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Optical response characterization of dyed-polymethyl methacrylate (PMMA) dosimeters under high-dose X-ray irradiation
No full textThis study assesses the suitability of commercial dyed polymethyl methacrylate (PMMA) dosimeters for high-dose radiation applications extending into the hundreds of kilograys. Three PMMA dosimeter types (Gammachrome YR+, Amber 3042, and Red 4034) were investigated using both online and post-irradiation optical transmission measurements in the visible spectral range. The objective was to evaluate their dose sensitivity beyond nominal operational limits and to characterize their optical response through multi-wavelength transmittance and radiation-induced attenuation (RIA) analyses. Dosimeters were exposed to X-rays at dose rates of 0.9 and 1.2 Gy[HO]/s, covering doses from 0.1 Gy to 282 kGy. Monte Carlo simulations using the PHITS code were performed to model radiation transport and dose deposition in the different materials. The results demonstrate a clear, dose-dependent optical response of dyed PMMA, with wavelength-specific behavior indicative of color-center formation and evolution. Recovery measurements show that the RIA signal is highly stable over several hours at nominal wavelengths, with only minor relaxation observed in the near-infrared region, supporting the applicability of these dosimeters for both real-time and passive measurements. Comparisons with Radiophotoluminescent (RPL) FD-7 dosimeters reveal consistent trends, suggesting the potential for establishing a conversion between RPL and PMMA dose responses. Overall, the findings support the extension of dyed-PMMA dosimetry beyond current commercial limits and contribute to the development of robust dosimetry techniques for extreme radiation environments
Enhanced strength-ductility synergy by integrating metastable and heterostructured design in FeNiCrV alloy
No full textEnhancing the strength of metallic materials usually compromises their ductility since both properties are intrinsically decided by chemical bond strength but with opposite dependencies. Despite great effort via microstructural regulation, tackling the strength-ductility paradox in metals and alloys remains a challenge. To achieve superior strength-ductility combination, here we report an integrated metastable and heterostructured alloy design strategy. Guided by ab-initio thermodynamics and dynamics calculations, a novel metastable Fe68Ni12Cr10V10 (at. %) dual-phase eutectic multicomponent alloy in which the martensitic transformation may occur under deformation was fabricated. By applying routine thermomechanical processing, a multi-heterostructured material characterized by alternating fcc and bcc lamellae, fully recrystallized fcc grains and unrecrystallized bcc grains, as well as a bimodal distribution of fcc grains, was obtained. Yield strength of the material is comparable to that of the high-strength bcc reference alloy, while its ductility also surpasses the ductile fcc reference alloy. By in-situ high-energy X-ray diffraction measurements, the superior strength-ductility synergy was found to originate from the coupled effects of hetero-deformation induced strengthening and transformation-induced plasticity. Specifically, the high strength is primarily ascribed to the strengthening imparted by alternating soft fcc and hard bcc lamellar structures. The exceptional ductility stems from multi-stage α'-martensite transformation over a broad strain range, which is unique to the multi-heterostructure. The synergistic effects of the heterostructure and the athermal transformation offer a practical route to endow advanced materials with superior mechanical properties
Optimisation and characterisation of neutron imaging beam at the TRIXIE instrument
No full textThe neutron imaging instrument TRIXIE is located at one of the horizontal beamlines of the research reactor LVR-15 in the Czech Republic. Before the construction of the TRIXIE instrument, the beamline was not equipped with a collimator; therefore, a new collimator had to be designed and implemented. The beamline was initially equipped with a meter-long single-crystal silicon filter. But, because of the lack of space in the beam (the size of the original filter limited the space for the collimator) and because the beamline needs to be filtered (the spectrum of an empty beamline roughly copies the reactor spectrum, with a high ratio of fast neutrons and gamma rays), a new filter had to be designed as well. The optimisation process of calculations of the collimator and filters of different materials and thicknesses was performed using the Monte Carlo calculation code MCNP. After the installation of the collimator and filters into the beamline, a series of measurements was performed to confirm the calculated results and to characterise the neutron beam
Single-specimen Positron Annihilation Spectroscopy using β emitters
No full textWe present a new isotope-based sample-source setup to enable bulk defect studies on single samples using positrons. For this technique, we employ the positron emitter 22Na (activity of 7 MBq) and modified our Coincidence Doppler Broadening Spectrometer (CDBs). Compared to the commonly used sandwich geometry, where the positron emitter is placed between two “identical” samples for conventional Positron Annihilation Spectroscopy (PAS), the new single specimen setup offers three major advantages: (i) only a single sample is required, (ii) annihilation radiation originating from the source itself or its supporting material is not detected, i.e., there is no source component, and (iii) unwanted -radiation emitted from the positron source (1275 keV -quanta in the case of 22Na) is efficiently suppressed. These three major improvements are demonstrated with Coincidence Doppler Broadening Spectroscopy (CDBS) on single-crystalline copper by comparing spectra recorded with both the sandwich method and a 30 keV positron beam. The Kapton source component is absent and a pure spectrum of bulk copper is obtained
Commissioning, Characterization, and First High-Dose-Rate Irradiations at a Compact X-Ray Tube for Microbeam and Minibeam Radiation Therapy
No full textPurposeMinibeam and microbeam radiation therapy promise improved treatment outcomes through reduced normal tissue toxicity at better tumor control rates. The lack of suitable compact radiation sources limits the clinical application of minibeams to superficial tumors and renders it impossible for microbeams. We developed and constructed the first prototype of a compact line-focus x-ray tube (LFXT) with technology potentially suitable for clinical translation of minibeams and microbeams.MethodsWe give an overview of the commissioning process preceding the first operation, present optical and radiological focal spot characterization methods, and dosimetric measurements. Additionally, we report on first preclinical in vitro cell and in vivo mouse brain irradiations conducted with the LFXT prototype.ResultsThe LFXT was high-voltage conditioned ≤300 kV. The focal spot characterization resulted in a strongly eccentric electron distribution with a width of 72.3 μm. Dosimetry showed sharp microbeam dose profiles with steep lateral penumbras and a peak-to-valley dose ratio above 10 throughout a 70-mm-thick polymethylmethacrylate (PMMA) phantom. An open-field dose rate of 4.3 Gy/s was measured at an acceleration voltage of 150 kV and a beam current of 17.4 mA at 150-mm distance from the focal spot. In vitro and in vivo experiments demonstrated the feasibility of the LFXT for minibeam and microbeam applications with field sizes of 1.5 to 2 cm. The mice displayed no observable side effects throughout the follow-up period after whole-brain 260-μm-minibeam irradiation.ConclusionWe successfully constructed and commissioned the first proof-of-concept LFXT prototype. Dosimetric characterizations of the achieved microbeam field showed the superiority of the LFXT compared with conventional x-ray tubes in terms of beam quality. In future developments, the remaining limitations of the prototype will be addressed, paving the way for improved minibeam and first ever microbeam radiation therapy in a clinical setting
Influence of mono- and divalent cations on heat induced gelation of protein from mealworm (Tenebrio molitor) at various structural length scales
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Magnetic phase diagram of magnetocaloric TmFeO
No full textNeutron diffraction experiments of TmFeO single crystals were performed in the external magnetic fields. The field along the axis increases temperature of spin-reorientation transition from phase to . Application of the field along axis led to the decrease of and to the formation of new phases. Based on the temperature and field dependence of the Bragg reflection intensity, the configuration of magnetically induced phases was proposed