REFERENCE NEUTRON FIELDS IN CALIBRATION LABORATORY; SIMPLE DOSIMETRIC PARAMETERS AND THEIR CHANGES IN TIME.

Area of Science:

• Nuclear Physics
• Radiation Dosimetry
• Metrology

Background:

• Calibration laboratories periodically revise dosimetric properties of calibration fields.
• Reference neutron fields from radionuclide sources are affected by isotopic impurities, leading to significant long-term admixtures and decay products.
• Neglecting these effects causes inconsistencies between observed and decay-curve-derived neutron emission rates.

Purpose of the Study:

• To present recent results on the long-term examination of neutron fields from 252Cf, 241AmBe, and 239PuBe sources.
• To compare current measurement data with historical data collected over nearly 30 years.
• To highlight discrepancies in neutron emission rates and decay curves of key isotopes.

Main Methods:

• Regular examination of bare 252Cf, 241AmBe, and 239PuBe sources in fixed geometry over decades.
• Periodic determination of neutron fluence rate, ambient dose equivalent rate, scattered components, dose rates, and radiation quality factors.
• Analysis of neutron emission rate growth and decay curve discrepancies.

Main Results:

• Observed growth in neutron emission from the 239PuBe source over time.
• Identified discrepancies between the decay curves of relevant isotopes and the actual neutron emission rates for 252Cf and 241AmBe sources.
• Demonstrated the long-term impact of isotopic impurities on neutron field characterization.

Conclusions:

• Periodic recalibration and analysis of radionuclide sources are essential for accurate neutron dosimetry.
• Isotopic impurities and their decay significantly influence neutron emission rates over extended periods.
• The findings underscore the need to account for these long-term effects in radiation protection and calibration practices.