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Beyond Californium-A Neutron Generator Alternative for Dosimetry and Instrument Calibration in the U.S
Roman K Piper1, Andrey V Mozhayev, Mark K Murphy
1*Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352; †National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899.
Health Physics
|July 28, 2017
Summary
Neutron calibration standards are shifting from Californium-252 (Cf) to more cost-effective neutron generators. This transition addresses the increasing cost of Cf sources and explores the practicality of generators for accurate dosimetry.
Area of Science:
- Nuclear physics and instrumentation
- Radiation detection and measurement
- Metrology and calibration standards
Background:
- Neutron survey instruments, area monitors, and personal dosimeters require reference neutron radiations for evaluation.
- Historically, (α,n) sources were primary, evolving to include californium-252 (Cf) spontaneous fission neutrons.
- The termination of the U.S. Department of Energy Cf Loan/Lease Program in 2009 led to increased costs for high-activity Cf sources.
Purpose of the Study:
- To review the characteristics of isotope-based neutron sources, particularly Cf.
- To explore isotope alternatives to Cf and the rationale for favoring electronically generated neutron options.
- To assess the practicality and technical challenges of implementing neutron generators as calibration standards.
Main Methods:
- Review of isotope-based neutron source characteristics, including Cf configurations (unmoderated and moderated).
- Analysis of neutron generators based on D-T and D-D fusion reactions as economically competitive alternatives.
- Evaluation of a D-T neutron generator system at Pacific Northwest National Laboratory (PNNL).
Main Results:
- Californium-252 offers favorable point source geometry and high dose rates but has become cost-prohibitive.
- Neutron generators are internationally recognized as important calibration standards and are economically competitive.
- Evaluation of a D-T system revealed specific characteristics crucial for adapting generators to calibration and testing tasks.
Conclusions:
- Neutron generators present a viable and increasingly favored alternative to isotope sources like Cf for calibration and testing.
- Adapting neutron generators requires careful consideration of their characteristics for accurate dosimetric quantity determination.
- Methods for modifying generated neutron spectra to simulate Cf or workplace environments are being developed.
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