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Summing coincidence errors using 152Eu lungs to calibrate a lung-counting system: are they significant?
Gary H Kramer1, Timothy Lynch, Maria Antonia Lopez
1Human Monitoring Laboratory, Environmental Radiation Hazards Division, Radiation Protection Bureau, 775 Brookfield Road, Ottawa, Ontario. gary_h_kramer@hc-sc.gc.ca
Health Physics
|January 28, 2004
Summary
A study on lung phantoms for radioactive material detection found that while 152Eu/241Am sources offer many energy lines, coincidence summing can cause significant bias in lung counting system calibrations. This effect necessitates system-specific evaluations.
Area of Science:
- Medical Physics
- Nuclear Detection and Measurement
- Radiation Safety
Background:
- Lung phantoms with 152Eu/241Am are used for in vivo radioactive material measurement calibration.
- The numerous energy lines of 152Eu can lead to coincidence summing, complicating calibration accuracy.
Purpose of the Study:
- To investigate the impact of coincidence summing from 152Eu/241Am lung phantoms on efficiency calibration for lung counting systems.
- To determine the reliability of using a 152Eu/241Am lung phantom for routine calibration across different laboratories.
Main Methods:
- A Summing Peak Effect Study was performed at three independent laboratories.
- Similar germanium detectors (38 cm2 x 25 mm or 38 cm2 x 30 mm) were used for measurements.
- Efficiency calibration data using a 152Eu/241Am lung phantom was analyzed.
Main Results:
- All laboratories observed sum peaks in their measurements.
- One laboratory reported minimal bias (<5%) with the 152Eu/241Am calibration.
- Other facilities detected substantial positive bias (up to 30%) between 140-190 keV, rendering the phantom unsuitable for routine calibration.
Conclusions:
- Coincidence summing effects are significant when using 152Eu for low-energy lung counting system calibration.
- The observed biases are system-dependent, highlighting the inadequacy of general calibration curves.
- Specific nuclide calibration factors are crucial for accurate in vivo measurements, rather than relying on a general 152Eu/241Am phantom calibration.