TEM study of ion beam induced amorphization of minerals

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5905745

Wang, Lu Min; Ewing, R C ^[1]

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1. Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Geology

Metamicitization is a radiation-induced, periodic-to-aperiodic phase transition caused by alpha-decay events of nuclides in the U[sup 235], U[sup 238] and Th[sup 232] decay series. Despite careful studies of natural specimens, poorly known ages and thermal histories make it difficult to analyze this phenomenon as a function of increasing dose. In this study, ion beam irradiations have been used to simulate the process in many different structure types, including olivine, zircon, zirconolite and neptunite. The irradiations were completed using the HVEM-Tandem facility at Argonne National Laboratory, which links an ion accelerator with a transmission electron microscope, so that the structural change of the target during irradiation can be monitored in situ by electron diffraction. In most cases, complete amorphization of the target occurs within several hours of the ion beam irradiation. The ions used are He, Ne, Ar, Kr and Xe with energy ranges of 200 keV to 1.5 MeV. The electron energy was kept at 300 keV during ion irradiations for in situ observation. Irradiations were performed under a controlled temperature which varies from near liquid helium temperature (15K) to 650 C. Complete amorphization was induced at fractions of one displacement per atom (dpa) damage level in all the minerals irradiated by Kr and Xe ions at room temperature. Critical amorphization dose increases with the decreasing complexity of the mineral structure, increasing ionicity of the bonding, and increasing irradiation temperature. High resolution transmission electron microscopy has also been performed to study in detail the formation of amorphous domains at low and moderate ion doses. Amorphous domains with the size of displacement cascades (calculated by computer simulations) have been observed.

• OSTI ID: 5905745
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360605* -- Materials-- Radiation Effects
58 GEOSCIENCES
580000 -- Geosciences
ALPHA PARTICLES
AMORPHOUS STATE
BEAMS
CHARGED PARTICLES
ELECTRON MICROSCOPY
ION BEAMS
IRRADIATION
MICROSCOPY
MINERALS
MORPHOLOGICAL CHANGES
OLIVINE
OXIDE MINERALS
PHASE TRANSFORMATIONS
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
SILICATE MINERALS
SIMULATION
TRANSMISSION ELECTRON MICROSCOPY
ZIRCON
ZIRCONOLITE