Design and performance of the micro-dose calibrator

Area of Science:

• Nuclear Instrumentation
• Medical Physics
• Radiochemistry

Background:

• Standard dose calibrators have limitations in measuring a wide range of radioactivity.
• Segmented well counters offer potential for extended operational range and improved accuracy.
• Existing methods for extending dose calibrator range often compromise spectrographic capabilities.

Purpose of the Study:

• To design and evaluate a new class of dose calibrator, the micro-dose calibrator.
• To assess the performance of a prototype micro-dose calibrator using a segmented well counter design.
• To determine the operational range, linearity, and stability of the micro-dose calibrator for various radionuclides and sample volumes.

Main Methods:

• Designed a micro-dose calibrator based on a segmented well counter with 8 NaI(Tl)/photo multiplier tube modules.
• Implemented N-fold coincidence mode with a pipeline coincidence processing algorithm for accurate decay counting.
• Applied a tri-functional model pulse pileup dead time correction to extend the measurement range.
• Evaluated performance using 18F and 137Cs sources, assessing linearity, stability, and volumetric accuracy with different sample geometries.

Main Results:

• Achieved an operational range of 1 kBq to 3.4 MBq for 18F with 1% linearity precision.
• Demonstrated excellent long-term stability with a 0.17% coefficient of variation over 9 days for a 137Cs source.
• Showed less than 1% variation in count rate across different radionuclides within the central well length.
• Exhibited less than 1% deviation from volumetric linearity for doses in insulin syringes and scintillation vials.

Conclusions:

• The micro-dose calibrator effectively extends the measurement range of radioactivity while maintaining accuracy and spectrographic capabilities.
• The N-fold coincidence mode and dead time correction are crucial for the device's performance.
• The prototype demonstrates suitability for accurate radioactivity measurements in diverse pharmaceutical and research settings.