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Time-resolved momentum distributions of positron-electron annihilation photons were investigated for various polymers by means of positron age-momentum correlation (AMOC) spectroscopy. The momentum distribution exclusively associated with orthopositronium (o-Ps) pick-off annihilation is found to be element-specific and can sensitively probe different light atoms such as C, O, F, and Si that constitute the surface of nanometer-sized free volumes. It is demonstrated that the chemical environment around free volumes in polymers for practical use can be probed by positron annihilation AMOC spectroscopy.

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Two years having passed since the nuclear crisis at Fukushima, radioactive 137 Cs with a half-life of ∼30 years has come to the forefront of our largest concern. To gain an insight into current unsuccessful 137 Cs decontamination from soil, heavily adhesive Cs adsorption, referred to as specific Cs adsorption here, is highlighted for layered clay minerals. Besides the interlayer Cs + cations, a population of Cs is able to adsorb on the surfaces of open nanospaces with their sizes of ∼0.3 and ∼0.9 nm, which are formed by one-and two-clay nanosheet insertion into interlayer spaces. They are adsorbed on the surfaces of the open nanospaces so strongly that they cannot be removed even by a hydrochloric acid solution of pH 1.0; these open nanospaces thus act as the specific Cs adsorption sites. The characteristic local molecular structures as a claynanosheet edge and a wedge-shaped frayed part available in the open nanospaces are responsible for the specific Cs adsorption. Radioactive 137 Cs that is not cleaned up after the decontamination work would originate from the specific Cs adsorption clarified in the present work.

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