direct (radiochemical) isotope dilution analysis 

https://doi.org/10.1351/goldbook.D01772
Isotope dilution analysis used for the determination of a non-radioactive element with the aid of one of its radionuclides.
Source:
PAC, 1994, 66, 2513. (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2521 [Terms] [Paper]