Standardisation of ²³¹Pa by defined solid angle and liquid scintillation methods at NPL.

Area of Science:

• Nuclear Physics and Metrology
• Radiochemistry and Isotope Science

Background:

• Protactinium-231 (Pa-231) is the longest-lived decay product in the Uranium-235 (U-235) decay chain.
• Accurate and traceable measurements of Pa-231 are essential for applications like geochronometry and nuclear forensics.
• International comparisons are vital for validating measurement standards.

Purpose of the Study:

• To determine the activity per unit mass of a Pa-231 solution.
• To participate in the international measurement comparison CCRI(II)-K2.Pa-231.
• To validate measurement techniques for Pa-231 standardization.

Main Methods:

• Three independent techniques were employed at the National Physical Laboratory (NPL).
• Defined solid angle alpha counting, utilizing a new instrument for BIPM comparison.
• 4π alpha liquid scintillation (LS) counting with the CIEMAT/NIST method.
• 4π(LS) alpha-gamma coincidence counting using a custom NPL system with HPGe spectrometry.

Main Results:

• Excellent agreement was achieved between the three independent measurement methods.
• The results contribute to the international CCRI(II)-K2.Pa-231 comparison.
• The study validates the reliability of the employed techniques for Pa-231 activity determination.

Conclusions:

• The study successfully established a precise activity per unit mass for Pa-231.
• The agreement between methods provides confidence in the traceability of Pa-231 measurements.
• These findings support accurate applications in nuclear dating and forensics.