Measurement of the gamma-ray emission probability of ^131mXe

Highlights: • ^131mXe was standardized by means of an internal gas proportional counting system. • The gamma-ray emission probability of ^131mXe was determined through HPGe spectrometer measurements. • The measured value is consistent within the uncertainty limit with those evaluated in previous literature reports. - Abstract: ^131mXe has been standardized by means of an internal gas proportional counting system, employing a length-compensated method. The activity concentration of ^131mXe was measured with a relative standard uncertainty of 0.6%. The gamma-ray emission probability of ^131mXe was then determined as 0.0196(4) by measuring a standard sample of ^131mXe using a high-purity germanium (HPGe) spectrometer.