Neutron time-of-flight detectors (nTOF) used at Sandia's Z-Machine.

Neutron time-of-flight (nTOF) detectors have been used on Sandia National Laboratories' Z-Machine for inertial confinement fusion and magnetized liner fusion experiments to infer physics parameters including the apparent fuel-ion temperature, neutron yield, the magnetic-radius product (BR), and the liner rho-r. Single-paddle, dual-paddle, and co-axial scintillation nTOF detectors are used in axial lines-of-sight (LOS) and LOS that are 12° from the midplane. Detector fabrication, characterization, and calibration are discussed.

Superlinearity, saturation, and the PMT-Tailoring and calibration methodology for prompt radiation detectors.

This work illustrates predominant measureable nonlinearities in photomultiplier tubes (PMTs) and introduces a controllable one called "Superlinearity," signifying both a positive nonlinear response and the ability to extend linear operation by counteracting gain saturation mechanisms - charge depletion, space-charge field limitation, and secondary emission surface effects. Recognizing superlinearity and its effect on the temporal step response leads to a true definition of linearity, free of a small-signal linear assumption. Furthermore, given the prevalent use of glass microchannel-plate (MCP) PMTs in favor of a faster impulse response in spite of a small charge limit, we are motivated to examine their nonlinear amplitude response and deploy tailored gain bias string methods to fully harness the maximum linear gain as is usually done for transmissive metal mesh and reflective metal dynode PMTs. Our characterization methodology applies standard NIST-traceable calibrated laboratory equipment with absolute input-referenced techniques, examining step responses over many orders of magnitude in controlled illumination. By doing so, we quantitatively reveal the superlinearity strength independent of charge depletion, yielding true linear responsivity and effectively doubling the small-signal linear limit; this is very relevant to PMT modeling and charge deconvolution efforts. With further development, the tailoring strategies we introduce could be applied to MCP detectors, extracting all useful capillary charge with a significant improvement in large linear signal quality.

The neutron imaging diagnostic at NIF (invited).

A neutron imaging diagnostic has recently been commissioned at the National Ignition Facility (NIF). This new system is an important diagnostic tool for inertial fusion studies at the NIF for measuring the size and shape of the burning DT plasma during the ignition stage of Inertial Confinement Fusion (ICF) implosions. The imaging technique utilizes a pinhole neutron aperture, placed between the neutron source and a neutron detector. The detection system measures the two dimensional distribution of neutrons passing through the pinhole. This diagnostic has been designed to collect two images at two times. The long flight path for this diagnostic, 28 m, results in a chromatic separation of the neutrons, allowing the independently timed images to measure the source distribution for two neutron energies. Typically the first image measures the distribution of the 14 MeV neutrons and the second image of the 6-12 MeV neutrons. The combination of these two images has provided data on the size and shape of the burning plasma within the compressed capsule, as well as a measure of the quantity and spatial distribution of the cold fuel surrounding this core.

Modeling the National Ignition Facility neutron imaging system.

Numerical modeling of the neutron imaging system for the National Ignition Facility (NIF), forward from calculated target neutron emission to a camera image, will guide both the reduction of data and the future development of the system. Located 28 m from target chamber center, the system can produce two images at different neutron energies by gating on neutron arrival time. The brighter image, using neutrons near 14 MeV, reflects the size and symmetry of the implosion "hot spot." A second image in scattered neutrons, 10-12 MeV, reflects the size and symmetry of colder, denser fuel, but with only ∼1%-7% of the neutrons. A misalignment of the pinhole assembly up to ±175 µm is covered by a set of 37 subapertures with different pointings. The model includes the variability of the pinhole point spread function across the field of view. Omega experiments provided absolute calibration, scintillator spatial broadening, and the level of residual light in the down-scattered image from the primary neutrons. Application of the model to light decay measurements of EJ399, BC422, BCF99-55, Xylene, DPAC-30, and Liquid A suggests that DPAC-30 and Liquid A would be preferred over the BCF99-55 scintillator chosen for the first NIF system, if they could be fabricated into detectors with sufficient resolution.

Biomaterials for drug delivery systems.

Drug delivery systems have unusual materials requirements which derive mainly from their therapeutic role: to administer drugs over prolonged periods of time at rates that are independent of patient-to-patient variables. The chemical nature of the surfaces of such devices may stimulate biorejection processes which can be enhanced or suppressed by the simultaneous presence of the drug that is being administered. Selection of materials for such systems is further complicated by the need for compatibility with the drug contained within the system. A review of selected drug delivery systems is presented. This leads to a definition of the technologies required to develop successfully such systems as well as to categorize the classes of drug delivery systems available to the therapist. A summary of the applications of drug delivery systems will also be presented. There are five major challenges to the biomaterials scientist: (1) how to minimize the influence on delivery rate of the transient biological response that accompanies implantation of any object; (2) how to select a composition, size, shape, and flexibility that optimizes biocompatibility; (3) how to make an intravascular delivery system that will retain long-term functionality; (4) how to make a percutaneous lead for those delivery systems that cannot be implanted but which must retain functionality for extended periods; and (5) how to make biosensors of adequate compatibility and stability to use with the ultimate drug delivery system-a system that operates with feedback control.

PIP: Drug delivery systems have unusual materials requirements which derive mainly from their therapeutic role; to administer drugs over prolonged periods of time at rates that are independent of patient-to-patient variables. The chemical nature of the surfaces of such devices may stimulate biorejection processes which can be enhanced or suppressed by the simultaneous presence of the drug that is being administered. Selection of materials for such systems is further complicated by the need for compatibility with the drug contained within the system. A review of selected drug delivery systems is presented. This leads to a definition of the technologies required to successfully develop such systems as well as to categorize the classes of drug delivery systems available to the therapist. A summary of the applications of drug delivery systems will also be presented. There are 5 major challenges to the biomaterials scientist: 1) how to minimize the influence on delivery rate of the transient biological response that accompanies implantation of any object; 2) how to select a composition, size, shape, and flexibility which optimizes biocompatability; 3) how to make an intravascular delivery system that will retain longterm functioning; 4) how to make a percutaneous lead for those delivery systems that cannot be implanted but which must retain functionality for extended periods; and 5) how to make biosensors of adequate compatability and stability for use with the ultimate drug delivery system--one operating with feedback control.

It is appropriate to create new pharmaceutical products within developing countries.

Arguments are presented for utilizing local product development as an appropriate way to solve many of the current medical problems of the Third World. Guidelines for selecting problems amenable to this approach are provided, and the risks attendant on such an activity outlined. It is suggested that organizations such as the World Health Organization can encourage this approach by helping to provide training in product development and by providing consulting services for organizations in the developing world.

Continuous intravenous arabinosyl cytosine infusions delivered by a new portable infusion system.

Eighty-six patients with acute leukemia were given 116 continuous intravenous arabinosyl cytosine (Ara-C) infusions (for 24 to 432 hours) with a new portable infusion device. The infusor is powered by interchangeable elastomeric 25 ml balloon reservoirs loaded from standard syringes. The reservoir contents are discharged at nearly constant pressure through an adjustable resistance element, thereby providing flow rates from 0.4 to 2.0 ml/hour. Serum levels of labeled Ara-C delivered by the infusor were found to achieve steady-state therapeutic levels within 24 hours. The average-flow-rate-to-indicator-setting ratio determined for each infusion via scalp vein needles was 0.9 +/- 0.2. Delivery through catheters was more reliable and an average-flow-rate-to-indicator-setting ratio of 0.1 +/- 0.1 was observed. The therapeutic effectiveness of Ara-C in combination with other agents was not compromised by this delivery system. Eleven of 14 patients who received all their induction Ara-C through the infusor achieved complete remission.

Correction of the atrophic alveolar ridge by interpositional bone grafting: a progress report.

A retrospective study of postoperative stability and osseous changes was made on nine patients with maxillary or mandibular atrophy who were treated with interpositional bone grafting techniques. There was minimal discernible positional change or resorption of the portion of the maxilla or mandible that was moved by interpositional grafting procedures. Sequential radiographs and cephalometric tracings showed early consolidation of the grafted bone, minimal resorption of the respositioned osseous segments, and a small decrease of alveolar ridge height during an average potsoperative follow-up period of seven months.

Cineholomicroscopy of small animal microcirculation.

A holomicrographic system capable of recording the dynamic microscopic events occurring in a living tissue has been developed. This paper discusses the system parameters, the basic configuration, and initial test results. The reconstructed real image from the hologram can be studied with a conventional microscope. The holographic system uses a collecting lens both in recording and in reconstructing. Test results reported include the dissolving of a gas bubble under increased pressure and the movement of polystyrene balls when ejected from a needle. Present resolution is greater than 3 micro, and object velocities greater than 25 mm sec(-1) can be recorded.

Influence of Selected Processing Variables on Holographic Film Parameters: Kodak SO-243.

The influence of selected processing variables on photographic film parameters of importance in optical data processing and holographic systems has been measured. Details of the tests chosen and their importance are given. Results are presented on amplitude transmittance, diffraction efficiency, and spatial frequency response characteristics for Kodak SO-243. Three developers (D-19, D-76, and Microdol-X) and two temperatures (24 degrees C and 30 degrees C) were chosen. The use of a gray base and the relatively low spatial frequency response somewhat limit the usefulness of this film. But for some applications its relatively fast speed may offset these features.