SU869473A1 - Method of measuring energy of electrons in beam - Google Patents

Abstract

METHOD OF MEASURING ELECTRON ENERGY IN A BEAM, which means that the electron beam is directed to the absorber, is recorded back to the 5sulfur electrons that left the surface outside of the beam and fell back to the absorber, which is different in that, in order to improve the measurement accuracy, they additionally register the backtrace These electrons emitted from the surface in the region of the beam incident on the absorber, and judging by the results of the registration, judge the energy of electrons in the beam. 00 as with 4 ;: with

Description

This invention relates to a measurement technique. A known method for measuring the energy of electrons in a beam from an accelerator consists in that a beam of electrons is directed to the surface of an invariant absorber, electrons are recorded in the absorber, and electrons that are back scattered by the absorber are detected outside the surface area on which the electron beam directly falls, and, according to the results of the registration, the electron energy in the beam is judged l There is also a known method of measuring the energy of electrons in the beam from the accelerator, which consists of that the electron beam is directed onto the surface of the invariant absorber, the backscattered electrons are recorded emerging from the surface outside the region of the beam incident on the absorber, to which directly the electron beam is recorded, the reverse electrons that are released at all distances from the beam axis are recorded and with respect to the results of the registration, judge about the electron energy in the beam z ... The method does not require the introduction of detectors into the absorber, but the sensitivity of this method is not high enough, especially when monitoring the energy of electrons in narrow beams, which limits the accuracy of measurements. The aim of the invention is to improve the measurement accuracy by increasing the sensitivity to changes in electron energy, especially in narrow beams. This goal is achieved by the method of measuring the electron energy in the beam, which implies that the electron beam is directed to the absorber, back-scattered electrons that leave the surface outside the incidence area of the beam to the absorber are recorded, and back-scatter electrodes are recorded, emerged from the surface in the region of the beam on the absorber, and by otnoteniyu registration results judge about the electron energy in the beam. Since the flow of reverse electrons passing from region 3 2 of the absorber onto which the beam directly falls is proportional to the beam current and decreases with increasing electron energy in the beam, and the flow of reverse electrons passing through the absorber surface region onto which the beam directly falls is proportional to the beam current and increases with increasing electron energy in the beam, the ratio of these flows does not depend on the beam current. The sensitivity of the ratio to the changes in the electron energy in the beam is equal to the sum of the sensitivities to the changes in the energy of each of the streams. Sensitivity of the flux of reverse electrons escaped from the absorber surface, onto which the beam directly falls, to changes in the electron energy of Bbmie, than the sensitivity to electron energy changes in the flux of reverse electrons escaped from the absorber surface at all distances x from the axis beam, especially for narrow beams. This determines the higher sensitivity of the proposed method, especially when measuring the electron energy in narrow beams in comparison with the known method. Fig. 1 is a diagram illustrating the proposed method for measuring the energy of electrons in a beam from an accelerator; Fig. 2 shows the radial current distributions of the backscattered electrons on the surface of the absorber at different electron energies in the beam, for a point monodirectional beam; in fig. 3 - the same for a narrow beam of a given cross section; in fig. 4 - the same for a wide beam of a given cross section; in fig. Fig. 5 shows the dependence of the current of the backscattered electrons emitted from the absorber surface outside the surface region on which the beam directly falls, and the current of the backscattered electrons leaving the absorber surface region on which the beam directly falls from the electron energy in the beam. Example. When measuring the deviation of the electron energy or a nominal value, for example, Ho 5 MeV (see Fig 1), in a beam collimated to a diameter of 2% 0.08 cm from a beta ron when irradiated, for example, absorbed from a material with a density p 8 g / cm and an effective atomic number Z 50, record the current of back-scattered electrons emitted from the surface of the sample outside the region with a radius (Q 0.1775 which is set according to the ratio 0.5 R (B) (R-g) 0.3 R (E), where R (E) is the electron range in an absorber with energy E equal to the average energy of electrons, for di of the range where the measurements are carried out are E 0.5, (, + 2. Where E, + E is the range in which measurements are made, for example, E, 4.5 MeV, aE 5.5 MeV, Simultaneously measure the current of reverse electrons emitted from the surface area of the absorber with a diameter of 2 g 0.08 cm, onto which the beam directly falls. The beam in this case is narrow, since Gdr (E) Finds the ratio of the results of registration and according to it the trial tons of energy, electrons in the beam, and both during measurement and calibration use the same constant absorber. The calculated distributions of the -current of back scattered electrons on the surface of the absorber P / gr. B / at different electron energies of a point-directed monodirectional beam with a unit current density are presented in P gp, E) in FIG. 2; Distributions are calculated by the Monte-Carlo method. The areas under the curve are numerically equal to the integral. The current backscattering coefficient, t, e, jP (i-pUp (3r kopU)) The distribution of back-scattered electrons over the absorber surface (g, E) for the example under consideration at electron energies of 4 MeV and bMeV at a unit beam current density is shown in FIG. 3 and 4. It can be seen that the distribution within the region r, for Hz, 0.04 cm (narrow beam) strongly depends on the energy (see Fig 3), while for Gd it is 0.44 cm (wide beam , Tjр R (B)) the dependence of the distribution within r, on the electron energy in the beam is much weaker (sJ, Fig.4) .. The effect of reducing the density of the mate The absorber’s rial (see FIG. 3,4) causes the same change in distributions as the increase in the electron energy in the beam, which requires that the absorber remains constant during calibration and measurements to ensure unambiguity. The result of recording the current of the reverse electrons left within the surface area with a radius of TO 0.04 cm Uj is proportional to the beam current 3 and the magnitude of DE1 {f (g, Е1гсЗг,. and the result of the registration of the current of back scattered electrons beyond the surface area of a burst with a radius of ((, 0.1775 CM (, proportion it is related to the beam current and the magnitude 00 2)). , Dependences, о i (.Е) and i (Е) for the considered example with unit beam current density are given in fig, 5, where Go 0.04 cm, p 8 g / cm; -R 0.0825 cm; D - 0.1 to 35 cm; GP - R -0.1775 cm; 1U - RO 0.22 cm; U - RO 0.135 cm, p 4 g / cm, Go 0.04 cm; U1 0.4825 cm, p 8 g / cm, Go 0.44 cm; Y11 -RO 0.5775 cm, p -8 g / cm Go 0.44 cm UP1 - Go 0.44 cm, p 8 g / cm; iX - TO 0.04 cm, p 8 g / cm; X - Go 0.04 cm, p 4 g / cm, Here is the dependence 00 iov J (EViJr, characterized by the prototype method. The curves Y and X affect the changes in the absorber density, through the corresponding radial distributions the dependences 1, (Е) and ijCE) illustrate the ambiguity in determining the electron energy in the beam when Ш10т-5 changes to carry the absorber material between the individual measurements. The ratio of the registration results for the proposed method (r / (Jn does not depend on the beam current JQ. 10 C | (E) l ,, iEV

At IT, the sensitivity of the ratio to changes in the electron energy in the beam for the proposed method is equal to

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EE a for the prototype method -LL For this example, S j is 0.9 MeV, and 5,.., 0.46 KeV. With a beam current density equal to 1, the average number of backscattered electrons from the absorber outside the surface with a radius R (, 0.1775 cm unit time interval, 1.510, the average number of backscattered electrons released from the absorber surface area to which beam P. 1 directly falls, and the average number of backscattered electrons released from the absorber surface at all distances x from the beam axis D 1.610 STI measurement equal to t, the RMS value of fluctuation of the values respectively equal minutes (about rms fluctuation ratios (, N, / at pealizatsii proposed method thus equal, j2 (q f IN,;.. ml m-gChtk7G Ch9gI-terser7

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, g 3 h /. and when implementing the prototype method d - I Tog It At the same time the minimum recorded relative deviation of the electron energy in the beam for the proposed method with instrumental instability is CO, 1 - g If 6 (.and that corresponds to (, (Jgj, and measurement time - ( 1. then the accuracy of the methods is determined by their sensitivity and the instability of the equipment. C- w с „o ((, 2 At the same time, the accuracy of the proposed, .., 1 method in K p I, .., is higher than the accuracy of the prototype method The proposed method for measuring the electron energy in the beam from the accelerator provides There is a higher sensitivity and accuracy of measurements of the electron energy in the beam than the known method, especially in narrow beams without the introduction of detectors in the absorber. The method is designed to study the instability of collimated fast electron beams from accelerator-based sources used in electronic flaw detection, thickness measurement and thickness gauging The advantages of the method are important in connection with the development of an energy range of 1-10 MeV.

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Claims (1)

METHOD FOR MEASURING ELECTRON ENERGY IN A BEAM, consisting in the fact that the electron beam is directed to the absorber, back-scattered electrons are detected that emerge from the surface outside the field of incidence of the beam on the absorber, characterized in that, in order to increase the measurement accuracy, back-scattered electrons from the surface in the region of incidence of the beam on the absorber, and judges the energy of electrons in the beam with respect to the registration results. Ξ ω 62 ^ 698> FIG. 1 869473 2