Abstract: The invention provides a detector assembly for use in a nucleonic level gauge comprising: a) at least one radiation detector; b) electronic apparatus for controlling the at least one detector and processing the electronic signals produced by the at least one detector; and c) a photomultiplier; wherein all of said components (a)-(c) are capable of being enclosed in an elongate, radiation-permeable housing having a cross-sectional area which is substantially uniform along the length of the housing. A detector apparatus may contain a plurality of such detector assemblies contained within a single housing. The detector is preferably an elongate plastic scintillator.

Abstract: Systems and methods for making and using a multi-blade collimator device are described herein. The collimator device can include a base member, a rotational member, and multiple X-ray-attenuating blades that fit together to define an aperture. The blades are typically disposed between the base member and rotational member. Additionally, the blades can be mechanically connected to or interfaced with the base member and the rotational member so that when the rotational member is rotated with respect to the base member, the blades move and cause the aperture to change in size. The aperture can be any shape, including polygonal, square, or rectangular. While the aperture's size can be increased and decreased, the shape and orientation of the aperture can remain substantially constant. The collimator can contain a single layer of blades or multiple layers of blades. Other embodiments are described.