A new NIST primary standardization of 18F

Area of Science:

• Nuclear Physics
• Radiochemistry
• Metrology

Background:

• Accurate standardization of radionuclides is crucial for reliable measurements in nuclear science and technology.
• Fluorine-18 (18F) is a widely used positron-emitting radionuclide in medical imaging, particularly Positron Emission Tomography (PET).
• Previous standardizations of 18F have relied on various techniques, necessitating ongoing efforts for improved accuracy and traceability.

Purpose of the Study:

• To establish a new primary standardization of 18F radioactivity.
• To provide updated calibration factors for NIST-maintained ionization chambers and dose calibrators.
• To compare the new standardization results with previous NIST reports and international key comparison reference values.

Main Methods:

• Primary standardization using live-timed beta-gamma anticoincidence counting.
• Confirmatory measurements employing liquid scintillation (LS) counting with efficiency tracing, triple-to-double coincidence ratio (TDCR) counting, and NaI/HPGe gamma-ray spectrometry.
• Utilizing an ionization chamber to link the new results with prior NIST standardizations.

Main Results:

• The new primary standardization of 18F is reported.
• Calibration factors for NIST ionization chambers were determined.
• The new value shows a 4% difference from previous NIST reports but agrees well with the 2005 key comparison reference value (KCRV).
• Evidence of cocktail instability was observed in one LS counting method.

Conclusions:

• The new primary standardization of 18F by NIST provides a more accurate reference value.
• The results contribute to improved traceability of radioactivity measurements for 18F.
• The findings highlight the importance of inter-method comparisons and ongoing validation of measurement techniques.