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An original system has been developed capable of performing three-dimensional Energy Recoil Detection Analysis (ERDA) of hydrogen in materials with scanned and finely focused heavy-ion beams. The technique is being used at the Lawrence Livermore National Laborotory Multi-user Tandem Laboratory to measure the hydrogen content in materials under consideration for use in the Yucca Mountain nuclear waste repository. From the measurement of hydrogen concentration profiles we can extrapolate reaction rates. A critical problem is the rate of dissolution of the glass being used. The HI-ERDA (Heavy Ion-ERDA) technique can provide this information which is needed in order to predict the overall rate of nuclear waste glass degradation in a waste repository. The technique is calibrated using a silicon wafer implanted with a known concentration of hydrogen. The sample is illuminated by a 35Cl ion beam that is micro-scanned across the sample. From these measurements we reconstruct three dimensional profiles of hydrogen content which can then be used to obtain spatially-resolved hydrogen depth profiles.

A wide variety of materials have been analyzed using the nuclear microprobe in Livermore, including metals, low density foams, compound semiconductors for room temperature detectors, glasses and particulates. A brief overview of our recent work is given, in addition to a broader discussion of three specific applications. In the first application, Ion Microtomography (IMT) is used to produce three-dimensional mass density maps of low density foams being developed as targets for Z-pinch physics experiments. In the second application, we produce two-dimensional elemental maps of CdZnTe crystals being developed as room temperature radiation detectors. The maps help determine the effect of local variations in stoichiometry on detector performance. Finally, we discuss the measurement of trace elements and radial diffusion profiles in superconducting wire using micro-scale Particle-Induced X-ray Emission (PIXE).

Nuclear microscopy is well suited for analyzing large particle populations as well as individual particles of interest in various types of collection samples. Unlike some commonly used in situ techniques, nuclear microscopy can quantitatively characterize particles embedded within the sample or particles that are too small to be reliably removed from their collection media. Additional advantages include its capability for the detection of minor and trace elements, its capability to simultaneously analyze multiple elements with little or no prior sample preparation, and its potential for automated analyses. Preliminary data are presented of particle size and composition measurements conducted on air filters. The potential of applying nuclear microscopy to the cataloging of micron-scale cometary remnants captured in low density aerogel collectors is also explored. Because of its importance to a variety of collection programs, an innovative high-throughput ion beam imaging and analysis system is being jointly developed by Sandia and Lawrence Livermore national laboratories for rapid quantitative particle characterization.

Significant developments have occurred in the technology of room-temperature PbI2 nuclear sensors which lead to some improvements in the detection of high energy gamma-rays. Discussion of crystal growth, purification, monitoring purification, and detector processing are reviewed as they relate to device performance.

The Ion Micro-Analysis Group (IMAG) in Livermore conducts quantitative trace elemental analysis with PIXE and depth profiling with IBS using an MeV ion microbeam. The system has the capability to produce two-dimensional trace element and IBS images. PIXE analyses have been conducted on HgI2 and PbI2 crystals and detector materials in order to identify and quantify near surface trace contaminants. IBS measurements have been conducted to investigate elemental depth distributions in various materials. The results of measurements on several different samples are reported and a discussion of factors affecting quantitative in vacuo microanalysis of these materials is presented.

Measurements of the transmitted energy straggling are made using a silicon surface barrier detector for 2 to 7 MeV protons incident on thin foil targets of Al, Ti, Ag and W. The straggling widths are studied as a function of target thickness, proton energy and target species. The combination of several incident energies with many target thicknesses provides data for the investigation of energy straggling in the region where Tschalar's theory is applicable. The theoretical estimates are found to agree with the measured values for higher energy beams, but are about 10% lower than the data for lower incident energies. A simple empirical expression for the straggling is given which agrees with the experimental data for energy losses up to 60%.

Radiation-resistant optical fibers fabricated with purified silica glass were irradiated at room temperature with 14-MeV neutrons from the RTNS-II. The induced loss in light transmission was measured in situ during irradiation. It was found that the fusion neutron response of the optical fibers can be approximately classed in three types as follows: (1) a large induced loss with little recovery; (2) a large induced loss with a quick recovery; and (3) a small induced loss with a saturated tendency. The induced-loss rate has been calculated on the basis of damage components that depend mainly on neutron fluence and show little recovery. Fusion neutron irradiation effects on related optoelectronic devices and their hardness levels are shown. These are the neutron fluences at which important performance parameters of the devices begin to degrade. The data are useful for fiber-optics design for fusion diagnostic systems. >

Rotating Target Neutron Source-II (RTNS-II) is a national facility for fusion materials research. It contains two 14 MeV neutron sources. Deuterons are accelerated to ∼ 400 keV and transported to a rotating titanium tritide target. Present source strength is greater than 1 × 10 13 n/s and source diameter is 1 cm fwhm. An air-levitated vacuum seal permits rotation of the target at 5000 rpm with negligible impact on accelerator vacuum system gas load. Targets are cooled by chilled water flowing through internal channels in a copper alloy substrate. Substrates are produced by solid-state diffusion bonding of two sheets, one containing etched cooling channels. An electroforming process is being developed which will reduce substrate cost and improve reliability. Titanium tritide coating thickness is ∼ 10 μm giving an initial tritium inventory for the present 23 cm diameter targets of 3.7 × 10 7 MBq. Operating interval between target changes is typically about 80 h. Thirteen laboratories and universities have participated in the experimental program at RTNS-II. Most measurements have been directed at understanding defect production and low-dose damage microstructure. The principal diagnostic tools have been cryogenic resistivity measurements, mechanical properties assessment and transmission electron microscopy. Some engineering tests have been conducted in support of near-term magnetic confinement experiments and of reactor materials which will see small lifetime doses.

Results are reported for an ongoing effort to optimize D + beam production by the MATS-III ion source used at RTNS-II. The three seven-aperture electrodes, originally consisting of water-cooled copper, have now been tested using uncooled molybdenum and with water cooling on the second (decel) electrode only. Details of the change, the results of the testing, and the benefits in operation, performance and cost are given.