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SnO2 is Cyanogen Chloride-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is zero-dimensional and consists of two tin;dihydrate molecules. Sn4+ is bonded in a linear geometry to two equivalent O2- atoms. Both Sn–O bond lengths are 1.83 Å. O2- is bonded in a single-bond geometry to one Sn4+ atom.
CoN4ClN2SnCl4 is Iron carbide-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four nitrogen molecules, four tin tetrachloride molecules, and four CoN4Cl clusters. In each CoN4Cl cluster, Co3+ is bonded in a tetrahedral geometry to four N+0.33- atoms. There are a spread of Co–N bond distances ranging from 1.61–1.86 Å. There are four inequivalent N+0.33- sites. In the first N+0.33- site, N+0.33- is bonded in a distorted bent 120 degrees geometry to one Co3+ and one Cl1- atom. The N–Cl bond length is 1.64 Å. In the second N+0.33- site, N+0.33- is bonded in a single-bond geometry to one Co3+ atom. In the third N+0.33- site, N+0.33- is bonded in a single-bond geometry to one Co3+ atom. In the fourth N+0.33- site, N+0.33- is bonded in a single-bond geometry to one Co3+ atom. Cl1- is bonded in a single-bond geometry to one N+0.33- atom.
(B)6Sn is Calcium hexaboride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional and consists of one tin powder molecule and one B framework. In the B framework, B is bonded in a 5-coordinate geometry to five equivalent B atoms. There is one shorter (1.70 Å) and four longer (1.77 Å) B–B bond length.
SnCCl3 crystallizes in the trigonal R3m space group. The structure is zero-dimensional and consists of three chloroform molecules and three tin powder molecules.
Cd(SnF2)3 is Cyanogen Chloride-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one cadmium molecule and three tin(ii) fluoride molecules.
(Co(CO)4)3SnCl crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four tin chloride (sncl) molecules and twelve Co(CO)4 clusters. In four of the Co(CO)4 clusters, Co+1.67+ is bonded in a trigonal pyramidal geometry to four C+1.33+ atoms. There is two shorter (1.77 Å) and two longer (1.78 Å) Co–C bond length. There are four inequivalent C+1.33+ sites. In the first C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. In the second C+1.33+ site, C+1.33+ is bonded in a distorted single-bond geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. In the third C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.15 Å. In the fourth C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In eight of the Co(CO)4 clusters, Co+1.67+ is bonded in a trigonal pyramidal geometry to four C+1.33+ atoms. There is two shorter (1.77 Å) and two longer (1.78 Å) Co–C bond length. There are four inequivalent C+1.33+ sites. In the first C+1.33+ site, C+1.33+ is bonded in a distorted single-bond geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. In the second C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. In the third C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.16 Å. In the fourth C+1.33+ site, C+1.33+ is bonded in a distorted linear geometry to one Co+1.67+ and one O2- atom. The C–O bond length is 1.15 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one C+1.33+ atom.
Mn(SnF2)3 is Cyanogen Chloride-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one manganese molecule and three tin(ii) fluoride molecules.
Co(SnF2)3 is Cyanogen Chloride-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one cobalt molecule and three tin(ii) fluoride molecules.
Zn(SnF2)3 is Cyanogen Chloride-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of three tin(ii) fluoride molecules and one zinc molecule.
Tb5Rh6Sn18 crystallizes in the cubic F-43m space group. The structure is three-dimensional and consists of four tin powder molecules and one Tb5Rh6Sn17 framework. In the Tb5Rh6Sn17 framework, there are two inequivalent Tb sites. In the first Tb site, Tb is bonded in a 1-coordinate geometry to three equivalent Rh and ten Sn atoms. All Tb–Rh bond lengths are 3.05 Å. There are a spread of Tb–Sn bond distances ranging from 2.91–3.41 Å. In the second Tb site, Tb is bonded in a 12-coordinate geometry to six equivalent Rh and twelve equivalent Sn atoms. All Tb–Rh bond lengths are 3.56 Å. All Tb–Sn bond lengths are 3.47 Å. Rh is bonded in a 9-coordinate geometry to three Tb and six Sn atoms. There are four shorter (2.69 Å) and two longer (2.83 Å) Rh–Sn bond lengths. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a tetrahedral geometry to four equivalent Tb atoms. In the second Sn site, Sn is bonded in a hexagonal planar geometry to three equivalent Tb and three equivalent Rh atoms. In the third Sn site, Sn is bonded in a 2-coordinate geometry to three Tb and two equivalent Rh atoms.
Cu(SnF2)3 is Cyanogen Chloride-like structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one cuprum molecule and three tin difluoride molecules.
An ongoing study at the Spallation Neutron Source (SNS) seeks to better understand and address potential multipacting issues associated with the Drift Tube Linac (DTL) RF vacuum windows. An analysis of several failed operational windows showed indications of excessive RF heating on the TiN-coated alumina ceramics. Coupled with vacuum bursts and arcing during conditioning and/or operational periods, these problems have been attributed to electron activity likely caused by multipacting. The status of the study, 3-D electromagnetic simulation results, mitigating techniques and a future experimental plan for studying multipacting in the SNS DTL vacuum windows are presented.
Nb₃Sn demonstrates steady advancements nowadays offering reduced power cost in superconducting radio-frequency cavities due to its high critical temperature, quality factor, and achieved accelerating gradient. However, theoretical estimates of its radio-frequency parameters have not been achieved due to several potentially limiting mechanisms: tin spots, patchy regions, defects, thermal impedance, and impurities. While some of these limitations have been intensively studied, impurity analysis in Nb$_3$Sn coatings have received less attention. We report an investigation of impurities in several vapor-diffused Nb₃Sn coated samples using time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and show allowable impurity levels in view of superconducting cavity performance. Challenges and lessons learned in maintaining clean Nb$_3$Sn coatings are also discussed.
Nb₃Sn promises better RF performance (Q and E_{acc}) than niobium at any given temperature because of superior superconducting properties. Nb₃Sn-coated SRF cavities are now produced routinely by growing a few microns thick Nb₃Sn films inside Nb cavities via the tin vapor diffusion technique. Sn evaporation and consumption during the growth process notably affect the quality of the coating. Aiming at favorable surface characteristics that could enhance the RF performance, many coatings were produced by varying Sn sources and temperature profiles. Coupon samples were examined using different material characterization techniques, and a selected few sets of coating parameters were used to coat 1.3 GHz single-cell cavities for RF testing. The Sn supply’s careful tuning is essential to manage the microstructure, roughness, and overall surface characteristics of the coating. We summarize the material analysis of witness samples and discuss the performance of several Nb₃Sn-coated single-cell cavities linked to Sn-source characteristics and observed Sn consumption during the film growth process.
Radiolytic hydrogen production and accumulation inside containment packages is a concern at any facility responsible for their packaging, storage, transportation, and/or disposal. When hydrogen gas accumulates to concentrations above the Lower Flammability Limit (LFL) which is 4% or 40,000 ppm in air, the possibility of a deflagration or explosion increases. This concern persists over the course of the package lifetime which is unlimited when disposed of by burial or in permanent repositories. Here, we report on a numerical model used to predict the concentration of hydrogen within each layer of a Model 9979 package containing a convenience can assembly. Simulations show the hydrogen concentration to always be highest in the inner convenience can containing the radioactive source. When the radioactive source is within the Los Alamos National Laboratory (LANL) Packaging Limits, the hydrogen concentration is shown to remain well below the LFL at all times including packaging, storage, transportation, and disposal. A hydrogen transport model is presented for a Model 9979 package system containing a nested arrangement of convenience cans, which are tin oxide coated steel cans of various sizes with a slip-lid assembly. The inner convenience can contains the radioactive source material along with an unknown quantity of incidental water acquired from humid air or processing. While visible organic materials such as paper and plastics were purposely excluded from the inner can, it is not possible to claim the wastes are entirely organic free. The inner convenience can is tape sealed and placed into a plastic bag which is horsetail closed (i.e., twisted and taped). The bagged can is placed into an outer convenience can that is also tape sealed. The can assembly is then placed into the 30 gallon drum and subsequently placed inside the 55 gallon drum in the 9979 package. Here we assume hydrogen gas is produced in the inner convenience can from alpha radiolysis of water at a rate dependent on the quantity of uranium isotopes and water present. The hydrogen transport model was used to calculate hydrogen accumulations within the package’s five layers at different times and conditions. These simulations serve two purposes; (i) to build confidence in the model by comparing predicted values to measured values, and (ii) to check the steady state hydrogen concentrations that are approached at long times in the package’s lifetime. Model simulations were compared to gas samples taken from the 30 gallon drum after storage at LANL’s Chemistry and Metallurgy Research (CMR) building for around 500 days. Hydrogen concentration calculations over much longer periods (i.e., more than 270 years) included extreme storage durations, transportation at extreme cold temperatures, and disposal of packages assuming different average temperatures.
The desire to improve nuclear material detection through portal monitors and other low resolution detectors has led to interest in benchmarking the performance of radiation transport codes. These codes can be used to generate a variety and quantity of spectra that may be cost prohibitive to measure directly. Particular characteristics of typical detection scenarios were isolated to compare the performance of radiation transport codes to laboratory experiments. These benchmark experiments were performed to validate simulations in a number of key areas. These experiments included high areal density configurations in both one- and three-dimensional configurations. In addition, off-angle measurements were conducted to investigate the impact of detector response assumptions on complex geometries, for example where an unknown source is not physically collocated with an apparent hot spot. Furthermore, by examining both simple shielding and backscatter configurations, isolation of the scatter emanating from the object and environmental background scatter contributions to the spectra could be elucidated. A series of experiments were performed in which the order of shielding layers and the thickness were evaluated to examine the ability of the simulations to address these variables. Experiments with increasing thickness of polyethylene around a neutron source also allows for examinations of the ability of the transport simulations to properly model n,γ reactions. Finally, depleted uranium (DU) measurements have more complicated spectra than the cobalt-60 and consequently allow for investigations into the ability of transport simulations to model self-shielding. In each case, the results of the experiments were compared to MCNP simulations to judge the performance of the code, as was done previously with GADRAS 18.7.9 simulations [7]. All of the benchmark measurements were taken with a liquid nitrogen cooled 140% high purity germanium (HPGe) detector with a bismuth collimator that had the front tin filter removed. The measurement location and detector configuration were subsequently used for all experimental configurations. The remainder of this report details the experimental measurements, Section 2 and the MCNP model, Section 3. Comparisons between the experimental results and MCNP-generated spectra are performed, Section 4. Section 5 compares the results obtained with MCNP with the previously reported results obtained with GADRAS [2]. Finally, Section 6 presents the conclusions.
Until this year the BISON fuel performance code has been developed primarily for pressurized water reactor (PWR), accident tolerant fuel (ATF), and advanced reactor (e.g., tri-structural isotropic (TRISO), metallic) analyses. The main focus of this work is to develop and document required material models that would aid predicting cladding failure with a specific hydride distribution to be investigated for boiling water reactor (BWR) applications in the next fiscal year. In terms of materials, the primary differences between a BWR and PWR is the use of gadolinia doping of the UO 2 fuel, the use of Zircaloy-2 for the cladding, and the addition of a liner on the inner surface of the cladding for improved pellet-clad mechanical interaction (PCMI)performance. The liner is typically made of pure zirconium or a lower tin content zirconium alloy (e.g. Zr-0.3%Sn). This work details the development and documentation of material and behavioral models for BWR analysis such as the addition of material and behavior models for gadolinia doped UO 2 , pure zirconium, Zr-0.3%Sn, and Zircaloy-2 as well as the ease-of-use additions to allow internal meshing capabilities to include liners. Another important aspect affecting cladding performance is hydrogen diffusion and hydride precipitation in the cladding. A model was added previously for non-lined, homogeneous claddings. In this work, instructions are provided on how to apply the model to BWR liner cladding. Representative experimental values are provided for the hydrogen diffusion parameters and precipitation-dissolution kinetics for typical liner materials of interest.
Fermilab’s PIP-II project’s superconducting linear accelerator will drive the next generation of particle accelerators through a revolution in beam intensity. Key to beam intensification are the high efficiencies of niobium-tin superconducting radiofrequency (SRF) cavities operating at cryogenic temperatures near 5 Kelvin. A multifaceted approach is employed to achieve and maintain the extreme temperature. Vacuum provides the first barrier to thermal convection. Physical thermal intercept zones further isolate the exterior shell vacuum vessel at 300 Kelvin from the supercooled beamline. The first thermal intercept lies just inside the exterior vacuum vessel forming the 40 Kelvin zone. This 40K thermal shield is the focus of this investigation. In preparation for operation, the thermal shield is cooled from 300K to 40K in a slow process over 2-1/2 days. The factors limiting the cooling rate are a high thermal gradient which produces thermal strain and high mechanical stress. D ecreasing the time required to reach operational temperatures is the desired research goal. Physical testing data and finite element method (FEM) computer models from the Single Spoke Resonator – 1 (SSR1) and Linac Coherent Light Source (LCLS-II) cryomodules will be evaluated to determine needed design changes. The thermal shield design for the High Beta 650 MHz (HB650) will be modified and analyzed using FEM computer models to determine maximum cooling rate with a target of 50 thermal cycles of life. Maximum allowable stress will be determined through low cycle fatigue calculations.