AtomLab 500 Radionuclide Calibrator: Advantages and Disadvantages of Built-in Attenuator Tube Linearity Test vs. Source Decay Method

Overview

Introduction: In the draft recommendation of the State Office for Nuclear Safety (SÚJB) the following quality assurance tests are prescribed for radionuclide calibrators: background, short-term stability, long-term stability, linearity, geometric efficiency (volume dependence). For the system linearity test, only the method based on source decay is recommended, however AtomLab 500 includes built-in linearity tests for both this method and the method with attenuation tubes (lineator). The purpose of the article is to compare both built-in methods and point out mutual advantages and disadvantages.

Method: Automated linearity test based on source decay and linearity test with attenuation tubes (lineator) according to the manufacturer's instructions AtomLab 500 (Biodex). Initial ^99mTc activities for the first method were 13.08 GBq and additional 37.4 MBq, measurement intervals of 6 h and test completion below 0.37 MBq, for the second method, ^99mTc activities for 2 different combinations of lineator tubes were 11.53 GBq and 1811 MBq and test execution within 6 minutes. The measured data were evaluated using radionuclide calibrator software (graphs, tables, deviations from linearity – ±5 % are allowed).

Results: Tables and semilogarithmic graphs of measured linearity test values based on source decay for two default activities (second low one was additional, see below) and tables of linearity test values with lineator for two activities and calculated deviations from system linearity. The test with the second low activity (37.4 MBq ^99mTc) in the first method was supplemented due to the unsatisfactory last value of the test with high activity (13.08 GBq ^99mTc) – the device passed overall.

Conclusion: The linearity test performed with the AtomLab 500 according to the manufacturer's instructions once every 3 months is shortened from the original 3–4 d for the method based on the decay of the source to approximately 25 min (including sample preparation) for the lineator method and the device is not blocked unnecessarily. The disadvantage is the necessity of calibrating the lineator before its 1st use, after replacement, damage, after intervention in the device and proving the linearity of the system by the default method based on the decay of the source before starting to use the lineator method.

Keywords:

technetium-99m – attenuation (shielding) tube – attenuator – background – short-term stability – long-term stability – linearity – geometric efficiency – volume dependence – molybdenum-99