What kind of standard can be used to calibrate my Isocomp gamma counter?
A standard is available from MGM Instruments for this purpose. The standard contains a very small amount (less than a tenth of a microcurie) of I129, which is used to simulate the I125 typically used in many radioisotope-labeled assays. The energy levels of the x-ray and gamma radiation of the two isotopes are very similar, making use of I129 practical. I125’s half-life (60 days) makes its use as a standard impossible, while I129’s half-life of 15.7 million years makes it a stable source suitable for use as a calibrator.
