High-accuracy Geant4 simulation and semi-analytical modeling of nuclear resonance fluorescence

Nuclear resonance fluorescence (NRF) is a photonuclear interaction that enables highly isotope-specific measurements in both pure and applied physics scenarios. High-accuracy design and analysis of NRF measurements in complex geometries is aided by Monte Carlo simulations of photon physics and transport, motivating Jordan and Warren (2007) to develop the G4NRF codebase for NRF simulation in Geant4. In this work, we enhance the physics accuracy of the G4NRF code and perform improved benchmarking simulations. The NRF cross section calculation in G4NRF, previously a Gaussian approximation, has been replaced with a full numerical integration for improved accuracy in thick-target scenarios. A high-accuracy semi-analytical model of expected NRF count rates in a typical NRF measurement is then constructed and compared against G4NRF simulations for both simple homogeneous and more complex heterogeneous geometries. Agreement between rates predicted by the semi-analytical model and G4NRF simulation is found at a level of ${\sim}1\%$ in simple test cases and ${\sim}3\%$ in more realistic scenarios, improving upon the ${\sim}20\%$ level of the initial benchmarking study and establishing a highly-accurate NRF framework for Geant4.Comment: 16 pages, 6 figures, revised for peer revie

Experimental demonstration of an isotope-sensitive warhead verification technique using nuclear resonance fluorescence

Future nuclear arms reduction efforts will require technologies to verify that warheads slated for dismantlement are authentic without revealing any sensitive weapons design information to international inspectors. Despite several decades of research, no technology has met these requirements simultaneously. Recent work by Kemp et al. [Kemp RS, Danagoulian A, Macdonald RR, Vavrek JR (2016) Proc Natl Acad Sci USA 113:8618--8623] has produced a novel physical cryptographic verification protocol that approaches this treaty verification problem by exploiting the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to verify the authenticity of a warhead. To protect sensitive information, the NRF signal from the warhead is convolved with that of an encryption foil that contains key warhead isotopes in amounts unknown to the inspector. The convolved spectrum from a candidate warhead is statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. Here we report on recent proof-of-concept warhead verification experiments conducted at the Massachusetts Institute of Technology. Using high-purity germanium (HPGe) detectors, we measured NRF spectra from the interrogation of proxy 'genuine' and 'hoax' objects by a 2.52 MeV endpoint bremsstrahlung beam. The observed differences in NRF intensities near 2.2 MeV indicate that the physical cryptographic protocol can distinguish between proxy genuine and hoax objects with high confidence in realistic measurement times.Comment: 38 pages, 19 figures; revised for peer review and copy editing; addition to SI for realistic scenario projections; minor length reduction for journal requirement

Observation of coherent π0\pi^0 electroproduction on deuterons at large momentum transfer

The first experimental results for coherent $\pi^0$-electroproduction on the deuteron, $e+d\to e+d +\pi^0$, at large momentum transfer, are reported. The experiment was performed at Jefferson Laboratory at an incident electron energy of 4.05 GeV. A large pion production yield has been observed in a kinematical region for 1.1$<Q^2<$1.8 GeV$^2$, from threshold to 200 MeV excitation energy in the $d\pi^0$ system. The $Q^2$-dependence is compared with theoretical predictions.Comment: 26 page

Validation of Geant4's G4NRF module against nuclear resonance fluorescence data from 238^{238}U and 27^{27}Al

G4NRF is a simulation module for modeling nuclear resonance fluorescence (NRF) interactions in the Geant4 framework. In this work, we validate G4NRF against both absolute and relative measurements of three NRF interactions near 2.2 MeV in $^{238}$U and $^{27}$Al using the transmission NRF data from the experiments described in arXiv:1712.02904. Agreement between the absolute NRF count rates observed in the data and predicted by extensive Geant4+G4NRF modeling validate the combined Geant4+G4NRF to within $15$--$20\%$ in the $^{238}$U NRF transitions and $8\%$ in $^{27}$Al, for an average $13\%$ discrepancy across the entire study. The difference between simulation and experiment in relative NRF rates, as expressed as ratios of count rates in various NRF lines, is found at the level of ${\lesssim}4\%$, and is statistically identical to zero. Inverting the analysis, approximate values of the absolute level widths and branching ratios for $^{238}$U and $^{27}$Al are also obtained.Comment: 12 pages, 4 figures, 4 tables; revisions after peer review comments, chiefly making the paper more concise and the reporting of results more clea

Neutron Beam Effects on Spin Exchange Polarized He-3

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable He-3 polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as the square root of the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the recombination-limited ion concentration, but is much larger than expected from earlier work.Comment: submitted to Physical Review Letter

Design and rationale of a randomized trial: Using short stay units instead of routine admission to improve patient centered health outcomes for acute heart failure patients (SSU-AHF)

Nearly 85% of acute heart failure (AHF) patients who present to the emergency department (ED) with acute heart failure are hospitalized. Once hospitalized, within 30 days post-discharge, 27% of patients are re-hospitalized or die. Attempts to improve outcomes with novel therapies have all failed. The evidence for existing AHF therapies are poor: No currently used AHF treatment is known to improve long-term outcomes. ED treatment is largely the same today as 40 years ago. Admitting patients who could have avoided hospitalization may contribute to adverse outcomes. Hospitalization is not benign; patients enter a vulnerable phase post-discharge, at increased risk for morbidity and mortality. When hospitalization is able to be shortened or avoid completely, certain risks can be mitigated, including risk of medication errors, in-hospital falls, delirium, nosocomial infections, and other iatrogenic complications. Additionally, patients would prefer to be home, not hospitalized. Furthermore, hospitalization and re-hospitalization for AHF predominantly affects patients of lower socioeconomic status (SES). Avoiding hospitalization in patients who do not require admission may improve outcomes and quality of life, while reducing costs. Short stay unit (SSU: <24 h, also referred to as an ‘observation unit’) management of AHF may be effective for lower risk patients. However, to date there have only been small studies or retrospective analyses on the SSU management for AHF patients. In addition, SSU management has been considered ‘cheating’ for hospitals trying to avoid 30-day readmission penalties, as SSUs or observation units do not count as an admission. However, more recent analyses demonstrate differential use of observation status has not led to decreases in re-admission, suggesting this concern may be misplaced. Thus, we propose a robust clinical effectiveness trial to demonstrate the effectiveness of this patient-centered strategy

An accelerator facility for intermediate energy proton irradiation and testing of nuclear materials

The bulk irradiation of materials with 10-30 MeV protons promises to advance the study of radiation damage for fission and fusion power plants. Intermediate energy proton beams can now be dedicated to materials irradiation within university-scale laboratories. This paper describes the first such facility, with an Ionetix ION-12SC cyclotron producing 12 MeV proton beams. Samples are mm-scale tensile specimens with thicknesses up to 300 um, mounted to a cooled beam target with control over temperature. A specialized tensile tester for radioactive specimens at high temperature (500+ {\deg}C) and/or vacuum represents the conditions in fission and fusion systems, while a digital image correlation system remotely measures strain. Overall, the facility provides university-scale irradiation and testing capability with intermediate energy protons to complement traditional in-core fission reactor and micro-scale ion irradiation. This facility demonstrates that bulk proton irradiation is a scalable and effective approach for nuclear materials research, down-selection, and qualification.Comment: Submitted to NIM B journa

Multiple Monoenergetic Gamma Radiography (MMGR) with a compact superconducting cyclotron

Smuggling of special nuclear materials (SNM) and nuclear devices through borders and ports of entry constitutes a major risk to global security. Technologies are needed to reliably screen the flow of commerce for the presence of high-$Z$ materials such as uranium and plutonium. Here we present an experimental proof-of-concept of a technique which uses inelastic ($p,p'$) nuclear reactions to generate monoenergetic photons, which provide means to measure the areal density and the effective-$Z$ ($Z_{\text{eff}}$) of an object with an accuracy which surpasses that achieved by current methods. We use an ION-12$^{ \text{SC}}$ superconducting 12~MeV proton cyclotron to produce 4.4, 6.1, 6.9, and 7.1~MeV photons from a variety of nuclear reactions. Using these photons in a transmission mode we show that we are able to accurately reconstruct the areal densities and $Z_{\text{eff}}$ of a test object. This methodology could enable mobile applications to screen commercial cargoes with high material specificity, providing a means of distinguishing common cargo materials from high-Z materials that include uranium and plutonium

Phenomenology of the Deuteron Electromagnetic Form Factors

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm^-1. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data.Comment: 18 pages (LaTeX), 2 figures Feb. 25: minor changes of content and in Table