Outer layer scintillating fiber for low-energy ß-ray detection.

Standard plastic scintillating fiber cannot detect low-energy ß-rays as the cladding prevents them from reaching the fiber core. We developed an outer-layer scintillating (OLS) fiber with a plastic scintillator on the outermost layer for low-energy ß-ray detection. The concept of fiber construction is presented. The fundamental optical properties of the OLS fiber, such as the emission spectrum, attenuation length, and scintillation decay time, were evaluated. Here, Ni-63 with a maximum energy of 67.0 keV was used as a low-energy ß-emitting nuclide. Simulation studies on the interaction between low-energy electrons emitted from Ni-63 and a single fiber were performed prior to actual measurements. The data showed that Ni-63 can be measured using silicon photomultiplier photosensors in a coincidence mode. The OLS fiber was effective for low-energy ß-ray detection.

Transformation of thylakoid membranes during differentiation from vegetative cell into heterocyst visualized by microscopic spectral imaging.

Some filamentous cyanobacteria carry out oxygenic photosynthesis in vegetative cells and nitrogen fixation in specialized cells known as heterocysts. Thylakoid membranes in vegetative cells contain photosystem I (PSI) and PSII, while those in heterocysts contain predominantly PSI. Therefore, the thylakoid membranes change drastically when differentiating from a vegetative cell into a heterocyst. The dynamics of these changes have not been sufficiently characterized in situ. Here, we used time-lapse fluorescence microspectroscopy to analyze cells of Anabaena variabilis under nitrogen deprivation at approximately 295 K. PSII degraded simultaneously with allophycocyanin, which forms the core of the light-harvesting phycobilisome. The other phycobilisome subunits that absorbed shorter wavelengths persisted for a few tens of hours in the heterocysts. The whole-thylakoid average concentration of PSI was similar in heterocysts and nearby vegetative cells. PSI was best quantified by selective excitation at a physiological temperature (approximately 295 K) under 785-nm continuous-wave laser irradiation, and detection of higher energy shifted fluorescence around 730 nm. Polar distribution of thylakoid membranes in the heterocyst was confirmed by PSI-rich fluorescence imaging. The findings and methodology used in this work increased our understanding of how photosynthetic molecular machinery is transformed to adapt to different nutrient environments and provided details of the energetic requirements for diazotrophic growth.