This PDF file contains the front matter associated with SPIE Proceedings Volume 8144, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

It has been reported that detectors made of lanthanum-cerium halides (LaBr₃:Ce and CeBr₃) have superior energy resolution for gamma-radiation detection compared to what is offered by conventional sodium iodide (NaI:T1) detectors. Although superior energy resolution may be observed, one major barrier that has hindered the rapid adaptation of lanthanum halides is their self-activity, due primarily to the presence of isotope ¹³⁸La, and the α contamination, due to the trace amount of actinides. It has also been observed that the lanthanum-cerium halides contain a substantial amount of self-activity caused by the radioactive isotope ¹³⁸La. Additionally, LaBr₃:Ce spectra are also affected by β contaminations in the low-energy region. To use either LaBr₃:Ce or CeBr₃ for high-sensitivity gamma detection, it may be necessary to have the self-activity as well as α and β contaminations removed or reduced. This paper describes a novel algorithmic approach for self-activity and contamination reduction for LaBr₃:Ce and CeBr₃ detectors using a third reference NaI:T1 detector. We present a computational procedure for separating self-activity from the gamma spectra obtained by LaBr₃:Ce detectors. With the self-activity spectra precalculated, it is possible to perform real-time self-activity removal. This procedure can be implemented as an automatic self-activity subtraction module for gamma-radiation detectors made of LaBr₃:Ce and/or CeBr₃ crystals. With this approach, it is possible to develop a new generation of LaBr₃:Ce detectors capable of producing spectra as clean as those obtained by conventional NaI:T1 detectors, but with much improved energy resolutions.

Neutron flux from linear accelerators is conventionally monitored using ionization chambers containing one or more foils thinly coated with a fissionable or fissile material. Due to the long pulse rise times resulting from the ionization mechanism, fission chambers are prone to pulse pile-up in high-neutron-flux environments. In addition, their relatively low efficiencies result in extremely long counting times in low-flux environments. To ameliorate these effects, a novel type of neutron flux monitor, consisting of fissionable material loaded in a liquid scintillator, has been developed, characterized, and tested in the beam line at the Los Alamos Neutron Science Center. This is a rugged, cost-efficient detector with high efficiency, a short signal rise time, and the ability to be used in low neutron-flux environments. Compared with a conventional fission chamber, the fissionable scintillator displays a significantly higher event rate. Related research on nanocomposite scintillators for gamma-ray detection suggests the possibility of extending this approach by synthesizing fissionable material nanoparticles and loading them into an organic scintillator. We will present results of the design and characterization process and an analysis of the results of the beam line experiments.

In recent years, composite scintillators consisting of nanosize inorganic crystals in an organic matrix have been actively developed. Ideally these scintillators would have efficiency and resolution similar to inorganic crystals, but at the same time would be inexpensive and easy to manufacture. In order to make composite scintillators optically transparent, McKigney et al. finds that nanosize inorganic crystals should be used in order to reduce optical scattering. One way to produce these nanosize inorganic crystals is through wet milling, where inorganic crystals are ground with microsize beads in an organic solvent to achieve size reduction. Milling is relatively simple in terms of preparation and equipment; however, milling is also known to introduce defects into the ground material. Therefore, a new light yield measurement technique is developed to evaluate the degree to which milling alters the light yield of the milled inorganic crystals. In this work, the light yield measurement technique is applied to samples containing BaFCl:Eu inorganic crystals milled in a tributyl phosphate (TBP) and cyclohexane mixture.

Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF₃:Ce) and cerium bromide (CeBr₃) without requiring the growth of large crystals. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have been seen in photoluminescence from silicon nanocrystals in a densely packed ensemble. We have fabricated nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr₃. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.

Evolution of c-axis oriented YBa₂Cu₃O_7-y (YBCO) thin films under 200 MeV Ag ion irradiation at 79 K is studied by in-situ temperature dependent resistivity and in-situ low temperature x-ray diffraction. The electronic energy loss (25.18 keV nm^-1) of these ions is shown to induce secondary electrons, which create oxygen disorder selectively in the CuO basal planes of fully oxygenated YBCO in a cylindrical region of radius 97 nm around the ion induced latent tracks of radius 1.9 nm. This technique provides a unique way of creating oxygen disorder in a fully oxygenated YBCO, which was not possible earlier.

The National Ignition Facility at Lawrence Livermore National Laboratory is the world's leading facility to study the physics of igniting plasmas. Plasmas of hot deuterium and tritium, undergo d(t,n)α reactions that produce a 14.1 MeV neutron and 3.5 MeV a particle, in the center of mass. As these neutrons pass through the materials surrounding the hot core, they may undergo subsequent (n,x) reactions. For example, ¹²C(n,n'γ)¹²C reactions occur in remnant debris from the polymer ablator resulting in a significant fluence of 4.44 MeV gamma-rays. Imaging of these gammas will enable the determination of the volumetric size and symmetry of the ablation; large size and high asymmetry is expected to correlate with poor compression and lower fusion yield. Results from a gamma-ray imaging system are expected to be complimentary to a neutron imaging diagnostic system already in place at the NIF. This paper describes initial efforts to design a gamma-ray imaging system for the NIF using the existing neutron imaging system as a baseline for study. Due to the cross-section and expected range of ablator areal densities, the gamma flux should be approximately 10^-3 of the neutron flux. For this reason, care must be taken to maximize the efficiency of the gamma-ray imaging system because it will be gamma starved. As with the neutron imager, use of pinholes and/or coded apertures are anticipated. Along with aperture and detector design, the selection of an appropriate scintillator is discussed. The volume of energy deposition of the interacting 4.44 MeV gamma-rays is a critical parameter limiting the imaging system spatial resolution. The volume of energy deposition is simulated with GEANT4, and plans to measure the volume of energy deposition experimentally are described. Results of tests on a pixellated LYSO scintillator are also presented.

The large fluence of 14-MeV neutrons produced in high-yield inertial confinement fusion (ICF) experiments creates a variety of backgrounds in x-ray imagers viewing the implosion. Secondary charged particles produce background light by Cherenkov emission, phosphor screen excitation and possibly scintillation in the optical components of the imager. In addition, radiation induced optical absorption may lead to attenuation of the signal. Noise is also produced directly in the image recorder itself (CCD or film) via energy deposition by electrons and heavy charged particles such as protons and alphas. We will present results from CCD background measurements and compare them to Monte Carlo calculations. In addition we show measurements of luminescence and long-term darkening for some of the glasses employed in imagers.

X-ray imaging is integral to the measurement of the properties of hot plasmas. To this end, a suite of gated x-ray imagers have been developed for use in a wide range of experiments at the National Ignition Facility (NIF). These instruments are sensitive to x-rays over the range of 0.7-90keV and can acquire images at 20ps intervals for source intensities ranging over several orders of magnitude. We review the design, technology, and construction of these instruments and present recent results obtained from NIF experiments in which gated x-ray imagers have played a key role. The radiation environment associated with Inertial Confinement Fusion (ICF) experiments presents unique challenges for x-ray imaging. We report on the performance of gated imagers that have been optimized for this harsh environment and describe diagnostics to be deployed in the near future that will provide x-ray images of imploding ICF capsules in the presence of backgrounds associated with neutron yields above 10¹⁶. Such images will provide crucial data that will enable even higher neutron yields and successful ignition.

Currently there is a significant amount of interest in standoff radiation detection. One of the biggest challenges is to separate small radiation signals from large varying background radiation. Many systems have been developed to address this problem that rely on coded-aperture and/or Compton imaging. These imaging systems tend to be large, heavy, complex, and therefore expensive. In this paper we report on the development of a self-occluding directional gamma radiation sensor that is relatively small (<40 kg), inexpensive, and simple in design. Laboratory and field measurements suggest that these sensors will work as well as the gamma imaging systems for many radiation detection applications at a fraction of the cost, weight, and complexity. An azimuth can be resolved with a standard deviation of 7° in 10 seconds for a source yielding 45 CPS at the detector in a 300 CPS background radiation field. This paper describes the self-occluding quad NaI directional gamma radiation detector, the impact of gamma energy and distance on angular precision and accuracy, and potential applications.

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.

The Calliope plant, a pool-type irradiation facility located at the Research Centre ENEA-Casaccia (Rome), is equipped with the ⁶⁰Co γ source in a high-volume shielded cell. Calliope facility is involved in radiation processing research on materials (polymers and optical components) and on devices to be used in hostile radiation environment such as nuclear plants, aerospace experiments and High Energy Physics experiments. The aim of this work is to give an overall picture of the activity we are carrying on at our laboratories with a mention to the possible applications in the field of scintillators and glasses, like doping effect to induce radiation resistance in scintillators, glasses for safe nuclear fuel disposal, suitable substitute oxides which can replace PbO in the preparation of lead-free glasses complying environmental regulations.

In this paper we describe a new nondestructive evaluation (NDE) technique called Compton Imaging Tomography (CIT) for reconstructing the complete three-dimensional internal structure of an object, based on the registration of multiple two-dimensional Compton-scattered x-ray images of the object. CIT provides high resolution and sensitivity with virtually any material, including lightweight structures and organics, which normally pose problems in conventional x-ray computed tomography because of low contrast. The CIT technique requires only one-sided access to the object, has no limitation on the object's size, and can be applied to high-resolution real-time in situ NDE of large aircraft/spacecraft structures and components. Theoretical and experimental results will be presented.

Polypropylene is irradiated by 6 MeV electrons in presence of Iodine and subsequently characterized by the techniques such as weight gain, weight loss, Energy Dispersive Spectroscopy (EDS), Scanning Electron microscopy (SEM), Ultraviolet Visible Spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray diffraction (XRD). It is unambiguously observed that the electron beam assists the doping and trapping of volatile Iodine in Polypropylene. Presence of the Iodine during irradiation strongly supports the radiation-induced decrease in the band gap up to almost visible region. Further, the doped Iodine strongly interacts and decreases the crystalline structure of the Polypropylene. It is also observed that the nanoclusters of Iodine having size around 100 nm are formed on the surface of Polypropylene due to electron irradiation.

Passive and active detection of gamma rays from shielded radioactive materials, including special nuclear materials, is an important task for any radiological emergency response organization. This article reports on the current trends and status of gamma radiation detection objectives and measurement techniques as applied to nonproliferation and radiological emergencies. In recent years, since the establishment of the Domestic Nuclear Detection Office by the Department of Homeland Security, a tremendous amount of progress has been made in detection materials (scintillators, semiconductors), imaging techniques (Compton imaging, use of active masking and hybrid imaging), data acquisition systems with digital signal processing, field programmable gate arrays and embedded isotopic analysis software (viz. gamma detector response and analysis software [GADRAS]¹), fast template matching, and data fusion (merging radiological data with geo-referenced maps, digital imagery to provide better situational awareness). In this stride to progress, a significant amount of inter-disciplinary research and development has taken place-techniques and spin-offs from medical science (such as x-ray radiography and tomography), materials engineering (systematic planned studies on scintillators to optimize several qualities of a good scintillator, nanoparticle applications, quantum dots, and photonic crystals, just to name a few). No trend analysis of radiation detection systems would be complete without mentioning the unprecedented strategic position taken by the National Nuclear Security Administration (NNSA) to deter, detect, and interdict illicit trafficking in nuclear and other radioactive materials across international borders and through the global maritime transportation-the so-called second line of defense.

To improve the resolution and field of view of high-energy Compton-scattered x-ray and gamma-ray imaging systems, we have developed and tested apodized imaging optics based on apertures with depth-dependent cross sections fabricated in an x-ray-absorbing material. Through ray-tracing modeling, we determined the optimum aperture shapes (apodizations) that maximize the field of view and/or resolution of the system. Such apodized apertures can be used either in single-aperture optics, or in coded-aperture arrays. Potential applications of this technology include nondestructive evaluation (NDE) of materials and structures, in particular Compton imaging tomography (CIT), x-ray and gamma-ray astronomy, and medical imaging.

X-ray imaging instruments will operate in a harsh ionizing radiation background environment on implosion experiments at the National Ignition Facility. These backgrounds consist of mostly neutrons and gamma rays produced by inelastic scattering of neutrons. Imaging systems based on x-ray framing cameras with film and CCD's have been designed to operate in such harsh neutron-induced background environments. Some imaging components were placed inside a shielded enclosure that reduced exposures to neutrons and gamma rays. Modeling of the signal and noise of the x-ray imaging system is presented.

Silicon-based photodetectors offer several benefits relative to photomultiplier tube-based scintillator systems. Solid-state photomultipliers (SSPM) can realize the gain of a photomultiplier tube (PMT) with the quantum efficiency of silicon. The advantages of the solid-state approach must be balanced with adverse trade-offs, for example from increased dark current, to optimize radiation detection sensitivity. We are designing a custom SSPM that will be optimized for green emission of thallium-doped cesium iodide (CsI(Tl)). A typical field gamma radiation detector incorporates thallium doped sodium iodide (NaI(Tl)) and a radiation converter with a PMT. A PMT's sensitivity peaks in the blue wavelengths and is well matched to NaI(Tl). This paper presents results of photomultiplier sensitivity relative to conventional SSPMs and discusses model design improvements. Prototype fabrications are in progress.