Magnesium aluminate spinel (MgO_nAl₂O₃) has potential applications to devices in fusion reactors, because of its excellent radiation resistance. During irradiation atomic redistribution of elements occurs which affects a materials properties in subtle ways. In order to gain an atomistic understanding of radiation induced structural change in MgO_nAl₂O₃, high angular resolution electron channeling x-ray spectroscopy (HARECXS) was utilized to determine ion configuration in the irradiated materials. HARECXS, a technique developed at Argonne National Laboratory, takes advantage of the fact that characteristic x-ray emission induced by electron channeling can be used explore the redistribution of elements at the atomic level.

TelePresence has become an integral component of these experiments. HARECXS measurements typically require data acquisition times that range from 5-24 hours. Remote collaborators work in teams, where one collaborator will start the experiment and then is replaced by another team member later in the day. Over the course of the experiments, collaborators remotely link into the experimental site, compare notes, display the data sets and plan additional measurements to be conducted during the next "run".

Over the course of the experiments, collaborators then remotely link into the experimental site, compare notes, display the data sets and plan additional measurements to be conducted during the next "run".

Fig. Caption: Collaborator's on-line during HARECXS experiments

In the figure below we compare some experimental results and theoretical calculations of the HARECXS channeling intensity for O, Mg, and Al Ka Lines as a function of orientation along a <400> direction between the {012} and {013} zones axes for perfect and irradiated MgAl₂O₄. In an ideal crystal 100% of the Magnesium is on the tetrahedral sites while 100% of the Aluminium on the octahedral sites.

Fig. Caption: Experimental (left) and Calculated HARECXS Intensity Profiles.

In this magnesium aluminate spinel study, we found that after irradiation by 1 MeV neon ions to a dose of ~2 dpa, that only 37% of the magnesium atoms remain on the tetrahedral sites while the 22% of the aluminum has shifted from an octahedral site to a tetrahedral site. This elemental redistribution occurs without destroying the crystallinity of the material, and only involves a redistribution of aluminum, magnesium, and the vacancies created by the high energy ions. The stablity of this material in irradiation environments is believed to come from a number of vacant sites in the spinel structure and how the different atoms redistribute themselves.