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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 15.1–16.8 MeV incident on radium. An upper limit for the 226Ac cross section is also reported. • Optimal cyclotron-based production of the medical isotope 225Ac requires knowledge of the 226Ra(p,xn) reactions. • We report thin-target cross-sections for production of 224Ac and 225Ac by protons of 15.1–16.8 MeV on radium. • An upper limit for the 226Ac cross section is also reported. • Production of 225Ac is observed to peak for a higher proton energy than predicted by commonly used simulation codes. [ABSTRACT FROM AUTHOR]

Highlights • Simulated photoneutron data for the thermal fission of U-233, -235, and Pu-239. • Large discrepancies comparing simulated yields to the recommended yields for U-235. • We show that the recommended yields are inconsistent with the recent nuclear data. • First time photoneutron group sets have been derived for isotopes U-233 and Pu-239. Abstract In this work we apply the G eant4 toolkit and recent fission yield data to calculate the photoneutron yield from the thermal fission of 233 , 235 U and 239 Pu within a quasi-infinite bath of D 2 O. 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 235 U 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. [ABSTRACT FROM AUTHOR]

This paper describes a method for more complete neutron detector characterization using Geant4’s Monte Carlo methods for characterizing overall detector response rate and Garfield interfaced with SRIM for the simulation of the detector’s raw pulses, as applied to a hybrid 10 B/ 3 He detector. The Geant4 models characterizing the detector’s interaction with a 252 Cf point source and parallel beams of mono-energetic neutrons (assuming ISO 8529 reference energy values) compare and agree well with calibrated 252 Cf measurements to within 6.4%. Validated Geant4 model outputs serve as input to Garfield+SRIM calculations to provide meaningful pulse height spectra. Modifications to Garfield for this work were necessary to account for simultaneous tracking of electrons resulting from proton and triton reaction products from a single 3 He neutron capture event, and it was further necessary to interface Garfield with the energy loss, range, and straggling calculations provided by SRIM. Individual raw pulses generated by Garfield+SRIM are also observed to agree well with experimentally measured raw pulses from the detector. [ABSTRACT FROM AUTHOR]

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 D 2 O, 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. [ABSTRACT FROM AUTHOR]

An attenuation-based muon computed tomography algorithm has been developed to enable imaging of large infrastructure using measurements from a single muon tracking module. The performance of the algorithm depends on the choice of reconstruction technique that is incorporated, and is evaluated for seven different reconstruction techniques from the computed tomography literature. The L1-Norm reconstruction technique proposed by Kudo et al. is found to provide the best overall performance. The least-squares conjugate gradient (LSCG) technique and the Simultaneous Iterative Reconstruction Technique (SIRT) are also capable of identifying special nuclear materials, but typically display higher levels of reconstruction artifacts in comparison with L1-Norm. A muon-tomography reconstruction of a simplified simulated reactor core using the L1-Norm algorithm is able to accurately reproduce the geometry, including the identification of missing fuel channels. [ABSTRACT FROM AUTHOR]

The Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new experimental facility for radioactive decay studies at the TRIUMF-ISAC laboratory. The performance of the 16 high-purity germanium (HPGe) clover detectors that will make up the GRIFFIN spectrometer is reported. The energy resolution, efficiency, timing resolution, crosstalk and preamplifier properties of each crystal were measured using a combination of analog and digital data acquisition techniques. The absolute efficiency and add-back factors are determined for the energy range of 80–3450 keV. The detectors show excellent performance with an average over all 64 crystals of a FWHM energy resolution of 1.89(6) keV and relative efficiency with respect to a 3 in . × 3 in . NaI detector of 41(1)% at 1.3 MeV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The SPICE spectrometer is a new in-beam electron spectrometer designed to operate in conjunction with the TIGRESS HPGe Clover array at TRIUMF-ISAC. The spectrometer consists of a large area, annular, segmented lithium-drifted silicon electron detector shielded from the target by a photon shield. A permanent magnetic lens directs electrons around the photon shield to the detector. Experiments will be performed utilising Coulomb excitation, inelastic-scattering, transfer and fusion–evaporation reactions using stable and radioactive ion beams with suitable heavy-ion detection. Good detection efficiency can be achieved in a large energy range up to 3500keV electron energy using several magnetic lens designs which are quickly interchangeable. COMSOL and Geant4 simulations have been used to maximise the detection efficiency. In addition, the simulations have guided the design of components to minimise the contributions from various sources of backgrounds. [Copyright &y& Elsevier]