Self-absorption correction in standardisation of 204Tl

Area of Science:

• Nuclear physics
• Metrology
• Radiochemistry

Background:

• Discrepancies exist in standardizing thallium-204 (204Tl) activity measurements.
• The Consultative Committee for Ionizing Radiation (CCRI) working group on 204Tl aims to resolve these standardization issues.
• Self-absorption in solid sources is a suspected cause of measurement discrepancies.

Purpose of the Study:

• To investigate the influence of self-absorption on the activity measurements of solid 204Tl sources.
• To develop methods for minimizing and correcting self-absorption in 204Tl standardization.
• To contribute to resolving discrepancies in 204Tl standardization methods.

Main Methods:

• Prepared quantitative solid 204Tl sources with varying carrier content using a specialized drying technique.
• Measured source activity using a 4pi pressurized proportional counter.
• Determined self-absorption by comparing measurements with liquid scintillation spectrometry (unaffected by self-absorption) as a reference, after correcting for foil and X-ray absorption.

Main Results:

• Self-absorption in solid 204Tl sources was found to be dependent on the dry mass of the source, exhibiting a linear relationship with the logarithm of the mass.
• For a typical source, the self-absorption correction required was as high as 8%.
• A method to minimize and correct for self-absorption in 204Tl and similar nuclides was described.

Conclusions:

• Self-absorption is a critical factor affecting the accuracy of solid 204Tl source standardization.
• The developed method provides a way to accurately correct for self-absorption, improving standardization reliability.
• This research aids in resolving existing discrepancies in 204Tl activity measurements.