Abstract: A liquid scintillation counter comprises a detector with a measuring chamber disposed on a horizontal plate having two holes and a device for delivering a test specimen to the measuring chamber, which is arranged under the plate and has a screw pair with a lead screw and a nut, guides with vertical slots to ensure progressive upward and downward movement of the nut and a shutter installed below at the outlet of the vertical slot. The nut mounts a receiving assembly secured so that it is found precisely within any hole in the plate after the nut is turned and lifted. Said nut has at least one roller secured on its butt end and interacting with the vertical slot, said roller cooperating with the shutter at the outlet of said vertical slot.