Negligible Irradiation Research Articles

A Novel BCC-Structure Zr-Nb-Ti Medium-Entropy Alloys (MEAs) with Excellent Structure and Irradiation Resistance.

Medium-entropy alloys (MEAs) are prospective structural materials for emerging advanced nuclear systems because of their outstanding mechanical properties and irradiation resistance. In this study, the microstructure and mechanical properties of three new single-phase body-centered cubic (BCC) structured MEAs (Zr40Nb35Ti25, Zr50Nb35Ti15, and Zr60Nb35Ti5) before and after irradiation were investigated. It is shown that the yield strength and elongation after fracture at room temperature are greater than 900 MPa and 10%, respectively. Three MEAs were irradiated with 3 MeV Fe11+ ions to 8 × 1015 and 2.5 × 1016 ions/cm2 at temperatures of 300 and 500 °C, to investigate the irradiation-induced hardening and microstructure changes. Compared with most conventional alloys, the three MEAs showed only negligible irradiation hardening and even softening in some cases. After irradiation, they exhibit somewhat surprising lattice constant reduction, and the microstructure contains small dislocation loops. Neither cavities nor precipitates were observed. This indicates that the MEAs have better irradiation resistance than traditional alloys, which can be attributed to the high-entropy and lattice distortion effect of MEAs.

Optical properties and far field radiation of periodic nanostructures fed by an optical waveguide for applications in fluorescence and Raman scattering

Various systems based on nanostructures built on optical waveguides have recently appeared in literature, since this configuration guarantees an efficient optical feeding to nano-elements and/or the possibility to manipulate guided signals. In this work, we present the analysis of the optical scattering properties of such type of structures, more specifically a periodic array of Au nano-cylinders or nano-domes fabricated upon an ion-exchanged waveguide, an integrated system considered for fluoroscopy and Raman spectroscopy. Absorption, scattering and extinction were calculated by means of Finite Difference Time Domain (FDTD) simulations and Scattering Theory. We took advantage of some particular adaptations to apply the classical scattering theory to this context, and used it to extract the far-field radiation pattern. We show that the rectangular periodicity allows to obtain highly collimated beams and negligible irradiation in a wide angle range, which enables the possibility to steer away the undesirable excitation signals from the detectors, avoiding a mixing with emitted photons from molecules. Our analysis suggests that, in the context of this setup and applications, the modeling of the nanostructures, which aims at the tuning of the plasmonic enhancement of the emission, can be relatively separated from the definition of spatial filtering through the periodic array. Our results add new considerations to the list of potentialities of this configuration for the development of efficient integrated surface enhanced spectroscopic setups.

Habitability and Biosignatures of Hycean Worlds

Abstract We investigate a new class of habitable planets composed of water-rich interiors with massive oceans underlying H2-rich atmospheres, referred to here as Hycean worlds. With densities between those of rocky super-Earths and more extended mini-Neptunes, Hycean planets can be optimal candidates in the search for exoplanetary habitability and may be abundant in the exoplanet population. We investigate the bulk properties (masses, radii, and temperatures), potential for habitability, and observable biosignatures of Hycean planets. We show that Hycean planets can be significantly larger compared to previous considerations for habitable planets, with radii as large as 2.6 R ⊕ (2.3 R ⊕) for a mass of 10 M ⊕ (5 M ⊕). We construct the Hycean habitable zone (HZ), considering stellar hosts from late M to Sun-like stars, and find it to be significantly wider than the terrestrial-like HZ. While the inner boundary of the Hycean HZ corresponds to equilibrium temperatures as high as ∼500 K for late M dwarfs, the outer boundary is unrestricted to arbitrarily large orbital separations. Our investigations include tidally locked “Dark Hycean” worlds that permit habitable conditions only on their permanent nightsides and “Cold Hycean” worlds that see negligible irradiation. Finally, we investigate the observability of possible biosignatures in Hycean atmospheres. We find that a number of trace terrestrial biomarkers that may be expected to be present in Hycean atmospheres would be readily detectable using modest observing time with the James Webb Space Telescope (JWST). We identify a sizable sample of nearby potential Hycean planets that can be ideal targets for such observations in search of exoplanetary biosignatures.

Design of the European DEMO vacuum vessel inboard wall

The pre-concept design of the DEMO Vacuum Vessel is going on in view of the 2020 gate review; moreover the nuclear heat loads on the vessel inner shell were determined and found to be about one order of magnitude higher compared to ITER. A subsequent thermal-structural analysis of the vessel inner shell revealed high thermal stresses and a large temperature gradient through the inner shell thickness. Given the simultaneous occurrence of primary membrane stresses in the entire vessel inboard wall and, in proximity of the vessel ribs, high bending stresses due to the coolant pressure, a survey of all options within the design rules was required to identify the inter-dependencies of the individual stress limits (primary membrane, primary bending, thermal membrane plus bending). In order to face this kind of issues a detailed assessment on the design of the inboard wall of DEMO Vacuum Vessel has been conducted and is presented here. The current work evaluates both P and S type damages for the inboard wall of DEMO Vacuum Vessel in case of high nuclear heat load, vacuum vessel coolant pressure and toroidal field coil fast discharge. The elastic analysis method has been used to check the rules for prevention of both types of damage. The rules applied to prevent the aforementioned damages are compliant to Level A criteria, in case of negligible creep and negligible irradiation. In order to check the structural integrity of the inboard wall of DEMO VV against high thermal and mechanical loads, optimization structural analyses were performed and checked against the rules provided in the applicable design code (RCC MRx).

Geographical miss during intracoronary irradiation: impact on restenosis and determination of required safety margin length

ObjectivesThe goal of this study was to evaluate the incidence and effects of underdosage of injured segments during intracoronary irradiation and to define the minimal length of safety margin required to avoid mismatched source placement. BackgroundUnderdosage of injured segments due to misplacement of active source has been suggested as the underlying mechanism for the occurrence of edge restenosis. MethodsBaseline angiograms of 112 vessels in 109 patients with in-stent restenosis undergoing coronary reintervention followed by intracoronary irradiation (192Ir: Checkmate, Cordis, Miami, Florida; 32P: Gallileo, Guidant, Houston, Texas; 90Sr/Y: Beta-Cath, Novoste, Norcross, Georgia) were analyzed. The distances between the outermost injury and outermost end of “reference isodose length” (RIL), defined as a segment with ≥90% of reference dose at 1 mm vessel wall depth, were measured. “Safety margin” was defined as the distance between the outermost injury and outermost end of the RIL, “geographical miss” (GM) as a complete injured segment not being covered by the RIL, and “restenosis” as the percent diameter stenosis >50%. ResultsBaseline angiographic analysis was performed for 224 edges in 112 vessels. Geographical miss was found in 46 (20.6%) edges. The incidence of target lesion restenosis within the 78 vessels with available follow-up was 43.3% for patients with GM versus 14.9% for patients with no GM (p = 0.005). Analysis of various injured segments exposed highest restenosis rates in injured segments with negligible irradiation (27.8%) in comparison with injured segments with dose fall-off (16.7%) or injured segments with full-dose irradiation (7.7%) (p = 0.006). Receiver operating curve analysis revealed a safety margin of 10 mm required per vessel (i.e., 5-mm safety margin/edge) to achieve 95% specificity of GM. ConclusionsGeographical miss is associated with a higher incidence of restenosis at the corresponding edges. Restenosis was more pronounced in injured segments with negligible irradiation than in injured segments at the dose fall-off zones. We recommend a safety margin of 10 mm per vessel to minimize GM.

Characteristics and performance of the Sunna high dose dosemeter using green photoluminescence and UV absorption readout methods.

Growth in the use of ionising radiation for medical sterilisation and the potential for wide-scale international food irradiation have created the need for robust, mass-producible, inexpensive, and highly accurate radiation dosemeters. The Sunna dosemeter, lithium fluoride injection-moulded in a polyethylene matrix, can be read out using either green photoluminescence or ultraviolet (UV) absorption. The Sunna dosemeter can be mass-produced inexpensively with high precision. Both the photoluminescent and the UV absorption reader are simple and inexpensive. Both methods of analysis display negligible humidity effects, minimal dose rate dependence, acceptable post-irradiation effects, and permit measurements with a precision of nearly 1% 1sigma. The UV method shows negligible irradiation temperature effects from -30 degrees C to +60 degrees C. The photoluminescence method shows negligible irradiation temperature effects above room temperature for sterilisation dose levels and above. The dosimetry characteristics of these two readout methods are presented along with performance data in commercial sterilisation facilities.

Is Negative Staining Capable of High Resolution?

Abstract Everyone presently answers “no” to this question, since this methodology for specimen preparation and preservation commonly is believed to be inherently limited to 20-25Å (2.0-2.5nm) resolution. Achievement of resolution levels smaller than this figure have been published only rarely. This report presents experimental evidence from electron diffraction showing that negative staining can preserve periodic protein structure to the level of at least 4Å. A suspension of bovine liver catalase crystals (orthorhombic: a= 69Å, b= 174Å, c= 206 Å [1]) is deposited on a hydrophilic carbon support and negatively stained using an on-grid protocol [2,3]. For low-dose electron diffraction with a JEOL 100CX transmission electron microscope (l00kV), the set-up for routine selected area diffraction is modified to keep the second condenser lens maximally overfocused; by a defocusing of the diffraction pattern, the grid can be surveyed and suitable thin single crystals centered in the diffraction aperture with only negligible irradiation.

Low-temperature growth of GaN by atomic nitrogen based on a dielectric barrier discharge

GaN films were deposited on sapphire(0 0 0 1) and Si(1 0 0) substrates by MOCVD using an atomic nitrogen source based on a dielectric barrier discharge (DBD) method. Molecule nitrogen and trimethylgallium (TMG) were separately delivered to the substrates. Wurtzite GaN films, with no trace of cubic GaN, were successfully grown on α-Al 2O 3 substrates even at relatively low temperatures (<800°C). Sapphire substrate RMS roughness was 5.01 and 4.93 Å before and after the exposure to DBD N-source, respectively. This shows negligible irradiation damage of accelerated N 2 + ion as well as the effect of smoothening the substrate surfaces with DBD N-source. The PL results exhibited small luminescence at the spectral region of blue and UV but a luminescence around the yellow region (2.5 eV) was detected. This is caused by oxygen impurity from AES analysis.

Effects of irradiation on low activation ferritic alloys

Low activation ferritic or martensitic alloys must have certain alloying elements either absent or in trace quantities, namely niobium, molybdenum, nickel, nitrogen and aluminum. Given these restrictions, nine bainitic and martensitic alloys have been designed as low activation materials covering the composition range Fe-2.25Cr to 12Cr and incorporating tungsten and/or vanadium additions for strengthening. The alloys have been fabricated, irradiated, tensile tested, and examined using transmission electron microscopy. The results demonstrate that low activation ferritic alloys are feasible. However, Fe-2.25Cr-V alloys are prone to carbide precipitation and irradiation hardening during irradiation at 420°C. Fe-2.25Cr-V and Fe-9Cr alloys are significantly weakened by irradiation at 585°C due to precipitate coarsening and dislocation recovery. The Fe-12Cr compositions appear to be the most interesting alloy class, showing negligible irradiation hardening at 420°C and only a moderate decrease in strength at 585°C.

Diffusion of krypton in rubidium chloride and its dependence on radiation damage

The diffusion of krypton in neutron irradiated rubidium chloride was determined by measuring the release of Kr-85m. After negligible irradiation the gas release mechanism corresponded to ideal diffusion. Above 360°C the process was characterized by an activation energy of 10 ± 2 kcal/mole and diffusion by an interstitial mechanism seems probable. Irradiation to high neutron doses resulted in a marked decrease of the measured diffusion coefficient. The healing out of damaged lattice regions was demonstrated as a rapidly increasing krypton release during an isothermal anneal. Possible diffusion mechanisms in the damaged lattice are discussed.

Boron Uptake in Mouse Brain Neoplasm

It was proposed (1) in 1940 that neoplastic cells may be destroyed in vivo if sufficient boron, in some suitable form, can be applied to the tumor in vivo and then irradiated with an adequate slow neutron flux. Such a boron-disintegration therapy3 is uniquely different from other types of irradiation processes because: 1. It is a nuclear disintegration process, not a radioactive process. This means that the dose can be accurately controlled and that the irradiation stops when the flux of slow neutrons is stopped. 2. Since the slow neutron flux results in a negligible irradiation to normal tissue, no irradiation occurs except where boron is present (assuming that the background of ~y-rays and fast neutrons is kept sufficiently low). This means that the dose is selectively administered only to those tissues containing boron, and thus the differential dose between normal and neoplastic tissue can be made as large as the differential boron content.