High-energy Xenon Ions Research Articles

Raman scattering in diamond irradiated with high-energy xenon ions

Accumulation of radiation damage and associated mechanical stresses in diamonds irradiated with 167 MeV Xe ions to fluences 1.0 × 1010 ÷ 8.15 × 1014 cm−2 have been studied using confocal Raman spectroscopy. The spectra were measured in a backscattering geometry across the irradiated layer by scanning the edge of single crystalline synthetic samples with nitrogen concentration 3 ÷ 5 ppm. All spectra were recorded at room temperature. Parameters of the 1332 cm−1 first-order Raman line – the FWHM and peak position, studied as function of Xe ion fluence, were used to characterize the structural disorder and mechanical stress level.

Physico-chemical fundamentals for high-temperature single-stage synthesis of compact ceramics based on zirconium nitride

The process of complete nitridization of zirconium tape samples in a nitrogen atmosphere at temperatures below and above the peritectic temperature has been implemented. Using the high resolution TEM method, it was found that the intragranular structure of the nitride is characterized by a high dislocation density (5 × 1011 cm−2). The hardness of the synthesized samples of ceramics corresponds to the hardness of single-crystal samples. Irradiation with high-energy xenon ions and gamma-irradiation does not lead to a change in the grain structure of ceramics.

Characterization of xenon ion and neutral interactions in a well-characterized experiment

Interactions between fast ions and slow neutral atoms are commonly dominated by charge-exchange and momentum-exchange collisions, which are important to understanding and simulating the performance and behavior of many plasma devices. To investigate these interactions, this work developed a simple, well-characterized experiment that accurately measures the behavior of high energy xenon ions incident on a background of xenon neutral atoms. By using well-defined operating conditions and a simple geometry, these results serve as canonical data for the development and validation of plasma models and models of neutral beam sources that need to ensure accurate treatment of angular scattering distributions of charge-exchange and momentum-exchange ions and neutrals. The energies used in this study are relevant for electric propulsion devices ∼1.5 keV and can be used to improve models of ion-neutral interactions in the plume. By comparing these results to both analytical and computational models of ion-neutral interactions, we discovered the importance of (1) accurately treating the differential cross-sections for momentum-exchange and charge-exchange collisions over a large range of neutral background pressures and (2) properly considering commonly overlooked interactions, such as ion-induced electron emission from nearby surfaces and neutral-neutral ionization collisions.

Stability of the structure of compact zirconium nitride ceramics to irradiation with high-energy xenon ions

X-ray diffraction and transmission electron microscopy (TEM) data demonstrate that irradiation with high-energy +24Xe136 ions causes no changes in the grain microstructure of compact zirconium nitride ceramics. According to Raman spectroscopy and high-resolution TEM data, the irradiated ceramics may have local distortions of the zirconium nitride lattice within regions on the order of the lattice parameter in size.

Structure of ion tracks in ceria irradiated with high energy xenon ions

Structure and accumulation behavior of ion tracks in CeO2 irradiated with 200 MeV Xe ions were examined by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to obtain fundamental knowledge on the microstructure evolution induced by fission fragments in nuclear fuels and transmutation targets, which is of importance for the development of advanced fuel/target materials at high burn-up conditions. Bright-field (BF) TEM images of ion tracks from an inclined direction showed Fresnel contrast along penetrating path of incident ions. The signal intensity of high-angle annular dark-field (HAADF) STEM images was decreased at the core damage region of ion tracks along the path of ions, revealing the reduction of atomic density inside the ion track. Preferential formation of smaller and larger ion tracks was observed at a high ion fluence of 1 × 1014 cm−2 compared to a low ion fluence of 1 × 1011 cm−2. Results were discussed due to the coalescences and incomplete recovery of the core damage regions during the overlap of high density electronic excitation damage, which is induced during the repetition of the formation and recovery of ion tracks within an influence region.

Irradiation of titanium, zirconium, and hafnium nitrides with high-energy ions

We have identified structural and morphological changes produced by irradiation with 167-MeV +24Xe136 ions to a fluence of 5.3 × 1014 cm–2 in Ti, Zr, and Hf nitrides prepared using oxidation-assisted engineering. Irradiation of TiNx and HfNx leads to the formation of nano- and micropores in the surface layer of the samples. The surface layer of ZrNx samples contains nanopores both before and after irradiation. The presence of pores in the unirradiated ZrNx samples probably ensures the possibility of structural relaxation without further pore formation under irradiation. The irradiated ZrNx samples have local crystal structure distortions unrelated to dislocations and attributable to the impact of high-energy xenon ions.

Behaviour of piezoelectric lead zirconate titanate irradiating with high-energy xenon ions

The characteristics of a detector fabricated using piezoelectric lead zirconate titanate (PZT) were studied by irradiating it with a 400 MeV/n xenon (Xe) beam while changing the beam flux intensity. The largest output signal was observed from the detector when the beam power per unit time was estimated to be largest. It was also found that the sensitivity per Xe ion of the detector seemed to be higher with decreasing the amount of the Xe ion flux within the limits of the experimental conditions.

Ionization and fragmentation of C60 by highly charged, high-energy xenon ions.

${\mathrm{C}}_{60}$ vapor was bombarded by $^{136}\mathrm{Xe}^{35+}$ and $^{136}\mathrm{Xe}^{18+}$ ions in the energy range 420--625 MeV to study the various ionization and fragmentation processes that occur. Since the center-of-mass energies used in this work exceeded those of previous studies by several orders of magnitude, new excitation and dissociation modes were expected and indeed found. Positive ions were extracted from the interaction region and their times of flight were measured both singly and in coincidence with other ionic fragments. A wide range of stable charge states and cluster sizes from monatomic carbon up to ${\mathrm{C}}_{60}$ was observed. Even-numbered carbon fragments dominated the heavier mass range but both even and odd carbon numbers occurred at lower masses. Evidence was found for three qualitatively different ionization and fragmentation channels suggesting different ranges of collision impact parameters: ionization of the parent ${\mathrm{C}}_{60}$ molecule, loss of even numbers of carbon atoms, and ``multifragmentation'' into many small fragments. This latter mode included the production of singly charged ${\mathrm{C}}_{\mathit{n}}^{+}$ fragments with all values of n being observed from n=1 up to at least n=19. We interpret our results in terms of a theoretical model that indicates that the total interaction cross section contains comparable contributions from (a) excitation of the giant dipole plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule. The distribution of fragment cluster masses for n\ensuremath{\lesssim}20 is reproduced by a ``percolation theory'' description analogous to that used to describe multifragmentation of nuclei by high-energy protons. \textcopyright{} 1996 The American Physical Society.