Radiological Risks of Neutron Interrogation of Food

In recent years there has been growing interest in the use of neutron scanning techniques for security. Neutron techniques with a range of energy spectra including thermal, white and fast neutrons have been shown to work in different scenarios. As international interest in neutron scanning increases the risk of activating cargo, especially foodstuffs must be considered. There has been a limited amount of research into the activation of foods by neutron beams and we have sought to improve the amount of information available. In this paper we show that for three important metrics; Activity, Ingestion Dose and Time to Background there is a strong dependence on the food being irradiated and a weak dependence on the energy of irradiation. Previous studies into activation used results based on irradiation of pharmaceuticals as the basis for research into activation of food. The earlier work reports that 24Na production is the dominant threat which motivated the search for 23(n;\gamma)24Na in highly salted foods. We show that 42K can be more significant than 24Na in low salt foods such as Bananas and Potatoes

ENDF/B-VII.0 Data Testing for Three Fast Critical Assemblies

In this report we consider three fast critical assemblies, each assembly is dominated by a different nuclear fuel: Godiva (U235), Jezebel (Pu239) and Jezebel23 (U233) [1]. We first show the improvement in results when using the new ENDF/B-VII.0 data [2], rather than the older, now frozen, ENDF/B-VI.8 data [3]. We do this using what we call a one code/ multiple library approach, where results from one code (MCNP) are compared using two different data libraries (ENDF/B-VII.0 and VI.8). Next we show that MCNP results are not specific to this one code by using what we call a one data library/multiple code approach; for this purpose we invited many codes to submit results using the ENDF/B-VII.0 data; the most detailed results presented in this report compare MCNP and TART. The bottom line is that we have shown that using the new ENDF/B-VII.0 data library with a variety of transport codes, for the first time we are able to reproduce the expected K-eff values for all three assemblies to within the quoted accuracy of the models, namely 1.0 +/- 0.001. This is a BIG improvement compared to the results obtained using the older ENDF/B-VI.8 data library. Another important result of this study is that we have demonstrated that currently there are many computer codes that can accurately use the new ENDF/B-VII.0 data

Investigating the Superconducting Properties and Surface Morphology of Sputtered Nb Films on Cu Due to Laser Treatment

Bulk niobium is currently the material of choice for superconducting radio frequency (SRF) cavities and is a well matured process. However, it is possible that SRF cavities could be further improved beyond bulk Nb by sputtering thin Nb films onto Cu cavities. Copper has a greater thermal conductivity than Nb and is also easier to machine, while sputtering films on the surface reduces the amount of Nb used to fabricate the whole cavity. However, sputtering Nb on Cu produces other issues, for example, the surface quality of the Cu affects the quality of the Nb deposited on the surface and therefore the superconducting parameters. As the Nb on the surface is not perfect, the magnetic field produced by the RF can enter the cavity earlier than expected, producing RF losses, which can in turn lead to a quench. One approach is to treat the Nb post deposition by irradiating the surface using a laser to polish the surface of the Nb and increase the surface magnetic field that the cavity can maintain while remaining in the Meissner state. A magnetic field penetration experiment designed and built at Daresbury Laboratory has been used to measure the field of full flux penetration to characterize the effect of the laser treatment on the superconducting properties of the Nb. Surface characterization and the response of the Nb in a dc magnetic field have also been performed to try and provide an explanation for the change in the superconducting properties. The results demonstrate that the laser treatment can lead to an increase in the magnetic field at which the flux penetrates from one side of the sample to the other, thus it could potentially improve the performance of Nb coated RF cavities

From cutting-edge pointwise cross-section to groupwise reaction rate: A primer

The nuclear research and development community has a history of using both integral and differential experiments to support accurate lattice-reactor, nuclear reactor criticality and shielding simulations, as well as verification and validation efforts of cross sections and emitted particle spectra. An important aspect to this type of analysis is the proper consideration of the contribution of the neutron spectrum in its entirety, with correct propagation of uncertainties and standard deviations derived from Monte Carlo simulations, to the local and total uncertainty in the simulated reactions rates (RRs), which usually only apply to one application at a time. This paper identifies deficiencies in the traditional treatment, and discusses correct handling of the RR uncertainty quantification and propagation, including details of the cross section components in the RR uncertainty estimates, which are verified for relevant applications. The methodology that rigorously captures the spectral shift and cross section contributions to the uncertainty in the RR are discussed with quantified examples that demonstrate the importance of the proper treatment of the spectrum profile and cross section contributions to the uncertainty in the RR and subsequent response functions. The recently developed inventory code FISPACT-II, when connected to the processed nuclear data libraries TENDL-2015, ENDF/B-VII.1, JENDL-4.0u or JEFF-3.2, forms an enhanced multi-physics platform providing a wide variety of advanced simulation methods for modelling activation, transmutation, burnup protocols and simulating radiation damage sources terms. The system has extended cutting-edge nuclear data forms, uncertainty quantification and propagation methods, which have been the subject of recent integral and differential, fission, fusion and accelerators validation efforts. The simulation system is used to accurately and predictively probe, understand and underpin a modern and sustainable understanding of the nuclear physics that is so important for many areas of science and technology; advanced fission and fuel systems, magnetic and inertial confinement fusion, high energy, accelerator physics, medical application, isotope production, earth exploration, astrophysics and homeland security

The joint evaluated fission and fusion nuclear data library, JEFF-3.3

The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides $^{235}$U, $^{238}$U and $^{239}$Pu, on $^{241}$Am and $^{23}$Na, $^{59}$Ni, Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy

Development of the self-modulation instability of a relativistic proton bunch in plasma

Self-modulation is a beam–plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment

Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients

We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)PRLTAO0031-900710.1103/PhysRevLett.125.264801]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement