Observations made in April 2013 of the radioxenon isotopes (133)Xe and (131m)Xe at measurement stations in Japan and Russia, belonging to the International Monitoring System for verification of the Comprehensive Nuclear-Test-Ban Treaty, are unique with respect to the measurement history of these stations. Comparison of measured data with calculated isotopic ratios as well as analysis using atmospheric transport modeling indicate that it is likely that the xenon measured was created in the underground nuclear test conducted by North Korea on February 12, 2013, and released 7-8 weeks later. More than one release is required to explain all observations. The (131m)Xe source terms for each release were calculated to 0.7 TBq, corresponding to about 1-10% of the total xenon inventory for a 10 kt explosion, depending on fractionation and release scenario. The observed ratios could not be used to obtain any information regarding the fissile material that was used in the test.

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We show that the approximate period problem for DNA alphabet is NP-complete.

A complex of equipment was designed for taking xenon samples from the ambient air, measuring concentrations of radioactive xenon isotopes ( 131 m Xe, 133 m Xe, 133 Xe, and 135 Xe), and transmitting results in the automatic mode. Xenon is extracted from the air stream using low-temperature adsorption on activated charcoal. Radiochemical purification of the adsorbed xenon is based on thermal desorption in a helium stream and the passage of gases liberated by the adsorber through a system of traps. The radionuclide concentrations in xenon samples are determined using the βγ coincidence method. When processing air samples of volume 12 m 3 and measuring their spectra over 10 h, the minimum detectable concentration of the prevailing radionuclide ( 133 Xe) in the air is no greater than 0.5 mBq/m 3 . The complex is designed for radiation monitoring under the Comprehensive Test Ban Treaty.

We consider the swap distance and the element duplication distance. We show that the swap centre permutation problem is NP-complete. We show that the element duplication centre problem is NP-complete.