IG-430, a fine-grained, isotropic graphite grade is a promising candidate for the future Very High Temperature Reactors (VHTR). IG-430 which provides higher density, strength, and thermal ...conductivity, has already been developed as a graphite for next-generation HTGR, and is expected to be employed. This graphite grade, however, is lacking enough database that is needed for design. The present study aims to enhance the database with experimental data focusing on the low temperature regime (90–210 °C) by using 120–200 MeV protons to irradiate the IG-430 graphite to peak fluence of ~1.2 1025 m−2. It is anticipated that radiation-induced changes in the graphite properties and damage to be more pronounced in this low temperature regime than in elevated temperatures where damage annealing is taking place simultaneously. IG-430 graphite was characterized following irradiation for mechanical property changes (modulus and strength), dimensional stability and irradiation-induced growth as well as microstructural changes using high energy X-rays and different X-ray diffraction techniques. In assessing proton irradiation effects on the IG-430 graphite grade, comparison of radiation effects was made with the IG-43 grade, the un-purified version of IG-430, as well as other isotropic graphite grades. IG-430 was shown in this study to be better graphitized than other isotropic graphite grades. The study also revealed that during proton irradiation at low temperatures (~100 °C) the IG-430 exhibits stored energy release.
Abstract
The Facility for Rare Isotope Beams (FRIB) began operation
with 1 kW beam power for scientific users in May 2022 upon
completion of 8 years of project construction. The ramp-up to the
...ultimate beam power of 400 kW, planned over a 6-year period, will
enable the facility to reach its full potential for scientific
discovery in isotope science and applications. In December 2023, a
record-high beam power of 10.4 kW uranium was delivered to the
target. Technological developments and accelerator improvements are
being made over the entire facility and are key to completion of the
power ramp-up. Major technological developments entail the phased
deployment of high-power beam-intercepting systems, including the
charge strippers, the charge selection systems, the production
target, and the beam dump, along with support systems, including
non-conventional utilities (NCU) and remote handling
facilities. Major accelerator improvements include renovations to
aging legacy systems associated with experimental beam lines and
system automation for improved operational efficiency and better
machine availability. Experience must be gained to safely handle the
increased radiological impacts associated with high beam power;
extensive machine studies and advanced beam tuning procedures are
needed to minimize uncontrolled beam losses for the desired
operating conditions. This paper discusses the technological
developments and accelerator improvements with emphasis on major
R&D efforts.
In search of a low-Z pion production target for the Long Baseline Neutrino Facility (LBNF) of the Deep Underground Neutrino Experiment (DUNE) four graphite grades were irradiated with protons in the ...energy range of 140–180 MeV, to peak fluence of ∼6.1×1020p/cm2 and irradiation temperatures between 120–200°C . The test array included POCO ZXF-5Q, Toyo-Tanso IG 430, Carbone-Lorraine 2020 and SGL R7650 grades of graphite. Irradiation was performed at the Brookhaven Linear Isotope Producer. Postirradiation analyses were performed with the objective of (a) comparing their response under the postulated irradiation conditions to guide a graphite grade selection for use as a pion target and (b) understanding changes in physical and mechanical properties as well as microstructure that occurred as a result of the achieved fluence and in particular at this low-temperature regime where pion graphite targets are expected to operate. A further goal of the postirradiation evaluation was to establish a proton-neutron correlation damage on graphite that will allow for the use of a wealth of available neutron-based damage data in proton-based studies and applications. Macroscopic postirradiation analyses as well as energy dispersive x-ray diffraction of 200 KeV x rays at the NSLS synchrotron of Brookhaven National Laboratory were employed. The macroscopic analyses revealed differences in the physical and strength properties of the four grades with behavior however under proton irradiation that qualitatively agrees with that reported for graphite under neutrons for the same low temperature regime and in particular the increase of thermal expansion, strength and Young’s modulus. The proton fluence level of ∼1020cm−2 where strength reaches a maximum before it begins to decrease at higher fluences has been identified and it agrees with neutron-induced changes. X-ray diffraction analyses of the proton irradiated graphite revealed for the first time the similarity in microstructural graphite behavior to that under neutron irradiation and the agreement between the fluence threshold of ∼5×1020cm−2 where the graphite lattice undergoes a dramatic change. The confirmed similarity in behavior and agreement in threshold fluences for proton and neutron irradiation effects on graphite reported for the first time in this study will enable the safe utilization of the wealth of neutron irradiation data on graphite that extends to much higher fluences and different temperature regimes by the proton accelerator community searching for multi-MW graphite targets.
The NT-02 neutrino physics target made of the isotropic graphite grade produced neutrinos for the MINOS and MINERVA high-energy physics experiments. The segmented, 95-cm-long NT-02 target was ...bombarded with a 340 kW, Gaussian 1.1 mm sigma beam of 120 GeV protons reaching6.516×1020protons on target and a peak fluence of8.6×1021protons/cm2. Reductions in detected neutrino events during the experiment were attributed to radiation-induced damage on the target material leading to the NT-02 target replacement. With future neutrino physics targets aiming at the multimegawatt power regime, identifying life expectancy or fluence thresholds of target materials is of paramount importance, and, therefore, pinpointing the exact cause and target failure mode triggering the neutrino yield reduction is critical. To help unravel the effects of the 120 GeV beam on the isotropic graphite structure at the microstructural or lattice level, x-ray beams from National Synchrotron Light Source II were utilized to study failed in-beam as well as intact NT-02 target segments. The primary objective was to arrive at a scientifically sound explanation of the processes responsible for the target failure by correlating macroscopic observations with microstructural analyses. Results from transmission electron microscopy studies were integrated in assessing the microstructural evolution. The x-ray diffraction study revealed (a) the diffused state reached by the graphite microstructure within the1σof the beam where the graphite lattice structure transforms into a nanocrystalline structure, a finding supported by electron microscopy examination, thus providing an indication of the fluence threshold, and (b) the dominant role of the irradiation temperature profile exhibiting a high gradient from the beam center to the heat sink and aggravating the damage induced in the microstructure by the high proton fluence. The effects of the 120 GeV protons on the isotropic graphite target structure are corroborated by observed damage induced by 160-MeV protons and by fast neutrons to comparative doses on similar graphite, an assessment that will aid the design of next-generation megawatt-class neutrino targets.
•A metastable β Titanium alloy Ti-15V-3Cr-3Sn-3Al irradiated with 30 GeV protons to about 0.1 dpa was studied to evaluate radiation damage effects for high-intensity proton accelerator beam window ...and target application.•A high density nanometer-sized precipitate was observed by TEM, which would be martensite α and athermal ω formed during the solution-treatment process. They did not appear to change substantially after irradiation with protons.•No obvious signature of radiation damage, such as dislocation loops along the proton beam profile or radiation-induced hardening, was identified.•The metastable β alloy may exhibit radiation damage resistance due to the existence of nano-scale precipitates, acting as sinks for radiation-induced point defects.
A foil of a metastable β Titanium alloy Ti-15V-3Cr-3Sn-3Al was irradiated at the J-PARC neutrino experimental facility with 1.4 × 1020 30 GeV protons at low temperature (100–130 °C at most), and microstructural characterization and hardness testing were conducted as an initial study on the radiation damage effects of Titanium alloy by the high energy proton beam exposure. Expected radiation damage at the beam center is about 0.06–0.12 displacement per atom. A high density (> 1023 m−3) of a nanometer-sized precipitate was observed by TEM studies, which would be identified as martensite α-phase and athermal ω-phase formed during the solution-treatment process to fabricate metastable β alloy. They did not appear to change substantially after irradiation with protons. In the irradiated specimen, we could not identify an obvious signature of radiation damage distributed along the proton beam profile. Very small, nanometer-scale black dots were present at a low density in the most highly irradiated region, and may be small dislocation loops formed during irradiation. The micro-indentation test indicated that the radiation exposure led to tiny increase in Vickers micro-hardness of ΔHV = 20 at beam center. Atom probe tomography reveals compositional fluctuations that reach a maximum amplitude of 10 at% Ti within a space of < 5 nm both before and after irradiation, which may also indicate presence of rich precipitates. These experimental results suggest this specific β alloy may exhibit radiation damage resistance due to the existence of a high density of nano-scale precipitates, but further studies with higher exposure are required to explore this possibility.
A comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and ...low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have been studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences ≥5×1020p/cm2 . The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiber-reinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation load-displacement behavior even after low dose levels (∼5×1018pcm−2 ). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence ∼5×1020pcm−2 . Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the “as-received” 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the c axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.
Beryllium is a material extensively used in various particle accelerator beam lines and target facilities, as beam windows and, to a lesser extent, as secondary particle production targets. With ...increasing beam intensities of future multimegawatt accelerator facilities, these components will have to withstand even greater thermal and mechanical loads during operation. As a result, it is critical to understand the beam-induced thermal shock limit of beryllium to help reliably operate these components without having to compromise particle production efficiency by limiting beam parameters. As part of the RaDIATE (radiation damage in accelerator target environments) Collaboration, an exploratory experiment to probe and investigate the thermomechanical response of several candidate beryllium grades was carried out at CERN’s HiRadMat facility, a user facility capable of delivering very-high-intensity proton beams to test accelerator components. Multiple arrays of thin beryllium disks of varying thicknesses and grades, as well as thicker cylinders, were exposed to increasing beam intensities to help identify any thermal shock failure threshold. Real-time experimental measurements and postirradiation examination studies provided data to compare the response of the various beryllium grades, as well as benchmark a recently developed beryllium Johnson-Cook strength model.
The Long Baseline Neutrino Facility (LBNF, formerly the Long Baseline Neutrino Experiment) is under design as a next generation neutrino oscillation experiment, with primary objectives to search for ...CP violation in the leptonic sector, to determine the neutrino mass hierarchy and to provide a precise measurement of θ23 . The facility will generate a neutrino beam at Fermilab by the interaction of a proton beam with a target material. At the ultimate anticipated proton beam power of 2.3 MW the target material must dissipate a heat load of between 10 and 25 kW depending on the target size. This paper presents a target concept based on an array of spheres and compares it to a cylindrical monolithic target such as that which currently operates at the T2K facility. Simulation results show that the proposed technology offers efficient cooling and lower stresses whilst delivering a neutrino production comparable with that of a conventional solid cylindrical target.
Canavan disease is a childhood leukodystrophy caused by mutations in the gene for human aspartoacylase ( ASPA), which leads to an abnormal accumulation of the substrate molecule N-acetyl-aspartate ...(NAA) in the brain. This study was designed to model the natural history of Canavan disease using MRI and proton magnetic resonance spectroscopy ( (1)H-MRS). NAA and various indices of brain structure (morphology, quantitative T1, fractional anisotropy, apparent diffusion coefficient) were measured in white and gray matter regions during the progression of Canavan disease. A mixed-effects statistical model was used to fit all outcome measures. Longitudinal data from 28 Canavan patients were directly compared in each brain region with reference data obtained from normal, age-matched pediatric subjects. The resultant model can be used to non-invasively monitor the natural history of Canavan disease or related leukodystrophies in future studies involving drug, gene therapy, or stem cell treatments.
Hexagonal boron nitride (h-BN) irradiated with 140 MeV protons Simos, N.; Kotsina, Z.; Sprouster, D. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
09/2020, Letnik:
479, Številka:
C
Journal Article
Recenzirano
Odprti dostop
Hexagonal boron nitride was irradiated with 140 MeV protons to a fluence of ~6 1020p/cm2 at Tirr ~200 °C. Isotropic graphite was also irradiated alongside h-BN under similar conditions and fluence to ...enable direct comparison of the two similar structures. The effects of proton irradiation on dimensional stability and microstructure were studied using precision dilatometry and energy dispersive Xray diffraction techniques revealing by direct comparison to graphite that h-BN can better resist radiation damage from bombardment when irradiated with protons impinging normal to the crystallographic planes or along the crystallographic c-axis. X-ray diffraction experiments also revealed a preferred orientation of the crystallites in bulk samples near the sample surface, an orientation influenced by irradiation. Thermal studies using differential scanning calorimetry and thermogravimetric analysis to 740 °C, augmented by precision dilatometry, provided evidence of subtle phase transitions attributed to residual w-BN in the matrix. Irradiation appears to induce shifting of such transitions.
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