Low-energy Pulsed Electron Beam Research Articles

Bacterial eradication by a low-energy pulsed electron beam generator

Low-energy electron beams (LEEB) are a safe and practical sterilization solution for in-line industrial applications, such as sterilizing medical products. However, their low dose rate induces product degradation, and the limited maximal energy prohibits high-throughput applications. To address this, we developed a low-energy ‘pulsed’ electron beam generator (LEPEB) and evaluated its efficacy and mechanism of action. Bacillus pumilus vegetative cells and spores were irradiated with a 250 keV LEPEB system at a 100 Hz pulse repetition frequency and a pulse duration of only 10 ns. This produced highly efficient bacterial inactivation at a rate of >6 log10, the level required for sterilization in industrial applications, with only two pulses for vegetative bacteria (20 ms) and eight pulses for spores (80 ms). LEPEB induced no morphological or structural defects, but decreased cell wall hydrophobicity in vegetative cells, which may inhibit biofilm formation. Single- and double-strand DNA breaks and pyrimidine dimer formation were also observed, likely causing cell death. Together, the unique combination of high dose rate and nanosecond delivery of LEPEB enable effective and high-throughput bacterial eradication for direct integration into production lines in a wide range of industrial applications.

Oxidation behavior of TiCr and TiMo alloys formed by low-energy pulsed electron beam impact

The titanium-based alloys with 2–3 at.% of chromium (TiCr) and molybdenum (TiMo) were produced on the top of titanium samples by means of the high-intense pulsed electron beam impact on the titanium with preliminary deposited Cr and Mo coatings. The TiCr and TiMo alloys were subjected to oxidation in open air atmosphere at temperature 600 °C. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-disperse X-ray microanalysis (EDX) were used for structure and elemental composition determination in the samples. The analysis of oxygen depth profiles showed the increase in oxygen penetration depth in the case of TiCr alloy in comparable to pure titanium. The oxygen concentration corresponding to stoichiometry of the oxide phase TiO2 was found on the depth equaled to the thickness of the TiCr alloy that shows the enhancement of the diffusion of oxygen in the modified layer. The diffusion of oxygen at the temperature of 600 °C is enhanced by decomposition of the solid solutions based on bcc β-Ti phase with free chromium and molybdenum atoms releasing. The free molybdenum atoms take part in the stabilization of TiO2 anatase phase while the free chromium atoms form intermetallic compound TiCr2 preventing the sample from oxidation.

Effect of electron beam irradiation on structural phase transformations of zirconia-based composite reinforced by alumina nanofibers and carbon nanotubes

Evolution of microstructure, elemental and phase composition of dense zirconia-based composite under irradiation with electron beam were investigated. Tetragonal zirconia-based composite reinforced by 5 wt% alumina nanofibers and 0.5 wt% single-walled carbon nanotubes was prepared by spark plasma sintering at a temperature of 1500°C. Irradiation of the composite was carried out with a low-energy pulsed electron beam of submillisecond duration in the following mode: beam energy density 15 J·cm−2; pulse duration 200 μs; pulse repetition rate 0.3 s−1; pulses quantity 10, 20, 30 and 40; residual gas pressure (argon) in the working camera 10−2 Pa. It has been established that electron beam treatment leads to the formation of modified multilayered surface, the thickness of which varies from 6 to 40 μm. Redistribution of Al atoms in the modified surface layer was detected. The phase evolution dependent on the quantity of irradiation pulses and manifested in the crystalline structure of material.

Structure and properties of the surface layer of «Ti/SiC-ceramic» system irradiated by low-energy pulsed electron beam

The results of the investigation of evolution structural phase states of the surface layer «film (Ti)/substrate (SiC-ceramics)» system subjected to processing with an intense pulsed electron beam are presented (Ti film 0.5 μm thick was deposited on the surface SiC ceramic). Samples of SiC ceramics obtained by SPS-sintering were used. Irradiation with an intense pulsed electron beam of submillisecond duration was carried out at the «SOLO» device under the condition: energy density of the electron beam of 15 J/cm2, pulse duration of 200 μs, quantity of pulses – 20 and 30. The X-ray diffraction analysis of the treated electron beam «Ti/SiC» system showed that under the specified irradiation regime the phase composition formed in the surface layer and the volume fraction of the phases depend on the quantity of irradiation pulses. At 20 pulses, following phase composition of the surface layer was formed: SiC – 18.5 %, TiC – 36.6 %, Ti5Si3 – 44.9 %; at 30 pulses, a phase relationship: SiC – 81.6 %, TiC – 12.7 %, Si – 0.5 %, C – 5.2 %. Scanning and transmission electron microscopy revealed, that irrespective of the quantity of pulses of the electron beam, takes place the formation of a surface layer with a globular structure, formed as a result of melting of the titanium film, which contains a droplet fraction. The particles of the drop fraction had a submicro-nanocrystalline structure and were enriched mainly by titanium, silicon and carbon atoms. It was established that electron beam treatment with 30 pulses leads to formation of round-shaped regions on the surface of irradiation, the microhardness of which varies from 55 GPa to 96 GPa, which is several times the microhardness of the initial SiC ceramic (36 GPa). It was suggested that these regions were formed as a result of electron beam treatment of the surface layer, which contains a drop fraction.

Processing of Polypropylene by Low-Energy Pulsed Electron Beam from Forevacuum Plasma Source

Influence of electron beam irradiation on the morphology and contact angle of polypropylene was investigated. Electron beam processing was carried out at 8 – 10 kV accelerating voltage and a pressure of 5 – 10 Pa. Beam current density was up to 4.5 A/cm2, and the pulse duration - from 150 to 300 μs. The morphology of irradiated polymer material was studied by scanning-electron and atomic-force microscopy methods. It was established formation of extended equally oriented “hills” divided by “valleys”. The height of hills increases with the growth of energy flux density per pulse.

Dynamic response of aluminum to pulsed energy deposition in the melt-dominated regime

The results of an experimental study of the dynamic response of aluminum exposed to a high-fluence low-energy pulsed electron beam are presented and compared with calculations based on two equations-of-state (EOS) models for metals in the melt-dominated regime. The first model, the widely used classical Mie-Grüneisen EOS, is a simplified scheme in which no thermodynamic distinction is made between solid and liquid phases. The second model - the so-called GRAY EOS recently developed at Lawrence Livermore Laboratories - is a three-phase EOS which provides a more detailed and thermodynamically complete description of metals in the melt region. The experimental studies consisted of measuring the dynamic response of 6061 aluminum to a pulsed 185-keV electron beam for fluences ranging from 15 to 50 cal/cm2, resulting in peak energy depositions of 450–1500 cal/g. The experimental condition produced a mass blow-off which was dominated by mass in the melt state. The response was characterized by simultaneous (for each electron pulse) measurements of impulse, transmitted stress, blow-off velocities, and mass loss. The experimental results were compared with the predicted response to the rapid heating calculated with a hydrodynamic computer code (RIP) in conjunction with the two EOS models. The essential result of the comparison was that after the onset of melting the simple Mie-Grüneisen model fails to give reasonable agreement with experiment, whereas the GRAY EOS provides acceptable agreement with the experimental results. In particular, the prediction of GRAY that the thermal pressure in the melt regime can be described by an effective ``average'' temperature-dependent Grüneisen parameter, which at the completion of melting is approximately 40% higher than the solid Grüneisen value, is clearly confirmed by the experiments. The results demonstrate the necessity of adequately taking melting into account in modeling material response to pulsed energy deposition.