Los Alamos second-generation system for passive and active neutron assays of drum-size containers

Improved analysis for matrix effect correction in LLW neutronic assay

“…Fission and fast interrogating neutrons crossing the Cd-B 4 C low-energy neutron shield are slowed down in the polyethylene and detected by the 3 He counters. Fission neutrons are discriminated from interrogating neutrons by a time analysis [1,2]. Graphite is used to maximise the die away time of the interrogating thermal neutron flux inside the cell.…”

“…The signal is fitted with exponential functions which are representative of the neutron transport properties of the materials inside the measurement device and the waste matrix components. The fit may need a different number of exponential functions depending on the matrix composition to be correctly performed, making the die-away analysis very difficult to use practically [2]. Therefore, the two improvements presented in the next sections have been explored to overcome this issue.…”

“…The DDA technique firstly described by Caldwell [1,2] is widely used to achieve low detection limits in waste drums. Nevertheless, one of the main limitations of the method comes from the large impact of the waste matrix on the interrogating and fissile neutron interactions and of the knowledge of the matrix composition, which is generally limited.…”

Neutron kinetics in moderators and SNM detection through epithermal-neutron-induced fissions

“…The most sensitive detection method of nuclear materials is arguably the Differential Die Away (DDA) technique [1][2][3]. DDA has the highest usable signal strength per interrogating neutron.…”

“…The DDA technique was initially developed and is still being used for the detection of small amounts of fissile material in scrap and waste generated in the nuclear fuel cycle [2,[14][15][16][17]. To achieve the sensitivities required for this application, the neutron source (typically a 14 MeV (d,T) neutron generator) and the interrogated object are positioned in close proximity inside a cavity.…”