Linearity check of an ionisation chamber through 99mTc half-life measurements

The half-life of 99mTc was measured at the JRC using the ionisation chamber 'IC1' (type Centronic IG12). The result, T1/2(99mTc) = 6.00660 (18) h, is in good agreement with literature data. One experiment was performed in IC1's default set-up with the ionisation current being integrated over an air capacitor and read out as a voltage increase over time. This ensured excellent linearity and precision throughout the dynamic range, but the maximum current was limited to 2 nA. In a second test, the current was directly read out with a Keithley 6517A electrometer. Applying correction factors for the automatic range switching of the electrometer, an acceptable linearity was demonstrated over a range of 12 half-life periods starting at 20 nA. Piecewise fitting of the decay curve over periods of 6 h yields the same 99mTc half-life value within 0.04 % (0.0025 h) standard deviation over an activity range spanning at least 10 half-life periods (3 orders of magnitude).

POMME Stefaan;  PAEPEN Jan;  VAN AMMEL Raf; 

2018-09-26

PERGAMON-ELSEVIER SCIENCE LTD

JRC111569

0969-8043,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC111569,   

10.1016/j.apradiso.2018.07.004,