change of the neutron yield.

Description

The solution relates to the field of analysis of materials by radiation methods, measurement of secondary emissions from exposure to bremsstrahlung and can be used to detect nuclear materials, including fissile materials, shielded by the contents of the analyzed objects (large sea containers, cars, wagons, buildings, etc. ) without opening them.

The photonuclear method for detecting nuclear materials is based on irradiating the analyzed object with pulsed high-energy bremsstrahlung and detecting neutrons emanating from nuclear materials as a result of photonuclear reactions. The energy of bremsstrahlung is selected above the threshold of photonuclear reactions in nuclear materials (2.2-6 MeV), but below the threshold of photonuclear reactions (<10 MeV) in the most common chemical elements that are part of structural materials or contained in the environment (soil, buildings) ) and household items. The main background (neutrons leaving the analyzed object in the absence of nuclear materials) is due to the presence in the natural composition of chemical elements of isotopes with a low threshold for photonuclear reactions, for example, a ¹³ C carbon isotope with a threshold (γ, n) of 4.9 MeV, an isotope ¹⁷ O oxygen with a threshold (γ, n) of the reaction 4.1 MeV, an iron isotope ⁵⁷ Fe with a threshold (γ, n) of the reaction 7.6 MeV [1]. For many tasks of remote control of nuclear materials, the photonuclear method is practically zero-phonon [1], and the quantity (mass, percentage) of nuclear materials in an object is proportional to the number of detected neutrons [2]. The error in measuring the quantity of nuclear materials δ ₀ is due to the error in measuring the number of neutrons δ _M and fluctuations in the neutron yield δ _N , which arise due to fluctuations in the current and energy of the electron beam generating bremsstrahlung [2]:

By stabilizing the characteristics of the equipment and choosing a neutron detection threshold, the error in measuring the number of neutrons δ _M can be reduced to less than 1%. Studies of the level of fluctuations in the current and energy of the electron beam show that in a typical linear electron accelerator they are about 5% [1], which leads to fluctuations in the neutron flux above 10%. Thus, the error in measuring the amount of nuclear materials is determined mainly by fluctuations in the neutron yield:

Closest to the proposed device (prototype) is a photonuclear device [3], containing a pulsed electron beam accelerator with a maximum energy greater than the threshold of photonuclear reactions, a converter for converting accelerated electron beam energy into energy of bremsstrahlung, an electron filter for absorbing electrons after passing through the converter, a collimator for the formation of a narrow beam of bremsstrahlung, neutron detectors, electronic equipment for detecting signals from the detector neutron s. The disadvantage of this device is that due to fluctuations in the energy and current of the electron beam, fluctuations in the neutron yield from the analyzed object occur, as a result of which the error in measuring the amount of nuclear materials increases.

To increase the accuracy of measuring the amount of nuclear materials in a photonuclear device containing an accelerator of a pulsed electron beam with a maximum energy greater than the threshold of photonuclear reactions, a converter for converting accelerated electron energy into energy of bremsstrahlung, an electron filter for absorbing electrons after passing through the converter, a collimator for generating a narrow beam flow radiation, neutron detectors, electronic equipment for recording signals from neutron detectors s, the electron filter is made in the form of a set of galvanically isolated metal plates, the charge induced on each plate during the passage of electrons is measured by a multichannel recorder, the deviation of the electron beam energy and current from the nominal value is determined by the charge distribution on the plates, and the deviation of the electron beam energy and current from the nominal value, the relative change in the neutron yield is calculated, the number of recorded neutrons is normalized to the relative change in the yield neutrons, which allows to reduce the error due to fluctuations in the neutron yield. The physical prerequisite for controlling the beam energy by measuring the charge distribution in the plates is the dependence of the charge distribution in the plates on the range of electrons, which depends on their energy.

Thus, the technical result of the claimed proposal is to increase the accuracy of measuring the quantity of nuclear materials.

The specified technical result is implemented using the set of essential features below.

A photonuclear device including a pulsed electron beam accelerator, converter, electron filter, collimator, neutron detectors, electronic equipment for recording signals from neutron detectors,

moreover

the electron filter is made in the form of a set of galvanically isolated metal plates, the device is additionally equipped with a means for measuring the charge induced on each of the galvanically isolated metal plates, made in the form of a multi-channel recorder and sequentially interconnectedly connected, a means of determining the deviation of the electron beam energy and current from the nominal value , a means of calculating the relative change in neutron yield, a means of normalizing the number of s neutrons on the relative change of the neutron yield.

The described set of essential features of the proposed photonuclear device is explained as follows: there is an electron accelerator with a maximum energy greater than the threshold of photonuclear reactions, a converter for converting accelerated electron energy into bremsstrahlung energy, an electron filter for absorbing electrons after passing through the converter, a neutron detector, and electronic equipment for detecting signals from a neutron detector, while

the electron filter is made in the form of a set of galvanically isolated metal plates, the total thickness of the metal plates is determined from the condition of complete absorption of electrons, the material is aluminum, the number of plates is at least two;

the charge induced on the plates is measured by a multichannel recorder that converts the charge into a digital value with a resolution of at least 8 bits;

preliminary, a numerical calculation or measurement of the dependence of the charge distribution on the plate on the plate number is performed for different beam energies W in the range of possible beam energy deviations; these data determine the calibration dependence 1 in the form W = F (q ₁ , q _{2, ..} q _{i, ..} q _N ) and the calibration dependence 2 in the form Q = φ (q _1, q _{2, ..} q _{i, ..} q _N ), where q _i is the charge induced on the plate with serial number i, which makes it possible to determine the energy W _e and the charge Q _e carried by the current per pulse of the electron beam, according to the dependence of the charge distribution on the plate on the number measured in the operating mode plates;

in the operating mode, the energy W _e and the charge transferred by the current per pulse, Q _{e of the} electron beam are calculated from the measured charge distribution from the plates using the calibration dependences 1 and 2;

preliminary, a numerical calculation or measurement of the dependence of the number of recorded neutrons on the energy W and and on the charge Q carried by the current per pulse of the electron beam in the range of possible energy deviations of the beam is performed; these data are used to construct the calibration dependence 3 in the form Y = f (W, Q);

using calibration curve 3, the correction factor is calculated where W ₀ is the nominal value of energy and Q ₀ is the nominal value of the charge;

the number of detected neutrons N _{em is} corrected: N _e = N _em · / k.

In the prior art, it is not known a means of the same purpose as the claimed utility model, which is inherent in all the essential features given in the independent claim of the utility model formula, including the purpose of the application, therefore, the proposed device is new.

The proposed device can be used in industry in the physical protection systems of nuclear facilities, in the customs control systems of containers and vehicles to identify nuclear materials in them. The proposed device allows you to determine the presence and measure the amount of nuclear materials in controlled facilities without violating the integrity of the facility. Therefore, the proposed device is industrially applicable and socially acceptable.

Figure 1 presents a block diagram of the proposed device, where the positions indicated:

1 - electronic accelerator,

2 - electron beam,

3 - converter

4 - bremsstrahlung,

5 - galvanically isolated filter plates,

6 - multi-channel recorder,

7 - collimator,

8 - container

9 - neutron detectors,

10 - nuclear material.

Figure 2. Presented: The geometry of the location of neutron detectors relative to the container.

Accordingly, in figure 2 are indicated:

8 - container

9 - neutron detectors.

The length of the detector is Ld = 300 cm, the height of the detector is Hd = 260 cm, the width of the detector is Wd = 80 cm, the length of the container is Lc = 240 cm, the height of the container is Hc = 240 cm, the distance from the detector to the axis of propagation of bremsstrahlung is Sd = 20 cm, the distance from the detector to the side wall of the container Sc = 20 cm, the distance from the detector to the roof of the container Dc = 30 cm.

In figure 3. shown: The dependence of the charge induced during the passage of the beam on the filter plates on the plate number at different beam energies. The data are normalized to the charge Q carried by the beam current per pulse.

Figure 4. shown: Dependence of the probability of detecting neutrons n _e on the beam energy. The data are normalized to 1 electron beam.

The inventive device operates as follows. A pulsed electron beam 2 emerges from the accelerator 1 and is converted by the converter 3 into bremsstrahlung 4. The filter plates 5 trap the remaining electrons, the charge from the plates is measured by multichannel registrars 6. The collimator 7 forms a sharply directed beam of bremsstrahlung 4, which irradiates the container 8. The neutron detectors 9 register neutrons from nuclear material 10.

With a specific implementation of the method:

- the electron accelerator 1 creates a pulsed beam with a nominal energy of W ₀ = 9 MeV, a pulsed current of 100 mA, a pulse duration of 1 μs, and a pulse repetition rate of 100 Hz, thus the charge transferred per pulse Q ₀ = 0.1 μC;

- the location of the neutron detectors relative to the container is shown in Figure 2 [4], the design of the detectors is taken from [5];

- the nuclear material is uranium-235 located in the center of the container;

- the container is filled with aluminum of medium density 0.5 g / cm ³ ;

- the duration of irradiation of the container 7 is 1 sec;

- fluctuations in the energy of the accelerator beam are 5%, current fluctuations - 5% [1];

- a copper converter 2 of 0.8 mm thickness converts the electron beam into a bremsstrahlung stream 3 with a maximum energy of 12 MeV;

- behind the converter 2 are installed galvanically isolated filter plates 4 of aluminum with a thickness of 7 mm each, a total of 3 plates;

- each plate is connected to a multichannel charge-sensitive amplifier of type CA-2614 manufactured by Center ADC LLC [6], which converts the charge induced on the filter plate 4 during the passage of each beam pulse to an analog voltage;

- the analog voltage using a multi-channel amplitude-to-digital converter (ADC) type LA-1.5RSI-U, manufactured by Rudnev-Shilyaev CJSC [7], is converted to a digital value and supplied to the computer in the form of the dependence of the charge induced on the plate from plate numbers;

- using the GEANT 3.21 program [8], the distribution of the charge induced on the plate, from the plate number, at different beam energies was previously calculated (Figure 3); this dependence calculated calibration dependence 1, which can be represented in the form of the expression:

,

- and calculated calibration dependence 2, which can be represented as

.

- using the GEANT 3.21 program, the dependence of the probability of neutron detection on the beam energy has been preliminarily calculated (Figure 4); this dependence calculated calibration dependence 3, which can be represented as an expression:

.

Using the measured charge distribution on the plates, using the calibration dependence 1, the energy W _e and the charge Q _e transferred per pulse of the electron beam are calculated. The error in determining the charges on the plates q ₁ , q ₂ , q ₃ is determined by the ADC capacity and is less than 1%, respectively, with the same error, the values of E _e and Q _{e are} determined.

Suppose that after the passage of a bremsstrahlung pulse, the values of the charges on the plates were q ₁ = 0.30, q ₂ = 0.49, q ₃ = 0.16, and the number of detected neutrons was N _em = 540. From calibration dependence 1, the energy W _e = 9.5 MeV is determined; from calibration dependence 2, the charge Q _e = 0.95 · Q _{0 is found} . The calibration factor 3 is used to calculate the correction factor . The adjusted value of the number of recorded neutrons N _e = 329.

In the proposed device, the influence of fluctuations in the neutron yield is compensated with an error determined by the error in measuring the charge on the plates using the ADC (δ <0.001), the error in measuring the amount of nuclear material can be reduced by more than 10 times in comparison with the prototype device.

SOURCES OF INFORMATION TAKEN INTO ACCOUNT:

1. Burmistenko Yu.N. Photonuclear analysis of the composition of the substance. M .: Energoatomizdat, 1986, 200 p.

2. Goldansky I., Kutsenko A.V., Podgoretsky M.I. Statistics of readings during registration of nuclear particles. - M .: Fizmatgiz, 1959, 411 p.

3. Mastny GF: Detection of subsurface fissionable nuclear contamination through the application of photonuclear techniques United States Patent 5495106. (Patent Number: US 5495106 (A), Date of publication: 1996-02-27, Inventor (s): MASTNY GARY F [ US], MPK: G01V 5/12; G01V 5/00; Application number: US 19940320612 19941006 - prototype.

4. Bakalyarov A.M., Bondur V.G., Germanov A.B. et al. Characteristics of instantaneous, delayed and delayed radiation during the control of highly shielded fissile materials using the pulsed photonuclear method // Atomic Energy, 2010, V.109, B.7, S.38-46.

5. Bakalyarov A.M., Germanov A.B., Karetnikov M.D. et al. Optimization of a neutron detector for controlling fissile materials using a pulsed photonuclear method // Atomic Energy, 2009, V.106, V.1, S.48-52.

6. Products of Center ADC LLC, http://www.centeradc.ru.

7. Products of Rudnev-Shilyaev CJSC, http://www.rudshel.ru.

8. GEANT3.21 Detector Description and Simulation Tool, Manual, CERN Program Library, CERN Geneva, Switzerland, 1993.

Claims (1)

A photonuclear device including a pulsed electron beam accelerator, converter, electron filter, collimator, neutron detectors, electronic equipment for recording signals from neutron detectors, characterized in that the electron filter is made in the form of a set of galvanically isolated metal plates, the device is additionally equipped with a charge measurement device induced on each of the galvanically isolated metal plates, made in the form of a multi-channel recorder, and a follower interdependently connected to means for determining the energy deviation and the electron beam current from the nominal value, means for calculating the relative change in the neutron yield, means for normalizing the detected neutrons number by the relative change of the neutron yield.