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PinheroLAB Irradiation Team Researching Radiation Damage
The PinheroLAB Irradiation Team has accomplished all of the goals set forth in their NEUP proposal. They have constructed an irradiation platform for bombarding specimens with energetic micro-focussed beams of fast protons or fast neutrons. At right is a high-resolution scanning electron microscope (HR-SEM) image of an irradiation region on the surface of highly-ordered pyrolytic graphite (HOPG). One can easily observe the changes in texture highlighting the dimensional changes induced by displacements in the bulk lattice of the crystal. HOPG is a model specimen for study since it is composed entirely of one element, carbon, and these carbon atoms are well-ordered into two dimensional (planar) hexagonal layers of graphene. Each layer is offset from adjacent (top and bottom neighbors) by an approximate half-lattice displacement. The result upon irradiation is that an incoming particle (protons and neutrons have nearly identical momentum) displaces atoms from the graphene lattice that then equilibrate into interstitial regions between layers, forming dislocation loops. These dislocation loops and coalesced atomic clusters are observed in the transmission electron microscope (TEM) image below along with a graphical distribution of cluster sizes.
Ultimately, these clusters result in a dimensional change in the HOPG crystal. Atomic force microscopy (AFM) has been employed to map topographical variations that help measure this dimensional change, and specifically the dimensional change resulting from the ruck & tuck mechanism discussed by MI Heggie. The AFM image is shown below.