For utilizing silicon photomultipliers (SiPMs) in space experiments, we conducted irradiation experiments of SiPMs with protons and iron ions. In particular, the relationship between the leakage ...current and the radiation dose was investigated under various irradiation conditions to determine techniques of mitigating damage caused by radiation. The leakage current was approximately proportional to the dose; however, the proportionality constant did not significantly vary with the irradiation conditions. The effects of annealing after irradiation tests indicated no substantial decrease in the leakage current. Conversely, while the leakage current increased with the dose, the SiPMs continued to operate even after 5 krad of irradiation, which corresponds to several years of radiation exposure in space at altitudes of ~400 km to 500 km. The results obtained from these irradiation tests are used to characterize a hard X-ray (> 60 keV) detector for space-based applications. This detector couples an inorganic scintillator with a high light yield, such as CsI(Tl), to a SiPM.
Six isoenergetic diets were formulated as follows: fish meal (FM) 700 g kg–1 (control, C), FM 300 g kg–1 + soy protein concentrate 300 g kg–1 (SPC), FM 300 g kg–1 + enzyme‐treated SPC 300 g kg–1 ...(ESC), FM 170 g kg–1 + soy protein isolate 300 g kg–1 (SPI), FM 160 g kg–1 + enzyme‐treated SPI 300 g kg–1 (ESI) and FM 150 g kg–1 + conglycinin 300 g kg–1(CG). Forty fish (3.9 g) were randomly distributed into each of eighteen 300‐L tanks, fed twice daily until satiation for 8 weeks. The final body weight, specific growth rate and condition factor did not show significant differences among the fish fed with diets C, SPC, ESC and ESI (p > .05). The survival was significantly lower in fish fed with diets SPI and CG. Feed efficiency was significantly higher in fish fed with diets SPC and C than in fish fed with other diets (p < .05). There were no significant differences in nutrients retention efficiencies in fish fed with diets C, SPC, ESC and ESI. A significantly higher phosphorus retention efficiency in fish fed with soymilk protein diets resulted in lower phosphorus discharge to the environment (p < .05). These results suggest that the soymilk proteins can comfortably replace 570–770 g FM kg–1 diet of red sea bream juvenile, which will ensure significant ecological benefits through reducing phosphorus load to the environment.
The release of radioactive isotopes (mainly 137Cs, 134Cs and 131I) from the crippled Fukushima Daiichi Nuclear Plant remains a serious problem in Japan. To help identify radiation hotspots and ensure ...effective decontamination operation, we are developing a novel Compton camera weighting only 1kg and measuring just ∼10cm2 in size. Despite its compactness, the camera realizes a wide 180° field of vision with a sensitivity about 50 times superior to other cameras being tested in Fukushima. We expect that a hotspot producing a 5μSv/h dose at a distance of 3m can be imaged every 10s, with angular resolution better than 10° (FWHM). The 3D position-sensitive scintillators and thin monolithic MPPC arrays are the key technologies developed here. By measuring the pulse-height ratio of MPPC-arrays coupled at both ends of a Ce:GAGG scintillator block, the depth of interaction (DOI) is obtained for incident gamma rays as well as the usual 2D positions, with accuracy better than 2mm. By using two identical 10mm cubic Ce:GAGG scintillators as a scatterer and an absorber, we confirmed that the 3D configuration works well as a high-resolution gamma camera, and also works as spectrometer achieving typical energy resolution of 9.8% (FWHM) for 662keV gamma rays. We present the current status of the prototype camera (weighting 1.5kg and measuring 8.5×14×16cm3 in size) being fabricated by Hamamatsu Photonics K.K. Although the camera still operates in non-DOI mode, angular resolution as high as 14° (FWHM) was achieved with an integration time of 30s for the assumed hotspot described above.
•We are developing a novel Compton camera weighting only 1kg and measuring just ∼10×10cm2 in size.•The camera realizes a wide 180°field of vision with a sensitivity about 50 times superior to other cameras being tested in Fukushima.•The depth of interaction (DOI) is obtained for incident gamma rays as well as the usual 2D positions.•We present the current status of the prototype camera (weighting ∼1.5kg and measuring 8.5×14×16cm3 in size) being fabricated by Hamamatsu Photonics K.K.
We present Suzaku X-ray observations along two edge regions of the Fermi Bubbles, with eight Asymptotically = to 20 ks pointings across the northern part of the North Polar Spur (NPS) surrounding the ...north bubble and six across the southernmost edge of the south bubble. After removing compact X-ray features, diffuse X-ray emission is clearly detected and is well reproduced by a three-component spectral model consisting of unabsorbed thermal emission (temperature kT Asymptotically = to 0.1 keV) from the Local Bubble, absorbed kT Asymptotically = to 0.3 keV thermal emission related to the NPS and/or Galactic halo (GH), and a power-law component at a level consistent with the cosmic X-ray background. We also derived an upper limit for any non-thermal X-ray emission component associated with the bubbles and demonstrate that, in agreement with the aforementioned findings, the non-thermal pressure and energy estimated from a one-zone leptonic model of its broadband spectrum, are in rough equilibrium with that of the surrounding thermal plasma.
We have analyzed all the archival X-ray data of 134 unidentified (unID) gamma-ray sources listed in the first Fermi/LAT (1FGL) catalog and subsequently followed up by the Swift/XRT. We constructed ...the spectral energy distributions (SEDs) from radio to gamma-rays for each X-ray source detected, and tried to pick up unique objects that display anomalous spectral signatures. In these analyses, we target all the 1FGL unID sources, using updated data from the second Fermi/LAT (2FGL) catalog on the Large Area Telescope (LAT) position and spectra. We found several potentially interesting objects, particularly three sources, 1FGL J0022.2-1850, 1FGL J0038.0+1236, and 1FGL J0157.0-5259, which were then more deeply observed with Suzaku as a part of an AO-7 program in 2012. We successfully detected an X-ray counterpart for each source whose X-ray spectra were well fitted by a single power-law function. The positional coincidence with a bright radio counterpart (currently identified as an active galactic nucleus, AGN) in the 2FGL error circles suggests these sources are definitely the X-ray emission from the same AGN, but their SEDs show a wide variety of behavior. In particular, the SED of 1FGL J0038.0+1236 is not easily explained by conventional emission models of blazars. The source 1FGL J0022.2-1850 may be in a transition state between a low-frequency peaked and a high-frequency peaked BL Lac object, and 1FGL J0157.0-5259 could be a rare kind of extreme blazar. We discuss the possible nature of these three sources observed with Suzaku, together with the X-ray identification results and SEDs of all 134 sources observed with the Swift/XRT.
Here, we report on a detailed investigation of the γ-ray emission from 18 broad-line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope data. We confirm the previously reported ...detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed γ-ray emission reveals in addition possible flux variability in both sources. No statistically significant γ-ray detection of the other BLRGs was found, however, in the considered data set. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in γ-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the γ-ray flux variability and a number of other arguments presented, indicates that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high-accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found that none were detected in γ-rays. A simple phenomenological hybrid model applied for the broadband emission of the discussed radio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is ≥ 1% on average for BLRGs, whereas it is ≤ 0.1% for Seyfert 1 galaxies.
Seven coral reef communities were defined on Shiraho fringing reef, Ishigaki Island, Japan. Net photosynthesis and calcification rates were measured by in situ incubations at 10 sites that included ...six of the defined communities, and which occupied most of the area on the reef flat and slope. Net photosynthesis on the reef flat was positive overall, but the reef flat acts as a source for atmospheric CO
2
, because the measured calcification/photosynthesis ratio of 2.5 is greater than the critical ratio of 1.67. Net photosynthesis on the reef slope was negative. Almost all excess organic production from the reef flat is expected to be effused to the outer reef and consumed by the communities there. Therefore, the total net organic production of the whole reef system is probably almost zero and the whole reef system also acts as a source for atmospheric CO
2
. Net calcification rates of the reef slope corals were much lower than those of the branching corals. The accumulation rate of the former was approximately 0.5 m kyr
−1
and of the latter was ~0.7–5 m kyr
−1
. Consequently, reef slope corals could not grow fast enough to keep up with or catch up to rising sea levels during the Holocene. On the other hand, the branching corals grow fast enough to keep up with this rising sea level. Therefore, a transition between early Holocene and present-day reef communities is expected. Branching coral communities would have dominated while reef growth kept pace with sea level rise, and the reef was constructed with a branching coral framework. Then, the outside of this framework was covered and built up by reef slope corals and present-day reefs were constructed.
We studied the taxonomic and morphological compositions of Pleistocene coral assemblages in 24 quadrats in Okinawa-jima, southern Central Ryukyus, and in 14 quadrats in Kikai-jima, northern Central ...Ryukyus. A total of 72 species belonging to 35 genera were identified in Okinawa-jima, whereas 65 species coming under 33 genera were recorded in Kikai-jima. Cluster analysis of the Bray-Curtis (BC) similarity coefficient produced 8 coral associations and 3 ungrouped taxa; they correspond to a wide range of reef environments, from shallow lagoon to lower reef-slope settings. The analysis of taxonomic similarities among quadrats leads to the identification of 7 clusters and 5 isolated quadrats. The segregation of quadrats indicating a same reef zone into distinctive groups or single branches in the cluster diagram reflects the within-reef-slope variability in community structure. Specifically, encrusting
Acropora palifera, indicative of the upper reef-slope zone, shows a great variability of associated coral species and morphologies. We also report differences in the geographic distribution of
Acropora palifera and
Platygyra contorta between present-day and Pleistocene reefs, which may be linked to changes in sea surface temperature. The decrease in the total species and generic richness recorded in modern reefs is not clearly detected in the fossil record. In addition, MDS ordination of the BC similarities highlights patterns of reef zonation and geographic differences in taxonomic composition. One-way tests of similarity (ANOSIM) show that differences in the composition of upper reef-slope coral assemblages between Okinawa-jima and Kikai-jima are not larger than those observed between southern and central Okinawa-jima. Finally, we report various types of coral successions. Sea-level changes resulted in transitions from one reef zone to another, whereas local disturbances are likely to have been responsible for the successions of distinctive coral assemblages with overlapping depth ranges, which reflect the within-reef-zone variability.
The Cute‐1.7+APD II, 10 × 15 × 20 cm3 in size and 5 kg in mass, is the third picosatellite developed by students at the Tokyo Institute of Technology. One of the primary goals of the Cute‐1.7+APD II ...mission is to validate the use of avalanche photodiodes (APDs) as a radiation detector for the first time in a space experiment. While the mission itself is immature compared to the forefront satellites of space plasma physics, use of APDs offers various possibilities regarding a brand‐new electron energy analyzer for medium‐energy electrons and ions (1–100 keV), as well as a high‐performance light sensor for the future X‐ray astronomy missions. The satellite was successfully launched by ISRO PSLV‐C9 rocket on 28 April 2008 and has since been in operation for more than a year. The Cute‐1.7+APD II carries two reverse‐type APDs to monitor the distribution of low‐energy particles (mainly electrons and protons) down to 9.2 keV trapped in a low Earth orbit (LEO), including the South Atlantic Anomaly (SAA) as well as aurora bands. We present the design parameters and various preflight tests of the APDs prior to launch, particularly, the high counting response and active gain control system for the Cute‐1.7+APD II mission. Examples of electron/proton distribution, obtained in continuous 12 h observations, will be presented to demonstrate the initial flight performance of the APDs in orbit.
Detection of low-intensity light relies on the conversion of photons to photoelectrons, which are then multiplied and detected as an electrical signal. To measure the actual intensity of the light, ...one must know the factor by which the photoelectrons have been multiplied. To obtain this amplification factor, we have developed a procedure for estimating precisely the signal caused by a single photoelectron. The method utilizes the fact that the photoelectrons conform to a Poisson distribution. The average signal produced by a single photoelectron can then be estimated from the number of noise events, without requiring analysis of the distribution of the signal produced by a single photoelectron. The signal produced by one or more photoelectrons can be estimated experimentally without any assumptions. This technique, and an example of the analysis of a signal from a photomultiplier tube, are described in this study.
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