The natural radionuclide (226Ra, 232Th and 40K) contents of building materials commonly used in South Korea have been determined by a gamma ray spectroscopy system using a high purity germanium detector. The radon exhalation rates and emanation coefficients of building materials have also been studied. The average concentrations of 226Ra, 232Th and 40K in building materials were in the range of 6.47-271 Bq.kg-1, N.D.-89.9 Bq.kg-1 and 16.8-1081 Bq.kg-1, respectively. The average radon exhalation rates and emanation coefficients were in the range of 0.0061-0.2404 Bq.kg-1.h-1 and 2.39-11.5%, respectively.
The joint strength and subsequent microstructural evolution of a friction stir spot-welded AA6061-T6 alloy was investigated according to the process parameters: tool rotation speed, dwell time and pin angle of the tool. A maximum tensile shear load of 2.78 kN was obtained from the joints generated under a combination of process variables like 1000 and 1500 rev min−1, 5 s, 5°. Under a fixed pin angle of 5° and a rotational speed of 1000 rev min−1, an increase in dwell time from 1 to 5 s resulted in a considerable increase in tensile shear load. An empirical process map under a fixed tool design is proposed to determine a feasible range of process conditions.
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