Methods and instruments for absolute measurements of specific activity of nuclides

The paper gives a description of some methods and instruments for measuring specific activity of nuclides. An installation with 4π-proportional counter is used for measurement of α- and β-radiations. For application in a coincidence circuit, the installation is supplied by blocks of detectors having crystalls of NaI. Dead-time of the channel with proportional counter equals to 4 mcs, resolution time of the coincidence circuit is variable from 0.4 to 2 mcs. To measure activity of nuclides with electron-capture decay, installation with 4π counter working under pre assure up to 2 MPa is used. Also, a method is given of determina tion of corrections in measurement by proportional counters. Corrections for self-absorption of α- andβ-particles a nd conversion electrons are determined by calculation. Self-absorption in the sources with radionuclides dacayed by electron capture is determined experimentally by means of ''weightless'' source which is prepared by the electrocalillar method. To check correctness of this approach, measurements of activity of 54Mn has been done by the coincidence method. Deviation of the results was more than 0.3%