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Side chain dynamics in semiconducting polymer MEH‐PPV
摘要： The characteristic nanoscale dynamics of the alkyl side groups in the light-emitting polymer poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] have been investigated using quasi-elastic neutron scattering (QENS). The measurements were taken below the polymer’s glass transition (T ≤ Tg ’ 353 K), where the main backbone is in a rigid state and does not contribute to the broadening of the QENS signal. An analytical diffusion model consisting of a static term and two dynamical components, characterizing the flexible side groups, provide an excellent fit to the experimental data. The two observed dynamical processes are all localized in character, with no meaningful dependence on temperature. The faster process, with characteristic timescale of (cid:2)18 ps at room temperature (RT), can be linked to the average mobility of the terminal protons of the alkyl chain, while the slower process, with characteristic timescale of (cid:2)170 ps at RT, to those protons at the other end of the alkyl chain, closest to the backbone. While the fraction of mobile protons contributing to the QENS signal increases with increasing temperature, the characteristic timescale and confining volume within which the protons are able to move locally depend chiefly on the polymer conformational state. ? 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47394.
关键词： quasi-elastic neutron scattering,semi-conducting polymer,optical and photovoltaic applications,polymer dynamics,spectroscopy
更新于2025-09-23 15:22:29
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Associated particle imaging instrumentation for future planetary surface missions
摘要： We have conducted ground tests to study the applicability of the Tagged Neutrons Method/Associated Particle Imaging methodology (TNM/API) for the making precise gamma ray spectroscopic measurements onboard lander missions to the Solar system planets. Our analysis was focused on the requirement to distinguish between the spacecraft background and the subsurface signal so as to correctly evaluate the elemental composition of planetary soils. The measurements were performed in a configuration where the gamma spectrometer was surrounded by significant amounts of material that imitated a spacecraft structure. It was found that the TNM/API can substantially suppress the spacecraft background and identify the true intensities of the gamma lines attributed to major soil elements such as O, Na, Mg, Al, Si and Fe and evaluate their concentrations with an accuracy of 2–10%.
关键词： Neutron generator,Elemental abundances,Surface operations,Associated particle imaging,Solar system,Tagged neutrons method,Active gamma spectroscopy
更新于2025-09-23 15:22:29
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Single photon detection with SiPMs irradiated up to 1014?cm?2 1-MeV-equivalent neutron fluence
摘要： Silicon photomultipliers (SiPM) are solid state light detectors with sensitivity to single photons. Their use in high energy physics experiments, and in particular in ring imaging Cherenkov (RICH) detectors, is hindered by their poor tolerance to radiation. At room temperature the large increase in dark count rate makes single photon detection practically impossible already at 1011 cm?2 1-MeV-equivalent neutron fluence. The neutron fluences foreseen by many subdetectors to be operated at the high luminosity LHC range up to 1014 cm?2 1-MeV-equivalent. In this paper we present the effects of such high neutron fluences on Hamamatsu and SensL SiPMs of different cell size. The advantage of annealing at high temperature (up to 175?C) is discussed. We demonstrate that, after annealing, operation at the single photon level with a SiPM irradiated up to 1014 cm?2 1-MeV-equivalent neutron fluence is possible at cryogenic temperature (77 K) with a dark count rate below 1 kHz.
关键词： Cryogenic temperature,Radiation damage,Single photon detection,SiPM,Neutron irradiation,Annealing
更新于2025-09-23 15:22:29
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Optical and infrared polarimetry of the transient LMXB Centaurus X-4 in quiescence
摘要： Aims. We present the ?rst optical and infrared polarimetric study of the low-mass transient X-ray binary Centaurus X-4 during its quiescent phase. This work aims to search for an intrinsic linear polarisation component in the system emitted radiation that might be due to, e.g., synchrotron emission from a compact jet, or to Thomson scattering with free electrons in an accretion disc. Methods. Multiband (BVRI) optical polarimetric observations were obtained over two nights in 2008 at the ESO La Silla 3.6 m telescope, equipped with the EFOSC2 instrument used in polarimetric mode. These observations cover about the 30% of the 15.1 h orbital period. We obtained J-band observations in 2007 with the NICS instrument on the Telescopio Nazionale Galileo (TNG) at La Palma, for 1 h total of observations. Results. We obtained 3σ upper limits to the polarisation degree in all of the optical bands, with the most constraining limit being in the I-band, where PI < 0.5%. We have noticed no signi?cant phase-correlated variability in any of the ?lters. The J-band observations provided a 6% upper limit on the polarisation level. Conclusions. The constraining upper limits on the polarisation in the optical (above all in the I-band), allowed us to estimate the contribution of the possible emission of a relativistic particles jet to the total system radiation to be less than 10%. This is in agreement with the observation of a spectral energy distribution typical of a single black body of a K spectral type main-sequence star irradiated from the compact object, without any signi?cant additional component in the infrared. Because of the low S/N it was not possible to investigate the possible dependency of the polarisation degree from the wavelength, which could be suggestive of polarisation induced by Thomson scattering of radiation with free electrons in the outer part of the accretion disc. Observations with higher S/N are required to examine this hypothesis in depth, searching for signi?cant phase-correlated variability.
关键词： X-rays: binaries,stars: jets,polarization,stars: neutron
更新于2025-09-23 15:22:29
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Optical and Radio Transients after the Collapse of Super-Chandrasekhar White Dwarf Merger Remnants
摘要： Super-Chandrasekhar remnants of double white dwarf mergers could sometimes collapse into a rapidly rotating neutron star (NS), accompanying with a mass ejection of a few times 0.01 Me. Bright optical transient emission can be produced by the ejecta due to heating by radioactivities and particularly by energy injection from the NS. Since the merger remnants before collapse resemble a star evolving from the asymptotic giant branch phase to the planetary nebula phase, an intense dusty wind is considered to be driven about several thousand years ago before the collapse and surround the remnant at large radii. Therefore, the optical transient emission can be somewhat absorbed and scattered by the dusty wind, which can suppress the peak emission and cause a scattering plateau in optical light curves. Several years later, as the ejecta ?nally catches up with the wind material, the shock interaction between them can further give rise to a detectable radio transient emission on a timescale of several tens of days. Discovery of and observations to such dust-affected optical transients and shock-driven radio transients can help to explore the nature of super-Chandrasekhar merger remnants and as well as the density and type ratios of double white dwarf systems, which is bene?cial in assessing their gravitational wave contributions.
关键词： stars: neutron,gravitational waves,radio continuum: general,white dwarfs,supernovae: general
更新于2025-09-23 15:22:29
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Directional fast neutron detection using a time projection chamber and plastic scintillation detectors
摘要： A new method for directional fast neutron detection is proposed based on a neutron time projection chamber (TPC) and position-sensitive plastic scintillation detectors. The detection system can efficiently locate the approximate location of a hot spot with 4π field-of-view using only the neutron TPC. Then, the system generates a high-resolution image of the hot spot using selected coincidence events in the TPC and the scintillation detectors. A prototype was built and tested using a 252Cf source. An efficiency of 7.1×10-3 was achieved for fast searching. The angular resolution was 7.8° (full width at half maximum, FWHM) for high-resolution imaging using the simple back projection method.
关键词： special nuclear material,neutron scatter imaging,time projection chamber,directional fast neutron detection,plastic scintillation detector
更新于2025-09-23 15:21:21
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Novel method exploration of monitoring neutron beam using Cherenkov photons in BNCT
摘要： Ensuring the stability of the neutron beam during boron neutron capture therapy (BNCT) is essential. The goal of this work was to explore a novel method using Cherenkov photons for real-time monitoring of neutron beam in BNCT. The Monte Carlo toolkit Geant4, was used to calculate the Cherenkov photons and dose based on a cubic phantom and Chinese hybrid radiation phantom under di?erent conditions. Based on the study on the cubic phantom, the change of neutron beam characteristics indeed have an impact on dose, which needs quality assurance. The relationship between Cherenkov photons and gamma dose was favorable. The maximum relative variation of the generation of Cherenkov photons is approximately 3.51%, even when the relative change of boron concentration reaching 60%. However, comparing the results of the neutron beam with the original characteristics, the maximum relative variation of Cherenkov photons reaches 14.75% and 14.68% for the usage of Neuboron- spectrum and 5-degree rotation of neutron beam ?eld orientation, respectively. Therefore, the intensity and distribution of Cherenkov photons can only be observably changed by neutron beam characteristics. Based on the Chinese hybrid radiation phantom, the changes in the intensity and distribution of Cherenkov photons can also be observed inside the phantom, and these changes are evident by a detector outside the phantom. Thus, Cherenkov photons has the potential application for neutron beam monitoring.
关键词： Neutron beam,Boron neutron capture therapy,Cherenkov photons,Monitoring
更新于2025-09-23 15:21:21
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Tracing Boron with Fluorescence and PET Imaging of Boronated Porphyrin Nanocomplex for Imaging Guided Boron Neutron Capture Therapy
摘要： Boron neutron capture therapy (BNCT) induces high-energy radiation within cancer cells while avoiding damage to normal cells that without uptake of BNCT drugs, which is holding great promise to provide excellent control over locally invasive malignant tumors. However, lack of quantitative imaging technique to determine local boron concentration has been a great challenge for nuclear physicians to apply accurate neutron irradiation during the treatment, which is a key factor that has limited BNCT’s application in clinics. To meet this challenge, this study describes coating boronated porphyrins with a biocompatible Poly(lactide–co-glycolide)–monomethoxy-poly(polyethylene-glycol) (PLGA-mPEG) micelle for selective tumor accumulation and reduced toxicity comparing with previously reported boronated porphyrin drugs. Fluorescence imaging and PET imaging were performed, unveiling the potential imaging properties of this boronated porphyrin nanocomplex (BPN) to locate tumor region and to determine tissue-localized boron concentration which facilitates treatment planning. By studying the pharmacokinetics of BPN with Cu-64 PET imaging, the treatment plan was adjusted from single bolus injection to multiple times of injections of smaller doses. As expected, high tumor uptake of boron (125.17±13.54 ppm) was achieved with an extraordinarily high tumor to normal tissue ratio: tumor to liver, muscle, fat and blood were 3.24±0.22, 61.46±20.26, 31.55±10.30 and 33.85±5.73, respectively. At last, neutron irradiation with BPN showed almost complete tumor suppression, demonstrating that BPN holds a great potential for being an efficient boron delivery agent for imaging-guided BNCT.
关键词： copper-64,boron neutron capture therapy,theranostics,positron emission tomography,micelle
更新于2025-09-23 15:21:21
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Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes
摘要： Context. The Crab pulsar is the only astronomical pulsed source detected at very high energy (VHE, E > 100 GeV) gamma rays. The emission mechanism of VHE pulsation is not yet fully understood, although several theoretical models have been proposed. Aims.In order to test new models, we measured the light curve and the spectra of the Crab pulsar with high precision by means of deep observations. Methods. We analyzed 135 h of selected MAGIC data taken between 2009 and 2013 in stereoscopic mode. In order to discuss the spectral shape in connection with lower energies, 5.5 years of Fermi-LAT data were also analyzed. Results. The known two pulses per period were detected with a signi?cance of 8.0σ and 12.6σ. In addition, signi?cant emission was found between the two pulses with 6.2σ. Conclusions. We discovered the bridge emission above 50 GeV between the two main pulses. This emission can not be explained with the existing theories. These data can be used for testing new theoretical models.
关键词： gamma rays: stars,pulsars: individual: Crab pulsar,stars: neutron
更新于2025-09-23 15:21:21
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Organic solar cells probed with advanced neutron scattering techniques
摘要： Neutron scattering techniques provide unique insights into the active layer morphology of organic solar cells. The nanoscale morphology, the thin film vertical composition, and the intermixing on a molecular level, which all strongly have an impact on the performance of organic solar cells, can be probed with neutrons. In addition to the static structure, also fast dynamics occurring in the active material is accessible with neutrons. This perspective letter highlights the power of grazing incidence small angle neutron scattering and quasi-elastic neutron scattering experiments after shortly introducing into the working principle of organic solar cells.
关键词： neutron scattering,grazing incidence small angle neutron scattering,morphology,quasi-elastic neutron scattering,organic solar cells
更新于2025-09-23 15:21:01