The National Ignition Facility at Lawrence Livermore National Laboratory is in need of a gamma-ray imaging diagnostic system to image imploding capsules for inertial confinement fusion experiments. A prototype system was designed and constructed to image 4.44 MeV gammas resulting from 12C(n,n’ γ)12C interactions with the plastic ablator. Testing of the system was undertaken at the OMEGA Laser at the University of Rochester using hard x-rays from an imploding capsule and at the High Intensity Gamma Source at Duke University using a 4.47 MeV gamma beam. The results of these tests produced a number of lessons and recommendations presented here.
Testing of the gamma ray imaging system will continue at the High Intensity Gamma Source (HIGS) at Duke University. Previous testing at OMEGA gave useful information but at much lower photon energies. Utilizing HIGS 108 gammas/s and its tight beam we will be able to characterize the system in the energy regime that it was designed for namely 4.44 MeV. HIGS offers the ability to tune the beam’s energy from 1-20 MeV by way of controlling the inverse Compton scattering off of a relativistic electron beam. With this feature characterization in a range of energies will be possible. Targets were made using a ray-tracing program that replicates a 12-micron ideal pinhole and a 20 cm long 300-micron gold penumbra aperture. The latter will require reconstruction of the coded images.
We have investigated the light-transport properties of scintillator arrays with long, thin pixels (deep pixels) for use in high-energy gamma-ray imaging. We compared 10x10 pixel arrays of YSO:Ce, LYSO:Ce and BGO (1mm x 1mm x 20 mm pixels) made by Proteus, Inc. with similar 10x10 arrays of LSO:Ce and BGO (1mm x 1mm x 15mm pixels) loaned to us by Saint-Gobain. The imaging and spectroscopic behaviors of these scintillator arrays are strongly affected by the choice of a reflector used as an inter-pixel spacer (3M ESR in the case of the Proteus arrays and white, diffuse-reflector for the Saint-Gobain arrays). We have constructed a 3700-pixel LYSO:Ce Prototype NIF Gamma-Ray Imager for use in diagnosing target compression in inertial confinement fusion. This system was tested at the OMEGA Laser and exhibited significant optical, inter-pixel cross-talk that was traced to the use of a single-layer of ESR film as an inter-pixel spacer. We show how the optical cross-talk can be mapped, and discuss correction procedures. We demonstrate a 10x10 YSO:Ce array as part of an iQID (formerly BazookaSPECT) imager and discuss issues related to the internal activity of 176Lu in LSO:Ce and LYSO:Ce detectors.
Successful images of hard x-rays were taken at the OMEGA Laser at the Laboratory for Laser energetics ant he University of Rochester. This facility served as a surrogate for the National Ignition Facility for which this system was designed. Eleven plastic shells filled with 3He pellets were imploded producing soft and hard x-rays. As the system was designed to image 4.44MeV gammas the hard x-rays were of particular interest. These bremsstrahlung x-rays were emitted for the outer plastic shell and imaged using the gamma ray imaging system 13 meters away. A number of filtering arrangements were used to do transmission radiography of the source providing spectrum information. A 200-micron pinhole aperture was used to image the source. These shots provide information critical in characterizing the performance of the system
Image intensifiers combined with columnar scintillators have found application in x-ray and gamma-ray, biomedical
imaging and other fields. In scintillator imaging, hundreds or thousands of optical photons can illuminate the
faceplate of the image intensifier in a small area, essentially simultaneously. This is a situation not found in the
typical design application for an image intensifier, night vision or low-light-level imaging. Microchannel plates
(MCPs) are known to exhibit gain saturation that could result in non-linear signal response in scintillator imaging,
limiting quantitative measurement capabilities. A calibrated LED photon source was developed that can provide a
known average number of photons per unit area in a small spot size, similar to that seen due to a gamma-ray
interaction in a BazookaSPECT imager. A BazookaSPECT imager is composed of a columnar scintillator and an
image intensifier, with output light optically imaged onto a CCD camera. The calibrated source was used to
investigate gain-saturation effects for two Proxivision, GmbH image intensifiers, a single-stage BV 2583 EZ and a
two stage BV 2583 QZ-V 100N in a BazookaSPECT imaging configuration. No gain saturation was found for the
single-stage image intensifier up to more than 100 optical photons per microchannel, but significant gain-saturation
non-linearities were measured in the two-stage image intensifier at high gains for >12 optical photons per
microchannel. Implications for scintillator imaging using such systems are discussed.
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 very first demonstration of our refreshable holographic display based on photorefractive polymer was published in
Nature early 20081. Based on the unique properties of a new organic photorefractive material and the holographic
stereography technique, this display addressed a gap between large static holograms printed in permanent media
(photopolymers) and small real time holographic systems like the MIT holovideo. Applications range from medical
imaging to refreshable maps and advertisement. Here we are presenting several technical solutions for improving the
performance parameters of the initial display from an optical point of view. Full color holograms can be generated
thanks to angular multiplexing, the recording time can be reduced from minutes to seconds with a pulsed laser, and full
parallax hologram can be recorded in a reasonable time thanks to parallel writing. We also discuss the future of such a
display and the possibility of video rate.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.