RU2761376C1 - Device for simulating high energy heavy ion beams of mixed radiation fields for the purposes of experimental radiobiology - Google Patents

Abstract

FIELD: radiation technology.

SUBSTANCE: invention relates to a device for simulating on high-energy accelerators of heavy ions of fields of mixed secondary radiation for irradiation of biological samples in them. The device contains a turret-type rotary drum, in which at least two converters are combined, consisting of a set of cylindrical or sector-shaped targets in various combinations. By rotating the drum with the help of an electric motor, the converters are alternately placed in a position where they are irradiated with a beam of iron nuclei with energy of 1 GeV/nucleon. The converters can also be rotated by means of an electric motor around their longitudinal axis, which coincides with the beam axis. The targets have a homogeneous structure (without grooves and voids) and different thicknesses along the beam. At least one of the converters can have at least one steel target in the set.

EFFECT: invention provides the possibility of forming fields of secondary mixed radiation in a wide range of energies for the purposes of radiobiological research with a homogeneous field of secondary mixed radiation behind the device in a space region sufficient to accommodate a large number of irradiated samples in it and ensure equality of their doses of radiation, as well as reproduction in the field of secondary mixed radiation behind the device not only of the specified spectra of linear energy transfers of secondary particles, but also of their specified energy spectra.

1 cl, 8 dwg, 2 tbl

Description

The scope of the invention. SUBSTANCE: invention relates to devices for simulating fields of mixed secondary radiation on high-energy accelerators of heavy ions for irradiation of biological samples in them. The invention is applicable in studies of the action of heavy charged particles of various energies at the molecular, cellular, tissue and organismal levels of the biological organization.

The level of the invention.

Interest in heavy charged particles (HCP) in radiobiology has intensified in recent years, when it became known about their effect on the central nervous system of animals. In this case, the mechanism of the effect of HGTs with large energy transfers (LETs) on biological structures is very different from the action of weakly ionizing types of radiation with small LETs and is mainly due to the occurrence of poorly reparable double-strand breaks in the DNA chain.

Radiobiological studies of the effect of heavy charged particles on biological objects are carried out using particle beams of accelerators. The most accessible beams of protons with energies of several hundred MeV; beams of high-energy heavy nuclei are available in the world only at a few heavy ion accelerators. In Russia, these works are carried out at the Laboratory of Radiation Biology of the Joint Institute for Nuclear Research (LRB JINR) using the Nuclotron of the High Energy Physics Laboratory, capable of accelerating nuclei to Z = 36 with energies up to 6 GeV / n (here Z is the nuclear charge).

In the course of experiments on these accelerators, in each session, biological samples are irradiated with monoenergetic particles of only one type, while a mixed field of particles of different types with different energies is of practical interest. It is known that, in addition to the absorbed dose, in assessing the severity of exposure, an important role is played by its quality, which is characterized, in the first approximation, by the LET of the particle. Unlimited LET is equivalent to the specific ionization energy loss of a particle, proportional to the square of its charge and increasing as the particle energy decreases. Thus, in each experiment on beams of monoenergetic particles, the effects of irradiation of samples with only one LET are studied. Such irradiation does not allow one to reveal the effects of simultaneous combined irradiation with particles with different LETs (possibly of a synergistic nature), i.e. make it difficult to adequately assess the risk of exposure to radiation with a complex and extended LET distribution. In order to correct the practice of radiobiological experiments at accelerators, which has developed due to objective technical difficulties, it is necessary to develop a new technique that will make it possible to simulate mixed radiation fields in experiments at accelerators with all the specifics, i.e. irradiate biological samples in the course of one session with a set of different particles with different energies simultaneously or sequentially in a relatively short time (assuming the additivity of the radiation effect).

The component and energy composition of the secondary radiation fields from fixed targets irradiated with beams of monoenergetic accelerated nuclei in accelerators is determined by the type of projectile nucleus, its energy, target material and its dimensions. Unfortunately, it is technically difficult and time-consuming to purposefully change the characteristics of the secondary radiation field during a radiobiological experiment at an accelerator without changing the type of projectile nucleus (i.e., replacing the ion source of the accelerator) and their energy.

In 2017, in [J.C. Chancellor, S. Guetersloh, K. Cengel, J. Ford, H.G. Katzgraber. Emulation of the space radiation environment for materials testing and radiobiological experiments. arXiv Peprint arXiv: 1706.02727v1 (2017); J.C. Chancellor, S.B. Guetersloh, R.S. Blue, K.A. Cengel, j.R. Ford, H.G. Katzgraber. Targeted nuclear spallation from moderator block design for a ground-based space radiation analog. arXiv Peprint arXiv: 1706.02727v2 (2019)] proposed a method for simulating secondary radiation fields with predetermined physical characteristics on heavy ion accelerators. In this case, to simulate a mixed field of secondary particles with a wide energy range, one type of projectile nuclei is used - a beam of iron nuclei with an energy of 1 GeV / n. To form the field of secondary radiation, a figured polyethylene moderator is used, irradiated by a uniform wide field of iron nuclei, in which, as a result of nuclear reactions of Fe nuclei with C and H nuclei, a set of fragments of the projectile nucleus is formed. Since different fragments are born mainly at different depths of the moderator and the ranges of fragments in polyethylene are also different, then to obtain a mixed field of fragments with a wide energy spectrum, the thickness of the moderator is made different in its different places due to several conical and cylindrical recesses (voids) in a homogeneous block of the moderator.

The authors did not report data on the specific design of the moderator, but gave only a basic description, therefore it is impossible to reproduce it. According to them, by changing the design within certain limits, they can achieve a good match of the total spectrum of the LET in the irradiated field with the results of measurements of the LET spectra in real conditions and have demonstrated the results of such simulations.

One of the authors of the above articles, Jeff Chancellor, registered a patent in his own name [US 2018/0022478 A1 dated 25.01.2018]. The essence of this invention is that a beam of iron nuclei with an energy of 1000 MeV / n; the field is formed by the interaction of iron nuclei with one static block (converter) of the moderator made of a hydrogen-rich substance (polyethylene) containing one or more layers and a plurality of voids located in one or more layers (Fig. 1); The specified LET spectrum of the particles of the secondary mixed radiation field is determined by the configuration of these voids. This patent is a direct prototype of the claimed invention.

As already mentioned above, a significant disadvantage of the prototype is a significant inhomogeneity of the simulated radiation field even at a distance of 1 meter from the rear end of the moderator block, which cannot be eliminated by introducing a layer of a substance with a large atomic number (for example, lead or tungsten), and the presence of which, moreover, , leads to a general decrease in the radiation energy at the exit from the unit. Another drawback is that, although the prototype simulates a given LET spectrum, it does not allow adequately investigating all the radiobiological effects of a mixed radiation field, since LET does not unambiguously characterize the type and energy of a particle: for example, a single-charged low-energy particle can have the same LET value , as well as a multiply charged particle with higher energy per nucleon. Therefore, the biological effects of heavy nuclei depend not only on the LET, but also on the track structure. As a result, in recent years, instead of the LET criterion (necessary, but insufficient), he uses the criterion of radiation quality Z ^{* 2} / β ² , where Z ^* is the effective charge of the nucleus, and β is its relative velocity, i.e., in fact, the kinetic energy ... In the description of the prototype, only data on the calculated LET spectra in the field behind the moderator block are given. Thus, in the prototype, only one parameter of the field of mixed radiation is reproduced, namely, the integral spectrum of the LET of its particles (the patent recognizes this), while in order to adequately simulate mixed radiation in a wide range of energies, it is necessary to recreate not only the spectrum of the LET, but also energy spectra of all field components.

Disclosure of invention

The technical objective of the invention is to create a device with improved, in comparison with the prototype, the possibility of forming fields of secondary mixed radiation in a wide range of energies for the purposes of radiobiological research; with a uniform field of secondary mixed radiation behind the device in a region of space sufficient to accommodate a large number of irradiated samples and ensure equality of their irradiation doses; reproduction in the field of secondary mixed radiation behind the device not only of the specified spectra of LET particles, but also of their specified energy spectra.

The technical result in the present invention is achieved due to the fact that:

- at least two converters are combined in a turret-type rotary drum with the ability to rotate both around the axis of the drum and around the axis of the beam of accelerated particles; thus, by rotating the drum, the converters are alternately installed in the position in which they are irradiated with a beam of accelerated particles;

- each converter is made in the form of a set in the form of a set of disk sector and cylindrical targets of a homogeneous structure (without recesses and voids) and different thicknesses. Sectoral disc targets and cylindrical targets can be in the converter set in various combinations. Also, as an option:

- at least one of the converters has at least one steel target in the set.

Description of figures

FIG. 1. Schematic design of the prototype in longitudinal section. On the left in FIG. 1 shows the flow of spatially uniformly distributed Fe nuclei. Behind the rear end of the moderator, in different places, field regions with different component and energy composition are formed, i.e. the generated field has significant inhomogeneity. A list of the components of the secondary mixed radiation field and their emission directions are shown in Fig. 1 on the right. To equalize the field uniformity, at the end of the polyethylene moderator, a layer of a substance with a high atomic number (in the figure marked in dark color) was added to increase the angular spread of particles emitted from the moderator. To improve the uniformity of the radiation field behind the moderator at the site of irradiation of the samples, it is also assumed that the distance from the rear end of the moderator to the sample will be at least 1 meter.

FIG. 2. Simplified design of the converter with two targets of different thickness, a - isometric view of the converter with a beam of iron nuclei incident on it; b - view from the side of a beam of iron nuclei; S ₁ and S ₂ - target areas;

FIG. 3. Simplified design of a converter with four targets of different thicknesses with an incident beam of iron nuclei. S ₁ S ₂ , S ₃ and S _{4 are the} areas of the corresponding sectoral targets. Target 1 has a sectoral angle of 360 ° and is a cylinder with an area S ₁ = S (the area of the circle - the end face of the target). The other targets have sectoral angles less than 360 °. d ₁ - d ₄ - sectoral target thicknesses. The total thickness of the targets D is as follows: D ₁ = d ₁ ; D ₂ = d ₁ + d ₂ ; D ₃ = d ₁ + d ₂ + d ₃ ; D ₄ = d ₁ + d ₂ + d ₃ + d ₄ .

FIG. 4. Schematic design of a turret-type rotary drum device for changing four converters on a beam of iron nuclei. The drum alternately sets the converters to the same position on the bundle of iron nuclei, a is a longitudinal sectional view of the rotary drum, b is a section of a drum with four converters. 1 - converters; 2 - irradiated sample; 3 - rotary drum.

FIG. 5. View from the side of the beam of iron nuclei of converter # 1 (a) and converter # 2 (b). The numbers in the figure indicate the target numbers.

FIG. 6. Calculated charge distribution of charged components in the total field of secondary mixed radiation of TZCH behind the simulator in the project of the channel for applied radiobiological research at the Nuclotron of JINR. The ordinate on the graph plots the flux density of secondary particles (fragments) with a charge Z (abscissa axis), normalized to 1 iron nucleus with an energy of 1 GeV / n that fell per second on the simulator.

FIG. 7. Calculated spectra of TZCH, as well as gamma-quanta and neutrons in the total field of secondary mixed radiation behind the simulator in the projected channel of applied radiobiological experiments at the JINR Nuclotron. The type of particle (fragment) is indicated on each figure. The abscissa shows the energy in MeV / n, the ordinate shows the energy flux density of the TSP, normalized to 1 iron nucleus / sec through the simulator.

FIG. 8. Calculated LET spectrum of all TZP particles in the total field of secondary mixed radiation behind the simulator in the projected channel of applied radiobiological experiments at the JINR Nuclotron at the location of the irradiated biological samples. The abscissa shows the LET in units of keV / μm. The ordinate is the particle flux density in the bin of the LET partition (step of the histogram), normalized to 1 iron nucleus / sec through the simulator.

Implementation of the invention

The presented invention describes a device for simulating mixed radiation fields at high-energy heavy ion accelerators (hereinafter referred to as a simulator for short in the text) using a wide homogeneous beam of iron nuclei with an energy of 1 GeV / n as in the prototype, but in contrast to the prototype, consisting of several blocks retarders (converters). Each converter is responsible for creating a partial field component behind the device with its own specific component and energy composition. The variability of the thickness of the moderator unit (converter) along the beam is achieved in a different way than in the prototype, not due to voids of different configurations. The invention uses converters consisting of sets of uniform sectoral or cylindrical and sectoral targets of the same diameter with different sectoral angles and thicknesses. Several converters with different sets of targets are combined in a revolving rotating drum (around the axis of the drum) for alternate installation of accelerated particles on the beam for irradiation. The moderator unit (converter) in the process of irradiation has the ability to rapidly rotate around the beam axis, and the rotary drum around its longitudinal axis by means of electric motors. The converter can be considered as a composition of several targets of different total thickness fixed in it. With a constant flux density of primary iron nuclei and a fast rotation of the converter around the beam axis, the number of nuclei irradiating different targets is proportional to the ratio of the target sector areas to the area of the circle.

FIG. 2 and 3 show simplified designs of a converter with two and four sector targets, respectively. When the converter rotates around the beam axis, each target sector will repeatedly describe a full circle, thus, the partial fraction of the radiation field behind the simulator from each sector target will be fundamentally uniform and, accordingly, the total field from the set of targets and converters will also be uniform. In this case, the irradiation of the samples can be carried out immediately after the converter, and there is no need to use an additional layer of a substance with a large atomic number, which lowers the particle energy, which is also a significant advantage over the prototype. The fraction of the contribution of the partial field from each target to the total field behind the converter is proportional to the ratio of its sectoral area to the area of the circle, and the predominant type of secondary particles (fragments of the projectile nucleus) behind it is determined by its total thickness. The total target thicknesses are selected on the basis of data on the cross section of interactions of the primary Fe nucleus and its fragments with polyethylene and correspond to the penetration depth of the selected groups of nuclei, at which the probability of their interaction with polyethylene is ~ 50%.

When using a primary beam of iron nuclei with an energy of 1 GeV / n, the energy of all secondary particles will practically not exceed this value, and the component composition of the HCP will have a charge distribution from atomic number 1 to atomic number 27 (cobalt). The reproduction of light components of the mixed field (i.e., singly charged particles and light nuclei) is a particular difficulty. Since most of the nucleus-nucleus interactions are peripheral, fragments of projectile nuclei with masses close to the mass of the projectile nucleus are born in them. So that, ultimately, only light components (especially protons) are present behind the converter, it is necessary to use a converter of great length, many times exceeding the ionization range of iron nuclei with an energy of 1 GeV / n. This reduces the yield of particles from the converter; therefore, it is impractical to increase the energy of the primary iron nuclei. It is impossible to adequately simulate the energy spectra of all components of the field of mixed radiation with one converter (even with a large number of targets); therefore, it is proposed to use several converters with different sets of targets, combined in a rotary drum (Fig. 4) for their quick replacement on the beam.

Each converter reproduces the spectra of predominantly one group of particles due to its own combination of targets of different thicknesses. But in the radiation field behind each converter there is also an admixture of particles from other groups. In the general case, the spectrum of particles of one i-type F (E) _i in the final field of mixed radiation behind the simulator is obtained by summing the spectra of particles of partial fields from all converters with weights determined by the irradiation time of each converter, i.e. superposition of partial fields.

- спектр частиц i-го типа излучения за конвертором

- время облучения конвертора

Т - время полной экспозиции облучения образцов за симулятором.where

- spectrum of particles of the i-th type of radiation behind the converter

- converter irradiation time

T is the time of the full exposure of the irradiation of the samples behind the simulator.

In this case, the spectrum of particles of the ith type behind each converter

- спектр i-го компонента поля из мишени k конвертора

- площадь секторальной мишени k в конверторе

S - площадь круга.where

is the spectrum of the i-th component of the field from the target k of the converter

is the area of the sectoral target k in the converter

S is the area of the circle.

As a result, the simulator is able to simulate the biological effects of irradiation of samples in the field of mixed radiation of TZCH with a predetermined ratio of the field components and their spectra by sequential irradiation of the samples behind the converters. The rate at which the absorbed radiation dose is accumulated is ultimately determined by the intensity of the primary beam of iron nuclei. Adequate modeling of the given spectrum of each particle in the total field of mixed radiation behind the simulator is achieved by selecting the following parameters: target thicknesses in each converter, taking into account the contribution (weight) of each target and the relative contribution (weight) of each converter to the exposure of the sample, which provides ample opportunities for variation component and spectral composition of the field.

The invention is intended for carrying out radiobiological experiments on the projected channel for applied research of the Nuclotron of the Joint Institute for Nuclear Research. Nuclotron is a cyclic synchrotron with a cycle frequency of 0.1 Hz. In the mode of slow beam extraction from the Nuclotron, the pulse duration is 5 sec. Thus, the change of the converter in the drum can be carried out in the intervals between the pulses of the accelerator. The maximum design intensity of a beam of nuclei of the Nuclotron with a booster when operating on applied channels will be ~ 5⋅10 ⁸ nuclei / cycle. A wide uniform beam of iron nuclei at the input of the device will be created by scanning it according to a given program. With a beam scanning cycle of ~ 90 msec and a slow beam extraction duration of 5 s, ~ 55 scans will occur per accelerator pulse, which will ensure statistical uniformity of the irradiation field even with small instabilities of beam extraction.

To confirm the possibility of implementing the invention, a project was created for an installation (simulator) with four converters in a drum on the projected channel for applied research of the Nuclotron. The inner diameter of converters and targets was set equal to 10 cm. The target material of the three converters is polyethylene with a density of 0.952 g / cm ³ . The fourth converter is heterogeneous, consisting of two targets - polyethylene and steel. The composition of the converters and the area fractions of the target segments are shown in Table 1.

FIG. 5 shows a view from the side of a beam of iron nuclei of converters # 1 (a) and # 2 (b).

The angles of the target sectors for converters # 1 and 2 are shown in Table 2. Converter # 3 is a polyethylene cylinder 50 cm thick, and converter # 4 is composed of two cylinders (steel 20 cm thick and polyethylene 30 cm thick).

FIG. 6 shows the calculated charge distribution of charged components in the total field of the secondary mixed radiation of the TSP behind the simulator with the design described above.

FIG. 7 shows the calculated energy spectra of the TPP, as well as gamma quanta and neutrons in the total field of secondary mixed radiation behind the simulator in the projected channel of applied radiobiological experiments at the JINR Nuclotron.

FIG. 8 shows the calculated LET spectrum in units of keV / μm of charged particles in the total field of the secondary mixed radiation of the TGP behind the simulator with the design described above at the location of the irradiated biological samples. It should be noted that the proposed simulator device makes it possible to reproduce the LET spectrum up to ~ 1000 keV / μm, i.e. to significantly higher values than the prototype.

In general, the above calculations prove that the proposed device (simulator) for the formation of fields of mixed radiation TZCH at high-energy heavy ion accelerators has significantly expanded capabilities in comparison with the prototype and can be used as a tool for promising radiobiological research.

Claims (2)

1. A device for simulating fields of mixed radiation on beams of high energy heavy ions for the purposes of experimental radiobiology, including a converter of secondary radiation fields with a target of a hydrogen-rich substance, characterized in that at least two converters are combined in a turret-type rotating drum with the ability to rotate both around the axis of the drum, and around the axis of the beam, and each converter is made in the form of a set of disk sector and cylindrical targets in various combinations of a homogeneous structure and different thicknesses. 2. A device according to claim 1, characterized in that at least one of the converters has at least one steel target in the set.

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