Calibrations: Calibrating a secondary standard ionization chamber for photon-emitting radionuclides in ISO 10R vials

Summary

NIST has begun a project to expand capabilities in calibrating short-lived radionuclides. Our customers—primarily the radiopharmaceutical segment—currently submit gamma-emitting sources in flame sealed glass ampoules for calibration. By calibrating our Secondary Standard Ionization Chambers for additional geometries, such as commonly used ISO standard crimp-sealed glass injection vials, we will be able to provide customers a simpler way for establishing traceability to the becquerel (Bq) and the International System of Units (SI).

Description

Testing with 3D-printed prototype holders (3 shown here) lead to the fabrication of the two aluminum and acrylic holders shown on the left. The source is loaded into the base of the holder and the holder lowered into the ionization chamber for measurement (opening covered by the plastic lid with “C” written on it).

Credit: NIST

Because sealed borosilicate glass ampoules preserve samples well, NIST has relied upon them for calibrations and long-term storage of samples and reference materials. Feedback from customers has suggested that they experience difficulty with the techniques used to seal and open these ampoules. They are, however, experienced using crimp-sealed vials for storage and dissemination of liquid pharmaceuticals, including vaccines and solutions for radiotherapy. To meet customer needs, we are working to expand our calibration services to include direct measurements in certain ISO standard vials. Advantages include (1) taking advantage of customer experience, (2) improved safety due to reducing sample handling (reducing personnel dose and chance of spills and contamination), and (3) improving throughput for both the customer and NIST.

For this new calibration geometry, we have chosen to use 10 mL crimp sealed vials, designated the ISO 10R vial. We chose this vial primarily due to flexibility, common use (Baker, 2005), and well defined design (ISO, 2018).

The larger dimensions of an ISO 10R vial, however, necessitate adaptations. We set up a larger Secondary Standard Ionization Chamber and are evaluating its performance. Tests were performed to assess the chamber’s optimal (axial and radial) location for highest response. Once that information was known, a sample holder was designed, prototyped, and built. This holder fits the new 10R vial, 5 mL glass ampoules, and reference sources that are routinely used to monitor stability (e.g., ²²⁶Ra)

There has been a lot of progress, but much work remains until these calibrations can be transferred to a new measurement service. The vial, new ionization chamber and electronics, and new holders require extensive measurements to understand the chamber response and associated uncertainties. We will continue comparing this chamber’s response to other chambers to understand, model, and predict response for new radionuclides. We hope to begin offering calibrations for ²²⁵Ac and ¹⁷⁷Lu using ISO crimp-sealed vials in FY26.

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References:
Baker, M., 2005. Calibration of the NPL secondary standard radionuclide calibrator for the new 10R Schott, Type 1+ vials. Applied Radiation and Isotopes 63, 71-77.

ISO, 2018. ISO 8362-1:2018 Injection containers and accessories — Part 1: Injection vials made of glass tubing. International Organization for Standardization (ISO), Geneva, Switzerland.