Abstract: An arrangement for the measurement of the height of a layer of a first liquid floating on a second liquid which comprises projection means for projecting a beam of optical radiation along an inspection path which is horizontal when the arrangement is in use, detector means for detecting radiation of the said beam after transmission along the inspection path, means for providing relative displacement in a direction which is vertical when the arrangement is in use between the said layer and the said inspection path whereby the said layer traverses the inspection path, the detector means being capable of observing the upper and lower surfaces of the said layer by detecting changes in an optical transmission property of the said beam occurring at the said surfaces and means for measuring the said relative displacement between the locations of the observed upper and lower surfaces.

Abstract: A gamma radiation camera system that utilizes a gamma blocking object which is removably located in the field of view of a gamma detector and blocks at least a portion of gamma radiation, emitted from a scene, from the detector and thereby forming a two-dimensional image of the scene. Further, individual components received by the detector from the scene provide an output signal to respective processing circuitry. The difference is then determined between components of a first output signal obtained when the object is present in the field of view of the detector and components of a second output signal obtained when the object is not present in the field of view.