The certified reference material of brown rice grain was developed for validation in measurements of massic activities 134Cs and 137Cs. The homogenized brown rice harvested from north east area of Japan at 2011 was used as raw material of the certified reference material. The certified values of 134Cs and 137Cs in brown rice grain certified reference material were determined using the calibrated Ge semiconductor detectors. The counting efficiencies of 134Cs and 137Cs on the Ge semiconductor detectors were calibrated by standard solutions of 134Cs and 137Cs traceable to the national standard. The certified values of the certified reference material is close to the radioactive caesium standard value in general foodstuff set by Ministry of Health, Labour and Welfare of Japan. The associated expanded uncertainties of the certified values were calculated from standard uncertainties related 134Cs and 137Cs measurements and homogeneities of 134Cs and 137Cs. The relative expanded uncertainties of massic activities of 134Cs and 137Cs are 5.9％ and 5.5％, respectively.
A procedure of sample preparation for certified reference materials (CRM) of radioactive caesium (134Cs+137Cs) using brown rice was developed. Paper bags contained brown rice grains which had representative radioactive concentration were selected for the sample preparation. These grains were homogenized by mixing gently with hand work, and divided in weight of 81.00±0.02 g. Each of them was densely packed in a U-8 container with an acrylic plate and a polystyrene foam spacer. All U-8 containers filled with brown rice grains were sterilized at 25 kGy (60Co). The radioactivity measurements of caesium for brown rice grains packed in U-8 containers showed the homogeneity of radioactivity among the samples. Furthermore, we showed that the moisture content of brown rice was stable in the presence of saturated aqueous solutions.
A proficiency test for radioactivity measurements of 134Cs and 137Cs by γ ray spectrometry was conducted in May and June 2013. Reference values in the proficiency test were validated by comparison with other international and domestic calibration institutes. A result of the proficiency test showed small deviation between the reference values and most of reported values from participants. Signals which urged check for their measurement were issued to values which have large deviation. The proficiency test clearly showed technical quality of participant for the radioactivity measurement.
We review the muon spin relaxation (μ+SR) work on battery materials to estimate a self-diffusion coefficient (D) of Li+ and Na+ ions, which is one of the most predominant parameters to determine the charge and discharge rate of batteries. Since the initial muon spin polarization of the surface muon beam is 100％ polarized, μ+SR detects the internal magnetic field(s) in materials even in zero applied field. Using this feature, we can separate the nuclear magnetic field from the electron magnetic field, leading to the measurements of D in materials containing magnetic ions. This is a significant advantage over NMR. In fact, D’s of Li+ and Na+ in several AMxOy (A=Li or Na, M=Mn, Fe, Co, Ni, …) compounds were successfully determined with μ+SR. Furthermore, we show that such information on D provides other significant parameters, such as, the carrier density, reactive surface area, and diffusion pathway in battery materials. Finally, we will give a prospect of the future research using a depth-resolved muon beam.
A simple survey of experimental studies ever carried out by means of inelastic neutron scattering is presented mainly on systems with strongly correlated electrons. We can see how much the technique has contributed to the understanding, in a microscopic way, of origins of various physical properties, such as unusual magnetic behavior of itinerant electron systems, high-Tc superconductivity and so on, which are considered to be central issues of the modern solid state science.