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The role of active-interrogation systems for nuclear security is to detect the presence of special nuclear material inside an object by observing the radiation emitted by that object when it has been exposed to known sources of external radiation. Because of the cost, complexity, and the need to avoid irradiating occupants, active-interrogation systems are intended for cargo applications where shielding can prevent detection by passive radiation detection systems. To ensure that active-interrogation systems for detection of special nuclear material are designed and tested to a consistent level of performance, technical standards are needed for evaluating such systems. This paper addresses the testing standards needed for active-interrogation systems to detect high atomic number materials, fissionable materials, and specific special nuclear materials. Because the use of special nuclear material for a testing standard is not practical, this work focuses on the determination of materials that could be used as surrogates in that they provide a similar response as targets of special nuclear materials. The results of this paper, determined through analytic calculations and radiation transport modeling, are based upon scenarios constructed and applied to specific active-interrogation modalities.

Background: Measurements of exclusive meson production are a useful tool in the study of hadronic structure. In particular, one can discern the relevant degrees of freedom at different distance scales through these studies. Purpose: To study the transition between non-perturbative and perturbative Quantum Chromodyanmics as the square of four momentum transfer to the struck proton, -t, is increased. Method: Cross sections for the $^1$H(e,e'$\pi^+$)n reaction were measured over the -t range of 0.272 to 2.127 GeV$^2$ with limited azimuthal coverage at fixed beam energy of 4.709 GeV, Q$^2$ of 2.4 GeV$^2$ and W of 2.0 GeV at the Thomas Jefferson National Accelerator Facility (JLab) Hall C. Results: The -t dependence of the measured $\pi^+$ electroproduction cross section generally agrees with prior data from JLab Halls B and C. The data are consistent with a Regge amplitude based theoretical model, but show poor agreement with a Generalized Parton Distribution (GPD) based model. Conclusion: The agreement of cross sections with prior data implies small contribution from the interference terms, and the confirmation of the change in t-slopes between the low and high -t regions previously observed in photoproduction indicates the changing nature of the electroproduction reaction in our kinematic regime., Comment: 9 pages, 5 figures Physical Review C, in press

A technique to determine the isotopic constituents of a mixed actinide sample has been proposed by a coincident alpha-conversion electron measurement. This presents a unique signature to allow the unfolding of isotopes that possess overlapping alpha particle energy and reduce backgrounds of an unseparated sample. The work presented here are results of conversion electron spectroscopy of 241 Am, 238 Pu and 239 Pu using a dual-stage peltier-cooled 25 mm 2 silicon drift detector and alpha spectroscopy with a passivated ion implanted planar silicon detector. The conversion electron spectra were evaluated from 20–55 keV based on fits to the dominant conversion electron emissions, which allowed the relative conversion electron emission intensities to be determined. These measurements provide crucial singles spectral information and calibration to aid in the coincident measurement approach. Furthermore, an alpha-conversion electron spectrometer was assembled using the silicon based detectors described and results of a coincident spectrum analysis is reported for 241 Am.

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the partonic dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available in particular for the longitudinal structure function. Here, we present separated structure functions for hydrogen and deuterium at low four-momentum transfer squared, Q2

The H1(e,e′K+)Λ reaction was studied as a function of the Mandelstam variable -t using data from the E01-004 (FPI-2) and E93-018 experiments that were carried out in Hall C at the 6 GeV Jefferson Laboratory. The cross section was fully separated into longitudinal and transverse components, and two interference terms at four-momentum transfers Q2 of 1.00, 1.36, and 2.07GeV2. The kaon form factor was extracted from the longitudinal cross section using the Regge model by Vanderhaeghen et al. [Phys. Rev. C 57, 1454 (1998)PRVCAN0556-281310.1103/PhysRevC.57.1454]. The results establish the method, previously used successfully for pion analyses, for extracting the kaon form factor. Data from 12 GeV Jefferson Laboratory experiments are expected to have sufficient precision to distinguish between theoretical predictions, for example, recent perturbative QCD calculations with modern parton distribution amplitudes. The leading-twist behavior for light mesons is predicted to set in for values of Q2 between 5 and 10GeV2, which makes data in the few-GeV regime particularly interesting. The Q2 dependence at fixed x and -t of the longitudinal cross section that we extracted seems consistent with the QCD factorization prediction within the experimental uncertainty.

The Ultra-Low Background Liquid Scintillation Counter developed by Pacific Northwest National Laboratory will expand the application of liquid scintillation counting by enabling lower detection limits and smaller sample volumes. By reducing the overall count rate of the background environment approximately 2 orders of magnitude below that of commercially available systems, backgrounds on the order of tens of counts per day over an energy range of ~3–3600 keV can be realized. Initial test results of the ULB LSC show promising results for ultra-low background detection with liquid scintillation counting.

A new ultra-low-background proportional counter design was recently developed at Pacific Northwest National Laboratory (PNNL). This design, along with an ultra-low-background counting system which provides passive and active shielding with radon exclusion, has been developed to complement a new shallow underground laboratory (~30 m water-equivalent) constructed at PNNL. After these steps to mitigate dominant backgrounds (cosmic rays, external gamma-rays, radioactivity in materials), remaining background events do not exclusively arise from ionization of the proportional counter gas. Digital pulse-shape discrimination (PSD) is thus employed to further improve measurement sensitivity. In this work, a template shape is generated for each individual sample measurement of interest, a “self-calibrating” template. Differences in event topology can also cause differences in pulse shape. In this work, the temporal region analyzed for each event is refined to maximize background discrimination while avoiding unwanted sensitivity to event topology. This digital PSD method is applied to sample and background data, and initial measurement results from a biofuel methane sample are presented in the context of low-background measurements currently being developed.

Nuclear resonance fluorescence is a physical process that provides an isotope-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample that is exposed to photons in the MeV energy range. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials such as 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct a a pair of measurements to search for a nuclear resonance fluorescence response of 235U above 3 MeV and of 238U above 5 MeV using an 8 g sample of highly enriched uranium and a 90 g sample of depleted uranium. No new signatures were observed. The minimum detectable integrated cross section for 235U is presented.

Physics experiments, environmental surveillance, and treaty verification techniques continue to require increased sensitivity for detecting and quantifying radionuclides of interest. This can be done by detecting a greater fraction of gamma emissions from a sample (higher detection efficiency) and reducing instrument backgrounds. A current effort for increased sensitivity in high resolution gamma spectroscopy will produce an intrinsic germanium (HPGe) array designed for high detection efficiency, ultra-low-background performance, and useful coincidence efficiencies. The system design is optimized to accommodate filter paper samples, e.g. samples collected by the Radionuclide Aerosol Sampler/Analyzer (RASA). The system will provide high sensitivity for weak collections on atmospheric filter samples, as well as offering the potential to gather additional information from more active filters using gamma cascade coincidence detection. The current effort is constructing an ultra-low-background HPGe crystal array consisting of two vacuum cryostats, each housing a hexagonal array of 7 crystals on the order of 70% relative efficiency per crystal. Traditional methods for constructing ultra-low-background detectors are used, including use of materials known to be low in radioactive contaminants, use of ultra pure reagents, clean room assembly, etc. The cryostat will be constructed mainly from copper electroformed into near-final geometry at PNNL. Details of the detector design, simulation of efficiency and coincidence performance, HPGe crystal testing, and progress on cryostat construction are presented.

High-purity copper has emerged as a preferred construction material for ultra-low-background HPGe spectrometers and offers excellent bulk radiopurity along with good electrical, thermal, and vacuum properties. Recently, these materials and techniques have been applied to the construction of low-background internal-source gas proportional counters. This work describes the design, construction, and testing of an ultra-low-background internal-source gas proportional counter built primarily of high purity electroformed copper. Energy resolution of ~10% FWHM at 59.5 keV has been achieved, a low-energy threshold of ~3 keV has been reached, and gas gain stability over a 4-week period has been demonstrated. Progress toward low-background operation is described.

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu+/Cu2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified. © 2001 Elsevier Science. All rights reserved

Liquid scintillation counters measure charged particle-emitting radioactive isotopes and are used for environmental studies, nuclear chemistry, and life science. Alpha and beta emissions arising from the material under study interact with the scintillation cocktail to produce light. The prototypical liquid scintillation counter employs low-level photon-counting detectors to measure the arrival of the scintillation. For reliable operation, the counting instrument must convey the scintillation light to the detectors efficiently and predictably. Current best practices employ the use of two or more detectors for coincidence processing to discriminate true scintillation events from background events due to instrumental effects such as photomultiplier tube dark rates, tube flashing, or other light emission not generated in the scintillation cocktail vial. In low-background liquid scintillation counters, additional attention is paid to shielding the scintillation cocktail from naturally occurring radioactive material present in the laboratory and within the instrument’s construction materials. Low-background design is generally at odds with optimal light collection. This study presents the evolution of a light collection design for liquid scintillation counting (LSC) in a low-background shield. The basic approach to achieve both good light collection and a low-background measurement is described. The baseline signals arising from the scintillation vial are modeled and methods to efficiently collect scintillation light are presented as part of the development of a customized low-background, high-sensitivity LSC system.

The spectral analysis of simultaneously observed photons in separate detectors may provide an invaluable tool for radioisotope identification applications. A general recursive method to determine the activity of an isotope from the observed coincidence signature rate is discussed. The method coherently accounts for effects of true coincidence summing within a single detector and detection efficiencies. A verification of the approach with computer simulations is also discussed.

The ability to conduct automated trace radionuclide analysis at or near the sample collection point would provide a valuable tool for emergency response, nuclear forensics and environmental monitoring. Pacific Northwest National Laboratory is developing systems for this purpose based on dual gamma-ray spectrometers, e.g. NaI(TI) or HPGe, combined with thin organic scintillator sensors to detect light charged particles. Translating the coincident signatures recorded by these systems, which include /spl beta//spl gamma/, /spl gamma//spl gamma/ and /spl beta//spl gamma//spl gamma/, into the concentration of detectable radionuclides in the sample requires generalized multicoincidence analysis tools. The development and validation of the Coincidence Lookup Library, which currently contains the probabilities of single and coincidence signatures from more than 420 isotopes, is described. Also discussed is a method to calculate the probability of observing a coincidence signature which incorporates true coincidence summing effects. These effects are particularly important for high-geometric-efficiency detection systems. Finally, a process for validating the integrated analysis software package is demonstrated using GEANT 4 simulations of the prototype detector systems.

Asymmetries in quasi-elastic 3 He ( e → , e ′ p ) have been measured at a momentum transfer of 0.67 (GeV/ c ) 2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3 He -ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

We report on the design and performance of compact detector packages currently installed in the four magnetic out-of-plane spectrometers for electron scattering experiments at the MIT-Bates Linear Accelerator Center. The detector packages have been designed to meet the mechanical requirements arising from out-of-plane particle detection. They offer good trajectory and momentum reconstruction, particle identification and time-of-flight measurements for electrons, pions, protons, and deuterons with large momentum bites and in broad kinematical ranges and high luminosities. The detectors have so far been used with great success in out-of-plane measurements of 12 C ( e → , e ′ p ) , 2 H ( e → , e ′ p ) , virtual Compton scattering below pion threshold and in studies of the N → Δ transition in both exclusive reaction channels 1 H ( e → , e ′ p ) π 0 and 1 H ( e → , e ′ π + )n .

Large-area horizontal drift chambers have been built for use in a proton polarimeter. A gas mixture of 20% argon and 80% ethane is used. The left–right assignment is achieved by measuring the difference of the signals induced on neighboring potential wires. A spatial resolution of 300 μm is achieved.

Precise data on the neutron magnetic form factor G_{mn} have been obtained with measurements of the ratio of cross sections of D(e,e'n) and D(e,e'p) up to momentum transfers of Q^2 = 0.9 (GeV/c)^2. Data with typical uncertainties of 1.5% are presented. These data allow for the first time to extract a precise value of the magnetic radius of the neutron., Comment: 10 pages, 2 figures, submitted to Physics Letters B

The effectiveness of conventional measurement techniques for environmental monitoring is limited by background and other interferences. We are exploring a new measurement approach involving the detection of α particles in coincidence with conversion electrons as a means to simultaneously assay environmental samples for multiple actinides without chemical separation. The initial target isotopes studied in this work are 238Pu, 239Pu, 240Pu and 241Am. We explore various aspects of the design, such as impact of the mounting of the source material, energy resolution requirements and impact of a background on isotopic uncertainties. We conclude that a dual gas-proportional counter and a dual-sided, large-area silicon detector could provide similar performance for the measurement scenario examined.

The recoil proton polarization has been measured in the $p(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}\stackrel{\ensuremath{\rightarrow}}{p}){\ensuremath{\pi}}^{0}$ reaction in parallel kinematics around $W\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1232\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$, ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.121\phantom{\rule{0ex}{0ex}}(\mathrm{GeV}/c{)}^{2}$, and $\ensuremath{\epsilon}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.718$ using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, ${P}_{x}/{P}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}11.4\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\pm\else\textpm\fi{}1.4)%$, ${P}_{y}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}43.1\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\pm\else\textpm\fi{}2.2)%$, and ${P}_{z}/{P}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(56.2\ifmmode\pm\else\textpm\fi{}1.5\ifmmode\pm\else\textpm\fi{}2.6)%$, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, $\mathrm{CMR}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}6.4\ifmmode\pm\else\textpm\fi{}{0.7}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.8}_{\mathrm{syst}})%$, was determined from ${P}_{x}$ in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.

We have built a polarimeter in order to measure the electron beam polarization in hall C at JLAB. Using a superconducting solenoid to drive the pure-iron target foil into saturation, and a symmetrical setup to detect the Moller electrons in coincidence, we achieve an accuracy of, 17 pages, 9 figures, submitted to N.I.M

Polarization transfer in the 4He ( e → ,e′ p → ) 3 H reaction at a Q2 of 0.4 (GeV/c)2 was measured at the Mainz Microtron MAMI. The ratio of the transverse to the longitudinal polarization components of the ejected protons was compared with the same ratio for elastic ep scattering. The results are consistent with a recent fully relativistic calculation which includes a predicted medium modification of the proton form factor based on a quark–meson coupling model.

In order to test modern theories of two-nucleon bound and scattering states, we have measured the spin polarization of ejectile protons in the electrodisintegration reaction d( e → ,e′ p → )n . Compared with spin-averaged observations, these observables offer the potential of enhanced sensitivity to details of the reaction process. The experiment was carried out in quasielastic kinematics ( q μ q μ =−2m p ω=−0.38 GeV2/c2). Protons were detected at two angles corresponding to neutron recoil momenta pr of 0 and 100 MeV/c. Full nonrelativistic calculations of the polarization transfer components sl and st, including leading order relativistic contributions, describe our measurements well, but calculations of the induced polarization sn at pr=100 MeV/c underpredict the experimental result.

We have measured the neutron electric form factor ${G}_{\mathrm{en}}$ via ${}^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}n)\mathrm{pp}$ at ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.67(\mathrm{GeV}/c{)}^{2}$ using the 3-spectrometer facility of the A1 Collaboration at the Mainz Microtron and a dedicated neutron detector. High pressure polarized ${}^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}$ gas was used as a target of polarized neutrons. ${G}_{\mathrm{en}}$ is determined from the ratio of the asymmetries ${A}_{\ensuremath{\perp}}{/A}_{\ensuremath{\parallel}}$ measured in quasifree kinematics with the target spin perpendicular and parallel to the momentum transfer. We find ${G}_{\mathrm{en}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.052\ifmmode\pm\else\textpm\fi{}0.011\ifmmode\pm\else\textpm\fi{}0.005$.

A series of high precision measurements on the N → Δ transition involving polarized beams, out-of-plane detection and focal plane polarimetry in the H( e →, e′p )π 0 and H( e →, e′π + ) n channels have been pursued at Bates during the last three years. They are geared towards the precise determination of the quadrupole amplitudes in the N → Δ transition and the isolation of the coherent, competing processes at low Q 2 .

The coincidence cross section and the interference structure function, ${R}_{\mathrm{LT}},$ were measured for the ${}^{12}\mathrm{C}{(e,e}^{\ensuremath{'}}p){}^{11}\mathrm{B}$ reaction at quasielastic kinematics and central momentum transfer of $|\stackrel{\ensuremath{\rightarrow}}{q}|=400\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{c}.$ The measurement was at an opening angle of ${\ensuremath{\theta}}_{\mathrm{pq}}=11\ifmmode^\circ\else\textdegree\fi{},$ covering a range in missing energy of ${E}_{m}=0$ to 65 MeV. The ${R}_{\mathrm{LT}}$ structure function is found to be consistent with zero for ${E}_{m}g50\mathrm{MeV},$ confirming an earlier study which indicated that ${R}_{L}$ vanishes in this region. The integrated strengths of the $p$- and $s$-shell are compared with a distorted wave impulse approximation (DWIA) calculation. The $s$-shell strength and shape are also compared with a Hartree Fock--random phase approximation (HF-RPA) calculation. The DWIA calculation does not succeed in giving a consistent description of both the cross section data and the extracted ${R}_{\mathrm{LT}}$ response for either shell. The HF-RPA calculation describes the data more consistently, which may be due to the inclusion of 2-body currents in this calculation.

We present a measurement of the induced proton polarization ${P}_{n}$ in ${\ensuremath{\pi}}^{0}$ electroproduction on the proton around the $\ensuremath{\Delta}$ resonance. The measurement was made at a central invariant mass and a squared four-momentum transfer of $W=1231 \mathrm{MeV}$ and ${Q}^{2}=0.126 {\mathrm{GeV}}^{2}{/c}^{2},$ respectively. We measured a large induced polarization, ${P}_{n}=\ensuremath{-}0.397\ifmmode\pm\else\textpm\fi{}0.055\ifmmode\pm\else\textpm\fi{}0.009.$ The data suggest that the scalar background is larger than expected from a recent effective Hamiltonian model.

The neutron magnetic form factor Gmn has been determined via a measurement of the ratio of cross sections D(e,e′n) and D(e,e′p). The absolute detection efficiency of the neutron detector was measured with high accuracy using tagged neutrons produced from H(n,p)n elastic scattering by means of a high intensity neutron beam. This approach minimizes the model dependence and improves upon the weakest points of previous experiments. Data in the range q2=0.2–0.8 (GeV/c)2 with uncertainties of

The first measurements of the induced proton polarization Pn for the 12C(e,e',p) reaction are reported. The experiment was performed at quasifree kinematics for energy and momentum transfer (w,q) = (294 MeV, 765 MeV/c) and sampled a missing momentum range of 0-250 MeV/c. The induced polarization arises from final-state interactions and for these kinematics is dominated by the real part of the spin-orbit optical potential. The distorted-wave impulse approximation provides good agreement with data for the 1 p3/2 shell. The data for the continuum suggest that both the 1s1/2 shell and underlying l > 1 configurations contribute.

Interferences in both decay counting and mass counting techniques limit their application for some environmental monitoring applications. For example, 238U interferes with 238Pu in mass spectrometry measurements, while in conventional alpha spectroscopy measurements it is nearly impossible to separate 238Pu from 241Am and 239Pu from 240Pu. These interferences are typically resolved by using chemical separation and/or different measurement techniques for different isotopes. We are investigating radiation detector concepts to simultaneously assay these four isotopes with minimal sample preparation by exploiting radiation signatures measured in coincidence with the predominate alpha decays of these isotopes. Particles in coincidence with the alpha decay include conversion electrons, gamma rays, x-rays, and Auger electrons. Each decay has a unique energy distribution enabling the separation of the isotopes. We are exploring two basic detector concepts to achieve these goals: a silicon-based design and a gas-detector design. The silicon system provides the potential for higher energy resolution at the cost of lower efficiency compared to a gas detector. In this paper, we will describe our evaluation of the different detector concepts, which will include estimations of potential detection efficiency, ability to resolve the isotopes, sample preparation and equipment requirements.

We have separated the longitudinal ({ital f}{sub 00}), transverse ({ital f}{sub 11}), and longitudinal-transverse interference ({ital f}{sub 01}) structure functions in the {sup 2}H({ital e},{ital e}{prime}{ital p}){ital n} reaction at {ital q}{searrow}{parallel}{approx_equal} 400 MeV/{ital c} and {omega}{approx_equal}110 MeV. A nonrelativistic calculation which includes effects due to final state interactions, meson exchange currents, and isobar configurations agrees with the measured {ital f}{sub 11} and {ital f}{sub 01} but overpredicts {ital f}{sub 00} by 25{percent} (2{sigma}). The data are also compared to the results of previous structure function measurements. {copyright} {ital 1996 The American Physical Society.}

A new ultra-low-background proportional counter was recently developed with an internal volume of 100 cm(3) and has been characterized at pressures from 1-10 atm with P-10 (90% Ar, 10% methane) gas. This design, along with a counting system providing event digitization and passive and active shielding, has been developed to complement a new shallow underground laboratory (30 m water-equivalent). Backgrounds and low-level reference materials have been measured, and system sensitivity for (37)Ar has been calculated.

This project seeks to identify a new signature for actinide element detection in active interrogation. This technique works by exciting and identifying long-lived nuclear excited states (isomers) in the actinide isotopes and/or primary fission products. Observation of isomers in the fission products will provide a signature for fissile material. For the actinide isomers, the decay time and energy of the isomeric state is unique to a particular isotope, providing an unambiguous signature for SNM. This project entails isomer identification and characterization and neutron population studies. This document summarizes activities from its third year - completion of the isomer identification characterization experiments and initialization of the neutron population experiments. The population and decay of the isomeric state in 235U remain elusive, although a number of candidate gamma rays have been identified. In the course of the experiments, a number of fission fragment isomers were populated and measured [Ressler 2010]. The decays from these isomers may also provide a suitable signature for the presence of fissile material. Several measurements were conducted throughout this project. This report focuses on the results of an experiment conducted collaboratively by PNNL, LLNL and LBNL in December 2010 at LBNL. The measurement involved measuring the gamma-rays emittedmore » from an HEU target when bombarded with 11 MeV neutrons. This report discussed the analysis and resulting conclusions from those measurements. There was one strong candidate, at 1204 keV, of an isomeric signature of 235U. The half-life of the state is estimated to be 9.3 {mu}s. The measured time dependence fits the decay time structure very well. Other possible explanations for the 1204-keV state were investigated, but they could not explain the gamma ray. Unfortunately, the relatively limited statistics of the measurement limit, and the lack of understanding of some of the systematic of the experiment, limit the authors to labeling the 1204-keV gamma ray as a very strong candidate for isomeric transition in 235U. Regardless of the physics origins, the time structure of the 1204-keV gamma ray can be used as at a minimum as an indication of fissile material, if the 1204-keV gamma ray is attributed to a fission product, or it may be a unique signature for 235U, if it is a signature of an isomeric state in 235U.« less

A large set of cross sections for semi-inclusive electroproduction of charged pions ($��^\pm$) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared $W^2$ > 4 GeV$^2$ and range in four-momentum transfer squared $2 < Q^2 < 4$ (GeV/c)$^2$, and cover a range in the Bjorken scaling variable 0.2 < x < 0.6. The fractional energy of the pions spans a range 0.3 < z < 1, with small transverse momenta with respect to the virtual-photon direction, $P_t^2 < 0.2$ (GeV/c)$^2$. The invariant mass that goes undetected, $M_x$ or W', is in the nucleon resonance region, W' < 2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark --> pion production mechanisms. The x, z and $P_t^2$ dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for $��^+$ and $��^-$) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of $d$ quarks are found to be slightly smaller than for $u$ quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed., Comment: Submitted to Nuclear Instruments and Methods

Identification and characterization of fissile material is of international concern because of the possibility of proliferation. For safeguards applications, techniques providing isotopic information are necessary [1]. However, few techniques can distinguish between fissile isotopes. Nuclear resonance fluorescence is one technique that can be used in applications to identify and quantify isotopic content. NRF has also been proposed in several detector systems as a viable way to identify fissile material in cargo containers [2, 3]. It is necessary to measure the characteristic resonances of each isotope that is to be distinguished in identification and assay applications.

We have extracted QCD matrix elements from our data on double polarized inelastic scattering of electrons on nuclei. We find the higher twist matrix element \tilde{d_2}, which arises strictly from quark- gluon interactions, to be unambiguously non zero. The data also reveal an isospin dependence of higher twist effects if we assume that the Burkhardt-Cottingham Sum rule is valid. The fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied at our low momentum transfer., formerly "Nachtmann Moments of the Proton and Deuteron Spin Structure Functions"

Short-lived isomers in fission fragments following bombardment of 45-MeV {sup 6}Li on {sup 232}Th were examined. Isomers in the A{approx}95, 122, and 132 mass regions were observed. New isomeric decays were observed in {sup 121}In[T{sub 1/2}=17(2) mus], {sup 123}In (T{sub 1/2}> or approx.100 mus), and {sup 125}Sb[T{sub 1/2}=25(4) mus]. These isomers are suggested to arise from nu(h{sub 11/2} x d{sub 3/2})7{sup -} and nu(h{sub 11/2} x s{sub 1/2})5{sup -} neutron core excitations coupling with the valence proton.

The lifetimes of the excited states of {sup 55}Mn between 1.5 and 2.7 MeV were measured using nuclear resonance fluorescence. The absolute lifetimes of the excited levels were determined from simultaneous measurements of manganese and aluminum. In this approach, the precisely known aluminum state serves as a means to normalize the results. Our findings differ from the evaluated level lifetimes in the Evaluated Nuclear Structure Data File (ENSDF), but agree with earlier nuclear resonance fluorescence measurements.

The differential cross-section for the exclusive process p(e, e0p) has been measured at Q2 5.7 and 7.0 (GeV/c)2, which represents the highest momentum transfer measurement of this to date, significantly higher than the previous highest at Q2 3.6 (GeV/c)2. Data was taken for centre-of-mass energies from threshold to 1.8 GeV, encompassing the S11(1535) resonance, which dominates the pη channel. The total cross section is obtained, from which is extracted the helicity-conserving transition amplitude A1/2, for the production of the S11(1535) resonance. This quantity appears to begin scaling as Q-3, a predicted signal of the dominance of perturbative QCD, within the Q2 range of this measurement. No currently available theoretical predictions can account for the behaviour of this quantity over the full measured range of Q2.

FY08 annual report for project the "Nuclear Resonance Fluorescence Imaging" project. Reviews accomplishments of last 3 years, including U-235 signature search, comparison of different photon sources, and examination of NRF measurements using monochromatic photon source.

Cross sections for the reaction {sup 1}H(e,e'{Pi}{sup +})n were measured in Hall C at Thomas Jefferson National Accelerator Facility (JLab) using the high-intensity Continuous Electron Beam Accelerator Facility (CEBAF) to determine the charged pion form factor. Data were taken for central four-momentum transfers ranging from Q{sup 2} = 0.60 to 2.45 GeV{sup 2} at an invariant mass of the virtual photon-nucleon system of W = 1.95 and 2.22 GeV. The measured cross sections were separated into the four structure functions {sigma}{sub L},{sigma}{sub T}, {sigma}{sub LT}, and {sigma}{sub TT}. The various parts of the experimental setup and the analysis steps are described in detail, including the calibrations and systematic studies, which were needed to obtain high-precision results. The different types of systematic uncertainties are also discussed. The results for the separated cross sections as a function of the Mandelstam variable t at the different values of Q{sup 2} are presented. Some global features of the data are discussed, and the data are compared with the results of some model calculations for the reaction {sup 1}H(e,e'{Pi}{sup +})n.

A search for nuclear resonance fluorescence excitations in {sup 235}U and {sup 239}Pu within the energy range of 1.0- to 2.5-MeV was performed using a 4-MeV continuous bremsstrahlung source at the High Voltage Research Laboratory at the Massachusetts Institute of Technology. Measurements utilizing high purity Ge detectors at backward angles identified 9 photopeaks in {sup 235}U and 12 photopeaks in {sup 239}Pu in this energy range. These resonances provide unique signatures that allow the materials to be non-intrusively detected in a variety of environments including fuel cells, waste drums, vehicles and containers. The presence and properties of these states may prove useful in understanding the mechanisms for mixing low-lying collective dipole excitations with other states at low excitations in heavy nuclei.

Nuclear resonance fluorescence (NRF) is a photon-based active interrogation approach that provides isotope-specific signatures that can be used to detect and characterize samples. As NRF systems are designed to address specific applications, an obvious first question to address is the type of photon source to be employed for the application. Our collaboration has conducted a series of NRF measurements using different photon sources to begin to examine this issue. The measurements were designed to be as similar as possible to facilitate a straight-forward comparison of the different sources. Measurements were conducted with a high-duty factor electron accelerator using bremsstrahlung photons, with a pulsed linear accelerator using bremsstrahlung photons, and with a narrow bandwidth photon source using Compton backscattered photons. We present our observations on the advantages and disadvantages of each photon source type. Issues such as signal rate, the signal-to-noise ratio, and absorbed dose are discussed.

The advanced Large-Area Plastic Scintillator (ALPS) Project at Pacific Northwest National Laboratory investigated possible technological avenues for substantially advancing the state-of-the-art in gamma-ray detection via large-area plastic scintillators. The three predominant themes of these investigations comprised the following: * Maximizing light collection efficiency from a single large-area sheet of plastic scintillator, and optimizing hardware event trigger definition to retain detection efficiency while exploiting the power of coincidence to suppress single-PMT "dark current" background; * Utilizing anti-Compton vetoing and supplementary spectral information from a co-located secondary, or "Back" detector, to both (1) minimize Compton background in the low-energy portion of the "Front" scintillator's pulse-height spectrum, and (2) sharpen the statistical accuracy of the front detector's low-energy response prediction as impelmented in suitable energy-windowing algorithms; and * Investigating alternative materials to enhance the intrinsic gamma-ray detection efficiency of plastic-based sensors.

Analyses of the electroproduction of pions in the {Delta}(1232) region have been taken to suggest that the dominance of the magnetic dipole amplitude persists up to the highest momentum transfer available. Actually, magnetic dipole dominance is consistent with the data but is not required by it. We show that the high-momentum-transfer QCD prediction of equality, modulo notation, between the electric quadrupole and magnetic dipole amplitudes is also consistent with the high-momentum-transfer data. Thus, while the present data do restrict the multipole amplitudes, to distinguish the two main possibilities further measurements are needed, and we comment on these.

Using anisotropic Ginzburg-Landau (GL) equations based upon a tensor effective-mass approximation, we study the vortex lattice geometry near the upper critical field {ital H}{sub {ital c}2}. We employ a scaling technique to reduce the first GL equation to isotropic form. This permits simple evaluation of the angular dependence of the upper critical field for arbitrary mass anisotropy. Although the mass tensor cannot be scaled out of the second GL equation, the two equations may be solved and the free energy evaluated. In the high-{kappa} limit appropriate, e.g., to the new high-temperature superconductors, the geometry of the fluxoid lattice is found to be hexagonal in scaled coordinates but with a preferred orientation relative to the underlying crystallographic axes. The internal magnetic fields both parallel and perpendicular to the vortex axis are determined for the special case of uniaxial anisotropy.