arXiv subjects

A. C. Hayes

Publications and source records attributed to A. C. Hayes.

At least 19 recordsLinked to original sources

arXiv2025

Novel Application of Neutrinos to Evaluate U.S. Nuclear Weapons Performance

There is a growing realization that neutrinos can be used as a diagnostic tool to better understand the inner workings of a nuclear weapon. Robust estimates demonstrate that an Inverse Beta Decay (IBD) neutrino scintillation detector built at the Nevada Test Site of 1000-ton active target mass at a standoff distance of 500 m would detect thousands of neutrino events per kTe of nuclear yield. This would provide less than 4% statistical error on measured neutrino rate and 5% error on neutrino energy. Extrapolating this to an error on the test device explosive yield requires knowledge from evaluated nuclear databases, non-equilibrium fission rates, and assumptions on internal neutron fluxes. Initial calculations demonstrate that prompt neutrino rates from a short pulse of Pu-239 fission is about a factor of two less than that from a steady state assumption. As well, there are significant energy spectral differences as a function of time after the pulse that needs to be considered. In the absence of nuclear weapons testing, many of the technical and theoretical challenges of a full nuclear test could be mitigated with a low cost smaller scale 20 ton fiducial mass IBD demonstration detector placed near a TRIGA pulsed reactor. The short duty cycle and repeatability of pulses would provide critical real environment testing and the measured neutrino rate as a function of time data would provide unique constraints on fission databases and equilibrium assumptions.

physics.ins-det↗

arXiv2023

Applications of Fission

This chapter is devoted to a discussion of applications of nuclear fission. It covers some aspects of the topics of nuclear reactors, nuclear safeguards and non-proliferation, reactor anti-neutrinos and nuclear medicine. It is, however, limited in scope and the reader is encouraged to explore the many other exciting sub-areas of the applications of nuclear fission.

physics.soc-ph↗

arXiv2023

First bromine doped cryogenic implosion at the National Ignition Facility

We report on the first experiment dedicated to the study of nuclear reactions on dopants in a cryogenic capsule at the National Ignition Facility (NIF). This was accomplished using bromine doping in the inner layers of the CH ablator of a capsule identical to that used in the NIF shot N140520. The capsule was doped with 3$\times$10$^{16}$ bromine atoms. The doped capsule shot, N170730, resulted in a DT yield that was 2.6 times lower than the undoped equivalent. The Radiochemical Analysis of Gaseous Samples (RAGS) system was used to collect and detect $^{79}$Kr atoms resulting from energetic deuteron and proton ion reactions on $^{79}$Br. RAGS was also used to detect $^{13}$N produced dominantly by knock-on deuteron reactions on the $^{12}$C in the ablator. High-energy reaction-in-flight neutrons were detected via the $^{209}$Bi(n,4n)$^{206}$Bi reaction, using bismuth activation foils located 50 cm outside of the target capsule. The robustness of the RAGS signals suggest that the use of nuclear reactions on dopants as diagnostics is quite feasible.

physics.plasm-ph↗

arXiv2022

Neutral-current neutrino cross section and expected supernova signals for $^{40}$Ar from a three-fold increase in the magnetic dipole strength

In view of the great interest in liquid argon neutrino detectors, the $^{40}$Ar($γ,γ'$)$^{40}$Ar$^{*}$ reaction was revisited to guide a calculation of the neutral current neutrino cross section at supernova energies. Using the nuclear resonance fluorescence technique with a monoenergetic, 99% linearly polarized photon beam, we report a three-fold increase in magnetic dipole strength at around 10 MeV in $^{40}$Ar. Based on shell-model calculations, and using the experimentally identified transitions, the neutral current neutrino cross sections for low-energy reactions on $^{40}$Ar are calculated.

nucl-ex↗

arXiv2022

First measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in an inertial confinement fusion implosion at the National Ignition Facility: Initial steps toward the development of a radiochemistry mix diagnostic

We report the first measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in a polar-direct-drive exploding pusher (PDXP) at the National Ignition Facility (NIF). This work is motivated by the need to develop alternative mix diagnostics, radiochemistry being the focus here. The target is composed of a $65/35\,\rm at.\,\%$ deuterium-tritium (DT) fill surrounded by a roughly $30\,μ\rm m$ thick beryllium ablator. The inner portion of the beryllium ablator is doped with $10\,\rm at.\,\%$ of $^{10}{\rm B}$. Radiation-hydrodynamics calculations were performed in 1D to optimize both the remaining boron rho-R and the DT neutron yield. A charged-particle transport post-processor has been developed to study $α$-induced reactions on the ablator material. Results indicate a large $^{13}{\rm N}$ production from $α$-induced reactions on $^{10}{\rm B}$, measurable by the radiochemical analysis of gaseous samples system at the NIF. The PDXP target N201115-001 was successfully fielded on the NIF, and nitrogen from the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction was measured. The $^{13}{\rm N}$ production yield, as well as the DT neutron yield, was, however, lower than expected. Some of the reduced yields can be explained by the oblate shape, but the ratios of the various radiochemical signals are not commensurate with expectations based on a simple reduction of the 1D results. Preliminary 2D radiation-hydrodynamics computations are consistent with the experimental measurements, and work is ongoing to extend the radiochemistry analysis into higher dimensions.

physics.plasm-ph↗

arXiv2019

Comparison between Variational Monte Carlo and Shell Model Calculations of Neutrinoless Double Beta Decay Matrix Elements in Light Nuclei

Benchmark comparisons between many-body methods are performed to assess the ingredients necessary for an accurate calculation of neutrinoless double beta decay matrix elements. Shell model and variational Monte Carlo (VMC) calculations are carried out for $A=10$ and $12$ nuclei. Different variational wavefunctions are used to evaluate the uncertainties in the {\it ab initio} calculations, finding fairly small differences between the VMC double beta decay matrix elements. For shell model calculations, the role of model space truncation, radial wavefunction choices, and short-range correlation are investigated and all found to be important. Based on the detailed comparisons between the VMC and shell model approaches, we conclude that accurate descriptions of neutrinoless double beta decay matrix elements require a proper treatment of both long-range and short-range correlations.

nucl-th↗

arXiv2019

Reactor Neutrino Spectral Distortions Play Little Role in Mass Hierarchy Experiments

The Coulomb enhancement of low energy electrons in nuclear beta decay generates sharp cutoffs in the accompanying antineutrino spectrum at the beta decay endpoint energies. It has been conjectured that these features will interfere with measuring the effect of a neutrino mass hierarchy on an oscillated nuclear reactor antineutrino spectrum. These sawtooth-like features will appear in detailed reactor antineutrino spectra, with characteristic energy scales similar to the oscillation period critical to neutrino mass hierarchy determination near a 53 km baseline. However, these sawtooth-like distortions are found to contribute at a magnitude of only a few percent relative to the mass hierarchy-dependent oscillation pattern in Fourier space. In the Fourier cosine and sine transforms, the features that encode a neutrino mass hierarchy dominate by over sixteen (thirty-three) times in prominence to the maximal contribution of the sawtooth-like distortions from the detailed energy spectrum, given $3.2\%/\sqrt{E_\mathrm{vis.}/\mathrm{MeV}}$ (perfect) detector energy resolution. The effect of these distortions is shown to be negligible even when the uncertainties in the reactor spectrum, oscillation parameters, and counting statistics are considered. This result is shown to hold even when the opposite hierarchy oscillation patterns are nearly degenerate in energy space, if energy response nonlinearities are controlled to below 0.5\%. Therefore with accurate knowledge of detector energy response, the sawtooth-like features in reactor antineutrino spectra will not significantly impede neutrino mass hierarchy measurements using reactor antineutrinos.

hep-ph↗

arXiv2018

Effect of Siegert's Theorem on Low-Energy Neutrino-Nucleus Interactions

We examine the importance of conserving the vector current in calculating low-energy neutrino-nucleus interactions by implicitly invoking Siegert's Theorem in describing the vector transverse electric current. We find that at low neutrino energies (E? <50 MeV), Siegert's Theorem can change neutrino cross sections for normal-parity non-spin-flip excitations by about a factor of two.The same is true of muon capture rates. At higher neutrino energies the effect of Siegert's Theorem diminishes, and by about 100 MeV the effect is very small.

nucl-th↗

arXiv2017

Weak Magnetism Correction to Allowed Beta-decay for Reactor Antineutrino Spectra

The weak magnetism correction and its uncertainty to nuclear beta-decay play a major role in determining the significance of the reactor neutrino anomaly. Here we examine the common approximation used for one-body weak magnetism in the calculation of fission antineutrino spectra, wherein matrix elements of the orbital angular momentum operator contribution to the magnetic dipole current are assumed to be proportional to those of the spin operator. Although we find this approximation invalid for a large set of nuclear structure situations, we conclude that it is valid for the relevant allowed beta-decays between fission fragments. In particular, the uncertainty in the fission antineutrino due to the uncertainty in the one-body weak magnetism correction is found to be less than 1%. Thus, the dominant uncertainty from weak magnetism for reactor neutrino fluxes lies in the uncertainty in the two-body meson-exchange magnetic dipole current.

nucl-th↗

arXiv2016

Nuclear Zemach Moments and Finite-Size Corrections to Allowed Beta Decay

The finite-size correction to $β$-decay plays an important role in determining the expected antineutrino spectra from reactors at a level that is important for the reactor-neutrino anomaly. Here we express the leading-order finite-size correction to allowed $β$-decay in terms of Zemach moments. We calculate the Zemach moments within a Hartree-Fock model using a Skyrme-like energy density functional. We find that the Zemach moments are increased relative to predictions based on the simple assumption of identical uniform nuclear-charge and weak-transition densities. However, for allowed ground-state to ground-state transitions in medium and heavy nuclei, the detailed nuclear structure calculations do not change the finite-size corrections significantly from the simple model predictions, and are only 10-15% larger than the latter even though the densities differ significantly.

nucl-th↗

arXiv2016

Reactor Neutrino Spectra

We present a review of the antineutrino spectra emitted from reactors. Knowledge of these and their associated uncertainties are crucial for neutrino oscillation studies. The spectra used to-date have been determined by either conversion of measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that makeup the spectra using modern databases as input. The uncertainties in the subdominant corrections to beta-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.

hep-ph↗

arXiv2015

The Possible Origin and Implications of the Shoulder in Reactor Neutrino Spectra

We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from $^{238}$U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a problem with the measured aggregate beta spectra, or the harder neutron spectrum at a light-water power reactor could affect the distribution of beta-decaying isotopes. In addition to the fissile actinides, we find that $^{238}$U could also play a significant role in distorting the total antineutrino spectrum. Distinguishing these and quantifying whether there is an anomaly associated with measured reactor neutrino signals will require new short-baseline experiments, both at thermal reactors and at reactors with a sizable epithermal neutron component.

nucl-th↗

arXiv2015

Electron-scattering form factors for 6Li in the ab initio symmetry-guided framework

We present an ab initio symmetry-adapted no-core shell-model description for $^{6}$Li. We study the structure of the ground state of $^{6}$Li and the impact of the symmetry-guided space selection on the charge density components for this state in momentum space, including the effect of higher shells. We accomplish this by investigating the electron scattering charge form factor for momentum transfers up to $q \sim 4$ fm$^{-1}$. We demonstrate that this symmetry-adapted framework can achieve significantly reduced dimensions for equivalent large shell-model spaces while retaining the accuracy of the form factor for any momentum transfer. These new results confirm the previous outcomes for selected spectroscopy observables in light nuclei, such as binding energies, excitation energies, electromagnetic moments, E2 and M1 reduced transition probabilities, as well as point-nucleon matter rms radii.

nucl-th↗

arXiv2014

Reaction-in-Flight Neutrons as a Test of Stopping Power in Degenerate Plasmas

We present the first measurements of reaction-in-flight (RIF) neutrons in an inertial confinement fusion system. The experiments were carried out at the National Ignition Facility, using both Low Foot and High Foot drives and cryogenic plastic capsules. In both cases, the high-energy RIF ($E_n>$ 15 MeV) component of the neutron spectrum was found to be about $10^{-4}$ of the total. The majority of the RIF neutrons were produced in the dense cold fuel surrounding the burning hotspot of the capsule and the data are consistent with a compressed cold fuel that is moderately to strongly coupled $(Γ\sim$0.6) and electron degenerate $(θ_\mathrm{Fermi}/θ_e\sim$4). The production of RIF neutrons is controlled by the stopping power in the plasma. Thus, the current RIF measurements provide a unique test of stopping power models in an experimentally unexplored plasma regime. We find that the measured RIF data strongly constrain stopping models in warm dense plasma conditions and some models are ruled out by our analysis of these experiments.

physics.plasm-ph↗

arXiv2014

Systematic Uncertainties in the Analysis of the Reactor Neutrino Anomaly

We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about 94% of the emitted antineutrino flux was detected in short baseline experiments. We find that the form of the corrections that lead to the anomaly are very uncertain for the 30% of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is as large as the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately 4%.

nucl-th↗

arXiv2012

Determining Reactor Flux from Xenon-136 and Cesium-135 in Spent Fuel

The ability to infer the reactor flux from spent fuel or seized fissile material would enhance the tools of nuclear forensics and nuclear nonproliferation significantly. We show that reactor flux can be inferred from the ratios of xenon-136 to xenon-134 and cesium-135 to cesium-137. If the average flux of a reactor is known, the flux inferred from measurements of spent fuel could help determine whether that spent fuel was loaded as a blanket or close to the mid-plane of the reactor. The cesium ratio also provides information on reactor shutdowns during the irradiation of fuel, which could prove valuable for identifying the reactor in question through comparisons with satellite reactor heat monitoring data. We derive analytic expressions for these correlations and compare them to experimental data and to detailed reactor burn simulations. The enrichment of the original uranium fuel affects the correlations by up to 3 percent, but only at high flux.

nucl-th↗

arXiv2011

Theory of Antineutrino Monitoring of Burning MOX Plutonium Fuels

This letter presents the physics and feasibility of reactor antineutrino monitoring to verify the burnup of plutonium loaded in the reactor as a Mixed Oxide (MOX) fuel. It examines the magnitude and temporal variation in the antineutrino signals expected for different MOX fuels, for the purposes of nuclear accountability and safeguards. The antineutrino signals from reactor-grade and weapons-grade MOX are shown to be distinct from those from burning low enriched uranium. Thus, antineutrino monitoring could be used to verify the destruction of plutonium in reactors, though verifying the grade of the plutonium being burned is found to be more challenging.

nucl-th↗

arXiv2009

Structure of the Particle-Hole Amplitudes in No-core Shell Model Wave Functions

We study the structure of the no-core shell model wave functions for $^6$Li and $^{12}$C by investigating the ground state and first excited state electron scattering charge form factors. In both nuclei, large particle-hole ($ph$) amplitudes in the wave functions appear with the opposite sign to that needed to reproduce the shape of the $(e,e')$ form factors, the charge radii, and the B(E2) values for the lowest two states. The difference in sign appears to arise mainly from the monopole $Δ\hbarω=2$ matrix elements of the kinetic and potential energy (T+V) that transform under the harmonic oscillator SU(3) symmetries as $(λ,μ)=(2,0)$. These are difficult to determine self-consistently, but they have a strong effect on the structure of the low-lying states and on the giant monopole and quadrupole resonances. The Lee-Suzuki transformation, used to account for the restricted nature of the space in terms of an effective interaction, introduces large higher-order $Δ\hbarω=n, n>$2, $ph$ amplitudes in the wave functions. The latter $ph$ excitations aggravate the disagreement between the experimental and predicted $(e,e')$ form factors with increasing model spaces, especially at high momentum transfers. For sufficiently large model spaces the situation begins to resolve itself for $^6$Li, but the convergence is slow. A prescription to constrain the $ph$ excitations would likely accelerate convergence of the calculations.

nucl-th↗