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To investigate the chemical effect on the muon capture process through a muon transfer reaction from a muonic hydrogen atom, the formation rate of muonic carbon atoms is measured for benzene and cyclohexane molecules in liquid samples. The muon transfer rate to carbon atoms of the benzene molecule is higher than that to the carbon atoms of the cyclohexane molecule. Such a deviation has never been observed among those molecules for gas samples. This may be because the transfers occur from the excited states of muonic hydrogen atoms in the liquid system, whereas in the gas system, all the transfers occur from the 1s (ground) state of muon hydrogen atoms. The muonic hydrogen atoms in the excited states have a larger radius than those in the 1s state and are therefore considered to be affected by the steric hindrance of the molecular structure. This indicates that the excited states of muonic hydrogen atoms contribute significantly to the chemical effects on the muon transfer reaction.

Additional file 1. Supporting figures and tables.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted in the large release of radionuclides into the environment. The release process and environmental behavior of volatile fission product such as radioactive Cs was mainly investigated. On the other hand, the studies of nonvolatile fuel elements, such as Pu, have still been limited. It is known that the amount of Pu released from the FDNPP accident was much smaller compared with that of radioactive Cs [1]. However, the existence of Pu isotopes from the global fallout which was mainly derived from the atmospheric nuclear weapon tests makes it difficult to accurately assess Pu contamination from the FDNPP accident. In many environmental samples, Pu was affected not only by the FDNPP accident but also by global fallout. It is necessary to distinguish the source of Pu contaminations to assess the accurate Pu contamination from the FDNPP accident. For identification of Pu contamination source, the Pu isotopic ratios provide important information. The ratios were completely different by the kinds of nuclear weapons and nuclear accidents. The Pu isotopic ratios were measured in some environmental samples around the FDNPP. However, the ratios varied by the researches due to the contamination by global fallout. Therefore, the ratios should be determined from the environmental samples which were not influenced by the global fallout. In the FDNPP accident, radioactive particles which were insoluble in water and containing highly concentrated radioactive Cs were reported [2]. The radioactive particles were estimated to be formed in the reactor during the meltdown and directly released from the reactor. Due to its insolubility, the radioactive particles kept their elemental composition in the environment and retained the original property at the time of emission from the reactor. In other words, the radioactive particles are free from the contamination of global fallout. In this study, we identified Pu isotopes in radioactive particles found around the FDNPP. We performed radiochemical analysis and inductively coupled plasma-mass spectroscopy (ICP-MS) measurements of Pu isotopes for radioactive particles. Figure 1 shows the scanning electron microscopy (SEM) image of the radioactive particle analyzed in this study. For this particle, 239+240Pu activity was (1.70 ± 0.20) × 10-5 Bq with a 240Pu/239Pu atom ratio of 0.330 ± 0.077. The Pu isotopic ratio was higher than the ratio from global fallout (0.18) [3], but consistent with the simulation results from the ORIGEN code [4] and measurement results from some environmental samples around the FDNPP that were considered less influenced by global fallout [1]. We successfully determined the accurate Pu isotopic ratios from the FDNPP accident by analyzing radioactive particles. In this presentation, the properties of the investigated radioactive particles will be presented, and detailed experimental method will also be shown. In addition, we will discuss about Pu isotopic ratios in radioactive particles and compare the results with other environmental samples., Envira2019, 5th International conference on Environmental Radioactivity Variations of Environmental radionuclides

Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes (239Pu, 240Pu and 241Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of 239+240Pu and 241Pu were (1.70-7.06)×10-5 Bq and (4.10-8.10)×10-3 Bq, respectively and atom ratios of 240Pu/239Pu and 241Pu/239Pu were 0.330-0.415 and 0.162-0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis.

A size-resolved, one-dimensional resuspension scheme for soil particles from the ground surface is proposed to evaluate the concentration of radioactivity in the atmosphere due to the secondary emission of radioactive material. The particle size distributions of radioactive particles at a sampling point were measured and compared with the results evaluated by the scheme using four different soil textures: sand, loamy sand, sandy loam, and silty loam. For sandy loam and silty loam, the results were in good agreement with the size-resolved atmospheric radioactivity concentrations observed at a school ground in Tsushima District, Namie Town, Fukushima, which was heavily contaminated after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Though various assumptions were incorporated into both the scheme and evaluation conditions, this study shows that the proposed scheme can be applied to evaluate secondary emissions caused by aeolian resuspension of radioactive materials associated with mineral dust particles from the ground surface. The results underscore the importance of taking soil texture into account when evaluating the concentrations of resuspended, size-resolved atmospheric radioactivity.

A large quantity of radionuclides was released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011, and those deposited on ground and vegetation could return to the atmosphere through resuspension processes. Although the resuspension has been proposed to occur with wind blow, biomass burning, ecosystem activities, etc., the dominant process in contaminated areas of Fukushima is not fully understood. We have examined the resuspension process of radiocesium (134,137Cs) based on long-term measurements of the atmospheric concentration of radiocesium activity (the radiocesium concentration) at four sites in the contaminated areas of Fukushima as well as the aerosol characteristic observations by scanning electron microscopy (SEM) and the measurement of the biomass burning tracer, levoglucosan. The radiocesium concentrations at all sites showed a similar seasonal variation: low from winter to early spring and high from late spring to early autumn. In late spring, they showed positive peaks that coincided with the wind speed peaks. However, in summer and autumn, they were correlated positively with atmospheric temperature but negatively with wind speed. These results differed from previous studies based on data at urban sites. The difference of radiocesium concentrations at two sites, which are located within a 1 km range but have different degrees of surface contamination, was large from winter to late spring and small in summer and autumn, indicating that resuspension occurs locally and/or that atmospheric radiocesium was not well mixed in winter/spring, and it was opposite in summer/autumn. These results suggest that the resuspension processes and the host particles of the radiocesium resuspension changed seasonally. The SEM analyses showed that the dominant coarse particles in summer and autumn were organic ones, such as pollen, spores, and microorganisms. Biological activities in forest ecosystems can contribute considerably to the radiocesium resuspension in these seasons. During winter and spring, soil, mineral, and vegetation debris were predominant coarse particles in the atmosphere, and the radiocesium resuspension in these seasons can be attributed to the wind blow of these particles. Any proofs that biomass burning had a significant impact on atmospheric radiocesium were not found in the present study.

We performed muon spin rotation and relaxation (mu SR) measurements in the caged-structure heavy-fermion system PrIr2Zn20 to elucidate its magnetic and superconducting properties. Temperature-independent mu SR spectra were observed below 1 K, indicating that the phase transition at 0.11 K is of a nonmagnetic origin, most probably pure quadrupole ordering. In the superconducting phase, no sign of unconventional superconductivity, such as superconductivity with broken time-reversal symmetry, was seen below T-c = 0.05 K. We also observed spontaneous muon spin precession in zero field in the paramagnetic phase below 15 K, suggesting that unusual coupling between Pr-141 nuclei and muons is realized in PrIr2Zn20.