Irradiation, electrons

As seen in Fig. 8.5, the damage rate per particle flux in electron irradiation is around 10 dpa/s/electrons/cm /s, which is almost one order of magnitude 

Since electrons with MeV order energies can produce uniform damage to a depth in the order of mm, tensile tests can be conducted as macroscopic mechanical testing. SAXS or SANS can be conducted as well as TEM, atom probe tomography analysis and positron annihilation spectroscopy measurements. In HVEM irradiation, time-dependent evolution of individual defect clusters such as an interstitial loop or a vacancy cluster can be investigated in an irradiated spot area. Microanalysis using an electron beam probe such as energy dispersive X-ray analysis is also applicable in the beam spot area. However, other analyses or measurements on such small areas are difficult to carry out. 

The electron bombardment of explosives has been undertaken by various investigators in an effort to initiate or decompose the material under study. One of the early investigations was undertaken by Kallmann and Schrankler [30], who bombarded TNT, mercury fulminate, nitrocellulose, and to some extent, picrates and azides with 10-kV, 1-mA electrons in vacuo but were unable to produce explosions. However, when heavy ions of argon and mercury were used, initiations were achieved with several substances with each of the ions. Muraour [31 ] subjected lead azide and silver acetylide to 90 kV at 3 mA for 3 min and only achieved explosion with silver acetylide. Both explosives blackened upon electron irradiation. Muraour believed that the explosion was either a thermal effect or that, by chance, a sufficiently large number of molecules decomposed at one point to bring about complete decomposition. 

Bowden and Singh [37, 38] achieved explosion of lead and silver azides when crystals were irradiated with an electron beam of 75 kV and 200 pA. Explosion was partly due to heating of the crystals by the electron beam. To substantiate this, crystals of potassium chlorate with a melting point of 334°C readily melted in the beam, showing a temperature rise close to the explosion temperature of the azides. Sawkill [97] investigated with an electron microscope the effect of an electron beam on lead and silver azides. If explosion did not take place, color changes and nucleation occurred cracks developed within the crystals which broke up into blocks about 10 cm across and were believed to be associated with a substructure in the crystals. In silver azide the progression to silver was pronounced but did not follow the thermal decomposition route. 

The decomposition of various azides by electron bombardment has been studied. Muller and Brous [98, 99] studied sodium azide, Groocock and Tompkins [100] investigated barium and sodium azides, and Groocock [101] investigated a-lead azide. In each case only gas evolution was studied and detected [102]. 

Steady-state electron bombardment of high explosives has been conducted. 

Explosive (mg) (R) (R/sec) loss Color change Test Result 

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The vacancy is very mobile in many semiconductors. In Si, its activation energy for diffusion ranges from 0.18 to 0.45 eV depending on its charge state, that is, on the position of the Fenni level. Wlrile the equilibrium concentration of vacancies is rather low, many processing steps inject vacancies into the bulk ion implantation, electron irradiation, etching, the deposition of some thin films on the surface, such as Al contacts or nitride layers etc. Such non-equilibrium situations can greatly affect the mobility of impurities as vacancies flood the sample and trap interstitials. 

The resins are commonly cured by the use of peroxide with or without cobalt accelerators, depending on whether the hardening is to be carried out at room temperature or at some elevated temperature. Electron irradiation curing, which can be completed within a few seconds, has, however, been introduced for coatings on large flat surfaces such as plywood, chipboard and metal panels. 

Radiation Safety of Gamma and Electron Irradiation Facilities, Safety Series No. 107, International Atomic Energy Ageney, Vienna, 1992. 

Key Words—Graphite, fullerenes, HREM, nanostructures, electron irradiation. 

High-resolution transmission electron microscopy (HREM) is the technique best suited for the structural characterization of nanometer-sized graphitic particles. In-situ processing of fullerene-related structures may be performed, and it has been shown that carbonaceous materials transform themselves into quasi-spherical onion-like graphitic particles under the effect of intense electron irradiation[l 1],... 

Fig. I. High-resolution electron micrographs of graphitic particles (a) as obtained from the electric arc-deposit, they display a well-defined faceted structure and a large inner hollow space, (b) the same particles after being subjected to intense electron irradiation (note the remarkable spherical shape and the disappearance of the central empty space) dark lines represent graphitic layers.

Fig. 2. HREM image of a quasi-spherical onion-like graphitic particles generated by electron irradiation (dark lines represent graphitic shells, and distance between layers is 0.34 nm).

The progressive ordering from the surface to the center has been experimentally observed in the case of the electron irradiation-induced formation of the quasi-spherical onion-like particles[25]. In this case, the large inner hollow space is unstable under electron bombardment, and a compact particle (innermost shell C( ) is the final result of the graphitization of the carbon volume (see Fig. 3e-h). 

Fig. 3. Schematic illustration of the growth process of a graphitic particle (a)-(d) polyhedral particle formed on the electric arc (d)-(h) transformation of a polyhedral particle into a quasi-spherical onion-like particle under the effect of high-energy electron irradiation in (f) the particle collapses and eliminates the inner empty space[25j. In both schemes, the formation of graphite layers begins at the surface and progresses towards the center.

Much care had to be taken during the TEM observations of silver nitrate filled tubes, because this salt is very sensitive to electron irradiation and the continuous filaments transformed quickly into a chain of silver particles (see Fig. 5) [22]. 

Enclosed nitrate filaments can be thermally decomposed to silver by a simple heat treatment. In opposition to electron irradiation that fragments the filaments, the simple heating yields continuous metal nanorods (see Fig. 6 for a silver filament generated by a 60 min. treatment at 400°C, pressure lO Torr). 

Fig. 5. HREM of enclosed silver particles in CNTs. The metallic particles were obtained by electron irradiation-induced decomposition of introduced silver nitrate. Note that the gases produced by the nitrate decomposition have eroded the innermost layer of the tube.

The decomposition of the nitrates produces oxygen molecules, and we have verified that if a mixture of silver nitrates and closed tubes is submitted to a thermal treatment (400°C) decomposing the salt, it is possible to observe filled CNTs (Ag, Co, Cu [34]). It appears that oxygen liberated during the thermal decomposition of the metal salt erodes the CNT tip and the yet un-decomposed salt then enters by capillarity (see Fig. 8). We have also observed during the electron-irradiation decomposition of enclosed nitrate that the liberated gases erodes the CNT cavity [22] (see the innermost tubes in Fig. 5). 

CNTs have been prepared recently by electrolysis and by electron irradiation of tube precursors. For example. Hsu e/ al. [30,31] have described the condensed-phase preparation of MWCNTs by an electrolytic method using a graphite rod (cathode) and carbon crucible (anode) (Fig. 6) in conjunction with molten LiCl as the electrolyte, maintained at 600°C under an Ar atmosphere. Application of a dc current (3-20 A, <20 V) for 2 min yielded MWCNTs (2-10 nm in diameter, >0.5 pm in length) consisting of 5-20 concentric layers with an interlayer... 

Electron irradiation (100 keV) of the sample, heated to 800°C, yields MWCNTs (20-100 nm in length) attached to the surface. Such nanotube growth does not take place if natural graphite, carbon nanoparticles or PTFE are subjected to electron irradiation. The result implies that the material may be a unique precursor for CNTs and may constitute a new preparation method. 

S. Muto and D. Scbryvers, Electron-irradiation-induced martensitic transformation in NixAljoO-x observed... 

HS(G)94 Safety in the design and use of gamma and electron irradiation facilities... 

Fig. 17. LHeT absorption of the Si-related LVMs in p+-GaAs Si after holes capture by (a) electron irradiation-induced effects and (b) deuterium-related neutralizing complexes. The spectral resolution is 0.1 cm1. J. Chevallier el al., Mat. Res. Soc. Symp. Proc. 104, 337 (1988). Materials Research Society. 

In high purity silicon below T = 140 K the Mu center is stable on the time scale of the muon lifetime (2.2 ps). However, in electron irradiated silicon Westhauser et al. (1986) have reported that Mu is metastable and makes a thermally induced transition to Mu at a temperature of 15 K. A similar transition between Mu and Mu was first discovered in diamond (Holz-schuh et al., 1982, Odermatt et al., 1988) and will be discussed in Sec-... 

Block copolymer micelles containing PB cores were cross-linked either by UV or fast electron irradiation [79-81]. This was accompanied by a shrinkage of the micelles. 

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