Response of synthetic diamond detectors in proton, carbon, and oxygen ion beams
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-07-15 |
| Journal | Medical Physics |
| Authors | SĂ©verine Rossomme, M. Marinelli, G. VeronaâRinati, F. RomanĂČ, G.A.P. Cirrone |
| Institutions | MedAustron, National Physical Laboratory |
| Citations | 16 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: High-LET Dosimetry with MPCVD Diamond
Section titled âTechnical Analysis and Documentation: High-LET Dosimetry with MPCVD DiamondâReference Paper: Rossomme et al. (2017). Response of synthetic diamond detectors in proton, carbon, and oxygen ion beams. Med. Phys. 44(10), 5445-5449.
Executive Summary
Section titled âExecutive SummaryâThis documentation analyzes the performance of synthetic diamond detectors (microDiamonds) in high Linear Energy Transfer (LET) particle beams, highlighting the critical role of material quality and geometry in clinical dosimetry applications.
- Application Focus: Relative dosimetry in nonmodulated particle beams (proton, carbon, and oxygen ions) used in particle therapy.
- Core Finding: Synthetic diamond detectors exhibit a significant under-response when exposed to high-LET carbon and oxygen ion beams, compared to low-LET proton beams.
- Quantified Dependence: The average LET dependence for high-LET ions was determined to be 0.026% (±0.013%) per keV/”m.
- Mechanism Identified: The under-response is attributed to increased electron/hole recombination within the thin (1 ”m) synthetic diamond layer, a direct consequence of high ionization density associated with high-LET particles.
- Material Implication: Replicating or improving this performance requires ultra-high purity Single Crystal Diamond (SCD) with minimized defect density to maximize Charge Collection Efficiency (CCE).
- 6CCVD Value Proposition: 6CCVD provides custom, high-purity MPCVD SCD wafers with precise thickness control (0.1 ”m to 500 ”m) and integrated metalization services, enabling researchers to engineer detectors optimized for high-LET environments.
Technical Specifications
Section titled âTechnical SpecificationsâThe following data points summarize the key parameters and results extracted from the study on PTW-60019 microDiamond detectors.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material Type | Synthetic Diamond (SCD) | N/A | Schottky Diode structure |
| Sensitive Volume Radius | 1.1 | mm | Circular geometry |
| Sensitive Volume Thickness | 1 | ”m | Thin diamond layer |
| Proton Beam Energy | 60 | MeV | Low LET regime |
| Carbon Ion Beam Energy | 62 | MeV/n | High LET regime |
| Oxygen Ion Beam Energy | 62 | MeV/n | High LET regime |
| Diamond Detector Bias | 0 | V | Used in passive (unbiased) mode |
| Ion Chamber Bias (Max) | +400 | V | Used to minimize ion recombination |
| Combined C/O LET Dependence | 0.026 ± 0.013 | % per keV/”m | Average under-response rate |
| Under-response (Carbon, 346 keV/”m) | 13 (±4) | % | Specific high-LET point |
| SCD Response Fit (Carbon) | y = (-2.51E-4) * LET + 1.01 | N/A | Linear fit of normalized response ratio |
| SCD Response Fit (Oxygen) | y = (-2.77E-4) * LET + 1.03 | N/A | Linear fit of normalized response ratio |
Key Methodologies
Section titled âKey MethodologiesâThe experimental investigation focused on comparing the response of five synthetic diamond detectors against standard ionization chambers in various particle beams.
- Beam Generation: Nonmodulated particle beams (proton, carbon, oxygen) were generated using cyclotron systems (Scanditronix MC62PF and K800 superconducting cyclotron).
- Beam Preparation: Beams were scattered by a tantalum foil and collimated using a 25 mm diameter brass aperture.
- Detector Orientation: MicroDiamond detectors were positioned with their axis parallel to the beam axis.
- Bias Conditions: Diamond detectors were operated without any bias voltage. Ionization chambers (Markus/Advanced Markus) were operated at high bias (+300 V or +400 V) to minimize ion recombination effects.
- Dosimetry Measurement: Detector response was measured as a function of depth in a computer-controlled motorized water phantom.
- Normalization: Integral detector response was normalized to unity over a specific low-LET entrance dose region (e.g., 1 cm to 1.28 cm for protons) to minimize beam instability effects.
- LET Correlation: Final results were presented as the ratio of normalized diamond response to normalized ionization chamber response, plotted against Linear Energy Transfer (LET) values derived from Geant4 Monte Carlo simulations.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights that the performance of diamond detectors in high-LET fields is fundamentally limited by recombination in the thin active layer. 6CCVDâs expertise in MPCVD growth and precision fabrication directly addresses these material limitations, enabling the next generation of high-fidelity particle dosimetry tools.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, the primary material requirement is ultra-high purity, low-defect Single Crystal Diamond (SCD) to maximize charge collection efficiency (CCE) and minimize recombination centers.
| 6CCVD Material Recommendation | Specification Focus | Relevance to High-LET Dosimetry |
|---|---|---|
| Optical Grade SCD | Low Nitrogen Concentration (< 1 ppb) | Reduces point defects (e.g., NV centers) that act as trapping sites, thereby minimizing electron/hole recombination and improving CCE in high-density ionization tracks. |
| High Purity PCD | Wafers up to 125 mm diameter | Suitable for large-area detector arrays or applications where the sensitive volume can be scaled up while maintaining robust mechanical properties. |
| Boron-Doped Diamond (BDD) | Custom doping levels available | Can be used to engineer specific conductivity profiles or p-n/p-i-n structures for active (biased) detector designs, offering alternatives to the passive Schottky diode used in the paper. |
Customization Potential
Section titled âCustomization PotentialâThe study utilized a specific detector geometry (1.1 mm radius, 1 ”m thick layer). 6CCVD offers the precision required to optimize these parameters for superior high-LET response.
- Precise Thickness Control: 6CCVD can supply SCD layers with thickness ranging from 0.1 ”m to 500 ”m. This allows researchers to systematically study the relationship between active layer thickness and recombination effects, crucial for optimizing CCE in the Bragg peak region.
- Custom Metalization: The microDiamond detectors rely on a Schottky diode structure. 6CCVD provides internal, high-precision metalization services, including deposition of Ti, Pt, Au, Pd, W, and Cu. We can fabricate the necessary contacts (e.g., Ti/Pt/Au stacks) directly onto the SCD surface, ensuring stable and reproducible electrical performance.
- Custom Dimensions and Polishing: We offer custom laser cutting and shaping services to match the exact 1.1 mm radius sensitive area or to create complex detector arrays. Our polishing capabilities ensure surface roughness of Ra < 1 nm for SCD, critical for stable Schottky contact formation.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in defect engineering and material optimization for radiation detection. We offer comprehensive support for projects focused on High-LET Particle Dosimetry and Charge Collection Efficiency (CCE) Optimization.
Our experts can assist in selecting the optimal SCD growth parameters (e.g., growth rate, gas mixture) to minimize the defects responsible for the observed recombination and under-response in carbon and oxygen ion beams.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Purpose In this work, the LET âdependence of the response of synthetic diamond detectors is investigated in different particle beams. Method Measurements were performed in three nonmodulated particle beams (proton, carbon, and oxygen). The response of five synthetic diamond detectors was compared to the response of a Markus or an Advanced Markus ionization chamber. The synthetic diamond detectors were used with their axis parallel to the beam axis and without any bias voltage. A high bias voltage was applied to the ionization chambers, to minimize ion recombination, for which no correction is applied (+300 V and +400 V were applied to the Markus and Advanced Markus ionization chambers respectively). Results The ratio between the normalized response of the synthetic diamond detectors and the normalized response of the ionization chamber shows an underâresponse of the synthetic diamond detectors in carbon and oxygen ion beams. No underâresponse of the synthetic diamond detectors is observed in protons. For each beam, combining results obtained for the five synthetic diamond detectors and considering the uncertainties, a linear fit of the ratio between the normalized response of the synthetic diamond detectors and the normalized response of the ionization chamber is determined. The response of the synthetic diamond detectors can be described as a function of LET as (â6.22Eâ4 ± 3.17Eâ3) âą LET + (0.99 ± 0.01) in proton beam, (â2.51Eâ4 ± 1.18Eâ4) âą LET + (1.01 ± 0.01) in carbon ion beam and (â2.77Eâ4 ± 0.56Eâ4) âą LET + (1.03 ± 0.01) in oxygen ion beam. Combining results obtained in carbon and oxygen ion beams, a LET dependence of about 0.026% (±0.013%) per keV/ÎŒm is estimated. Conclusions Due to the high LET value, a LET dependence of the response of the synthetic diamond detector was observed in the case of carbon and oxygen beams. The effect was found to be negligible in proton beams, due to the low LET value. The underâresponse of the synthetic diamond detector may result from the recombination of electron/hole in the thin synthetic diamond layer, due to the high LET âvalues. More investigations are required to confirm this assumption.