geometry factor

in radioanalytical chemistry
https://doi.org/10.1351/goldbook.G02624
The average solid @A00346@ in steradians at source subtended by the aperture or sensitive volume of the detector, divided by 4π.
Source:
PAC, 1994, 66, 2513. (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2520 [Terms] [Paper]