Proton Transmitting Energy Spectra and Transmission Electron Microscope Examinations of Biological Samples

Transmission energy spectra of 530 keV H^(+) ion penetrating 140μm thick seed coat of maize and fruit peel of grape with thickness of 100μm were measured.The result indicates that these thick biological targets,as seen by the penetrating ions,are inhomogeneous,and there are open“channel like”paths along which the incidentions can transmit the targets easily.While most of the incident ions are stopped in the targets,some of the transmitting ions only lose a small fraction of their initial incident energy.The transmission energy spectra show a pure electronic stopping feature.Transmission electron microscope(TEM)micrographes taken from the samples of seed coat of maize and fruit peel of tomato with thickness of 60μm indicate that 150keV electron beam from the TEM can penetrate the thick samples to give very good images with clear contrasts.

Formation of Endohedral Complexes in Collisions of H_(2 ) and D_(2) with C_(60)

Formations of endohedral complexes in collisions of H_(2) and D_(2) with C_(60) molecules have been studied using a molecular dynamics simulation method.H@C_(60) complex is produced when a H_(2) molecule collides with a C_(60) molecule dong the direction from the center of a hexagonal ring into the center of the C_(60) at collision energy E0=40 eV.At the same collision condition,a D2 molecule colliding with a C_(60) molecule forms a D_(2)@C_(60) complex。

Deep Penetration of Charged Particles in Biological Samples

Experimental evidence of abnormally deep penetration in some botanical targets by low-energy ion beams is presented.The energy spectra of 818 keV He^(+)ions penetrating a 70μm thick seed coat of maize,fruit peel of grape and of tomato all have a common feature.The leading edges of these broad spectra indicate that some of the penetrating ions pass through the thick targets easily and only lose a small fraction of their initial incident energy.Rutherford backscattering spectrometry and electron microprobe measurements are used to determine the argon concentration in multilayer samples of the seed coat of maize implanted by 200 keV Ar^(+)ions.The results show that about 10%of the Ar^(+)ions can penetrate deeper than~100μm in these samples.

Influence of Temperature and Species in the Feedstock on the Growth of Single-Wall Carbon Nanotubes

A molecular dynamics simulation method is used to study the growth of narrow single-wall carbon nanotubes.It is found that the growth temperature and the species of small carbon clusters in the feedstock are important for the quality of the nanotubes grown.There is a temperature range of 1000-1500 K in which the narrow armchair single-wall carbon nanotubes can grow rapidly via adduction of C2 dimers,even without the existence of catalysts.The narrow zigzag tubes cannot keep open-ended growth.If the feedstock consists of various species of carbon clusters,the tubes cannot keep open-ended growth.At higher temperatures,the narrow nanotubes close rapidly in the noncatalytic environment,and the products grown are fullerene-like capsules.

Collision Direction Dependence of React ion Channels and Reaction Products in Molecular Collisions Between Two C_(60) Molecules

The reaction channels and the reaction products in the collisional reactions between two C60 molecules are found to be sensitively dependent on the relative orientation between the colliding partners.The detailed collision processes and the stable structures of the products are studied by using a molecular dynamics simulation method combined with a Langevin molecular dynamics scheme.The defects of the reaction products are also analyzed.

An Improved Calculation of Nonlinear Stopping Power of an Electron Gas for Slow Hydrogen Ions

The stopping power of an electron gas for hydrogen ions is calculated based on the full self-consistent nonlinear density-functional frame.Three different configurations of hydrogen ions are considered and a criterion to test the validity of the self-consistent calculation is proposed.Comparison of calculation with available experimental data shows good agreement.