Isotope injection substance, injection method and injector therefore

An isotope substance for injection into fluid, especially a well fluid, for the provision of radioisotope tracers in the fluid comprises radioactive solid particles suspended in a carrier comprising a gel or other semiviscous material. Injection of the substance is achieved by an extruding device, and this extruding device can comprise a plunger-in-cylinder apparatus adapted to be fitted to a fluid conduit, for example at one leg of a T-piece of the conduit. The apparatus preferably has a cone form discharge nozzle for restricted discharge of the isotope substance from the apparatus into the fluid and discharge of the substances can be achieved by the supply of high pressure fluid to one side of the plunger within the cylinder of the apparatus. (author)