RU2729064C1 - Method of converting nuclear energy (energy of radioactive decay and/or fission) into optical energy and device for implementation thereof - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to a means of converting nuclear energy (energy of radioactive decay and/or fission) into optical energy and can be used for pumping active medium of a laser. Invention provides passage of nuclear particles through at least one layer of activated scintillator to obtain radiation of narrow spectrum or several narrow spectra in range from infrared (IR) to ultraviolet (UV) and subsequent conversion of obtained radiation into energy of coherent laser radiation. Wherein an arrangement is made for an activated scintillator at a certain distance to the active medium of the laser in a solid or liquid aggregate state and transmitting said pumping radiation from the activated scintillator to the active laser medium through the gradient waveguide with introduction of said radiation through the side surface of the waveguide, partially or over its entire length and/or through its end surface.EFFECT: high efficiency of converting energy of nuclear radiation into energy of a narrow-spectrum photon and obtaining a pumping means for lasers with high specific power.2 cl, 3 dwg, 2 tbl

Description

The invention relates to quantum electronics and can be used for the transformation of nuclear energy (the energy of particles in the radioactive decay of isotopes and isomers and the energy of fission fragments) into a luminous flux of a narrow spectrum, followed by its use for pumping the active medium of a laser to obtain a beam energy output with a high conversion efficiency ...

It is known that when the products of a nuclear reaction pass through a substance, energy is transferred from these products to particles of the substance, while the energy of the so-called ionizing radiation (nuclear particle) is spent in the process of collisions for the ionization of the substance and for radiation with different types of scattering and transitions electrons of excited levels. For different particles and their energies, the process of deceleration in matter occurs according to different laws. The overwhelming share of energy in nuclear reactions falls on charged particles: electrons and positrons in beta decay, helium-4 nuclei in alpha decay, and fission fragments in nuclear fission by neutrons. Neutral particles, with the exception of gamma quanta, do not have a large effect on the ionization process and interact, mainly, with atomic nuclei by scattering in collisions.

During the movement of particles in a substance, one of the most important characteristics is the free path of particles or the extrapolated path length, which depends on the type of particles, their initial energy and properties of the substance. In essence, this is the distance that a particle travels in such a substance before the complete loss of initial energy. Table 1 shows the extrapolated values of the electron ranges (in cm) in some substances depending on their energy.

As it moves through the substance, the particle spends its energy on the excitation of the atomic levels of this substance, which, in turn, emit electromagnetic waves during the reverse transition of electrons. As the deceleration proceeds, the processes of ionization of the surrounding matter begin to prevail with the production of secondary particles-electrons, which, in turn, lose energy for deceleration according to the same principle and, ultimately, recombine with previously ionized atoms also with the emission of radiation. In most cases, when nuclear particles pass through the depth of a substance, the process of their deceleration leads to its heating, thus, almost all radiation (including the energy of a nuclear particle) is converted into heat.

At the same time, in the case of using nuclear energy for pumping lasers, the following problem arises. The most effective for energy concentration is the solid active medium of the laser. This is indisputable due to the high concentration of atoms in the solid. Nuclear energy sources are also the most powerful in terms of the ratio of kW / kg and kW / liter today. However, to this day it has not been possible to combine both of these advantages in order to provide the best pumping for powerful and compact laser devices. Nuclear energy has a very hard spectrum and has a detrimental effect on the matrix of a solid-state (or fiber) laser. Nuclear-pumped gas lasers are known. However, they have huge dimensions with low power, and the energy input into the active medium, for a number of insurmountable technical reasons, does not exceed 35 J / liter. The most promising method of pumping solid-state (and fiber) lasers today is considered to be LED (following the example of YAG lasers). But this pumping method is coupled with the power supply of the system, has a low efficiency (the theoretical limit is 20%) and requires a large supplied power supply for a powerful laser. This again brings the problem back to converting primary energy (in this case nuclear) into electricity in the traditional way. In addition, electrically pumped lasers have a so-called LC problem. L is the inductance of the battery charging circuit, and C is the capacity. The charging and discharging times of the batteries supplying the laser depend on these parameters.

From the general state of the art, a class of substances is known that have the ability to emit light upon absorption of ionizing radiation (nuclear particle) - gamma quanta, electrons, alpha particles, fission fragments, etc. - the so-called scintillators. Traditionally, scintillators are used exclusively as particle detectors (scintillation nuclear radiation detectors). In a scintillation detector, the light emitted during scintillation is collected on a photodetector (as a rule, it is a photomultiplier tube (PMT) photocathode. Photodiodes and other photodetectors are used much less often), converted into a current pulse, amplified and recorded by one or another recording system. The number of photons emitted by a scintillator when it absorbs a certain amount of energy (usually 1 MeV) is called light yield. A large light yield is considered to be 50-70 thousand photons per MeV. To date, materials have been obtained on the basis of strontium iodide crystals doped with cerium, terbium, neodymium, europium with a photon yield of up to 120,000, and a conversion capacity of up to 34% in terms of primary energy. Studies of ceramics using gadolinium and metal-organic plastics show great promise. (Goloshumova A.A. Ph.D. thesis, "Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences named after V.S.Sobolev", 2016).

When nuclear particles pass through the scintillator, as a result of their deceleration, part of the energy is converted into radiation, which can leave the substance even at a considerable depth of the particle track. The proportion of this radiation depends on many factors. To increase the light yield and create a narrow emission spectrum of a moving particle, so-called activated scintillators are used. In this case, alloying atoms (ions) are introduced into the matrix of the basic substance. A plasma (plasmons) is formed along the track of a moving particle, especially a heavy multiply charged ion, through which energy is transferred from the matrix of the main substance to the atoms of the activator, and they, in turn, emit photons of a certain wavelength with some broadening of the spectrum.

Particles of different nature, but with the same energy when absorbed in a scintillator, give a different light yield. Particles with a high ionization density (protons, alpha particles, heavy ions, fission fragments) give in most scintillators fewer photons than gamma quanta, beta particles, muons or X-rays, while the ratio of the light yield of this type of particle to the light yield of gamma quanta with equal energy is called quenching factor (from the English quenching - "quenching").

High-energy electrons (up to energies of the order of pair production) spend almost all their energy on the formation of radiation in the scintillator and their quenching factor is of the order of unity. Fission fragments are heavy (about 80-140 amu) multiply charged (Z about 40-50) ions with a specific primary energy of about 1 MeV / nucleon. Such ions leave a bright thick trace in the scintillator, surrounded by a "broom" - a shower of secondary ionization electrons that leave their tracks. Despite the fact that the quenching of fission fragments in inorganic scintillators is no more than 25%, and in organic scintillators it is only about 5%, according to the law of conservation of energy, the rest of its share during deceleration falls on ionization and radiation during deceleration of secondary particles - electrons. Thus, without taking into account the heat losses at low and ultra-low energies at the end of deceleration and for absorption in the matrix, as well as with insignificant radiation of the matrix itself in comparison with activators, a large fraction of the energy of the fission fragment is ultimately converted into radiation of a narrow spectrum. That is, it makes sense to talk about the integral quenching factor, which, estimated and taking into account the energy removal by secondary fission neutrons, will be about 80%. It should be noted that scintillators can also produce a multi-frequency spectrum when doped with atoms of several chemical elements. In contrast to the use of scintillators as a detector, where the place, the rate of production of photons and their absorption by the activators themselves are of fundamental importance, here only the total energy output in a given spectrum makes sense, that is, a certain integral value.

Thus, according to the authors, the use of an activated scintillator in combination with a layer of nuclear material mixed into it or deposited on it, emitting nuclear particles independently and / or when irradiated from an external source, will make it possible to obtain a narrow-spectrum light energy flux converted with high efficiency, used for pumping the active medium of the laser. As analogs of such a conversion method, technical solutions under RF patents Nos. 2247451 and 2295184 can be mentioned. The first fundamental difference between the claimed solution and those presented in these patents is a more general approach to the conversion of primary nuclear energy and its use for pumping laser levels. The second fundamental difference is the use of a wider range of nuclear reactions, including nuclear fission, as a primary source of energy, which makes it possible to control the processes of energy release and obtain much higher power of devices, as well as to avoid parasitic heating of devices during their shutdown, regardless of their design and structural features. ... And the third fundamental difference is the way the nuclear fuel is placed in the scintillator. This can be either a suspension of dispersed particles with a diameter less than about 1/5 of the wavelength of the emitted spectrum, and long fibers of approximately the same diameter in concentrations that do not degrade the optical properties of the medium, or thin alternating layers of nuclear material deposition and thicker scintillators. But also partial or complete replacement of some atoms of the matrix or the scintillator activator with nuclear fuel atoms (isotopes) can be used, provided that these atoms have chemical affinity or replace an ordinary atom with its (working, giving primary energy) isotope. An example is the affinity of actinium-228 and lanthanum. That father-in-law, in a scintillator containing lanthanum, it is possible to replace it with an isotope of actinium; or substitution of strontium in the iodide crystal for strontium-90 isotope. And by analogy - the use of fuel isotopes of uranium-235 (233) and plutonium-239 in scintillators with related elements, for example, "glowing" uranium glasses. A similar solution was proposed by the authors in patent No. 2694362 dated 12.07.2019.

Thus, the problem solved when creating the claimed method is the possibility of using self-decaying (radioactive) materials, fissile nuclear fuel, etc. to obtain optical energy of laser radiation, in particular, in the possibility of using for these purposes relatively cheap sources of nuclear energy, including nuclear waste, etc. The technical result achieved when solving the problem is the possibility of increasing the efficiency of conversion of nuclear energy into the energy of the photon flux of a narrow spectrum, with the simultaneous possibility of significantly reducing the size of such converters, increasing their service life and reducing the cost.

To achieve this result, a method for obtaining coherent radiant energy is proposed, in which the passage of nuclear particles through at least one layer of an activated scintillator is provided to obtain pumping radiation of a narrow spectrum or several narrow spectra in the range from infrared (PC) to ultraviolet (UV) and subsequent conversion of the obtained pumping radiation into the energy of coherent laser radiation, including the location of the activated scintillator at a certain distance to the active medium of the laser in a solid or liquid aggregate state and the transfer of the said pumping radiation from the activated scintillator to the active medium of the laser through a gradient waveguide with the introduction of this radiation through the side surface the waveguide partially or along its entire length and / or through its end surface.

To achieve the set result, it is also proposed to convert nuclear energy (energy of radioactive decay and / or energy of fission of atomic nuclei) into energy of coherent laser radiation (nuclear photo-energy converter), containing at least one layer of an activated scintillator with at least one emitting surface, in contact with which a gradient waveguide is located, connected with the active medium of the laser in a solid or liquid aggregate state, with a pumping frequency lower than or close to the most probable frequency of the narrow emission spectrum of the activated scintillator, while nuclear fuel is embedded in the activated scintillator layer in the form of granules and / or fibers, and / or such a layer is located in contact with at least one layer of nuclear fuel and / or atoms of nuclear fuel replace chemical elements similar to them in the composition of the scintillator itself.

Further disclosure of the technical feasibility of the claimed group is illustrated by the following figures:

in fig. 1 shows the process of capturing radiation from a scintillator by such a gradient waveguide;

in fig. 2. the given diagram of one of the possible options for the technical solution of the gradient waveguide;

in fig. 3 is a diagram of one of the basic embodiments of the claimed method. Within the framework of the claimed group of inventions for pumping the active medium (AS) of a laser, it is necessary to achieve saturation of laser levels in excess of 50% of their concentration in the AS during times of the order of life of this level. The most promising authors consider the use of a glass laser-doped active medium, which makes it possible to obtain a product of any shape in a wide range of volumes and with a wide range of doping concentrations up to 10% mass fraction (see the products of Lytkarinsky Optical Glass Plant, Shvabe). However, this does not remove the problem of rapidly supplying a significant amount of energy (a certain input of energy) to an AS of small volume (high concentration of laser atoms). In the currently existing technical solutions for solid media (lamp, diode, solar pumping) there is a paradigm laid down since the days of lamp-pumped ruby lasers. It was theoretically and experimentally established that, to achieve inversion, the power density of radiation supplied to a ruby crystal (garnet, glass, ceramic, or fiber with a similar content of laser levels) is comparable to the power density of the discharge in a xenon lamp, and the size of the pumping device is approximately equal to the size of the AS. For example, a ruby AS requires a pump power density of the order of 1000-10000 W / cm ³ with a flash time of the order of 1 ms. Energy contribution of the order of 1-10 J / cm ³ (Yu.V. Baybarodin, Fundamentals of laser technology).

Nuclear reactions (especially the fission reaction) may well provide such energy input and even power both in the flash mode (train pumping) and in the stationary pumping mode. However, there is a problem of the pumping device - the scintillator medium. If a device with such an energy release is created, then the scintillator medium will instantly collapse due to thermal overloads.

Therefore, to implement the method in this invention, the design of a pumping medium with a volume much larger than the volume of an AS laser with a specific energy release of the order of 1-10 J / cm ³ (relatively dim glow in the volume of the scintillator) and with a high power density in a pulse in the the same 1000-10000 W / cm ³ for a pulse time of 1 ms), but with the number of pulses of the order of 1 per second, which will give a time-reduced thermal load on the medium no more than 1-10 W / cm ³ . Then it remains to solve the problem of transporting this radiation scattered over a large volume and its concentration into a small volume of the AS laser. For this purpose, the claimed device uses a gradient waveguide (or a system of such waveguides alternating with layers of a scintillator with nuclear fuel embedded in it).

The pumping device, as one of the design options, is a cylinder of large diameter D with a coaxially located insert of small diameter d (D >> d) in the form of an active laser medium, an AS, limited by an optical cavity in the form of a mirror surface. The space between D and d consists of alternating layers of a scintillator with embedded nuclear fuel (optionally with forced cooling elements) and gradient waveguide disks - flat disk-shaped gradient waveguides. In these waveguides, the receiving surface of the radiation is the lateral surface, the outer end (edge) D is mirror-like, and only the inner end (edge) of small diameter d and width h serves as the output surface. The gradient of the refractive index is directed from the radiation receiving surface along the thickness of the disk. Each scintillator layer clamped by two such discs constitutes an element of the pumping device. All elements of the pumping device are tightly pressed by the sides of the waveguides with the maximum n along the entire length of contact of their radiating inner ends (edges) with the AS rod of small diameter d.

A gradient waveguide (GW) is a (waveguide) device for transmitting electromagnetic energy in the form of electromagnetic waves with a cross-sectional refractive index. There are GWs with a stepped distribution n and with a smooth, for example, parabolic, secant or other, given by the function n (x, y, z) in general form in Cartesian coordinates or n (r) in the often widespread cylindrical geometry. The essence of the phenomenon of capture and transport of radiation along the GW is described by the law of total internal reflection. Technically, n varies by doping transparent materials (glasses, plastics, crystals, and ceramics) with certain additives (metal ions, borates, germanates, cerium oxides, praseodymium, etc.) that are transparent in a given optical frequency range. The refractive index also depends significantly on the radiation wavelength. For the near and mid-IR range (neodymium laser), according to reference data, for example, industrially and commercially produced glasses have a range of n in the range from 1.45 (fluorinated quartz) to 3.05 (IKS32). But there are also materials with n> 4 (ceramics, crystals and glass doped with germanium). There are also materials with n <1.36 (LiF doping). (see Optical materials. Part 2 Tutorial for designers of optical systems and devices; VA Zverev, EV Krivopustova, TV Tochilina, St. Petersburg National Research University of Information Technologies, Mechanics and Optics).

According to David Bailey and Edwin Wright (Fiber Optics. Theory and Practice. ISBN 5-9579-0093-1), since the fiber is cylindrical, the rays entering the fiber form a cone. All rays entering the core from the inside of this cone will fall on the shell at an angle greater than the critical one, so they can safely propagate along the fiber. This cone is called the "receiving cone".

Half (θ ₁ ) of the angle at the top of the receiving cone is called the “receiving angle”. Its value depends on the refractive indices of the core, shell and air (moreover, air has a refractive index of 1) or any other material of the light source. A ray of light entering the core at an angle greater than θ ₁ will be scattered in the cladding. A ray of light entering at an angle of exactly θ ₁ will fall on the core-cladding interface at a (critical) angle θ _C and will move parallel to this boundary.

A special measure is used to indicate the collecting capacity of the fiber. It is called the numerical aperture. Numerical aperture is the sine of the receiving angle, that is:

NA = sin (θ ₁ ).

It can also be expressed in terms of a fiber refractive index multiplier.

If there are two fibers with the same core diameter but different numerical apertures, the larger aperture fiber will receive more light energy from the light source than the smaller aperture fiber. If there are two fibers with the same aperture but different diameters, the larger diameter fiber will receive more light energy into the core than the smaller diameter fiber.

Optical fibers with large apertures or diameters receive more light than fibers with smaller apertures or diameters. Fibers with larger apertures and diameters are more suitable for low-cost transmitters, such as LEDs, which cannot concentrate the output energy into a narrow coherent beam (like lasers) and emit at a large angle. However, the disadvantage of a fiber with such parameters is the large dispersion (scattering) of the light introduced into the core, and therefore, a decrease in the transmission bandwidth of the fiber transmission. On the other hand, a fiber with a smaller aperture or diameter will have a higher bandwidth. This is because relatively parallel light rays enter the core and their dispersion along the fiber will be less. The disadvantage in this case is the need for more expensive light sources (such as lasers), providing narrower beams of light, and more accurate alignment of the transmitter and core.

Bailey and Wright consider the case of radiation input from the GW end with the side surface closed by a protective casing. Most often, such a scheme is used when pumping fiber lasers. This is due to the very small diameter of the fiber core, which in this case is the AS of the laser. Such a fiber is single-mode and has a very low difference in the refractive index Δn ~ 0.01, weakly absorbs multimode radiation at the end. However, due to its multiple reflection along the length of the coaxial GW, the effect of side pumping is created, which is more uniform.

In our case, we consider the lateral entrance of radiation into a plane GW from a scintillator of rather moderate intensity through planes of a large area and its transport by a waveguide to a narrow end, which also contacts the solid AS of the laser along the lateral surface. In this case, the reception cone degenerates into a radiation loss cone, which is obvious from Fig. 1.

будет находиться в пределах от

до

и

из расчета в половину телесного угла на каждую группу ГВ.In this case, point radiation sources are located in a spatially extended flat slit filled with a scintillator between two GWs of the same length. With the linear dimensions of the HS of the order of hundreds of mm and the width of no more than 1 mm, the edge effects can be neglected in the first approximation. Then our angle of entry of radiation (capture)

will range from

before

and

at the rate of half the solid angle for each group of HS.

≈0,88, что соответствует углу

≈ 1,076 радиан. Тогда

≈ 0,5 радиана. При условии равновероятного распределения излучения сцинтилляций это значит, что ГВ увлекает более 2/3 излучения при первом же контакте с ним. Но это не означает, что 1/3 излучения теряется, поскольку:For a wave of the order of 0.760 - 1.550 μm using only glass as the basis for the HS (range n), we obtain

≈0.88, which corresponds to the angle

≈ 1.076 radians. Then

≈ 0.5 radians. Provided that the distribution of scintillation radiation is equiprobable, this means that the GW carries away more than 2/3 of the radiation at the first contact with it. But this does not mean that 1/3 of the radiation is lost, because:

- it is possible to manufacture a combined GW with a large n _max ;

- the system is completely surrounded by a mirror resonator, and the longer the photon moves in the medium, the more likely it is to scatter from the corners of the loss cone;

- scintillator activators are also absorbers of their own radiation, while they also re-emit it; In other words, radiation in the scintillator can undergo significant diffuse scattering due to a succession of absorption and repeated radiation by the activator atoms (the matrix itself is transparent) and can also be captured by the gradient waveguide when it passes through it again taking into account the capture angles, or goes to the next iteration.

Structurally, it is possible to implement a practical scheme of the claimed converter, in which a certain volume of a conditionally transparent elastically scattering radiation medium with a flash source (with absorption and backward radiation) of photons, limited by a mirror reflector and a radiation drain surface - the side surface of the laser AS, which is similar to a large sphere with an inner mirror surface of diameter D, filled with a substance transparent for photons with inclusions of atoms that absorb and after a very short time re-emit these photons, and a drain hole with a diameter d << D. Inside the sphere, a flash of N photons occurs with a total total energy E = hν × N. Then, during the flash time t >> τ, where τ = D / C, which will depend on the speed of light in the medium C and on d / D - geometry ( t≥τ × [D / d] ² and τ≥τ * is the lifetime of an excited state when a photon is absorbed / emitted by an activator), with a reflection coefficient of ~ 1 and a loss coefficient in the medium close to 0, all this radiation and all the flash energy comes out through the hole d in a time of the order of (1 _... 2) t, while the spatial distribution of radiation from the hole d will be the same as that of the original flash, for example, according to Poisson - uniformly in 2π on the plane perpendicular to the normal to d. That is, the brightness (energy / time / source area = W / cm ²⁾ grows downstream of the small aperture, compared to the brightness on the surface of this sphere as a ≈ [D / d] ^2/2.

In any case, all radiation generated in the volume of the pumping device V, taking into account losses in materials and on reflecting surfaces, will inevitably be transferred into the volume v << V of the laser active medium.

Since in a GW, in the absence of significant absorption (losses in modern waveguides are approximately 0.2-1 dB / km, and the radius of flat waveguides does not exceed tens of cm, and the size of the entire structure between external resonators is hundreds of cm), the light flux is Ф = const, then its the density F / S (and hence the brightness W / cm ² ) when entering through the side surface of a group of HW and exiting through the end (edge) with a smaller area will grow in proportion to the ratio of these areas (a similar geometry is considered in the work "On increasing the brightness of optical radiation", IN Sissakian, AV Schwarzburg, AV Shepelev; "Computer Optics", No. 9, pp. 36-48; 1991, ICNiTI Central Design Bureau for Unique Instrumentation RAS, p. 45, Fig. 4; RF patent 2024895 "Method of lighting objects" dated 15.12.1994).

Known methods of introducing radiation into a gradient waveguide (GW) from the end and from the lateral surface (see "Waveguide Photonics", NV Nikonorov, SM Shandarov, ITMO, 2008 Fig. 5.3, p. 60).

In our case, a possible material for the receiving surface is glass with a minimum n (1.45 is given in estimates and up to 1.35 is known for quartz glass). For the overwhelming majority of scintillators suitable for our purposes, we have n ₃ : for the strontium iodide matrix (SrI ₂ : Eu, Ce, Tb, Nd, etc.) n = 2.05; for strontium titanate (SrTiO ₃ ) n = 2.41; CsI: Tl n = 1.79; LaBr ₃ (Ce) n = 1.9; PbWO ₄ n = 2.19; BGO n = 2.15, etc. (Manufacturer's data. Leningrad Laser Systems. ITMO Technopark). In this case, the gradient waveguides and the scintillator layer will form a single waveguide system with a source of diffuse radiation in the local maximum n central over the section and limited from all sides, except for the exit end (edge) by a mirror resonator.

, испытав диффузное отражение на границе волновода, будут иметь большую вероятность захвата, которая будет расти с итерациями к примерно как

при условии случайного распределения. Также возможно применение известного метода повышения яркости с помощью клиновидного волновода. В этом случае волноводный диск выполняется в клиновидном сечении с заострением к большему диаметру, что обеспечит выход захваченного излучения через «раствор» клина с ростом яркости. Однако надо учесть, что в волновод будет поступать и УСИ (усиленное спонтанное излучение) из АС лазера с высокой радиальной составляющей. А сужение градиентного волновода часто используют именно для вывода многомодового излучения. Поэтому для возврата мод с направлением по радиусу от центральной оси необходима смена угла на π, то есть гладкое боковое зеркало с высоким коэффициентом отражения - боковой резонатор. Схема подобных улучшений изображена на фиг. 2. Приведенная схема технического решения находится в рамках заявленного способа ядерной накачки твердотельного (или жидкостного) лазера и, по мнению авторов, позволит повысить ее оптические характеристики, КПД накачки и компактность устройств, но не является принципиальной с точки зрения осуществимости способа.In order to improve the capture of radiation by the waveguide and its transportation to the laser AS, it is possible to use a number of already known technical solutions. For example, to reduce the number of photon transformations in the scintillator, a diffusely reflecting waveguide surface with maximum n can be fabricated. Then the photons hitting the loss cone

, having experienced diffuse reflection at the waveguide boundary, will have a high capture probability, which will grow with iterations to approximately as

subject to random distribution. It is also possible to apply the known method of increasing brightness using a wedge-shaped waveguide. In this case, the waveguide disk is made in a wedge-shaped section with a sharpening to a larger diameter, which will ensure that the trapped radiation escapes through the "opening" of the wedge with increasing brightness. However, it should be taken into account that ASE (amplified spontaneous emission) from an AS laser with a high radial component will also enter the waveguide. And the narrowing of the gradient waveguide is often used precisely for the output of multimode radiation. Therefore, to return the modes with a direction along the radius from the central axis, it is necessary to change the angle to π, that is, a smooth side mirror with a high reflection coefficient - a side resonator. A diagram of such improvements is shown in FIG. 2. The presented scheme of the technical solution is within the framework of the claimed method of nuclear pumping of a solid-state (or liquid) laser and, in the authors' opinion, will improve its optical characteristics, pump efficiency and compactness of devices, but is not fundamental from the point of view of the feasibility of the method.

Let us estimate the required parameters of the pumping device and the AL laser of realistic dimensions. Let's set the following parameters:

the outer end (edge D) of such discs is covered with a reflective layer, the inner (edge d) is open for emission of radiation. In this case, the surface area receiving radiation scintillator disc 2 is S _n = 2 × (D ² -d ²⁾ π / 4 ≈ πD ^2/2. And the area of radiation emission in AC: S _n = 3πdh (1 scintillator layer 2 mm and 2 waveguides 0.5 mm each - for 3 mm of the AS rod length).

Thus, the gradient waveguide is a brightness (power density) concentrator released in the volume of a disk stack in a scintillator with fuel cells. At d ~ 1 cm, D ~ 15 cm, h ~ 0.1 cm in terms of brightness, its gain by the waveguide will be about 60 times! In other words, in order to provide a pump power density in the AS of the order of 10 ³ W / cm ² in the pumping medium, it is necessary to provide an energy release to the receiving surface of the waveguides of the order of 7 W / cm ² , which is quite realizable even in a stationary mode. In this case, the volumetric power density in the AU will reach 1000 W / cm ³ , and the volumetric power density in the scintillator is about 70 W / cm ³ , which also fits into the framework of permissible loads. It should be understood here that the diameter D can be increased and the load on the scintillator can be decreased, although it is limited by engineering considerations. For example, for a scintillator based on ZnS crystals (C _p ≈ 1.8 J / cm ³ K) with a conversion capacity of about 25% (heating ~ 200 W / cm ³ ), even without cooling, the time of continuous operation at this power density will be about 1 2 seconds until the medium heats up above 100 K from the initial temperature.

It should be especially emphasized that it is inexpedient to focus on a ruby laser for at least two reasons. First, its AS is a crystal with a very insignificant variation in the density of laser ions Cr ³⁺ , which does not allow power maneuver and requires a high power density in the AS for stationary operation (which was rightly noted by the expert). But solid-state lasers are not limited to artificial ruby and garnet crystals! In this sense, neodymium glass is an ideal candidate for an AU. It allows you to create speaker systems with Nd ²⁺ content from hundredths of% to 10% of the mass fraction of neodymium! That is, on its basis it is possible to create lasers from high-power pulsed to weak stationary ones, and it is ideally suited in terms of neutron-physical and other parameters to the claimed pumping method (data on glasses were given earlier with reference to manufacturers: Shvabe concern and Lytkarinsky plant optical glass "). Secondly, the ruby laser is three-level, and the neodymium laser is four-level, which gives a significant gain in efficiency.

The literature indicates the attainable parameters of the surface power density and the specific energy input into the AS of solid-state lasers. In this case, it is extremely incorrect to rely on the power density alone, since the accumulation of parasitic heat in the laser AS and the conditions for its cooling depend on the temporal characteristics of the pulse. Today, in solid AS the following are achievable: W ~ 10 ¹² W and P ~ 10 ¹⁰ W / cm ² , but at τ ~ 1 ns in the pulsed mode (or Q-switched mode), which corresponds to an energy input of the order of E ~ 1 kJ / cm ³ ( and the energy in the beam is about 1 kJ) and leads to the destruction, for example, of the same neodymium glass SNLG (GLS22 or QX / Nd) at E / S ~ 22 J / cm ² - see.

https://ru.wikipedia.org/wiki/Fiber laser, as well as a dissertation for the degree of candidate of technical sciences, Moscow-2013, Glushchenko Ilya Nikolaevich, “Neodymium and ytterbium thermally stable and chemically resistant glasses on a phosphate basis for diode pumped lasers ": C _p ~ 2 J / gK, T mel _. ~ 1100-1300 ° C. The work was performed at the Federal State Budgetary Institution of Science, Institute of General Physics. AM Prokhorov of the Russian Academy of Sciences (GPI RAS), ctata:

“Laser studies of neodymium glasses SNLG in continuous and repetitively pulsed modes were carried out jointly with the staff of the Laboratory of Physical and Applied Problems of Solid-State Lasers of the GPI RAS. The samples of industrial glass GLS22 at our disposal made it possible to directly compare the laser properties of industrial and developed glasses. Investigations of the lasing characteristics of active elements (AEs) made of these glasses were carried out under experimental conditions as close to each other as possible in order to correctly compare their laser properties. The concentration of neodymium ions in both glasses was 2 × 10 ²⁰ cm ^-3 . A simple scheme of a resonator with mirrors deposited directly on the ends of the active elements was used. The working length of the active elements was 2.5 mm. A diode array with a fiber output of radiation (~ 803 nm) with an output power of up to 12 W. The pump radiation was focused on the AE into a spot 150 mm in diameter as a pump radiation source.

CW lasing was obtained on SNLG with an output power of 300 mW at 3.2 W pumping, and on GLS22 - 160 mW at 1.4 W pumping, with the corresponding values of the differential efficiency of 13.4 and 16.25% (see Fig. 7 ). A further increase in the pump power led to the destruction of the AE (the appearance of cracks) in the zone of action of the pump radiation.

Lasing studies were carried out up to the destruction of the AE on a series of 3 laser elements of each type. " End of quote.

From the above data, it is obvious that the pumping was carried out in the AS volume of the order of V ~ πd ² L / 4 ≈ π × (0.015) ² × 0.25 / 4 ≈ 4.42 × 10 ^-5 cm ³ with constant generation of 300 mW. Then the limiting volumetric power density of radiation in the AU (with constant generation of 300 mW) will be about 6-7 kW / cm ³ . And the pump power density is ~ 18 kW / cm ² and 73 kW / cm ³ at 3.2 W of pump power.

This data is also consistent with data from other sources, for example: https://studopedia.ru/7_148041_tverdotelniy-lazer.html; "Physics of Lasers" by V.S. Airapetyan, O.K. Ushakov, Novosibirsk, SGGA, 2012, see below, table 2, the main parameters of the technical parameters of neodymium lasers.

The use of fissile materials as a fuel, as opposed to radioisotopes, makes it possible to control the reaction and release of energy in

pumping device. And, as a consequence, it makes it possible to create stationary lasers. And pulsed with a train pumping with the help of "nuclear flash".

Let us estimate the power density in the pumping device in the "nuclear flash" and stationary operation of a nuclear laser-reactor system (see G. A. Bat (ed.), V. D. Baibakov, M. S. Alkhutov "Fundamentals of theory and methods calculation of nuclear power reactors ", Energoatomizdat, 1982; Abagyan LP, Bazazyants N.O., Nikolaev M.N., Tsibulya AM" Physics of nuclear reactors "; Lukin A.V. (ed.)" Pulsed nuclear reactors RFNC - VNIITF ", Snezhinsk: RFNC-VNIITF, 2002. Physics of nuclear reactors. 1994. Issue 2." Pulse reactors and simple critical assemblies "; Proceedings of the conference" Problems of nuclear-pumped lasers and pulsed reactors. "Snezhinsk, 2003; Dyachenko PL ., Kukharchuk OF, Fokina OG, Shchukin AN "Optimization of pump pulse parameters in the reactor-laser facility of stand" B "; Proceedings of the conference" Physics of nuclear-pumped lasers and pulsed reactors. "Obninsk, 2007 ; Dyachenko PP, Fokin GN "Ignition reactor and pump pulse parameters in a reactor-laser system").

LYAN is a nuclear-pumped laser, usually a laser-reactor system, where the system for pumping the laser with nuclear fission energy is at the same time part of the core (core) of a nuclear reactor. Provided that the pumping device is of sufficient size and critical, it can itself be a reactor core (this is most effective). However, in existing installations (for example, BARS-6), a pumping device consisting of more than 500 laser elements (LAEL) is only part of the core and no more than 30% of the total energy of a nuclear reactor is released in it. There are also small laboratory samples irradiated by an external neutron flux from the source reactor, which do not affect its characteristics with their secondary neutrons. In this case, the pumping devices are subcritical reactors with an external source of primary neutrons, K _eff << 1 and with a small neutron multiplication factor K _um . At present, LYAN uses exclusively a gas-assisted AS laser, since the pumping is performed by direct contact of fission fragments with the AS material. This entails a lot of disadvantages, namely: large dimensions and low specific energy and pump power.

The method proposed in this application with the help of an "intermediary" - scintillation radiation - makes it possible to exclude direct contact of nuclear particles of high destructive force with the AC substance and, thereby, to switch to the use of concentrated solid (or liquid) AC, and make the pumping device compact even when reaching critical parameters (pumping device = core, reactor core).

And be that as it may, in all options for organizing nuclear pumping of a laser, the rate of fission reactions is calculated through the neutron flux: R _f = Ф _n × Σ _f , where R _f is the number of fission reactions per unit time per unit volume (in our case, a scintillator with fuel), Ф _n is the neutron flux density (Ф _n = nV), Σ _f is the macro section of the fission reaction (Σ _f = N _top × σ _f ).

From the data presented in the literature, it is known that in stationary thermal (slow) neutron nuclear reactors Φ ~ 10 ¹² -10 ¹⁴ neutron / (cm ² × s), and in stationary fast reactors Φ ~ 10 ¹⁴ -10 ¹⁵ neutron / (cm ² × from). For pulsed reactors, respectively: slow - Ф ~ 10 ¹⁸ -10 ¹⁹ neutron / (cm ² × s) with a pulse time from 10 ms to seconds, fast - Ф ~ 10 ¹⁶ -10 ¹⁷ neutron / (cm ² × s) at pulse time 100 μs - 10 ms.

≈ 1,45×10²¹ атомов/см³.The concentration of nuclear fuel in the scintillator is estimated from considerations of the homogeneous approximation (fine particles), provided that the transparency of the material is not disturbed. For the previously specified geometry of the pumping device, D ~ 15 cm and the length L is taken from considerations of dimensions AC (L / d ~ 20) will be 20 cm. The volume of the pumping device is about 3500 cm ³ . 2/3 of this volume is occupied by a scintillator with fuel nano-sized granules or fibers of their uranium-235 or plutonium-239 with an enrichment of at least 93%. We proceed from considerations that the presence of such objects with a volumetric content of up to (1 ... 3)% (Let v = 60 cm ³ ) does not have a noticeable effect on the optical properties of the scintillator with a layer thickness of about 1 mm on waveguides. Then, in the homogeneous approximation for uranium-235, we obtain the concentration (in the total volume of the scintillator with waveguides) about

≈ 1.45 × 10 ²¹ atoms / cm ³ .

For a slow reactor in the one-group approximation σ _f ≈ 500 × 10 ^-24 cm ² . Then, for a stationary (permanent) reactor with a conditionally identical neutron flux in all areas of the pumping device Ф ~ 3 × 10 ¹² cm ^-2 s ^-1, we obtain the specific rate of fission reactions: R _f = Ф _n × Σ _f ≈ 2.2 × 10 ¹² fission reactions in 1 cm ³ in 1 second in a stationary mode. One reaction of fission of uranium-235 by thermal neutrons gives about 160 MeV energy in the form of fission fragments. Then the nuclear specific power released in the pumping device is Р = R _f E _f ≈ 56 W / cm ³ . From this power, modern scintillators based on SrO ₂ - Eu with a gradient waveguide can output into the AS up to 34% of the released nuclear energy in the form of a narrow spectrum of pumping radiation (Г ~ 15-30 nm). In this case, the power density in a given design will be increased 60 times. Thus, the constant heat release in the scintillator will be 37.5 W / cm ³ , and the power density of the pump photon flux in the AS will be about 6000 W / cm ³ . This fully corresponds to the modern capabilities of laser scintillation materials. With an efficiency of 2%, this will give a constant output power density in the beam of 2400 W / cm ² , which fits into the limit of the threshold of energy destruction of optics with an operating time of 1-4 seconds (see Table 2).

For the variant of pumping by a fast reactor in a pulsed regime (with τ ~ 1 ms, which is comparable to the lifetime of a laser level in Nd ²⁺ - train pumping), we also use the one-group and homogeneous approximation. For uranium-238, the fission microsection is σ _f ≈ 2 barn, and the neutron flux density is assumed to be Ф = 5 × 10 ¹⁶ neutrons / cm ³ s ¹ . The rest of the geometric and material characteristics of the speaker and the pumping device are left unchanged. Then, R _f = Ф _n × Σ _f ≈ 1.45 × 10 ¹⁴ fission reactions in 1 cm ³ in 1 second. The total nuclear power will be about 12 MW, the total energy release - about 12 kJ, of which about 8 kJ into heat. The density of the pumping power in the volume of the pumping device will be about 1150 W / cm ³ , the nuclear power - 3700 W / cm ³ (the total pump power will be about 4 MW, and the energy input to the AS is ~ 4 kJ), and the power density directed to the AS is ~ 250,000 W / cm ³ . In this case, the energy release in the pumping device: specific - 3.7 J / cm ³ ; in AS: specific - 250 J / cm ³ , total - 4000 J; the energy in the beam is expected to be about 1000-2000 J at a radiation power of about 1000-2000 kW. Thus, the pumping power flux in the AC of about 60 kW / cm ² and the specific energy input to the AC of ~ 250 J / cm ^{3 are} sufficient for generation and do not exceed the permissible values. E / S ≈ 65 J / cm ² - see tab. 2. This proves that in the pulsed mode the proposed method of pumping the laser is quite applicable, while in our case the pulse time is not on the scale of 10 ^-9 -10 ^-7 s, but on the order of the time of the working pulse of the pumping nuclear reactor, that is, in the range of 10 ^-4 -10 ^-2 s.

With reference to FIG. 3, the simplest diagram of the claimed nuclear energy converter with its primary transformation into a narrow radiation spectrum with a one-sided irradiation scheme and the subsequent direction of this primary radiation to the receiving device (laser AC) may consist of the following elements:

1 - activated scintillator layer;

2 - granules of nuclear fuel dispersed into it;

3 - mirror (if necessary, to artificially limit the emitting surface);

4 - a protective layer of a clean (without fuel) activated scintillator (optional);

5 - receiving surface - a gradient waveguide for transporting and concentrating the energy of a narrow spectrum of primary radiation to the AS laser.

Thus, in all types of devices operating on the basis of the claimed method of converting nuclear energy, the main elements are: 1) fuel pellets / fibers or deposition layers containing nuclear material - a source of primary energy; 2) a scintillator with atoms - activators - a converter of the energy of nuclear particles from fuel granules / fibers or layers of deposition or the energy of nuclear particles from the nuclei of atoms of their own composition into the primary radiation of a narrow spectrum, depending on the type of activator in the range from IR to UV; 3) a receiver of photonic energy - this can be directly the medium of its further conversion or transmission over a distance: the active medium of a laser with appropriate pump levels, or a waveguide for transporting this radiation.

Within the scope of the claimed group of inventions, the possibility of increasing the efficiency of pumping the active medium of a laser is due to the conversion of primary nuclear energy into a complementary spectrum of radiation exciting laser levels. The absence of direct contact of the active medium (AS) of the laser with fast nuclear particles excludes rapid critical damage to structures and dramatically increases the service life of the devices. In turn, the possibility of using gradient waveguides in the claimed group of inventions (for example, optical fibers or fiber-optic cables with a cross-sectional refractive index n of a light-conducting material) makes it possible to transport the obtained radiation of the scintillator over the required distances.

In order to avoid the negative impact of nuclear radiation on the laser AS, the thickness of the scintillator layer in the case of using it together with a layer of nuclear fuel is selected from the condition that such a thickness exceeds the long path of primary particles - carriers of nuclear energy. For the same purposes, in the case of using a scintillator layer with embedded nuclear fuel particles, the thickness of such a layer is selected from the condition of optimization between the energy output in the form of a narrow spectrum and the bandwidth of the layer (transparency and losses) for operating frequencies and in the presence of a "clean" a protective layer of the scintillator between the laser radiation and the layer with embedded fuel. In this case, the thickness of the protective layer is not less than the path length of particles - carriers of nuclear energy in it. Special conditions for the design of such devices arise when fissile material is used as fuel. In this case, an important factor is the resistance of structural elements and substances to large neutron fluxes and taking into account the interaction of fission spectrum neutrons and / or moderating neutrons with substances that are part of all elements and structures of devices.

Requirements for fuel pellets / fibers / layers generally depend on the type of nuclear fuel (fissile material or a specific radioactive element), the type and energy of its particles. For example, fragments of uranium nuclear fission in metallic uranium have a path length of about 6-8 microns, and in a scintillator based on zinc sulfide (ZnS) crystals, about 20-25 microns. Electrons in the decay of strontium-90 into yttrium-90 with an energy of about 550 keV have a path length in the same scintillator of 50 μm, and in the decay of yttrium into zirconium-90 - an energy of about 2.3 MeV and a range of 500 μm. In strontium itself, these electrons have ranges of the order of that in aluminum, that is, 60 μm and 450 μm, respectively. These parameters affect the geometric requirements for the dispersion or thickness of the fuel layer and its volume fraction in the mixture. The characteristic size of the granules, the diameter of the fiber or the thickness of the fuel layer should be such that the energy loss when leaving the fuel into the scintillator of a nuclear particle - the primary energy carrier - should be minimal, and the ratio of the fuel volume to the scintillator volume should not be so large that nuclear particles during their deceleration in the environment, the mixtures did not lose much energy when meeting with other fuel pellets or fibers. On the other hand, increasing the volumetric content of nuclear fuel as an initial energy source is preferable from the point of view of power and compactness of devices. A practical solution to the problem lies in the optimization of this parameter, as well as in the creation of scintillation materials containing nuclear fuel in their composition without deterioration of optical properties. Also, the size of the fuel pellets or the diameter of the fuel fibers should be less than the wavelength of the radiation generated in the scintillator, and the main peaks of the spectrum should not coincide with the absorption spectra of fuel atoms. Otherwise, the effect of inelastic scattering of photons on granules with a loss of energy may occur, as well as the effect of self-extinguishing of scintillations on fuel atoms. Especially, it should be emphasized that the dispersed or layered arrangement of the fuel relative to the scintillator layer does not significantly affect the physicochemical and optical properties of the scintillator itself, in contrast to the homogeneous mixture of fuel atoms in the scintillator. For example, the dissolution of uranium salts in a scintillator can lead to a change in its optical properties and a significant loss of useful radiation energy. The task of selecting the substances of the fuel cells (granules, fibers or layers), scintillator and activator matrices, matrices and dopants for the AS laser, as well as optimization of the design of the energy converter and its structural dimensions, as well as the selection of auxiliary parts (if necessary), are posed and is solved depending on the type and purpose of the converter and the characteristics required from it.

Claims (2)

1. A method of obtaining coherent radiant energy, in which the passage of nuclear particles through at least one layer of an activated scintillator is provided to obtain pumping radiation of a narrow spectrum or several narrow spectra in the range from infrared (IR) to ultraviolet (UV) and subsequent conversion of the obtained pumping radiation into the energy of coherent laser radiation, including the location of the activated scintillator at a certain distance to the active medium of the laser in a solid or liquid aggregate state and the transfer of the said pumping radiation from the activated scintillator to the active medium of the laser through a gradient waveguide with the introduction of this radiation through the lateral surface of the waveguide in part or throughout its length and / or across its end surface. 2. A converter of nuclear energy (energy of radioactive decay and / or energy of fission of atomic nuclei) into the energy of coherent laser radiation (nuclear photoconverter of energy), containing at least one layer of an activated scintillator with at least one emitting surface, in contact with which there is a gradient a waveguide connected to the active medium of a laser in a solid or liquid aggregate state, with a pumping frequency lower than or close to the most probable frequency of a narrow emission spectrum of an activated scintillator, while nuclear fuel in the form of granules and / or fibers is embedded in the activated scintillator layer, and / or such a layer is located in contact with at least one layer of nuclear fuel and / or atoms of the nuclear fuel replace chemical elements similar to them in the composition of the scintillator itself.

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