Radiation attenuation by single-crystal diamond windows
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-12-22 |
| Journal | Journal of Applied Crystallography |
| Authors | Malcolm Guthrie, Ciprian G. Pruteanu, Mary-Ellen Donnelly, Jamie J. Molaison, A. M. dos Santos |
| Institutions | Carnegie Institution for Science, Oak Ridge National Laboratory |
| Citations | 22 |
| Analysis | Full AI Review Included |
Radiation Attenuation Correction in High-Pressure Neutron Diffraction: MPCVD Diamond Solutions
Section titled âRadiation Attenuation Correction in High-Pressure Neutron Diffraction: MPCVD Diamond SolutionsâThis document analyzes the research âRadiation attenuation by single-crystal diamond windows,â detailing the critical role of high-quality Single Crystal Diamond (SCD) in high-pressure neutron diffraction and outlining how 6CCVDâs advanced MPCVD materials and precision engineering services meet these stringent requirements.
Executive Summary
Section titled âExecutive SummaryâThe paper identifies and successfully corrects a significant source of error in Time-of-Flight (TOF) neutron diffraction experiments using Diamond Anvil Cells (DACs): pressure-induced Bragg attenuation within the single-crystal diamond (SCD) windows.
- Core Challenge: Severe, strain-dependent Bragg attenuation (losses) in SCD DAC windows, reducing incident beam intensity by up to 75% for specific neutron wavelengths (e.g., {111} reflections) at maximum load (40.4 GPa).
- Material Necessity: High-purity Single Crystal Diamond (SCD) is essential due to its low mass absorption for neutrons and exceptional mechanical stability for ultra-high pressure generation.
- Correction Methodology: A novel semi-empirical model using Gaussian summation was developed to deconvolve and fit the pressure-dependent attenuation spectra from the upstream and downstream SCD anvils.
- Validation: Applying the correction yielded substantial improvements in the quality of Rietveld refinements, decreasing the weighted residual $\chi^2$ value by up to 25% for high-pressure nickel datasets.
- Required Specifications: DAC windows require highly polished, thick SCD material (1-3 mm) with precise culet geometry (1.5 mm diameter) to function correctly under extreme mechanical strain.
- 6CCVD Value Proposition: 6CCVD delivers custom, high-optical-purity SCD wafers and substrates with the necessary thickness, polishing (Ra < 1 nm), and precision geometry required for replicating and advancing these extreme environment experiments.
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters were reported or derived from the experimental setup and results focusing on single-crystal diamond performance under extreme strain:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material Used | Single Crystal Diamond (SCD) | N/A | Used as high-pressure DAC windows. |
| Max Sample Pressure Achieved | 40.4 | GPa | Corresponds to a maximum mechanical load of 6.3 tonnes. |
| Nominal SCD Thickness (Path) | 1 - 3 | mm | Thickness traversed by the incident neutron beam. |
| Diamond Culet Diameter | 1.5 | mm | Geometry used for high-pressure application. |
| Max Attenuation Observed | ~75 | % | Reduction in beam intensity due to {111} Bragg dips at 40.4 GPa load. |
| Strain Dependence | Pronounced & Linear | N/A | Minimum transmission decreases approximately linearly with increasing load/pressure. |
| Critical Diffraction Angles | 70 < 2$\theta$ < 110 | ° | Angular aperture range for sample diffraction measurements. |
| Refinement Improvement ($\chi^2$) | Up to 25 | % | Improvement in Rietveld fit quality after attenuation correction. |
| Reference Sample Material | Ni powder (FCC structure) | N/A | Used to test correction efficacy up to 40 GPa. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully characterized and corrected diamond Bragg attenuation using an integrated approach combining extreme pressure physics and TOF neutron diffraction data processing.
- High-Pressure Configuration: Measurements utilized large-volume neutron DACs employing 1.5 mm SCD culets, designed for transmission geometry at the SNAP beamline (SNS, Oak Ridge).
- TOF Diffraction Setup: Diffraction and transmission data were collected using Time-of-Flight (TOF) energy-dispersive neutron methods, with detectors centered at $2\theta$ = 90° and covering a range of ±20°.
- Transmission Spectroscopy: The total transmitted neutron intensity was measured downstream using a 3He gas monitor, generating a spectrum exhibiting sharp dips characteristic of diamond Bragg scattering losses.
- Semi-Empirical Modeling: A model based on the summation of Gaussians was fitted to the measured transmission spectra. This model incorporated crystal orientation (UB matrix), three angular adjustments ($\alpha$, $\beta$, $\gamma$), a load-dependent scale factor ($\delta$), and adjustable dip areas ($k_n$).
- Upstream Deconvolution: The model allowed the deconvolution and separate extraction of the transmission spectra corresponding only to the upstream diamond, which is the only attenuation source affecting the incident beam interacting with the sample.
- Correction Application: The extracted upstream attenuation was converted from TOF to $d$ spacing and applied to the time-focused Ni powder diffraction data via simple division to yield corrected diffraction intensities for Rietveld analysis.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the absolute necessity of high-quality, large-volume SCD material for advanced high-pressure diffraction studies. 6CCVD is uniquely positioned to supply the diamond windows required to replicate, extend, and industrialize this methodology.
Applicable Materials
Section titled âApplicable MaterialsâThe foundation of this extreme environment research is material quality. 6CCVD recommends:
- Optical Grade Single Crystal Diamond (SCD): Required for maximizing transparency to neutron radiation and ensuring the structural integrity necessary to withstand pressures exceeding 40 GPa without failure.
- Ultra-Thick Substrates: While standard SCD is typically < 500 ”m, this application requires windows up to 3 mm thick. 6CCVD offers custom SCD Substrates up to 10 mm in thickness for demanding high-pressure cell applications.
Customization Potential
Section titled âCustomization PotentialâThe success of DAC experiments hinges on precise material dimensions and surface preparation. 6CCVDâs capabilities directly address the requirements detailed in the paper:
| Research Requirement | 6CCVD Custom Capability | Benefit to Customer |
|---|---|---|
| Window Thickness (1-3 mm) | SCD Substrates up to 10 mm. | Ensures reliable SCD windows for extreme pressure/large beam volume DACs. |
| Culet Dimensions (1.5 mm diameter) | Precision Laser Cutting and Shaping. | Allows rapid fabrication of custom geometries (culets, flats, and seats) up to 125 mm diagonal (PCD) or large SCD plates. |
| Surface Quality (Minimized Scattering) | Ultra-Smooth Polishing (Ra < 1 nm for SCD). | Guarantees minimal surface scattering and consistent optical transparency for precise beam transmission measurements. |
| Future Adaptations (e.g., heating) | Custom Metalization (Ti, Pt, Au, W, Cu). | Enables integration of electrical circuits or heating elements directly onto the SCD surface for combined high-P/high-T experiments. |
Engineering Support
Section titled âEngineering SupportâThe complexity of correcting for strain-induced Bragg attenuation requires deep understanding of diamond crystallography and mechanical properties.
- DAC Design Consultation: 6CCVDâs in-house PhD team provides specialized material selection and orientation advice for new High-Pressure Neutron Diffraction and synchrotron DAC projects.
- Crystallographic Expertise: We assist researchers in optimizing SCD orientation (e.g., minimizing interaction with specific reciprocal lattice vectors) to reduce Bragg attenuation effects for chosen incident beam energies.
- Quality Assurance: We guarantee the tight tolerances and superior crystallinity required for materials subjected to multi-tonne loads, ensuring reproducible results for measurements up to 40.4 GPa and beyond.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
As artificial diamond becomes more cost effective it is likely to see increasing use as a window for sample environment equipment used in diffraction experiments. Such windows are particularly useful as they exhibit exceptional mechanical properties in addition to being highly transparent to both X-ray and neutron radiation. A key application is in high-pressure studies, where diamond anvil cells (DACs) are used to access extreme sample conditions. However, despite their utility, an important consideration when using single-crystal diamond windows is their interaction with the incident beam. In particular, the Bragg condition will be satisfied for specific angles and wavelengths, leading to the appearance of diamond Bragg spots on the diffraction detectors but also, unavoidably, to loss of transmitted intensity of the beam that interacts with the sample. This effect can be particularly significant for energy-dispersive measurements, for example, in time-of-flight neutron diffraction work using DACs. This article presents a semi-empirical approach that can be used to correct for this effect, which is a prerequisite for the accurate determination of diffraction intensities.