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6CCVD Research

Alpha Particle Measurement of Radioactive Substances in Nitric Acid Using a Single-crystal CVD Diamond Radiation Detector

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-05-22
JournalSensors and Materials
AuthorsKengo Oda, Junichi H. Kaneko, Akiyoshi Chayahara, Takehiro Shimaoka, Hideaki Yamada
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Executive Summary

Section titled “Executive Summary”
  • Value Proposition: Explores the use of single-crystal CVD diamond radiation detectors for measuring alpha particles in nitric acid, relevant to nuclear fuel reprocessing.
  • Advantage: Single-crystal CVD diamond enables detailed energy information acquisition compared to polycrystalline alternatives.
  • Method: Fabricated a detector using a 10 mm2 single-crystal CVD diamond substrate and grew a single-crystal CVD diamond membrane via direct wafer method.
  • Performance: Achieved 99.1% charge collection efficiency for 5.486 MeV alpha particles with energy resolutions of 0.55% and 0.54% for holes and electrons, respectively.
  • Nitric Acid Compatibility: Successfully measured alpha particle spectra from thorium oxide in 5 mol/L nitric acid, demonstrating compatibility.
  • Gamma Ray Resistance: Continuous measurements over 72 hours confirmed minimal influence from gamma rays.
  • Potential: Shows promise for use in nuclear fuel reprocessing facilities, with potential for high-temperature operation.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Substrate Size10mm2Single-crystal CVD diamond substrate
Membrane Thickness66”mFreestanding single-crystal CVD diamond membrane
Alpha Particle Energy5.486MeVAlpha particles from 241Am source
Charge Collection Efficiency99.1%For both holes and electrons
Energy Resolution (Holes)0.55%ΔE/E
Energy Resolution (Electrons)0.54%ΔE/E
Nitric Acid Concentration5mol/LAlpha particle measurement in solution
Preamplifier Output Signal Rise Time~30nsMeasurement with nitric acid
Substrate Temperature (Synthesis)870°CCrystal growth
Gas Pressure (Synthesis)110TorrCrystal growth
CH4 Concentration (Synthesis)1.0%Crystal growth
O2 Concentration (Synthesis)0.5%Crystal growth
Leakage Current (-264V)7pATi/Au-Pt electrodes
Leakage Current (+264V)7pATi/Au-Pt electrodes
Applied Voltage (Solution)-33VAlpha particle measurement in solution
Measurement Time (Solution)72hAlpha particle measurement in solution
Counting Rate (Solution)0.02cpsAlpha particle measurement in solution

Key Methodologies

Section titled “Key Methodologies”
  1. Substrate Preparation: Used a 10 mm2 single-crystal CVD diamond substrate.
  2. Epitaxial Growth: Stacked an approximately 50 ”m thick epitaxial growth layer.
  3. Ion Implantation: Carbon ions were implanted to form an ion implantation layer at 1.6 ”m depth.
  4. Diamond Synthesis: Epitaxially grew diamond using microwave plasma CVD system with:
    • Substrate temperature: 870 °C
    • Gas pressure: 110 Torr
    • CH4 concentration: 1.0%
    • O2 concentration: 0.5%
  5. Membrane Formation: Removed the ion implantation layer by electrochemical etching to create a freestanding membrane.
  6. Electrode Deposition: Formed Ti/Au ohmic-contact anode and Pt ohmic-contact cathode electrodes by evaporation. Electrode thickness was approximately 100 nm.
  7. Solution Preparation: Prepared a 5 mol/L nitric acid solution by diluting 13 mol/L nitric acid.
  8. Alpha Particle Measurement: Dispersed thorium oxide in the 5 mol/L nitric acid solution and measured alpha particle spectra.

Commercial Applications

Section titled “Commercial Applications”

Based on the technology and its characteristics, here are some potential commercial applications:

  • Nuclear Fuel Reprocessing: Monitoring alpha particle activity in nitric acid solutions.
  • Nuclear Waste Management: Characterizing radioactive waste materials.
  • Radiation Detection: General purpose radiation detection in harsh environments.
  • High-Energy Physics: Detection of charged particles in high-radiation environments.
  • Homeland Security: Detection of radioactive materials for security purposes.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

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