Session KH: Applications

Photo-fission Methods to detect Fissile Materials

A mission objective of various national security agencies is to develop systems that can detect fissile material. There are a myriad of researchers at national laboratories, academic institutions, and industry who are investigating various methods to detect fissile materials. These methods are broken down into active or passive detection systems. Examples of active systems include neutron or photon sources to stimulate and/or scatter from materials. Our focus has been to use photons near the fission barrier of various actinides to excite fission modes and measure the correlated and uncorrelated neutrons. We will present and discuss results from recent measurements. We will present the overall results of our effort and discuss some of the open questions.   

Parameterization for light ion production from electromagnetic dissociation

Light ion (hydrogen and helium isotopes) production from relativistic nucleus-nucleus collisions is important in space radiation protection problems, when galactic cosmic rays interact with spacecraft. In fact, for thick spacecraft shields, such as the International Space Station, light ion and neutron production can dominate the contribution to dose equivalent. Both strong and electromagnetic interactions can contribute to light ion production. The present work extends a previous parameterization of electromagnetically produced light ions, so that particle branching ratios are described more realistically.   

Charge-to-Mass Dispersion Methods in Knockout-Ablation Fragmentation Models

Breakup of high-energy heavy ions in nuclear collisions is an important process in space radiation transport, shielding and risk assessment since the secondary particles produced by these collisions have ranges greater than their parent nucleus, and are damaging to humans and spacecraft components. This work uses a quantum-mechanical optical potential knockout-ablation model to estimate these collision cross sections in order to investigate differences in isotope and element production cross sections as a result of utilizing two different models of charge-to mass ratios for the projectile prefragments produced by the abrasion/knockout process. One model commonly used, a hypergeometric model, assumes that the distribution of abraded nucleons is completely uncorrelated. However, it permits some unrealistic distributions, such as removing all neutrons in the knockout stage, while leaving all protons intact. Another model, developed for use with a classical geometric, clean-cut abrasion model, is based upon the zero point vibrations of the giant dipole resonance of the fragmenting nucleus. In this work we compare fragment production cross section predictions using the two charge dispersion models with published experimental data.   

Actinide Studies with Ultracold Neutrons

Understanding the aging of nuclear material components is critical to the mission of the National Nuclear Security Administration, and has applications for the nuclear energy industry and space science. The mechanism describing the energy transfer of fission fragments to the material is not well understood and represents one of the modern challenges facing nuclear scientists. A new technique in which ultracold neutrons (UCNs) are used to induce fission at specific depths near the material surface is being developed at the Los Alamos Neutron Science Center. We have performed the first characterizations of fission rates and material sputtered from the surface as a function of UCN energy. We will present an update on the development of a new beamline and detection scheme and preliminary results from the 2014 accelerator cycle.   

First Measurement of Reaction-in-Flight Neutrons at the National Ignition Facility

The first measurement of reaction-in-flight (RIF) neutrons, also known as tertiary neutrons, has been performed at the National Ignition Facility (NIF) using an activation technique. Thulium foils positioned at 50 cm from the burning deuterium-tritium (DT) capsule have been exposed to the characteristic DT neutron spectrum. The high-energy part of these neutrons with energies above 15.0 MeV can produce $^{167}$Tm via the $^{169}$Tm(n,3n) reaction. The 208-keV $\gamma $-ray, emitted from the decay of $^{167}$Tm with a half-life of 9.2 days, has been measured using two clover detectors. The first preliminary result implies that the ratio of RIF neutrons (E$_{\mathrm{n}}$\textgreater 15.0 MeV) versus the total neutrons is 1x10$^{-4}$ $\pm$ 3x10$^{-5}$. The important implication of these measurements on our knowledge of the charged-particle stopping power in strongly coupled quantum-degenerate plasma will be presented.   

New developments in proton radiography at LANSCE

In a new application of nuclear physics, a facility for using proton for flash radiography has been developed at the Los Alamos Neutron Science Center (LANSCE) [1]. Protons have proven far superior to high energy x-rays for flash radiography. Although this facility is primarily used for studying very fast phenomena such as high explosive driven experiments, it is finding increasing application to other fields, such as tomography of static objects [2], phase changes in materials [3], and the dynamics of chemical reactions [4]. The advantages of protons will be discussed and data from some of the recent experiments will be presented.\\[4pt] [1] Morris, C., et al., \textit{Journal of Applied Physics}, \textbf{109} 104905 (2011).\\[0pt] [2] Morris, C., et al., \textit{Review of Scientific Instruments} \textbf{84} 023902 (2013).\\[0pt] [3] Clarke, A., et al., \textit{Scientific reports}, \textbf{3} 2020 (2013).\\[0pt] [4] Bernert, T., et al., \textit{Solid State Sciences}, 2013. \textbf{22} 33(2013).   

Nuclear resonance fluorescence in U-238 using LaBr detectors for nuclear security

Recently, a nondestructive measurement method of shielded fissional isotopes such as 235U or 239Pu has been proposed for the nuclear security. These isotopes are measured by using nuclear resonance fluorescence (NRF) with monochromatic energy gamma-ray beams generated by laser Compton-scattering (LCS). We have proposed that one measure scattered gamma-rays from NRF with LCS gamma-ray beams using the LaBr3(Ce) detectors. The LaBr3(Ce) crystals include internal radioisotopes of a meta-stable isotope 138La and alpha decay chains from some actinides as 227Ac. There is a broad pump at about 2 MeV. This pump is considered to be an overlap of alpha-rays from decay chains of some actinides but its detailed structure has not been established. Here we have measured NRF spectra of 238U using the LCS gamma-rays with energy of about 2.5 MeV at the HIgS facility of the Duke University. The background has been evaluated using a simulation code GEAT4. The 9 peaks, 8 NRF gamma-rays plus the Compton scattered gamma-ray of the incident beam, are finally assigned in an energy range of about 200 keV at about 2.5 MeV. The 8 integrated NRF cross-sections measured by LaBr3(Ce) have been consistent with results by an HPGe detector. The three levels are newly assigned using the HPGe detector. Two of them are also measured by LaBr3(Ce).   

Particles Production in Extensive Air Showers: GEANT4 vs CORSIKA

Air shower simulations are essential tools for the interpretation of the Extensive Air Shower (EAS) measurements. The reliability of these codes is evaluated by comparisons with equivalent simulation calculations, and with experimental data (when available). In this work, we present GEANT4 calculations of particles production in EAS induced by primary protons and Iron in the PeV ($10^{15}$ eV) energy range. The calculations, using different hadronic models, are compared with the results from the well-known air shower simulation code CORSIKA, and the results of this comparison will be discussed.   

Improved Neutron Capture Gamma-Ray Data and Evaluation

The neutron-capture reaction is of fundamental use in identifying and analyzing the gamma-ray spectrum from an unknown object as it gives a fingerprint of which isotopes are present. Many isotopes have capture gamma lines from 5-10 MeV potentially making them easier to detect against background lines. There are data gaps in the Evaluated Nuclear Data File (ENDF) libraries used by modeling codes (the actinides have no lines for example) and we are filling these with the Evaluated Gamma-ray Activation File (EGAF), using an IAEA atlas of reactor measured lines and cross sections for over 260 isotopes. For medium to heavy nuclei, the unresolved part of the gamma cascades is not measured and are modeled using the statistical nuclear structure code Dicebox [1, 2]. ENDF libraries require cross sections for neutron energies up to 20 MeV and we plan to continue this approach through the resolved resonance region.   

Reaction Rate Measurements at the National Criticality Experiments Research Center

With the resumption of regular operations of the Los Alamos Critical Assemblies at the National Criticality Experiments Research Center (NCERC), located at the Nevada National Security Site, we have embarked upon a series of campaigns to restore the capability to perform integral reaction rate and fission product yield measurements using historical radiochemical methods. This talk will present an overview of the current and future experimental plans, including results from our experimental campaigns on the Comet/Zeus and Flattop assemblies.   

Development of HTS magnets for application

We have been developing magnets utilizing high-temperature superconducting (HTS) wires for this decade. We built three model magnets, a mirror coil for an ECR ion source, a set of coils for a scanning magnet and a super-ferric dipole magnet to generate magnetic field of 3 T. They were excited with AC/pulse currents as well as DC currents. Recently we fabricated a cylindrical magnet for a practical use which polarizes ultracold neutrons (UCN). It consists of 10 double pancakes and the field strength at the center is higher than 3.5 T which is required to fully polarize 210 neV neutrons. It was successfully cooled and excited. The magnet was used to polarized UCN generated by the RCNP-KEK superthermal UCN source, One dipole magnet has been manufactured which is used as a switching magnet after the RCNP ring cyclotron and is excited by pulse currents. It becomes possible to deliver beams to two experimental halls by time sharing. Their designs and performances are presented in the talk.