Relationship between electromagnetic and acoustic emissions during plastic deformation of gamma-irradiated LiF monocrystals

• Published in: Journal of applied physics 2011-07, Vol.110 (2), p.024907-024907-9
• Main Authors: Hadjicontis, V., Mavromatou, C., Mastrogiannis, D., Antsygina, T. N., Chishko, K. A.
• Format: Article
• Language: English
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CRACKS; DEFORMATION; DISLOCATIONS; ELECTROMAGNETIC PULSES; FRACTURES; GAMMA RADIATION; INDUCTANCE; IONIC CRYSTALS; LITHIUM FLUORIDES; MATERIALS SCIENCE; MONOCRYSTALS; PHOTON EMISSION; PHYSICAL RADIATION EFFECTS; PLASTICITY; POLARIZATION; RADIATION DOSES; SENSORS; SLIP; STRAIN HARDENING; VACANCIES
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3608247

Simultaneous measurements of acoustic emissions (AE) and electromagnetic emissions (EME) during plastic deformation and destruction under uniaxial compression along 〈 001 〉 direction are made on LiF monocrystals after gamma irradiation by 60 Co source. The irradiation doses are 1, 2, and 10 Mrad. The EME measurements in the radio-frequency range are carried out using two types of electromagnetic sensors: (i) a simple electrical stub antenna and (ii) a toroidal inductance coil. Two checking experiments on unirradiated crystals are performed as the starting point to discover the effect of gamma irradiation on acoustic and electromagnetic emissive ability of plastically deformed ionic crystals. Unirradiated LiF monocrystals demonstrate high-intensive EME at easy glide and work hardening stages, as well as at the fracture during destruction of the sample. At radiation doses more than ∼1 Mrad, in the active loading stage the EME of LiF monocrystals vanishes, except few individual electromagnetic pulses (only at 1 and 2 Mrad doses), which are time correlated with well-defined drop-jumps on the loading diagram and therefore can be associated with macroscopic crack openings. Moderate electromagnetic activity in irradiated crystals occurs only in the final stage of deformation at the complete fracture of the sample. Thus, after gamma irradiation the formation of polarization currents due to dynamic interaction between charged vacancies and moving dislocations is suppressed, and only EME connected with the redistribution of the free charge on the crack branches is observed. Acoustic emission diagrams of low-irradiated LiF are typical for the work hardening stage in crystals containing a great amount of strong point stoppers. At larger irradiation doses the AE diagram displays quite different behavior at low- and high-loading regions with a sharp boundary between them. The low-loading region shows poor AE activity, which changes sharply into high-active burst-like emission with an increase in loading. The boundary between two regions shifts to higher loadings with radiation dose. The higher is the radiation dose the lower is the relative intensity of AE in the high-stressed region. The physical mechanisms of EME and AE in gamma-irradiated ionic crystals are discussed.