On the ionization loss spectra of high-energy channeled negatively charged particles
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Regular Article - Experimental Physics
On the ionization loss spectra of high-energy channeled negatively charged particles S. V. Trofymenko1,2,a , I. V. Kyryllin1,2,b 1
Akhiezer Institute for Theoretical Physics, National Science Center “Kharkov Institute of Physics and Technology”, Akademicheskaya Str., 1, Kharkiv 61108, Ukraine 2 V.N. Karazin Kharkiv National University, Svobody Sq. 4, Kharkiv 61022, Ukraine
Received: 30 April 2020 / Accepted: 5 June 2020 © The Author(s) 2020
Abstract The ionization loss spectra of high-energy negatively charged particles which move in the planar channeling mode in a silicon crystal are studied with the use of numerical simulation. The case when the crystal thickness is on the order of the dechanneling length ld is considered. It is shown that in this case the shape of the spectrum noticeably depends on ld . The evolution of various characteristic parameters of the spectrum with the change of ld is investigated. A method of the experimental determination of ld on the basis of the measurement of the ionization loss spectrum is proposed.
1 Introduction When a charged particle penetrates through matter it loses part of its energy on excitation and ionization of the atoms, which makes up the particle ionization loss. In sufficiently thin targets the value of such a loss is stochastic. It is distributed according to the law, which was first derived in [1] and further elaborated in [2–4]. In amorphous targets such a distribution (or spectrum), known as the Landau distribution, has a single maximum, which corresponds to the most probable value of the particle energy loss (MPEL). If a charged particle enters a crystalline target at a small angle with respect to crystallographic axes or planes, the channeling effect may occur [5]. It happens as a result of the particle capture by the potential wells formed by the atomic strings or planes. The channeling motion of a particle in a crystal can break down due to its incoherent scattering either on thermal vibrations of the atoms (mostly for negative particles) or on the subsystem of the atomic electrons (mostly for positive particles). In the case of negatively charged particles the decrease in the number of channeled particles with a e-mail:
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the crystal thickness behaves almost exponentially [6]. The distance on which the number of channeled particles in the incident beam decreases by a factor of e (due to the particle transition to the over-barrier regime of motion) is known as the dechanneling length ld . For positive particles (protons, positrons etc.) the channeling effect results in the decrease of the particle MPEL compared to the case when the crystal is disoriented (in this case the crystal resembles an amorphous medium) and the particle penetrates the whole target in the over-barrier regime. It is associated with the fact that, due to the repulsive nature of the force between the particle and the atomic stings or pla
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