Transformation and Accumulation of Energy in Solids under Irradiation of Low and Intense Beams of Charged Particles

Transformation and Accumulation of Energy in Solids under Irradiation of Low and Intense Beams of Charged Particles

A. N. Valyaev^a, V. K. Struts^b

^aNuclear Safety Institute, Russian Academy of Sciences, Moscow, Russia, 115191 ^bNuclear Physics Institute, Tomsk, Russia, 634000

Abstract. All observed phenomenon under irradiation are determined by processes of energy transformation in matter. It is the point for understanding of nature and mechanisms of radiation–stimulated effects and their influence on transportation of particles beams through mediums. The motivation of this work is to analyze of known published data and our own experience [1–14] for development of the general scheme of transformation and accumulation of energy in solids, when nuclear reactions are not initiated, i. e. only electron and atomic subsystems may be excited. The physics of beam interaction with solids is presented on the atomic, micro, and macro levels. We demonstrate the possibilities of this scheme in the interpretation of the complex so-called long-range effects under intense pulsed response. Some applications for radiation technologies are under consideration.

GENERAL

The physical and chemical processes under irradiation of any matter are depended on: (1) parameters of irradiation source; (2) characteristics of medium for irradiation; (3) initial properties of matter. Our proposed general scheme of transformation and accumulation of radiation energy in solids is included 33 blocks (Figure 1) [1, 2]. It allows to watch the possible channels of energy redistribution in temporal sequence from the beginning of irradiation (block b1) till the formation of stable structure (b32), determined modified properties (b33). All blocks are connected with each others and present the main radiation-stimulated processes. The based blocks are b1 (irradiation), b2 (target) and b3 (medium). As for b1 and b3, it is possible to obtain for them the necessary information before irradiation and to correct their parameters during irradiation. But there are principal difficulties to realize it for b2, because initial properties of solids may be greatly varied from the beginning of irradiation, especially under intense pulsed response.

Irradiation (b1) includes: its type; particles composition, their charges and contains in beam; energetic spectra; frequency of pulses; total current and energy in pulse, their densities and radial distributions. Target (b2): type of material, initial damages, chemical and structure-phase compositions, that are depended on initial thermal and chemical treatments; its shape and geometric sizes: foils, plates, multilayers with their compositions; (3) target orientation in respect to beam direction. The last factor determines the peculiarities of beam-target interaction. Under intense pulsed responses the superdense excitations of electron (ES) and atomic (AS) subsystems with their intense energy exchange result the phase transitions and the different aggregate states may be existed simultaneously in solid, liquid and plasma phases (so called flush- states) with its non-uniform distributions  in irradiated volume[4, 7]. It greatly complicates the analysis of structure — phase damages and the theoretical descriptions. Medium (b3) includes the irradiation conditions for target. ES (b4) and AS (b6) excitations. At first the general beam energy results on collective ES excitation (plasmons) and only ~1 % of its value transfers on direct AS excitation. That is why ES processes often initiate and determine some post effects in AS. We describe them later. Target warming (b9) is interpreted as an energy of thermal field (b10) of excited phonons (b8). This energy is transformed in two directions as slow and fast stages. The slow stage is resulted from an existence of small temperature gradients: (1) in irradiated volume from an non-iniform absorbed energy profile; (2) between: irradiated and non-irradiated volumes; (3) target surfaces and medium. The slow relaxation is realized through temperature-deformation field (b13) with structure-phase damages (b15), heat removal to medium (b27) and thermo-diffusion (b21), that stimulates low intense mass transfer (b29). The fast stage is developed as thermal shock (b11) under intense pulsed irradiation (10^–8–10^–6 s; 10⁸–10¹⁰ W/cm² ;1–100 J/cm²/pulse) with minimum heat removal to medium (b27).The generation of elastic (b12) and shock (SW) waves (b14) is resulted from thermal shock and  intense plasma ablation (b26) from the irradiated surface. The recoil impulse generates additional compression in target, that reinforces SW amplitude. The experiments and models of different authors for radiation-stimulated SW, elastic-plastic and elastic waves, calculations of their profiles, phase transitions and  mass transfer mechanisms are presented in our review of topical problems [4]. Ablation (b26) is caused with intense pulsed irradiation. Its general laws, possible mechanisms and theoretical models are presented in works, mentioned in [1–4]. With increasing of beam intensity and fluence for the single pulse of irradiation, the energy beam consumption on ablation and its intensity are also greatly increased. Mechanical stresses (b16) are resulted from: (1) electromagnetic excitation of elastic waves: path 1–2–4–29–6–8–12–16 in Figure 1; (2) implantation stresses, generated by ballistic mixing of beam particles with matrix atoms: 1–2–5–16; (3) additional mechanical impulse is created under stopping of beam particles in  ballistic mixing: 1–2–5–6–8–12–16; (4)  the recoil impulse under ablation: 1–2–4–26–14–16; (5) (5) thermal  stresses, generated; (a) on fast stage: 1–2–4–30–8–9–10–11–14–16 and 1–2–4–30–8–9–10–11–12–16; (b) on slow stage: 1–2–4–30–8–9–10–13–16. Energetic and temporal estimates for these processes are given in [1, 2]. Mechanical stresses cause defects generation (b17), chemical reactions (b18) and barodiffusion (b19). Chemical reactions are possible under SW loading. The noticed processes together with radiated-stimulated (b31) and thermal (b21) diffusions induce mass transfer. Mass transfer (b29) is determined by the effects, presented in b17, b18, b19, b21, b31, b32 and b33. It is mostly detected under intense irradiation and causes different damages both in irradiated and non-irradiated volumes: variation of initial mass and dislocation densities [1-9], nucleation of microcracks and brittle fracture [5], redistribution of alloys elements in steels [1, 6], formation of new non-equilibrium phases and compounds in multilayers in result of rapid liquid-phase melting and mixing [1, 3, 4, 11]. Structural-phase damages (b15), stable structure (b32) and modificated properties (b33) The formation of stable structure may be lasted till a few months or already years after irradiation. But its intensity is essentially decreased in time. The general problem is the connection of radiation damages with stable structure and modificated properties. It is also actual for improving the operating characteristics of materials.