G. F. Stone

High-energy x-ray response of photographic films: models and measurement

A detailed characterization has been established for the new, high-sensitivity double-emulsion Kodak Direct Exposure Film (DEF). The experimental data base consisted of density-versus-exposure measurements that were duplicated at several laboratories for x radiations in the 1000–10,000-eV region. The absorption and geometric properties of the film were determined, which, along with the density-exposure data, permitted the application of a relatively simple analytical model description for the optical density, D, as a function of the intensity, I (photons/μm2), the photon energy, E (eV), and the angle of incidence, θ, of the exposing radiation. A detailed table is presented for the I values corresponding to optical densities in the 0.2–2.0 range and to photon energies, E (eV), in the 1000–10,000-eV region. Experimentally derived conversion relations have been obtained that allow the density values to be expressed as either diffuse or specular. Also presented here is a similar characterization of the complementary, single-emulsion x-ray film, Kodak SB-5 (or 392). For the 1000–10,000-eV region this x-ray film is appreciably less sensitive but has higher resolution.

Demonstration of X-ray Holography with an X-ray Laser

An x-ray hologram was made by means of an x-ray laser and a laser-quality near normal incidence x-ray mirror. The high brightness and large coherence lengths of x-ray lasers now offer the potential for in vitro three-dimensional high-resolution holographic images of dynamically varying biological microstructures.

A hardened gated x-ray imaging diagnostic for inertial confinement fusion experiments at the National Ignition Facility.

A gated x-ray detector is under development for use at the National Ignition Facility that is intended to provide plasma emission images in the presence of neutron yields up to 10(15) expected during inertial confinement fusion experiments with layered cryogenic targets. These images are expected to provide valuable time-resolved measurements of core and fuel symmetries. Additional capabilities of this instrument will include the ability to make spatially resolved electron temperature measurements. A description of this instrument and its operation is given with emphasis on features that differentiate it from previous designs.

Demonstration of x-ray microscopy with an x-ray laser operating near the carbon K edge

High-brightness and short-pulse-width ( approximately 200 ps) x-ray lasers offer biologists the possibility of high-resolution three-dimensional imaging of specimens in an aqueous environment without the blurring effects associated with natural motions. As a first step toward developing the capabilities of this type of x-ray microscopy we have used a tantalum x-ray laser (lambda = 4.483 nm) together with an x-ray zone plate lens to image a test pattern. The observed image shows a detector-limited resolution of approximately 75 nm and paves the way to three dimensional biological imaging with high spatial resolution (20-30 nm).

Improved gas-filled hohlraum performance on Nova with beam smoothing

Gas-filled hohlraums are presently the base line ignition target design for the National Ignition Facility. Initial Nova [E. M. Campbell et al. Rev. Sci. Instrum. 57, 2101 (1986).] experiments on gas-filled hohlraums showed that radiation temperature was reduced due to stimulated Brillouin and stimulated Raman scattering losses and that implosion symmetry had shifted compared with vacuum hohlraums and calculations. Subsequent single beam experiments imaging thermal x-ray emission showed the shift is due to laser–plasma heating dynamics and filamentation in a flowing plasma. Experiments using a single beam have shown that scattering losses and effects of filamentation are reduced when the beam is spatially smoothed with a random phase plate or kinoform phase plate. Scattering is further reduced to less than 5% of the incident laser energy when temporal smoothing is added.

Production and characterization of large plasmas from gas bag targets on Nova

Large plasmas are created by illuminating gas‐filled thin‐walled balloon‐like targets using the Nova laser [E. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)]. The targets consist of a 5000–6000 A skin surrounding 1 atm of neopentane, which, when ionized, becomes a plasma with an electron density of 1021 electrons/cm3. X‐ray images of the gas bag target are used to evaluate the size and uniformity of the plasma by comparison with LASNEX [R. M. More, J. Quant. Spectrosc. Radiat. Transfer 27, 345 (1982)] simulations. The gas bags are heated with converging and diverging beam spots. The most uniform plasmas are created by illuminating the target with large converging beam spots that overlap to cover most of the surface of the gas bag. The gas bag plasma is heated to a peak temperature of approximately 3.5 keV, with 25 kJ of 3ω laser light in a 1 ns square pulse.

X-ray and neutron sensitivity of imaging plates

Periodic sensitivity calibration of imaging plates (IP) is crucial for quantitative understanding of x-ray data obtained at the National Ignition Facility (NIF). To test the x-ray sensitivity of the IPs and the scanners, we developed an x-ray exposure station based on radioactive isotopes (55Fe, 109Cd, and 241Am). This apparatus provides a convenient setup for a periodical test of the IP’s and the scanners. On NIF implosion experiments with deuterium-tritium mixture fuel, the neutrons produced in the capsule hit the imaging plates and impose background signal. Therefore it is also important to know the neutron sensitivity of the IPs. The sensitivity for 14 MeV neutrons was measured on high neutron yield shots at the OMEGA laser facility. The measured sensitivities were compared with the results of Monte Carlo simulations.

Experimental study of neutron induced background noise on gated x-ray framing cameras

A temporally gated x-ray framing camera based on a proximity focus microchannel plate is one of the most important diagnostic tools of inertial confinement fusion experiments. However, fusion neutrons produced in imploded capsules interact with structures surrounding the camera and produce background to x-ray signals. To understand the mechanisms of this neutron induced background, we tested several gated x-ray cameras in the presence of 14 MeV neutrons produced at the Omega laser facility. Differences between background levels observed with photographic film readout and charge-coupled-device readout have been studied.

Improvements to a MCP based high speed x-ray framing camera to have increased robustness in a high neutron environment

As neutron yields increase at the National Ignition Facility (NIF) the need for neutron ‘hardened’ diagnostics has also increased. Gated Imagers located within the target chamber are exposed to neutrons which degrade image quality and damage electronics. In an effort to maintain the signal to noise ratio (S/N) on our images and mitigate neutron induced damage, we have implemented numerous upgrades to our X-ray framing cameras. The NIF Gated X-ray Detector (GXD), design has evolved into the Hardened Gated X-ray Detector, HGXD. These improvements are presented with image data taken on high yield NIF shots showing enhanced image quality. Additional upgrades were added to remotely locate sensitive electronics and ease operational use.

Phototocatalytic Lithography of Poly(propylene sulfide) Block Copolymers: Toward High-Throughput Nanolithography for Biomolecular Arraying Applications

Photocatalytic lithography (PCL) is an inexpensive, fast, and robust method of oxidizing surface chemical moieties to produce patterned substrates. This technique has utility in basic biological research as well as various biochip applications. We report on porphyrin-based PCL for patterning poly(propylene sulfide) block copolymer films on gold substrates on the micrometer and submicrometer scales. We confirm chemical patterning with imaging ToF-SIMS and low-voltage SEM. Biomolecular patterning on micrometer and submicrometer scales is demonstrated with proteins, protein-linked beads. and fluorescently labeled proteins.