Recently, damage to Welsh onion, carrot, and Chinese chive by Bradysia odoriphaga Yang & Zhang, 1985 was reported from Saitama and Gunma Prefectures, Japan. Molecular identification methods are ...required to differentiate this species from other domestic sciarid flies. First, a PCR method using species-specific primers was developed to discriminate this species from three other sciarid species, Bradysia impatiens (Johannsen, 1912), Pnyxia scabiei (Hopkins, 1895), and Lycoriella ingenua (Dufour, 1839). Second, the applicability of a nondestructive DNA extraction method for this species was determined for cases where further morphological identification was required. It could be used for the morphological identification of specimens in addition to PCR using species-specific primers and DNA barcoding. Third, the lower limit of the proportion of this species in bulk samples of sciarid flies was determined. In larvae and male adults, one individual of this species could be detected in bulk samples (up to 800 individuals) of other species by PCR using species-specific primers. Further, it was revealed that specimens on the monitoring traps in the field should be collected within 8 days, regardless of the season. By combining these methods, an efficient identification method for monitoring this species was established using PCR with species-specific primers.
Positron emission tomography (PET) has been extensively studied and clinically investigated for dose verification in proton therapy. However, the production distributions of positron emitters are not ...proportional to the dose distribution. Thus, direct dose evaluation is limited when using the conventional PET-based approach. We propose a method for estimating the dose distribution from the positron emitter distributions using the maximum likelihood (ML) expectation maximization (EM) algorithm combined with filtering. In experiments to verify the effectiveness of the proposed method, mono-energetic and spread-out Bragg-peak proton beams were delivered by a synchrotron, and a water target was irradiated at clinical dose levels. Planar PET measurements were performed during beam pauses and after irradiation over a total period of 200 s. In addition, we conducted a Monte Carlo simulation to obtain the required filter functions and analyze the influence of the number of algorithm iterations on estimation. We successfully estimated the 2D dose distributions even under statistical noise in the PET images. The accuracy of the 2D dose estimation was about 10% for both beams at the 1- values of relative error. This value is comparable to the deviations in the measured PET activity distributions. For the laterally integrated profile along the beam direction, a low error within 5% was obtained per irradiation value. Moreover, the difference of estimated proton ranges was within 1 mm, and 2D estimation from the PET images was completed in 21 ms. Hence, the proposed algorithm may be applied to real-time dose monitoring. Although this is the first attempt to use the ML-EM algorithm for dose estimation, the proposed method showed high accuracy and speed in the estimation of proton dose distribution from PET data. The proposed method is thus a step forward to exploit the full potential of PET for in vivo dose verification.
The Transiting Exoplanet Survey Satellite (TESS) exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long gamma-ray burst (GRB) detected by Swift-BAT but ...without prompt XRT or UVOT follow-up due to proximity to the Moon. The afterglow has a late peak at least 1000 s after the BAT trigger, with a brightest-detected TESS data point at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of the rising light curve. Using ground-based photometry, we estimate a photometric redshift of z(sub phot) = 3.29 ± 0.40. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor Γ(sub BL) range from 90 to 133. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of R = 15.1 mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect ∼1 GRB afterglow per year above its magnitude limit.
X-ray computed tomography (CT) is an essential technology in modern medicine, as it enables three-dimensional non-destructive observation of the inside of the body. Contrast-enhanced CT scanning is ...widely performed for lesion-enhanced imaging. However, conventional X-ray CT systems integrate all incident X-ray signals, leading to the acquisition of monochromatic energy information and the prevention of material identification and quantitative evaluation of the concentration of contrast agents. Recently, photon counting CT (PC-CT) has been attracting attention as a new system for solving these problems. PC-CT utilizes the energy information of individual X-ray photons, enabling the identification of target materials. We have performed demonstrations combining the PC-CT system that we developed with fast scintillators and multi-pixel photon counters. In this study, we report on the initial results of in-vivo X-ray CT imaging with our established PC-CT system. We injected an iodine contrast agent into a mouse and visualized the spatial distribution of the contrast agent. Subsequently, we performed K-edge imaging and concentration mapping with the obtained CT images in multiple energy bands. The obtained images displayed successful three-dimensional contrast enhancement and a concentration map of the kidney and bladder in the mouse, indicating significant potential for the clinical application of this silicon photomultiplier-based PC-CT system.
X-ray imaging with computed tomography (CT) is widely used for nondestructive imaging of the interior of the human body. In the next decade, photon-counting X-ray CT is expected to reduce the dose ...needed and enable multicolor imaging. Recently, we proposed a novel photon-counting method that uses a multipixel photon counter (MPPC), with a significantly high signal gain (∼106) and fast temporal response (a few nanoseconds), combined with a high-speed scintillator. To realize photon-counting CT imaging in a wide area irradiated by an extremely high X-ray flux (106-107 Hz/mm2), a multichannel MPPC system is required. Thus, we developed a large-scale integrated circuit (LSI) with ultrafast signal-processing capability for use with a 16-channel MPPC. The developed LSI can extract a pulse current from an MPPC array with a large detector capacitance (∼200 pF) by utilizing an electrical circuit with low input impedance. The LSI offers a high photon count rate above 25 MHz/pixel with noise equal to 1.7 μA for a dynamic range of ∼ 1.3 mA and an energy resolution of 32 % (FWHM) at 60 keV, thereby enabling ultrafast multicolor CT imaging.
Since the accident at the Fukushima Daiichi Nuclear Power Plant ∼10 years ago, various studies have been conducted focusing on the decontamination of radioactive materials and the decommissioning of ...the remains of the reactor. It is crucial to identify the locations of radioactive materials for the decontamination of a building that is exposed to high radiation doses. One of the most widely used methods is the visualization of gamma rays with energy information using a photon-counting imager. However, the existing imagers have limited functionality, making it difficult to implement them in such an environment. Therefore, we have developed a novel pinhole gamma imager containing multi-pixel photon counters (MPPCs) combined with fast scintillators, which are processed using fast signal-processing analog and digital large integrated circuits under high-dose environments. The two-dimensional sensor array developed in this study can obtain incident gamma-ray photon energies with a counting rate of a few MHz/mm2. Furthermore, we were able to perform two-dimensional gamma-ray imaging of an extremely strong radiation source of 60Co with ∼45 TBq, by combining the sensor array with the dedicated tungsten collimator and housing.
All-sky surveys of X-ray transient objects in the soft X-ray band are essential for observing high-redshift events to probe unexplored physical conditions in the early universe and discovering ...mysterious electromagnetic counterparts of gravitational-wave sources. HiZ-GUNDAM is a future satellite mission that intends to perform a wide-field survey in the soft X-ray band (0.4–4 keV). The HiZ-GUNDAM X-ray detector has Si pixel sensors that require fine positioning accuracy (e.g. tens of micrometers), high detection efficiency, a large detection area (tens of cm2) and, a relatively high frame rate of ∼10 frames per second that can be achieved by a back-illuminated Si CMOS image sensor. One of the most promising candidates is GSENSE6060BSI with 6144 × 6144 pixels fabricated by Gpixel Inc. In this paper, for the initial performance test, we used a smaller-sized CMOS sensor, GSENSE400BSI-TVISB, which is similar to GSENSE6060BSI in terms of pixel characteristics, such as pixel size, epilayer thickness, and resistivity, except for the number of pixels (2048 × 2048). We conducted a detailed study on the spectroscopic performance of GSENSE400BSI-TVISB in the soft X-ray band and its radiation tolerance for space applications. For the spectroscopic performance, low-energy X-ray lines such as Al-Kα (1.5 keV), Mn-Kα (5.9 keV), and Mn-Kβ (6.5 keV) were clearly detected. Furthermore, using the obtained X-ray events, we estimated >50% detection efficiency in the 0.4–4 keV band, corresponding to a ∼10-μm Si thickness of the detectable layer. We also performed radiation tolerance tests against gamma rays from 60Co, 100-MeV protons and 5.5-MeV alpha rays (5–30 krad, corresponding to 6–30 year operation in orbit). After the irradiation tests, we observed that GSENSE400BSI-TVISB has strong radiation tolerance for our purpose: the lower detectable energy of ∼0.4 keV can be obtained if the CMOS is operated with an exposure of 0.1 s at −20 °C.
ABSTRACT A bright long gamma-ray burst GRB 141207A was observed by the Fermi Gamma-ray Space Telescope and detected by both instruments onboard. The observations show that the spectrum in the prompt ...phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index ( = +0.2 to +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. We discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by the X-Ray Telescope on-board Swift are consistent with synchrotron emission in a radiative external forward shock.
Abstract
Extragalactic X-ray absorption and optical extinction are often found in gamma-ray burst (GRB) afterglows, and they could be tracers of both circumburst and host galaxy environments. By ...performing spectral analyses of the spectral energy distribution of nine short GRB (SGRB) afterglows with a known redshift, we investigated the ratio of the equivalent hydrogen column density to the dust extinction, $N_{\rm H}^{\rm rest}/A_{V}^{\rm rest}$, in the rest frame of each SGRB. We found that the distribution of $N_{\rm H}^{\rm rest}/A_{V}^{\rm rest}$ is systematically smaller than for long GRBs, and is roughly consistent with the gas-to-dust ratio in the Milky Way. This result means that the measured gas-to-dust ratio of SGRBs would originate from the interstellar medium in each host galaxy. This scenario supports the prediction that SGRBs occur in non-star-forming regions in the host galaxies.
Monitoring the in vivo dose distribution in proton therapy is desirable for the accurate irradiation of a tumor. Although positron emission tomography (PET) is widely used for confirmation, the ...obtained distribution of positron emitters produced by the protons does not trace the dose distribution due to the different physical processes. To estimate the accurate dose from the PET image, the cross sections of nuclear reactions that produce positron emitters are important yet far from being sufficient. In this study, we measured the cross sections of
O(p,x)
O,
O(p,x)
N, and
O(p,x)
C with a wide-energy range (approximately 5-70 MeV) by observing the temporal evolution of the Cherenkov radiation emitted from positrons generated via β
decay along the proton path. Furthermore, we implemented the new cross sectional data into a conventional Monte Carlo (MC) simulation, so that a direct comparison was possible with the PET measurement. We confirmed that our MC results showed good agreement with the experimental data, both in terms of the spatial distributions and temporal evolutions. Although this is the first attempt at using the Cherenkov radiation in the measurements of nuclear cross sections, the obtained results suggest the method is convenient and widely applicable for high precision proton therapy.
PDF
