RU2356036C2 - Method of detecting and identifying covered dangerous objects - Google Patents

Abstract

FIELD: physics, measurements.

SUBSTANCE: invention is intended for detecting and identifying covered dangerous objects. The proposed method comprises the steps that follow. The hydrogen isotope ion flow is generated and modulated for ions to be extracted from the source and to be accelerated towards the target, whereon neutrons are generated. Aforesaid neutrons irradiate the object under control from three different points of the target location relative to the said object. The gamma-quantums of radiative capture or non-elastic scattering are registered and the time, the gamma-pulses arrive to the detector at, are recorded. Note here that ions are accelerated by variable high-frequency electric field and their flow is modulated after extraction from the ion source by phase grouping in the first accelerating section and accelerated. The accelerator target position is changed relative to the controlled object by translating the accelerator or controlled object perpendicular to ions (neutron flow) acceleration direction and the spatial coordinates of required object are defined in the Cartesian axials referenced to the controlled object with the help of an appropriate set of equations.

EFFECT: increased validity of detection and identification of covered dangerous objects in radiation control process.

2 cl

Description

The invention relates to nuclear methods of introscopy, specifically to a technique for detecting and identifying hidden dangerous objects in bulky transportation vehicles (heavy containers, cars, etc.) using neutron fields generated in charged particle accelerators.

Known means of detection and identification of explosive and narcotic substances using the interaction of neutrons with the nuclei of the elements that make up these substances [1]. Such interactions include nuclear reactions of inelastic scattering, radiation capture and activation, as a result of which gamma quanta are formed, the spectrum of which allows the indicated identification to be carried out.

Closest to the proposed technical solution is a control method for heavy containers and vehicles, described in [2], which can be taken as a prototype.

According to the prototype method, the control object is irradiated from three spatially separated points (d-t) -neutrons generated by a neutron generator based on a direct-acting accelerator tube. In this case, preliminary klystron modulation of the deuteron flux in the ion source is carried out in order to obtain a short neutron pulse (several ns). Such a neutron pulse should, in the opinion of the authors of the prototype, provide the necessary degree of localization of the dangerous object.

The disadvantage of this method is the presence of a large instantaneous current density of deuterons obtained in the process of klystron modulation, which will prevent the extraction of deuterons in the diode gap of the accelerator tube in accordance with the Boguslavsky-Child-Langmuir law (law "3/2") [3]. As a result, in the diode gap it will be impossible to accelerate a sufficient number of deuterons to the target in order to obtain the neutron flux necessary to provide an acceptable detection sensitivity and identification of the hidden object, as well as satisfactory measurement statistics. In addition, the isotropy of the emission of (d-t) neutrons from a target of a neutron generator based on a direct-acting accelerator tube does not allow one to obtain directed neutron radiation fluxes due to the small momentum of an accelerated deuteron.

The technical result of the proposed method is to increase the reliability of detection and identification of hidden hazardous objects in the process of radiation control by increasing the average neutron flux directed to the control object while eliminating the noted disadvantages of the prototype.

This result is achieved by the fact that in the known method [2], which includes the formation and modulation of the ion flux, their extraction from the ion source, subsequent acceleration to the target, neutron generation, neutron irradiation of the control object from three points spaced in space with subsequent registration of gamma quanta at the same points and fixing the time of arrival of gamma quanta relative to a neutron burst, ions according to the proposed method are accelerated in an alternating electric field, and modulation of their flow is carried out after extraction from an ion source simultaneously with their acceleration as a result of grouping in the first accelerating section. The position of the accelerator target relative to the control object is changed during the translational movement of the accelerator or control object so that the direction of ion acceleration (neutron flux) does not change relative to the Cartesian coordinate system associated with the control object. Measure the time of arrival of gamma rays for a given energy region of their spectrum corresponding to the spectrum of an identifiable hazardous substance embedded in a computer information processing program. Finally, the spatial coordinates of the desired object in this coordinate system are determined using the system of equations

where i = 1, 2, 3,

τ _i is the arrival time of gamma rays with energy in a given energy region,

x, y - coordinates of the desired item to be determined, perpendicular to the direction of acceleration of ions,

z is the coordinate of the desired item to be determined, directed along the line of acceleration of ions,

x _0i , y _0i — coordinates of the accelerator target perpendicular to the direction of ion acceleration,

z _0i is the coordinate of the accelerator target, directed along the ion acceleration line,

k is the number of nucleons in the nucleus of an accelerated ion of a hydrogen isotope,

A is the atomic number of the target nucleus of the accelerator,

T is the kinetic energy of the accelerated ion,

Q is the energy yield of the nuclear reaction,

M is the mass of the neutron.

The system of calculation equations (1) is obtained by considering the process of neutron formation in the target as a result of (p, n) or (d, n) nuclear reaction. In accordance with the law of conservation of energy, the following relationship holds:

where T _i - kinetic energy of the formed new nucleus,

v _i is the neutron velocity.

The law of conservation of momentum is conveniently written taking into account the above conditions for the orientation of the accelerator relative to the object of control in the following form:

where e _z is a unit vector directed along the z axis,

n is a unit vector that determines the direction of departure of a new core,

r is the radius vector with coordinates {x, y, z},

r _0i is a vector defining the coordinates of the accelerator target {x _0i , y _0i , z _0i }.

By squaring equation (3) and excluding the energy T _i from equation (2), we obtain, after simple transformations, the expression for the velocity of a neutron falling at the point of a dangerous object

If we neglect the time taken by the gamma quantum to travel from the place of its birth in the region of the object to be detected to the detector (<10 ns) compared to the time taken by the neutron to travel from the target to the specified object (> 100 ns), then this distance is divided by neutron velocity we arrive at the system of equations (1).

Test computer analysis of system (1) showed that in order to maintain acceptable accuracy of the location of a dangerous object, it is necessary to designate the limits of the change in the coordinates of the location of the accelerator target relative to the maximum linear size of the control object L. These limits can be denoted using the following approximate inequalities:

where h _i , H _i are the minimum and maximum distances of the accelerator target from the control object, respectively.

When these inequalities are fulfilled, the absolute localization error will not exceed 10% of L.

To implement the proposed method, a resonant accelerator of protons or deuterons with an energy of 2 to 20 MeV with a resonant frequency of ~ 100 MHz can be used. The accelerator for higher energy is not advisable to use because of its large size.

In the process of control, the position of the accelerator is fixed, after which the acceleration of protons or deuterons to the target containing deuterium, tritium, lithium or beryllium is carried out. Possible uses of other neutron-forming substances depending on the energy of accelerated particles.

When the front of the neutron flux reaches a hidden object, a gamma-ray flux is generated, some of which reaches the detector located next to the accelerator target. This process occurs almost instantly, because the neutron speed is much less than the speed of light.

Determining the arrival time of a gamma-ray pulse with a given energy distribution corresponding to the nuclei of the elements that make up the hazardous substance to the detector for three different accelerator location points, substituting these values in the system of equations (1) and solving this system, we find the coordinates of the hidden dangerous object sought. In particular, if the object of detection is an explosive substance (hexogen, octogen, etc.), then identification should be carried out by the energy gamma spectra of nitrogen, carbon, oxygen and hydrogen.

To take spectrograms, a gamma spectrometer connected to a detection system consisting of a scintillation crystal, a light-to-electric signal converter, and a multi-channel amplitude analyzer can be used. As such crystals, compounds NaI (Tl), CsJ (Tl), LiI (Eu), ViGe ₃ O ₁₂ , CdWO ₄ , etc., in which short bursts of light (scintillation) are excited, can be used . Moreover, the energy of such a flash is proportional to the energy of the detected photon.

The scintillating volume is optically coupled to an electronic photomultiplier or LED, which convert light flashes into electrical pulses. Their amplitudes after the process of formation and calibration also turn out to be proportional to the energies of gamma rays. Then the stream of these pulses enters the multichannel amplitude analyzer, which provides information about the energy spectrum of gamma rays. After its computer processing according to well-known algorithms used, for example, in gamma-spectrometric elemental analysis of rocks [4], the final signal is generated for fixing the time τ _i . The computer gives this signal after the coincidence of the measured spectrum of gamma radiation with the reference specified in the computer.

The described measurement procedure is carried out three times, for different positions of the target relative to the control object, so that the number of equations in system (1) is equal to the number of unknowns. For this, the accelerator is moved relative to the control object or vice versa. In principle, to increase the accuracy of measurements, control can be carried out from a larger number of points. In this case, the system of equations (1) becomes overdetermined and the least-squares apparatus should be used to solve it.

Consider, as an example of the implementation of the proposed method, the control of a container with a characteristic linear size of ~ 10 m. In this case, with a localization accuracy of the hazardous object of ~ 10%, the distance between the leading and trailing edges of the neutron packet should not exceed ~ 1 m. Let be used as a neutron generator resonant deuteron accelerator with a tritium target with an energy of 2 MeV. The neutron energy in this case is estimated at about 15 MeV. This corresponds to a neutron velocity of ≈5.10 ⁷ m / s. The order of the target – object distance is estimated in accordance with inequalities (5) ~ 10 m. Therefore, to ensure the indicated degree of localization, the duration of the deuteron current pulse on the target should be ~ 10 ns, which is quite achievable for an ion resonance accelerator. As a registration system, standard gamma-field spectrometry tools used, for example, in nuclear geophysics can be used.

The proposed method will significantly increase the efficiency of detection, localization and identification of dangerous objects in bulky transportation means by increasing the sensitivity and reliability of control.

Information sources

1. Maglich BC et al. 4 ^th International Symposium on Technology and the Mine Problems, March 13-16, Naval Postgraduate Schol, Monterey, California, p. 89.

2. Karetnikov M.D., Meleshko E.A., Yakovlev G.V. A method for generating nanosecond neutron pulses and its possible use. Sat materials of the interdisciplinary scientific and technical conference "Portable neutron generators and technologies based on them", VNIIA, 2003, p.110-116.

3. Lebedev A.N. Physical processes in high current diodes. M., MEPhI, 1995, 60 p.

4. Exploratory nuclear geophysics. Handbook of geophysics. M., Nedra, 1986, 432 p.

Claims (2)

1. A method for detecting and identifying hidden dangerous objects, in which they generate and modulate a stream of hydrogen isotope ions, extract them from an ion source, accelerate them to a target, generate neutrons on a target, irradiate neutrons with a neutron from three different target locations relative to the monitored object, register gamma-quanta of radiation capture or inelastic scattering and fix the arrival times of gamma-pulses to the detector, characterized in that the ions accelerate by an alternating high-frequency electric field m, and modulate their flow after extraction from an ion source, by phase grouping in the first accelerating section simultaneously with their acceleration, change the position of the accelerator target relative to the control object by translational movement of the accelerator or control object perpendicular to the direction of ion acceleration (neutron flux) and determine spatial coordinates of the desired object in the Cartesian coordinate system, rigidly connected with the control object, using the system of equations

where i = 1, 2, 3,

τ _i is the arrival time of gamma rays with energy in a given energy region;
x, y - coordinates of the desired item to be determined, perpendicular to the direction of acceleration of ions;
z is the coordinate of the desired item to be determined, directed along the line of acceleration of ions;
x _0i , y _0i — coordinates of the accelerator target, perpendicular to the direction of ion acceleration;
z _0i is the coordinate of the accelerator target, directed along the ion acceleration line;
k is the number of nucleons in the nucleus of an accelerated ion of a hydrogen isotope;
A is the atomic number of the target nucleus of the accelerator;
T is the kinetic energy of the accelerated ion;
Q is the energy yield of the nuclear reaction;
M is the mass of the neutron. 2. The method according to claim 1, characterized in that the coordinates of the location of the accelerator target are changed within:

where h _i , H _i are the minimum and maximum distances of the accelerator target from the control object, r _0i is the vector defining the coordinates of the accelerator target {x _0i , y _0i , z _0i }, L is the maximum linear size of the control object.