T. Vilaithong

Ion beam induced Deoxyribose Nucleic Acid transfer

We report our observations of the interaction of energetic ions with bacterial cells, inducing direct deoxyribose nucleic acid (DNA) transfer into Escherichia coli (E. coli). Argon- and nitrogen-ion beams were used to bombard the bacteria E. coli in a vacuum with energy of 26 keV and fluence in the range 0.5–4×1015 ions/cm2. Three DNA plasmids, pGEM2, pGEM-T easy, and pGFP, carrying different marker genes, were subsequently transferred (separately) into the appropriately ion-bombarded bacteria and successfully expressed. The results of this study indicate that ion beams with an energy such that the ion range is approximately equal to the cell envelope thickness, at a certain range of fluence, are able to generate pathways for macromolecule transfer through the envelope without irreversible damage.

A study of low-energy ion beam effects on outer plant cell structure for exogenous macromolecule transferring

Abstract The aim of this study was to investigate low-energy ion beam effects on inducing exogenous macromolecule transfer through cell walls into cells and the related dependence. The experiment focused on 20–30 keV Ar ion implantation in various plant tissues to doses ranging from 1014 to 1016 ions/cm2. Auxiliary 15–30 keV N ion implantation in the plant tissues as well as 25 keV Ar ion implantation in bacteria of E. coli was also carried out. The effects of ion beam bombardment on the outer cell structure and the ability of transferring large exogenous molecules of Trypan blue (TB) and plasmid DNA were investigated. Typical results show that the 20 keV Ar ion implantation only leads to retaining of the TB dye in the cell wall whereas the 30 keV Ar ion implantation can allow the dye to enter the cell. A discussion based on simulations of the ion implantation processes indicates that the cell wall composed of cellulose microfibrils is in a porous structure so that ions at certain low energies with appropriate doses can increase permeability of the cell wall and induce exogenous macromolecule transferring.

Ion penetration depth in the plant cell wall

Abstract This study investigates the depth of ion penetration in plant cell wall material. Based on the biological structure of the plant cell wall, a physical model is proposed which assumes that the wall is composed of randomly orientated layers of cylindrical microfibrils made from cellulose molecules of C6H12O6. With this model, we have determined numerical factors for ion implantation in the plant cell wall to correct values calculated from conventional ion implantation programs. Using these correction factors, it is possible to apply common ion implantation programs to estimate the ion penetration depth in the cell for bioengineering purposes. These estimates are compared with measured data from experiments and good agreement is achieved.

Characteristics of heavy ion beam-bombarded bacteria E. coli and induced direct DNA transfer

Abstract The goal of the work described here was to study ion beam interactions with bacteria and thus develop an understanding of the mechanisms involved in ion bombardment-induced direct gene transfer into bacterial cells. Ar ion beams at an energy of 26 keV and fluences ranging from 5×10 14 to 4×10 15 ions/cm 2 were used to bombard bacterial cells of Escherichia coli strain DH5α. The bacteria were able to survive the low-temperature and low-pressure treatment conditions for at least a few hours. The ion bombardment created novel crater-like structures on the surface of the bacterial cell envelope, as observed by scanning electron microscopy. Four variously sized DNA plasmids carrying the ampicillin resistance gene were transferred and expressed in E. coli cells bombarded with ion fluences of 1×10 15 and 2×10 15 ions/cm 2 . The dependence of the DNA transfer on the plasmid DNA size, ion fluence and incubation time all suggests that the ion beam-induced surface crater-like structures provide the pathway for the mechanism that is responsible for the ion beam-induced DNA transfer.

Some investigations of ion bombardment effects on plant cell wall surfaces

Abstract Recent developments in the field of ion beam bioengineering, for example our own work demonstrating ion beam-induced transfer of exogenous macromolecules into the interior cell region, have underscored the need for a better understanding of the effects of ion bombardment on the cell wall material. We describe here, our investigations of ion beam sputtering of plant cell wall material and ion beam-induced damage to the cell wall. The presently available ion implantation simulation programs are not adequate, and experimental results are not available, either. We have indirectly estimated the surface sputtering yield of plant cell wall composed of C6H12O6-compound by remodeling the cell wall material so as to use partial mass densities and surface binding energies in the available ion implantation programs. For bombardment with a 30-keV Ar-ion beam, the sputtering yield from the cell wall is estimated to be approximately 10 atoms/ion, which is somewhat greater than the value predicted by direct program simulation, but in good agreement with experimental results. We have also performed electron microscopy on the ion-bombarded cell walls. The micrographs show novel microcrater-like structures on the cell wall subsequent to ion bombardment, which could be the ion beam-generated pathways for exogenous macromolecule transfer.

Optical emission spectra of a copper plasma produced by a metal vapour vacuum arc plasma source

Optical emission spectroscopy in the range 200-800 nm was applied for investigation of the copper plasma produced by a metal vapour vacuum arc plasma source. The experiments were conducted for the cases when the plasma was guided by straight and Ω-shaped curved solenoids as well as without solenoids, and also for different vacuum conditions. It was found that, besides singly- and doubly-charged ions, a relatively high concentration of excited neutral copper atoms was present in the plasma. The relative fraction of excited atoms was much higher in the region close to the cathode surface than in the plasma column inside the solenoid. The concentration of excited neutral, singly- and doubly-ionized atoms increased proportionally when the arc current was increased to 400 A. Some weak lines were attributed to more highly ionized copper species and impurities in the cathode material.

Development of an encapsulated scintillating fiber detector as a 14-MeV neutron sensor☆

Abstract A scintillating fiber detector has been developed and tested for use as a 14-MeV neutron sensor. The detector, designated an “Encapsulated Scintillating Fiber Detector (EFD)”, is composed of a parallel array of 0.5 × 0.5 × 15 mm BCF-12 plastic scintillating fibers encapsulated in clear BC-600 optical cement. The 85 fibers from a 12 × 12 mm square array, with a separation gap of 0.8–1 mm, in the center of the 40 mm diameter × 15 mm thick hardened optical cement. It can be directly coupled to an ordinary 2 in. diameter photomultiplier tube and its simple electronics. The response of the detector to gamma-rays from isotopic sources, as well as to 2.6- and 14-MeV monoenergetic neutrons from a neutron generator has been evaluated. The detector shows 3 distinct properties simultaneously, i.e. (1) good gamma-ray pulse height reduction, (2) discrimination against 14-MeV neutrons entering at angles non-parallel to the fiber axis, and (3) production of a full energy peak of 14-MeV recoil protons in the direction of the fiber axes. Investigations by Monte Carlo simulation are also included.

Friction modification of WC-Co by ion implantation

Abstract This study focuses on the effects of ion implantation on the friction modification of WC-Co cermet. Samples were implanted with Ar, C, N, O and B ions at 120–140 keV, and underwent tribological tests, mainly within the elastic region, against the cermet itself using varied loads. The experimental results show that the C ion implantation most significantly reduces the friction coefficient, and that the effect increases with the ion dose, whereas N, O and B ion implantations increase microhardness. A modified friction model suggests that the contributors to the friction modification are attributed to the compromise between microhardness and toughness, depending on the microstructure or phase and the ion-implantation-induced surface compression stress, which depends on the ion size.

Low cost high resolution thermoluminescence spectrometer

A high-resolution thermoluminescence dosimetry (TLD) spectroscopy reader has been developed in order to perform detailed quantitative studies of the kinetics of TLD materials. The key features of this system are high wavelength resolution (1.3 nm), low cost, and compact size. In addition, the spectrometer is fiber optic coupled to the sample material isolating the system from thermal influences and electrical noise generated by the heating system. Temperature rate control can be computer set with a heat rate accuracy of better than 0.12% and a temperature readout accuracy of 1 °C or better. Analysis of all three parameters: temperature, wavelength, and intensity, is easily visualized with integrated 2D/3D analysis software. Preliminary analysis on TLD300 samples irradiated with 60Co from 5 to 60 Gy show temperature peaks and wavelength locations consistent with other published measurements. Details of the hardware system and software are discussed along with sample results.

A heavy ion implanting facility at the Chiang Mai University

Abstract Nitrogen ion implantation is widely used to improve the wear and corrosion resistance of metals and alloys. Different kinds of ions, including metal and heavier ions can be used for this purpose. The proposed ion implanter as a 0°- and a 45°-beam line. The 0°-beam line has been installed and tested by using an RF source with an ion energy of about 140 keV. The nitrogen beam current is about 200 μA at the target position. The beam can be magnetically swept to cover a 10 cm × 10 cm target area. Preliminary tests with an ion dose of about 10 17 ions/cm 2 improved the hardness of stainless steel and aluminium samples. The 45°-beam line and the analyzing magnet are under construction. When this will be completed, the present RF ion source will be replaced by a Danfysik 910 ion source which can be used for producing metal and heavier ions.