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•Self-assembly of synthesized multi-responsive block copolymer was examined.•Copolymer solution exhibits phase separation/micellization in presence of stimuli.•Unusual pH dependent ...behavior was observed.•Positively charged PDMPA block and SDS forms wormlike micelles in acidic pH.•Turbidity, SANS, cryo-TEM results are in good agreement and support each other.
Stimuli responsive double hydrophilic diblock copolymers poly(N-isopropylacrylamide)-b-poly(N,N-dimethylaminopropylacrylamide) (PNIPAM-b-PDMPA) with constant degree of polymerization (DP) of PNIPAM (=127) and varying DP of PDMPA (=31 and 66) were synthesized by RAFT polymerization, and characterized by NMR, FTIR and GPC. In dilute aqueous solutions, the copolymers remain as unimers in equilibrium with loosely bound aggregates and form aggregates with PNIPAM core in the presence of NaCl or at temperatures above the LCST of PNIPAM. However, at higher temperatures i.e. above cloud point temperature (CPT) of PNIPAM127-b-PDMPA66, core–shell micelles are formed with PNIPAM core. The CPT of both block copolymers decrease in the presence of NaCl and in acidic pH, but increases with increase in DP of PDMPA. The copolymer showed enhanced surface activity in the presence of NaCl. The temperature dependent micellization observed from NMR is supported by turbidity and fluorescence. PDMPA is highly protonated in acidic pH; cryo-TEM and SANS confirm the formation of threadlike micelles in the presence of SDS.
We have developed a novel low-cost gamma-ray imaging Compton camera γI that has a high detection efficiency. Our motivation for the development of this detector was to measure the arrival directions ...of gamma rays produced by radioactive nuclides that were released by the Fukushima Daiichi nuclear power plant accident in 2011. The detector comprises two arrays of inorganic scintillation detectors, which act as a scatterer and an absorber. Each array has eight scintillation detectors, each comprising a large CsI (Tl) scintillator cube of side 3.5cm, which is inexpensive and has a good energy resolution. Energies deposited by the Compton scattered electrons and subsequent photoelectric absorption, measured by each scintillation counter, are used for image reconstruction. The angular resolution was found to be 3.5° after using an image-sharpening technique. With this angular resolution, we can resolve a 1m2 radiation hot spot that is located at a distance of 10m from the detector with a wide field of view of 1sr. Moreover, the detection efficiency 0.68cps/MBq at 1m for 662keV (7.6cps/μSv/h) is sufficient for measuring low-level contamination (i.e., less than 1μSv/h) corresponding to typical values in large areas of eastern Japan. In addition to the laboratory tests, the imaging capability of our detector was verified in various regions with dose rates less than 1μSv/h (e.g., Fukushima city).
We have investigated InGaN-based multi-striped orthogonal photon-photocarrier propagation solar cell (MOP3SC) in which sunlight propagates in a direction being orthogonal to that of photocarriers ...generated by the sunlight. Thanks to the orthogonality, in MOP3SC, absorption of the sunlight and collection of the photocarriers can be simultaneously and independently optimized with no trade-off. Furthermore, by exploiting the degree of freedom along the photon propagation and using multi-semiconductor stripes in which the incoming photons first encounter the widest gap semiconductor, and the narrowest at last, we can convert the whole solar spectrum into electricity resulting in the high conversion efficiency. For processing MOP3SC, we have developed Clean Unit System Platform (CUSP), which turns out to be able to serve as clean versatile environment having low power-consumption and high cost-performance. CUSP is suitable not only for processing devices, but also for cross-disciplinary fields, including medical/hygienic applications.
Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic rays. A prediction ...was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very high energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the northwest radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ~0.1 Delta *mG. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intracluster medium. The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy.
We have observed the giant radio galaxy Centaurus A and the globular cluster omega Centauri in the TeV energy region using the CANGAROO III stereoscopic system. The system has been in operation since ...2004 with an array of four Imaging Atmospheric Cerenkov Telescopes (IACT) with similar to 100 m spacings. The observations were carried out in 2004 March and April. In total, approximately 10 hr of data were obtained for each target. No statistically significant gamma-ray signal has been found above 420 GeV over a wide angular region (a 1 degree radius from the pointing center), and we derive flux upper limits using the wholefield of view. Implications for the total energy of cosmic rays and the density of the cold dark matter are considered.
We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov telescope array, of a very high energy gamma-ray signal from the unidentified gamma-ray source HESS J1614--518, which was ...discovered in the H.E.S.S. Galactic plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9 Delta *s level during an effective exposure of 54 hr from 2008 May to August. The spectrum can be represented by a power law: (8.2 ? 2.2stat ? 2.5sys) X 10--12 X (E/1 TeV)-- Delta *g cm--2 s--1 TeV--1 with a photon index Delta *g of 2.4 ? 0.3stat ? 0.2sys, which is compatible with that of the H.E.S.S. observations. By combining our result with multiwavelength data, we discuss the possible counterparts for HESS J1614--518 and consider radiation mechanisms based on hadronic and leptonic processes for a supernova remnant (SNR), stellar winds from massive stars, and a pulsar wind nebula (PWN). Although a leptonic origin from a PWN driven by an unknown pulsar remains possible, hadronic-origin emission from an unknown SNR is preferred.
We developed an omnidirectional Compton camera for radioactive environmental monitoring which can visualize gamma rays with energy below 250 keV emitted from various radiopharmaceuticals used in ...nuclear medicine facilities to prevent occupational radiation exposure. An omnidirectional Compton camera based on high light yield scintillators CsI(Tl) or NaI(Tl) developed in our previous studies is a promising system for environmental radiation monitoring because it has a wide field of view and high sensitivity for sub-MeV gamma rays. However, its sensitivity rapidly decreases below 250 keV because photoelectric effect becomes more dominant than the Compton scattering process due to their large effective atomic numbers (approximately 50). Thus, CaF2(Eu) was adopted, which has both low effective atomic number (approximately 15) and high light yield. Four CaF2(Eu) crystals were arranged symmetrically to achieve a relatively uniform acceptance in all directions. Similarly, the detector rotation technique was adopted to suppress artificial patterns in a reconstructed gamma-ray image because of the small number of crystals. Through experiments in a laboratory and at a nuclear medicine facility, the capability of the camera to visualize gamma rays in energies from 250 keV to 60 keV with reasonable observation time for practical clinical use was confirmed.
SS433, located at the center of the supernova remnant W50, is a close proximity binary system consisting of a compact star and a normal star. Jets of material are directed outwards from the vicinity ...of the compact star symmetrically to the east and west. Non-thermal hard X-ray emission is detected from lobes lying on both sides. Shock accelerated electrons are expected to generate VHE gamma rays through the inverse-Compton process in the lobes. Observations of the western X-ray lobe region of SS433/W50 system have been performed to detect VHE gamma rays using the 10
m CANGAROO-II telescope in August and September, 2001, and July and September, 2002. The total observation times are 85.2
h for ON source, and 80.8
h for OFF source data. No significant excess of VHE gamma rays has been found at three regions of the western X-ray lobe of SS433/W50 system. We have derived 99% confidence level upper limits to the fluxes of gamma rays and have set constraints on the strengths of the magnetic fields assuming the synchrotron/inverse-Compton model for the wide energy range of photon spectrum from radio to TeV. The derived lower limits are
4.3
μ
G for the center of the brightest X-ray emission region and
6.3
μ
G for the far end from SS433 in the western X-ray lobe. In addition, we suggest that the spot-like X-ray emission may provide a major contribution to the hardest X-ray spectrum in the lobe.
We have observed the supernova remnant MSH 15-52 (G320.4-1.2), which contains the gamma-ray pulsar PSR B1509-58, using the CANGAROO-III imaging atmospheric Cerenkov telescope array from 2006 April to ...June. We detected gamma rays above 810 GeV at the 7 capital sigma level during a total effective exposure of 48.4 hr. We obtained a differential gamma-ray flux at 2.35 TeV of (image cm super(-2) s super(-1) TeV super(-1), with a photon index of image, which is compatible with that of the H.E.S.S. observation in 2004. The morphology shows extended emission compared to our point spread function. We consider the plausible origin of the high-energy emission based on a multiwavelength spectral analysis and energetics arguments.
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