A compact neutron generator is being developed based on a novel coaxial dipole permanent magnet electron cyclotron
resonance (ECR) ion source. The ion source is capable of generating a high fraction of atomic ion species and can operate
at low pressure. Multiple deuterium ion (D+) beamlets are extracted from the plasma ion source and accelerated to a beam-loaded
titanium target creating 2.4 MeV neutrons as a result of the D-D fusion reaction at the target surface. This paper
describes the design of the ECR-based neutron generator as well as reports on preliminary simulation and experimental
results of the ion source performance.
CaF2:Eu is an attractive radiation detection material because it is inert, non-hygroscopic, shock resistant, and can be less
expensive than other radiation detection materials. A CaF2:Eu scintillation detector was constructed to identify whether
energy dependent differences in (n,p) and (n,α) cross sections could be exploited to distinguish fission neutrons from D-D
neutrons in an active interrogation system. Experimentally, the charged particles are difficult to distinguish from the
significantly larger number of γ-rays produced in (n,γ) reactions. In addition, modeling results show that fission neutrons
produce only slightly higher charged particle production rates than D-D neutrons. For charged particle production in
CaF2:Eu to succeed in fission neutron detection, a superior γ-ray discrimination technique is required.
J. Reijonen, N. Andresen, F. Gicquel, R. Gough, M. King, T. Kalvas, K.-N. Leung, T.-P. Lou, H. Vainionpaa, A. Antolak, D. Morse, B. Doyle, G. Miller, M. Piestrup
We report here on the development of neutron and photon sources for use in imaging and active interrogation
applications, where there is a growing urgency for more advanced interrogation tools. These devices include high yield
D-D, D-T and T-T fusion reaction based neutron generators and also low energy nuclear reaction based high-energy
gamma generators. One common feature in these various devices is the use of a high-efficiency, RF-induction discharge
ion source. This discharge method provides high plasma density for high output current, high atomic species from
molecular gases for high efficiency neutron or gamma generation and long lifetime. Predictable discharge characteristics
of these plasma generators allow accurate modeling for both the beam dynamics and for the heat loads at the target spot.
Current status of the neutron and gamma generator development with experimental data will be presented.
Sandia is evaluating methods for identifying and quantifying trace signatures in field collection samples to support national deterrence policies. The first step in this process is to identify which combination of major, minor, and trace elements in a recovered collection sample provides the most reliable forensic information, and then to be able to quickly, accurately, and, in some cases, nondestructively measure these components. Conventional approaches have typically required a long, complex series of sample preparations followed by radiochemical analysis, often yielding only qualitative results. We report on our investigations to assess accelerator-based ion beam analysis methods by cross-calibrating with other methods, performing in-air analyses of bagged samples in anticipation of inspecting poorly constituted radioactive materials, and quantifying the uncertainties for detected elements.
High-energy photons and neutrons can be used to interrogate for heavily shielded fissile materials inside sealed cargo containers by detecting their prompt and/or delayed fission signatures. The FIND (Fissmat Inspection for Nuclear Detection) active interrogation system is based on a dual neutron+gamma source that uses low-energy (< 500 keV) proton- or deuteron-induced nuclear reactions to produce high intensities of mono-energetic gamma rays and/or neutrons. The source can be operated in either pulsed (e.g., to detect delayed photofission neutrons and gammas) or continuous (e.g., detecting prompt fission signatures) modes. For the gamma-rays, the source target can be segmented to incorporate different (p,γ) isotopes for producing gamma-rays at selective energies, thereby improving the probability of detection. The design parameters for the FIND system are discussed and preliminary accelerator-based measurements of gamma and neutron yields, background levels, and fission signals for several target materials under consideration are presented.
Transmission electron microscope (TEM) tomography provides three-dimensional structural information from tilt series with nanoscale resolution. We have collected TEM projection data sets to study the internal structure of photocatalytic nanoparticles. Multiple cross-sectional slices of the nanoparticles are reconstructed using an algebraic reconstruction technique (ART) and then assembled to form a 3D rendering of the object. We recently upgraded our TEM with a new sample holder having a tilt range of ±70° and have collected tomography data over a range of 125°. Simulations were performed to study the effects of field-of-view displacement (shift and rotation), limited tilt angle range, hollow (missing) projections, stage angle accuracy, and number of projections on the reconstructed image quality. This paper discusses our experimental and computational approaches, presents some examples of TEM tomography, and considers future directions.
More recent Russian grown single crystals of Cd0.8Zn0.2Te (CZT) were evaluated using proton induced x ray emission (PIXE), x ray diffraction (XRD), photoluminescence (PL), infra red (IR) transmission microscopy, leakage current measurements and response to nuclear radiation. Whereas in the past the Russian grown samples were not acceptable for gamma ray detectors application, the present samples had a somewhat better crystallinity and a higher resistivity, and did even show distinct photopeaks for an 241Am spectrum. Differences in the material properties between various Russian (n- and p-type) and U.S. (n-type) CZT are described.
We have applied several techniques, including photoluminescence, proton-induced x-ray emission, photocurrent, and alpha particle response mapping, for mapping micron- and millimeter-scale variations in cadmium zinc telluride. We have correlated the degree of inhomogeneity determined by these techniques with performance of gamma-ray spectrometers fabricated from the material.
Because of the large number of different gamma-ray detectors available, including both scintillation and semiconductor types, extensive analysis may be required to determine which detector system is optimal for a given application. In the selection of detectors for remote monitoring of nuclear materials, a methodology has been developed to assess which detectors are best suited for this application. The analysis provides a numerical ranking of the performance of each detector thereby reducing the large set of all potential detectors to a small tractable set of most promising candidates. The basis for the evaluation will be discussed, along with the application of the methodology to a wide range of scintillator and semiconductor detector materials. The most promising scintillator and semiconductor materials are identified for remote monitoring applications.
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