4. Other substances or articles (not being an instrument, apparatus or appliance) which consist of or contain or generate a radioactive substance and which—
(a)consist of or contain or generate that substance in order, when administered, to utilise the radiation emitted therefrom, and
(b)are manufactured, sold or supplied for use wholly or mainly by being administered to one or more human beings solely by way of a test for ascertaining what effects it has when so administered.