SU1723677A1 - Method of generation of pulses of annihilation gamma quanta and device to implement it - Google Patents

Abstract

The invention relates to the generation of gamma-ray fluxes and can be applied in thermo-nuclear research. The purpose of the invention is to increase the flux density of gamma rays and the spectral density of the radiation. The method is carried out by accumulating a positron-electron plasma in a magnetic trap such as a mirror cell. The source of positrons is a radioactive isotope of copper 2eCi with a specific activity of 1013 - 1014 decay / s. and a half-life of 12.88 hours set in one of the cork-necks of the magnetic trap. By using the positron-electron plasma of the increasing magnetic field in time in each cycle, its retention time is within 1 ± 10 s. An additional coil is installed in the second neck of the magnetic trap and coaxially, which opens this neck and is connected so that the direction of its magnetic field is opposite to the direction of the main field, the cork coil, and the total strength of these fields is equal to or less than the quasi-stationary field in the center of the trap. After opening the trap, the positron-electron plasma flow is directed to the converter. The invention makes it possible to obtain annihilation γ-ray pulses with an energy of about 0.511 MeV and a power flux density in the range 1.0E - 109 W / cm2. 2 sp .. f-ly, 1 ill. NJ Yu SO smiling h | VI

Description

The invention relates to the generation of gamma-quanta streams, as well as to thermo-nuclear studies, in particular, to systems for confining hot plasma in the form of direct traps with magnetic mirrors (mirror cells). .

A known method of generating high y-radiation fluxes with a photon energy of up to several megaelectronvolts, which means that high-energy electrons

from the high current Aurora type electron accelerator are directed to the target and, interacting with it, are converted into a bremsstrahlung flux with a power of up to 1012 W / cm2.

The disadvantage of this method is the wide frequency spectrum in which y-quanta are generated, which leads to a low spectral density of the radiation, as well as the need to create a complex and energy-consuming installation.

There is a method of creating y-radiation fluxes with a high spectral density, which consists in using the effect of studying high-energy electrons or positrons in channeling in crystals.

The disadvantage of this method is the low radiation flux density and the large size of the installation.

A known method of generating weak annihilation y-photon fluxes is that positrons from an isotopic source (Na22 is the most common), not subjected to magnetic confinement and accumulation, are directed directly to the sample, where they are annihilated by emitting γ-quanta.

The disadvantage of this method and device is the low intensity of radiation, which limits the scope of applicability of the method to exclusively diagnostic tasks.

The purpose of the invention is to increase the flux density of annihilation γ-rays and the spectral density of the radiation.

To achieve this goal, a method involving obtaining a stream of positrons from an isotopic source and the direction of this stream to the sample under study, which is a converter, uses a radioactive isotope having a half-life (fvi) as a isotopic source, much longer plasma retention time in the trap determined within 1–10 s and having an induced / -activity of 10–1014 decouples per second, and the positrons emitted by the source are injected into the volume of the trap affected by the magnetic field configuration, keep and accumulate a relativistic electron-positron plasma in a trap until a density reaches 10-10 and, turning on the opposite magnetic field in the free throat zone of the magnetic trap such that the resultant and stationary field in the throat zone coincides with the quasistationary field, in the center of the trap Vdop.kat. -Frops + trap center, E, the rise time of the oncoming magnetic field, determining the opening time of the trap; is taken in the interval

- Totcr y

where L is the trap length:

v characteristic of the velocity of the plasma particles,

open the trap and direct the positron-electron plasma bunch to the convertible

five

0

five

0

five

0

five

0

torus of material providing the maximum yield of y-quanta, when the conditions

,,

where A-hA / t are the paths of positrons and y-quanta in the received material:

4k is the thickness of the converter.

The positron isotope source used in the proposed method is made of copper isotope 29CU64, having a half-life of p / 2 12.88 h. For giving copper 29Ci63 specific radioactivity of 10 - 1014 decay ./. C. it is irradiated with a stream of neutron neutrons with a density of 5 1014 - 5 1015 for 30 - 50 hours. At the same time, the mass of the isotopic source is in the range of 1 - 100g.

In the method, it is possible to adiabatically compress the cloud of the relativistic plasma by an increasing magnetic field in time in order to further increase its stability. In this case, the rate of increase of H is determined by the ratio)

dH (rut) n,. -one

gi- - Nmacd; t YI

where Nmax (pd) is the maximum attainable value of the magnetic field at point n;

Gu is the time the plasma is trapped.

The limiting density of a relativistic positron-electron plasma, obtained by the proposed method, is 10-10. In this case, the ratio

A Tu Pred V, where A is the activity of the isotope source;

V is the volume of the magnetic trap.

A converter consisting of a foil of a material with a low reflection coefficient of electrons and positrons from the surface, having a thickness Ac greater than the mean free path of positrons, but much smaller than the mean free path of annihilating γ rays

And Ak "Ak / where the positrons annihilate.

If the density of the 1+ positron flux satisfies the condition

55

p (g / cm is its density; m is the rest mass of the positron; y is the relativistic factor,

This material evaporates and is a dense, cold, slightly ionized plasma. about .

Its temperature is determined from the condition

1/4 then Pnred V U GP C

ABOUT

where (7 5.67 W-cm 2 grad 4 - is constant Stefan-Boltzmann.

The degree of monochromaticity of y-quanta is then determined from the condition

Av RT ° v

10 5U

coal 2

where Av and V are the width of the spectral line and the frequency of the y quantum, respectively,

R 1.38 erg / deg. - constant Boltzmann.

The source gives a radiation in the solid angle of 4 p-steradians.

To implement the proposed method of generating annihilation γ quanta, you can use a device consisting of a positron source in the form of an isotopic source and a converter, in which the positron source is made in the form of a magnetic trap such as a cork tube, including a vacuum chamber, a magnetic plasma confinement system in the center within 5–15 kgf and with a sweeping ratio from 3 to 5, a vacuum system and a positron emitter in the form of a screen made of copper foil, cm thick, activated by current teylovyh neutrons to obtain induced ft-activity in the range 1013 - 1014 decomposition / sg.. installed in the zone of one of the stoppers of the magnetic trap, perpendicular to its longitudinal axis, the second of the trap throat of the trap, in addition to the coil of the main stopper magnetic field, has an additional coil concentric to it and creating an opposite magnetic field of such magnitude that the sum of The magnitudes of these magnetic fields in the vicinity of the trap axis coincide or less than the intensity of the quasistationary magnetic field in the center of the trap. To turn on an additional coil and maintain the duration of the current pulse through it, which determines the duration of the opening of the Totcr trap. within - gokr "Shch, you can use a known device switching currents. At the same time, the choice of the foil thickness of the copper source is associated with the condition of the absence of self-absorption of positrons in the source and, accordingly, with the indicated activity of 1013-1014 decay. conditions of its non-melting.

The drawing schematically shows

a device with which you can implement the proposed method.

The device contains a vacuum chamber 1 of a magnetic trap, a source of 2 positrons, a coil 3 for creating a cork magnetic field, an additional coil 4, an additional source of power for an additional coil, a converter 6, a cloud 7 of a relativistic electron-positron plasma and

magnetic lines of force 8.

The method is carried out as follows.

With the help of vacuum units, the volume of the magnetic trap is pumped out to

pressure P 10 Torr, by means of a remote mechanism, isotope source 2 is installed in the zone of one of the cork-necks of the trap and, having turned on the power supply of the main coils 3 of the magnet,

the positrons are accumulated in a stationary or time-increasing magnetic field. After that, an additional coil 4 is inserted, which opens another trap mouth, and

The clot 7 of the electron-positron plasma is released to the converter, where the γ-radiation pulse is generated.

The specific implementation of the present invention is as follows.

in a way.

A 29C isotope source (having a half-life of 12.88 hours) is made from 29Ci63 material irradiated in a sod reactor for 30–50 h.

as a foil with a thickness not exceeding the length of the positron run (-) With a given source surface size of 0.1 - 0.2 m, and with an average density of neutron flux on the original preform,

equal to 5 -1015 cm 2s 1, an isotope is obtained with decay activity. / S. g. If the characteristic retention time of the relativistic electron-positron plasma is about 1 - 10s4; 1015-10 accumulates in the trap

positrons.

The limiting density at which plasma retention is possible is up to 10 cm. whence the volume of plasma is 1.0-0.01 m3.

The converter is made of light metal such as aluminum. Its area must be no less than the cross-sectional area of the additional coil, and the thickness of the material is cm.

The inclusion of an additional coil and the output of positrons to the converter is carried out after the maximum filling of the trap with positrons has been reached. In this case, an additional coil can provide opening of the trap and the expiration of plasma from it during a time of 10 to 10 s.

The use of the invention makes it possible to create technically simple, compact monochromatic y-radiation sources with a photon energy of about 0.511 MeV and a flux density of power up to 10-109 W / cm2.

Claims (1)

Claim 1. A method for generating gamma-quanta annihilation pulses, including obtaining a stream of positrons from an isotopic source and directing it to a converter that converts the incident positron flux into gamma-quanta annihilation radiation, in order to increase the density flux annihilation gamma quanta and spectral density of the radiation, as positron source use / radioactive isotope with induced specific activity 1013-10 decay. / S.g. and with a mass of 1-100 g, a stream of positrons with a characteristic velocity v and electrons emitted by this source is directed into a magnetic trap of a plug configuration of length L with a plug ratio between 3-5 and a magnetic field in the center of the trap within 5-15 kGs, nde accumulate positrons in the positron-electron plasma with With a density of 1010–1012 and with a retention time Gu of 1–10 s, then the trap is opened during L / vg Tu by decreasing the magnetic field in one of the necks of the magnetic trap, and the resulting positron – electron plasma flow from the open trap neck is directed to the converter while the material of the positron source is chosen from the condition that its half-life must be longer than the time that the positron-electron plasma is kept in a magnetic trap. 2, A device for generating annihilation gamma-quanta pulses, which are tactile in that they use a positron source in the form of a flat foil with a thickness less than the mean free path of positrons from a 2/Ci active copper isotope and set it perpendicularly and coaxially with the magnetic field of the trap in one of its mouths, the second mouth of the trap is opened in t-10 seconds with the help of an additional magnetic coil coaxial with the trap installed in the second mouth of the trap by creating a counter-holding magnetic field of additional magnetic field, equal in magnitude to the difference of the magnitudes of the magnetic fields in the throat and center of the trap, and the flow of positron-electron plasma from this throat is directed to a converter made in the form of plates of aluminum, or beryllium, or titanium, of thickness Ds within Ls A /, where A +, the lengths of the positrons and gamma quanta in the material of the converter.