1. Experimental Data Sets

Solutions were prepared from CRM standards and further diluted with nitric acid and distilled water. Samples were placed in polyethylene vials before transport to an inner SLOWPOKE-2 irradiation site where they were exposed to a predominately thermal neutron flux for 60 s. After irradiation the samples were sent to an array of 3He detectors which recorded the DN emissions as a function of count time up to 3 minutes. Further details regarding the delayed neutron counting system and these measurements can be found in references 1 and 2 respectively. Experimental data has been corrected for dead time effects and neutron background contributions [3]. Measurements have been normalized by fissile mass [g] and detection efficiency (33 %) to obtain DN emission rate, Q(t) [s-1g-1]. Each isotope (233U, 235U and 239Pu) was irradiated and counted in triplicate, the provided measurements represent their average Q(t). 2. MCNP Simulations Atomic Energy of Canada Limited has provided a MCNP input deck containing LEU SLOWPOKE-2 dimension and material specifications, the contents of which are detailed in Ref. 4. This input deck was modified to include a polyethylene vial within an inner irradiation site to determine a higher fidelity neutron flux spectrum. This flux was recreated within the vial solution of a second input deck, which includes the irradiation of a fissile solution for 60 s and the recording of subsequent DN emissions from the vial. The DN emission Rate, Q(t) [s-1g-1] was compared to the normalized measurements described in the previous section. The final deck simulated energy deposition within the 3He detectors, Figure 4. MCNP6v1 was used in the following simulations (load date: 05/08/13)