This paper introduces Gnowee, a modular, Python-based, open-source hybrid metaheuristic optimization algorithm (available from https://github.com/SlaybaughLab/Gnowee). Gnowee is designed for rapid convergence to nearly globally optimum solutions for complex, constrained nuclear engineering problems with mixed-integer (MI) and combinatorial design vectors and high-cost, noisy, discontinuous, black box objective function evaluations. Gnowee’s hybrid metaheuristic framework is a new combination of a set of diverse, robust heuristics that appropriately balance diversification and intensification strategies across a wide range of optimization problems. There are many potential applications for this novel algorithm both within the nuclear community and beyond. Given that a set of well-known and studied nuclear benchmarks does not exist for the purpose of testing optimization algorithms, comparisons between Gnowee and several well-established metaheuristic algorithms are made for a set of 18 established continuous, MI, and combinatorial benchmarks representing a wide range of types of engineering problems and solution space behaviors. These results demonstrate Gnoweee to have superior flexibility and convergence characteristics over this diverse set of design spaces. We anticipate this wide range of applicability will make this algorithm desirable for many complex engineering applications.

The  ¹⁶⁰Gd(p,n)¹⁶⁰Tb excitation function was measured between 4-18 MeV using stacked-target activation at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Nine copper and eight titanium foils served as proton fluence monitor foils, using the  ^natCu(p,x)⁶⁵Zn,  ^natTi(p,x)⁴⁸V, and  ^natTi(p,x)⁴⁶Sc monitor standards, respectively. Variance minimization using an MCNP v.6.2 model reduced the systematic uncertainties in proton energy and fluence. A priori predictions of the  ¹⁶⁰Gd(p,n) reaction using ALICE, CoH, EMPIRE, and TALYS, as well as the TENDL database, are compared to the experimentally measured values.

While the nonproliferation community has long acknowledged the possibility of nuclear terrorism, its prevention has become a central focus area in recent years. For decades it has been assumed that, with access to special nuclear material (SNM), the steps to indigenously develop an improvised nuclear device are within the reach of non-state actors. At the same time, indigenous production of SNM has generally been dismissed as infeasible. Recognizing how recent trends of technology democratization, the open exchange of information, and globalization have eroded certain barriers to proliferation by non-state actors, this research explores the pathways a non-state actor could take to indigenously develop SNM and develops a method to determine the comparative attractiveness of each pathway, given the current capabilities of non-state actors. Additionally, it considers avenues for further investigation to identify countermeasures for SNM production, including countermeasures specific to non-state actors.

An energy tuning assembly (ETA) was designed to be fielded at the National Ignition Facility (NIF) to modify the characteristic D-T fusion spectrum to include a prompt fission neutron spectral component. The ETA was characterized at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory to measure the shaped spectrum from an incident deuteron breakup neutron source, test the proposed neutron spectroscopy techniques used to inform the flux measurements at NIF, and validate the ability to predict ETA performance using a Monte Carlo Neutral Particle (MCNP) simulation. Activation foils (i.e., Ni, In, Au, Al) were exposed to a collimated 33-MeV deuteron-breakup beam originating from a tantalum breakup target. The source spectrum absent the ETA was characterized using a set of activation foils and the STAYSL unfolding code. Finally, the ETA-modified spectrum was obtained using activation foil unfolding with a [Formula presented]=1.32. The ETA-modified unfolded spectrum agreed with the MCNP-simulated prediction in the energy range of 0.1–14 MeV, but exhibited disagreements in the 10 eV–100 keV region. This work demonstrates shaping of the NIF neutron spectrum via the ETA to be a viable path forward for tailored neutron beams at NIF.

States facing the decision to develop a nuclear weapons program do so within a broader context of their relationships with other countries. How these diplomatic, economic, and strategic relationships impact proliferation decisions, however, remains under-specified. Adding to the existing empirical literature that attempts to model state proliferation decisions, this article introduces the first quantitative heterogeneous network analysis of how networks of conflict, alliances, trade, and nuclear cooperation interact to spur or deter nuclear proliferation. Using a multiplex network model, we conceptualize states as nodes linked by different modes of interaction represented on individual network layers. Node strength is used to quantify factors correlated with nuclear proliferation and these are combined in a weighted sum across layers to provide a metric characterizing the proliferation behavior of the state. This multiplex network modeling approach provides a means for identifying states with the highest relative likelihood of proliferation—based only on their relationships to other states. This work demonstrates that latent conflict and nuclear cooperation are positively correlated with proliferation, while an increased trade dependence suggests a decreased proliferation likelihood. A case study on Iran’s controversial nuclear program and past nuclear activity is also provided. These findings have clear, policy-relevant conclusions related to alliance posture, sanctions policy, and nuclear assistance.