Abstract: Attenuator compositions useful as reagents in an improved internal sample attenuator counting method for radioimmunoassays are described. These compositions comprise an attenuator material that have a high capacity to absorb emitted radiation from a radioligand of the radioimmunoassay and are combined with an immunologically reactive material which interacts with components of the radioimmunoassay or combined with an absorbent of the free radiolabelled component to separate bound from free radioligand.

Abstract: A method of analysis in which a radioactive substance is distributed in a liquid phase and a solid particle phase and radiation from one phase is measured while attenuating the radiation from the other phase, the radiation from said other phase being shielded according to the invention by virtue of the fact that said phase is mixed with and/or contains a radiation-absorbing material in such a quantity and concentration that the dominant portion of the radiation from this phase will be absorbed.