Design and Fabrication of the Uranium Drum Standards

The segmented gamma scanner has become an important instrument for assaying the special nuclear material content of low-density scrap and waste in 55-gal. drums. To perform these assays accurately, we need appropriate standards to calibrate the response of the system including the detector efficiency, the absorber in front of the detector, and the collimator geometry. A set of three uranium drum standards has been fabricated at Los Alamos. This paper discusses a Monte Carlo calculation to optimize the design of the drum standards. The drum standards are prepared using 20 modular 4-f bottles in each drum. This paper also describes the fabrication procedure, which includes weighing the uranium oxide and the chemical analyzing of the uranium concentration. Also presented is the vertical scanning data of the 4-t bottles to assure uniform mixing of the uranium and the diluent. Finally, the nondestructive measurements for checking consistency among the three drum standards are discussed.