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The defects that result from proton and neutron irradiation of tungsten were studied using a field ion microscope. The initial stages of radiation damage can be examined by noting the configuration, density, and type of defect. This study used medium-energy protons as well as a spallation neutron flux for the irradiation.
Annealed tungsten was examined in the field ion microscope in both an unirradiated and irradiated condition. Irradiations were conducted using protons and spallation neutrons at the Los Alamos Meson Physics Facility (LAMPF). Temperature was controlled in the proton irradiations (by water cooling) to less than 323 K. The temperature for the neutron irradiations was measured at 398 K. The concentration of vacancies that survived recombination and were observed with the field ion microscope were 1 to 3% of the calculated displacements per atom (dpa). The remainder are suspected to have undergone vacancy-interstitial recombination resulting from a fluence of 1022 and 1024 protons per square metre was observed to be 2.5 × 10−3 and 8 × 10−3, respectively. The neutron-irradiated samples contained a vacancy concentration of 4 × 10−3 after a fluence of 1023 neutrons per square metre. Depleted zones containing 1000 or more vacant lattice sites along with smaller zones containing from 30 to 300 vacant lattice sites were observed in the irradiated material. The shape of the smaller zones was irregular and elongated in at least one direction while the larger depleted volumes split into “nodes”.
Unirradiated samples of the same stock were examined for artifacts and defects. The calculated equilibrium vacancy concentration at 300 K is 10−50. Only one vacnacy and one small void volume were found in the unirradiated samples examined.
The data indicated that the number of vacancies increases with increasing fluence. The most numerous defect for both the proton and neutron irradiations was the single vacancy. Depleted zones were of two basic sizes, 30 to 300 vacant lattice sites or over 1000 vacant lattice sites.
field ion microscopy, vacancy concentration, depleted zones, protons, spallation neutrons, LAMPF
Graduate student, New Mexico Institute of Mining and Technology, Socorro, NM
Professors, New Mexico Institute of Mining and Technology, Socorro, NM
Associate group leader, Los Alamos National Laboratory, Los Alamos, NM
Research scientist, Institute of Atomic Energy,