Construction and Calibration of the NIST Large-Area-Source X-Ray Counting System
J M R Hutchinson1, M P Unterweger1, P A Hodge1
1National Institute of Standards and Technology, Gaithersburg, MD 20899.
Summary
The NIST constructed a large area x-ray counting system to calibrate plutonium-238 sources. This system accurately measures x-ray and alpha particle emission rates for calibrating alpha-particle surface monitors.
Area of Science:
- Nuclear Physics
- Metrology
- Radiation Detection
Background:
- Accurate calibration of radioactive sources is crucial for various scientific and industrial applications.
- Plutonium-238 (²³⁸Pu) is a significant alpha emitter used in radioisotope thermoelectric generators and requires precise characterization.
Purpose of the Study:
- To describe the construction and calibration of the National Institute of Standards and Technology (NIST) large area x-ray counting system.
- To calibrate ²³⁸Pu sources for both total x-ray emission rate and emission rate through a defined aperture.
- To determine alpha particle emission rates from these sources for subsequent calibration of alpha-particle surface monitors.
Main Methods:
- Construction of a specialized large area x-ray counting system at NIST.
- Calibration of ²³⁸Pu sources (8 in x 5 in) emitting L x rays (12-20 keV).
- Measurement of total x-ray emission rate and rate through a 3-inch diameter aperture.
- Calculation of alpha particle emission rates based on established x-ray to alpha particle abundance ratios.
Main Results:
- The NIST large area x-ray counting system was successfully constructed and calibrated.
- ²³⁸Pu sources were calibrated for their total x-ray emission rate and the rate through a central aperture.
- Alpha particle emission rates were derived from the calibrated x-ray data.
Conclusions:
- The developed system provides a reliable method for calibrating large area x-ray emissions from ²³⁸Pu sources.
- The calibrated sources and their derived alpha emission rates will be used to calibrate alpha-particle surface monitors, enhancing measurement accuracy in related fields.
