Potrblog has submitted a sample of US beef to an independent testing lab. Cesium-137 and barium-140 were detected at a high confidence level, and, in addition, a whole slew of radionuclides was detected at lower levels. It is likely that one or more of these other nuclides was present in the sample.
The cow involved was slaughtered in July 2011. This means it had been exposed to radioactive fallout from the Fukushima nuclear disaster for 4 months. The average age for cattle at slaughter is 20 months. In addition, the gestation period is 9 months. Thus we can expect the amount of beef contamination to increase until 29 months from March 2011, which takes us well into 2013.