E.T. Rand’s research while affiliated with Canadian Nuclear Laboratories and other places

Cross sections for production of the medical isotope 225Ac by the 226Ra(p,2n) reaction have not previously been measured in fine steps over the relevant energy region, and no measurements are presently available in the literature for the actinium contaminant isotopes created by the adjacent 226Ra(p,n)226Ac and 226Ra(p,3n)224Ac reactions. We report thin-target cross-section measurements for production of 224Ac and 225Ac by protons of 15.1 to 16.8 MeV incident on radium. An upper limit for the 226Ac cross section is also reported.

The specific activity of the $\beta$ β decay of $^{39}$ 39 Ar in atmospheric argon is measured using the DEAP-3600 detector. DEAP-3600, located 2 km underground at SNOLAB, uses a total of (3269 ± 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector is well-suited to measure the decay of $^{39}$ 39 Ar owing to its very low background levels. This is achieved in two ways: it uses low background construction materials; and it uses pulse-shape discrimination to differentiate between nuclear recoils and electron recoils. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is (0.964 ± 0.001 $_\textrm{stat}$ stat ± 0.024 $_\textrm{sys}$ sys ) Bq/kg $_\textrm{atmAr}$ atmAr , which is consistent with results from other experiments. A cross-check analysis using different event selection criteria and a different statistical method confirms the result.

The specific activity of the beta decay of $^{39}$Ar in atmospheric argon is measured using the DEAP-3600 detector. DEAP-3600, located 2 km underground at SNOLAB, uses a total of (3269 $\pm$ 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector with very low background uses pulseshape discrimination to differentiate between nuclear recoils and electron recoils and is well-suited to measure the decay of $^{39}$Ar. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is [0.964 $\pm$ 0.001 (stat) $\pm$ 0.024 (sys)] Bq/kg$_{\rm atmAr}$ which is consistent with results from other experiments. A cross-check analysis using different event selection criteria provides a consistent result.

In this work, an experimental assessment is made of the performance of an integrated system for the detection of shielded nuclear material that features muon tomography and polyvinyl toluene bi-panel detector systems. Experimental setups consisting of a barrel of sand containing a lead flask and/or depleted uranium were defined, and were measured in turn by each detection system. For each system detection parameters for the presence of depleted uranium were put forward that can be used to integrate the two detection systems in a quantitative manner. In the integrated system, the detectability of differences between setups using a given detection parameter is quantitatively assessed through the use of relative operating characteristic (ROC) curves. Furthermore, in an effort to enhance detection sensitivity, pairs of parameters were combined, through sorting on either maximum or average values, to produce “data fusion” ROC curves. The efficacy of this approach and the complementarity of the detection techniques employed are discussed.

DOI:https://doi.org/10.1103/PhysRevD.105.029901

We present an algorithm that utilizes data generated by cosmic-ray muon-scattering tomography for passive nondestructive detection of dense objects. Our clustering-based approach uses a nonparametric statistical test based on a reference case to determine the presence of high-density high-Z material, such as illicit nuclear material hidden inside a shipping canister. The algorithm outputs a single decision value for the absence or presence of illicit material without the need to perform a detailed visual tomographic reconstruction and/or the need to rely on human interpretation, in contrast to many other muon-based imaging techniques. The performance of the algorithm is demonstrated using experimental data obtained with the Cosmic-Ray Inspection and Passive Tomography detector from two setups consisting of a lead flask, a 55-gallon drum filled with sand, and 2 kg of metallic depleted uranium (DU). The results of these experiments illustrate that the high-density lead flask can be automatically distinguished from the background, with an area under the receiver-operating-characteristic curve (AUC) of 0.90 using less than 90 s of data; the lead flask with 2 kg of DU inside can be detected within the 55-gallon drum containing sand in under 5 min with an AUC of 0.91. Our experimental results illustrate the efficacy of this algorithm for the identification of dense objects using reference background measurements. Practical applications of this algorithm are discussed.

Experimental demonstrations are reported of the complementarity of passive gamma-ray spectroscopy, passive neutron counting, and passive muon scattering tomography, in the simultaneous detection of shielded nuclear material. The demonstrations were applied to a number of experimental configurations that emulate various scenarios that may be encountered in the context of nuclear safeguards, or the security of nuclear facilities. In each case, the experimental analysts were blind to the contents of each configuration as they attempted to deduce the presence or absence of nuclear materials using data collected simultaneously from the three detection techniques. Analysis of data collection times was at first restricted to 10 minutes, and then to 2 hours, both with nuclear material (if present), and without nuclear material (as background from the shielded arrangement). The results of these experiments show how these techniques complement each other in the detection of shielded nuclear material.

In this work we apply the Geant4 toolkit and recent fission yield data to calculate the photoneutron yield from the thermal fission of 233,235U and 239Pu within a quasi-infinite bath of D2O. The simulation results were fit to a series of exponential terms enabling a direct comparison to historical “11 group” photoneutron data and the application for use in kinetics analyses. Large discrepancies were observed comparing the simulation results to the recommended 235U photoneutron yields (Laughton, 1998) within the shortest (<100 s) and longest (>10⁵ s) half-life groups. These results raise concerns on the validity of the yields derived from experimental data. A detailed discussion on the origin of the historical data is presented as well as explanations for the observed disagreement.

Neutronic transient measurements of substitution cores composed of low enriched uranium oxide driver fuel and uranium-plutonium (as simulated mid-burnup natural uranium), plutonium-thorium, or uranium-233-thorium mixed oxide fuels in a heavy water moderated lattice are presented. The measurements recorded flux at several detector locations outside the core while reactivity insertions of varying scale were conducted. The results provide valuable data to explore point and 3D reactor models. Inverse point-kinetics analyses of the recorded flux indicate that delayed parameters tabulated by only the fission-rate per nuclide provide similar results to adjoint-weighted kinetics parameters calculated by MCNP6 via the iterated fission probability method, on the timescale of delayed neutrons. However, the inadequacy of the conventional delayed photoneutron parameters, which are based on measurements of uranium-235 in D2O, is clearly shown in the computed reactivity. The importance of delayed photoneutrons in heavy water reactor kinetics necessitates an improved understanding of the delayed photoneutron group structure by nuclide and appropriate adjoint-weighting for photoneutrons.