(Wednesday, 8/1/2018) 10:30 AM - 11:00 AM
Room: Exhibit Hall | Forum 6
Purpose: While anomalous decay rates in radionuclides that decay via electron capture and isomeric transition are known to be affected by chemical environment, activity anomalies for alpha and beta decay remain enigmatic. In apparent violation of the presumably immutable nuclear decay law, recent measurements have demonstrated anomalous variations in decay rate. Besides the inherent scientific curiosity, such variations in could affect total dose and dose-rate in temporary brachytherapy (both LDR and HDR), 60Co-based teletherapy and Gamma Knife radiosurgery.
Methods: Several independent sources of radionuclide decay experiments were used to initially demonstrate anomalous variations including: 1. data prospectively collected at Purdue University2. datasets acquired at Brookhaven National Laboratory, Physikalisch-Technische Bundesanstalt and Children’s Nutrition Research Center3. published data.Some raw data was acquired during calibration sequences, precision measurements or in establishing references.
Results: Unanticipated variations from the expected exponential decay patterns have been observed and are characterized by:1. oscillations demonstrating a strong annual periodicity2. short-duration deviations from expected decay rates.Annual periodicity has been observed in 14 radionuclides, whereas short-duration deviations have been observed in 4 radionuclides. The annual oscillation amplitude varies by radionuclide and is typically less than 0.5%. The short-duration deviations appear to be more substantial (>100% difference in apparent half-life) persisting for up to two days. Short-duration deviations resulted in apparent decay rate changes that persisted hours to days. Detector sensitivities are too low to explain these variations by seasonal fluctuations in temperature or humidity.
Conclusion: Anomalous variations in decay rates with an annual periodicity have been observed in 14 radionuclides (including 60Co, 90Sr/90Y, 137Cs and 226Ra). Short-duration deviations have been observed in 54Mn 60Co, 90Sr/90Y and 226Ra. Additional work is underway to elucidate the underlying nuclear mechanisms behind these variations as well as the potential dosimetric implications of short-duration variations in clinical radionuclides.
Funding Support, Disclosures, and Conflict of Interest: J Welsh is an adviser/consultant ProTom International
Keywords
Not Applicable / None Entered.
Taxonomy
IM- Nuclear Medicine General: radionuclide calibration
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