Narrow Results

The tidelands (tidal flats) of the seaside district of Tohoku, Japan, which play an important role in maintaining the diversity of the marine ecosystem, were almost completely destroyed by the massive tsunami that occurred on March 11, 2011. The tsunami also brought large quantities of contaminated sludge from the bottom of the sea to the coastal lands including the tidelands. In this study, we collected sludge samples from three tidelands: the Tsugaruishi estuary tideland (Iwate pref.), the Orikasa estuary tideland (Iwate pref.), and the Gamou tideland (Miyagi pref.). We then analyzed the samples using PIXE in accordance with a powdered-internal-standard method that we developed. In order to investigate the effects of the contaminated sludge on the ecosystem, we gathered and analyzed various kinds of wild plants and seaweed. We found that the tidelands are contaminated with heavy elements, such as arsenic, lead, zirconium, and barium, although the contamination is less serious in the vicinity of the beach.

A method of quantitative analysis which is capable of analyzing powdered samples consisting of high-Z elements, such as ash, soil and aerosol, is developed. It is confirmed that an internal standard method using a powdered internal standard, which has almost the same particle size as that of a sample, gives quantitative values of concentration with satisfactory accuracy and reproducibility. It was successfully applied to standard samples such as NIST-Urban particulate matter (1648), GBW-Tibet soil (08302), BCR-City waste incineration ash (0497) and also to a practical fly-ash sample. As a result, it is found that the effect of self-absorption in the target is not negligible even for samples whose particle size is less than 4 μm, and a method of correcting it is established. Firstly, the effective thickness for self-absorption is estimated by comparing peak yields of a certain element for two measuring conditions of beam irradiation from the surface and from the back of the target. The correction factors can be estimated by using the effective thickness, values of concentration of principal elements and their photon absorption cross sections. For practical samples whose compositions are unknown, it is confirmed that accurate correction coefficients can be derived by carrying out an iterative calculation until a self-consistent solution between values of concentration of the main constituents and the correction factors is obtained.

A possible mechanism for the formation of heavy-mass elements in supernovae is the rapid neutron-capture-mechanism ($r$-process). It depends upon the electron-fraction $Y_e$, a quantity which is determined by beta-decay-rates. In this paper, we focus on the calculation of electroweak decay-rates in presence of massive neutrinos. The resulting expressions are then used to calculate nuclear reactions entering the rapid-neutron capture. We fix the astrophysical parameters to the case of a core-collapse supernova. The neutrino sector includes a mass scheme and mixing angles for active neutrinos, and also by including the mixing between active and sterile neutrinos. The results of the calculations show that the predicted abundances of heavy-mass nuclei are indeed affected by the neutrino mixing.

The Coulomb and Proximity potential Model (CPPM) is improved by introducing an accurate empirical expression for the nuclear surface diffuseness parameter in the expression for the proximity potential. Within the improved CPPM, the decay half-lives of experimentally detected cluster emissions from heavy elements are calculated. The results of the calculations using the Universal Decay Law (UDL) [Qi et al., Phys. Rev. Lett. 103 (2009) 072501], the improved empirical formula of Sahu et al. (ImSahuB) [Wang et al., Chin. Phys. C 45 (2021) 044111], and the empirical formula of Horoi [J. Phys. G. Nucl. Part. Phys. 30 (2004) 945] are compared with the predictions of the improved CPPM. The lowest standard deviation is obtained for the predictions using the improved CPPM. The model’s predictive power increases significantly when the proximity potential is modified by including the diffuseness parameter. Furthermore, improved CPPM is employed to calculate the decay half-lives of undiscovered cluster emissions from heavy elements, a valuable information for upcoming experimental investigations. The calculated values are compared with the predictions of the UDL, Horoi formula and the improved empirical formula of Sahu et al. (ImSahuB). There is a high degree of agreement between the improved CPPM, UDL, and Horoi formula predictions. The ImSahuB formula predict decay half-life one or two order magnitudes lower than the predictions of the other models.

Mendeleev’s periodic table, elaborated 150 years ago, marked a seminal point in the progress of the natural sciences. This work is a tribute to that discovery. It seeks to trace the concentrations of the heavy elements Cd, Hg, Pb, Th and U in the geothermic micro-ecology of three sites at the Los Azufres (Mexico) volcanic complex. The relatively new technique of Polarised Energy Dispersive X-ray Fluorescence (PEDXRF) spectrometry was used to determine the elemental concentrations in the virgin volcanic substrate (VS), hydrothermal spring sediment (S), and in the plant matter (P) and rhizospheric soil (RS) of the primitive extremophilic plants growing at the fumaroles. This micro-ecological niche with its primitive plants, is shown to mimic the paleo environment during the Ordovician-Devonian periods. We observe that (1) the RS is the least dense and contains the most organic matter and that (2) the P and RS combined retain the largest fraction of the heavy elements. The former implies that the first plants that colonised land during the Ordovician period were efficient agents of pedogenesis; the latter implies that biogeochemical processes were a crucial component of environmental heavy element recycling during the aforesaid paleo periods. This last question in particular should be taken into account in the various extant hypotheses correlating the first land plants with the drastic environmental changes during the Ordovician period.

In-flight separators used in heavy-element research will be discussed including new experimental developments. Based on almost 40 years of experience with in-flight separators for superheavy element research a next generation separation system for heavy-ion fusion and transfer products is due. The use of radioactive beams at Coulomb barrier energy available at the Low-Energy Branch of the SuperFRS for isotope production will be discussed briefly.