An investigation of the transition effect in layered absorbers

Abstract

The problem of radiation protection has become important with the development of high-energy particle accelerators. High-energy particles passing through a shield generate showers in it. There is an indication in the papers [1][2][3][4][5] that dampingofa shower occurs more rapidly in an inhomogeneous medium than in a homogeneous one. In order to design a layered shield, it is necessaryto know the quantitative variations of the shower's characteristics in an inhomogeneous medium.Instruments are employed in high-energy physics whose operation is based on the complete or partial absorption of the initial particle's energy. Such instruments are used mainly to measure the initial particle's energy. Inhomogeneity of the medium spoils the development of a shower, which results in errors in the measurement of the initial particle's energy.The number of charged particles in the region of a shower's maximum is approximately inversely proportional to the critical energy [6]. Therefore, the number of particles in a shower upon its crossing the boundary separating two media varies inversely as the ratio of their critical energies. The variation of a shower's characteristics upon its passage through inhomogeneous media, which is called the transition effect, is especially noticeable beyond the shower's maximum. A sharp variation in the number of particles results in the fact that it is impossible to neglect the perturbations even for perturbing layer thicknesses of 0.1 radiation length (r. l.).Processes associated with electron absorption due to ionization losses make the largest contribution to the variation in the number of particles in a shower after its passage through a perturbing layer. An indirect measurement of the number of particles in a shower before and after a perturbing layer which would permit estimating the validity of theoretical models for the process in question is of interest. Experimental MethodThe investigations were conducted on the accelerator of the Kharkov Engineering Physics Institute of the Ukrainian SSR Academy of Sciences. The electron beam's energy was 1 GeV with an energy spread of AE/E ~ 1%. The beam current was controlled by a secondary emission monitor. The transition effect was measured after passage of the particles through a copper absorber of variable thickness {0.5, 3, and 8 r.l. ). Behind the main absorber was mounted a perturbing layer of carbon whose thickness was varied from 0.1 to 0.5 r. 1. Initially, the number of particles in the shower Was measured in the presence of the perturbing layer. Then the perturbing layer was replaced with a copper layer equal to it in radiation length, and the number of particles in the shower was measured.The number of charged particles in the shower was measured by a secondary emission monitor [7]. The output of electrons from thin foils under the action of fast charged particles can be divided into two groups: the high-energy part --the so-called secondary electrons ejected immediately by the primary particle; and the low energy part --the tertiary ...

Spectra of Low-Energy Secondary Electrons in the Interaction of Relativistic Electrons With Aluminum Foil

“…In the region of negative voltages, the measured dependence of the yield is approximated by a curve of the type (1). The value of the coefficient p 1 indicates the yield of above-barrier electrons, which can also be approximately determined from the data in Fig.…”

“…The value of the coefficient c 1 , represents the total yield of the secondary low-energy emission plus the high-energy background. By subtracting the background value p 3 , see (1), from c 1 , we obtain the value of the total yield of secondary low-energy electron emission, which can also be approximately estimated from the data shown in Fig. 3.…”

“…One of the important directions in the experimental study of the interaction of high-energy electrons with thin foils (amorphous, single-crystal, single-layer, and multilayer ...) is directly related to obtaining absolute and relative data on secondary electron emission [1]. Of particular interest in such studies is the comparison of the integral and spectral yields of secondary electrons from the first and second surfaces of the samples during research.…”

On the ionization loss spectra of high-energy channeled negatively charged particles

“…The length of dechanneling is the parameter which allows one to determine the thickness of the crystal up to which the particles move inside it in the channeling mode. Attempts to determine the dechanneling length of negatively [11] (110) e − 0.855 21.1 [12] (110) e − 0.855 48.0 [13] (110) e − 0.855 9.7 [14] (110) e − 1.2 24.2 [15] (110) π − 150 6.2 [16] (111) e − 23.6 [11] (111) e − 0.855 23.7 [17] (111) e − 0.855 15.9 [14] (111) e − 3.35-14 15.3 [18] (111) e − 0.5-100 27 [19] (111) e − 50 6.6 [20] charged particles have been repeatedly made previously by means of theoretical calculations, numerical simulations and experiments. In [11], on the basis of the comparison of the root mean square angle of multiple scattering with the critical angle of planar channeling, it was found that the dechanneling length is linearly proportional to the energy of the charged particles:…”

“…There are several experimental methods which allow determining the value of the dechanneling length in a crystal. These methods are associated with the detection of the yield of the atomic electrons knocked out from the crystals [15], with the measurement of the low-energy channeling radiation or high-energy bremsstrahlung [12] and with the measurement of the deflection angle of the particles after their passage through a bent crystal [16][17][18]. In the present paper we propose a new method of the dechanneling length determination through the analysis of the particle ionization energy loss spectra in crystals.…”