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A buried aluminum nitride (AIN) layer was formed by nitrogen ion implantation into pure aluminum with doses of 10, 18 and 28 × 1017 N+ cm−2 at 200 keV. In order to analyze the profile of the implanted nitrogen in aluminum, 3.5 MeV 4He+ backscattering was used, in preference to 2.0 Mev 4He+ backscattering. A rectangular-like profile of the implanted nitrogen was obtained from the Rutherford backscattering spectra after the dose of 10 × 1017 N+ cm−2. The nitrogen to aluminum ratio at the rectangular-like profile is about 0.9–1.0. The results of X-ray diffraction and transmission electron diffraction indicated that aluminum nitride structure is essentially the hexagonal crystal. Aluminum nitride with f.c.c. structure also appeared on nitrogen implantantion into aluminum. This is a transient structure. The resistivity of AIN formed by nitrogen implantation into aluminum is about (1.4−2.0) × 1012 Ω cm.

Airborne microwave measurements of precipitation associated with Super Typhoon Flo in the western North Pacific were conducted during September 16-18, 1990. The sensor package aboard the NASA DC-8 aircraft included a dual-frequency precipitation radar at 10 GHz and 34 GHz and a host of radiometers operating at 10 GHz, 18 GHz, 19 GHz, 34 GHz, and 92 GHz, as well as three frequencies near the strong water vapor absorption line of 183.3 GHz. The measurements were made during a few passes over the storm center, and active and passive microwave signatures of the rainbands were detected with a fine spatial resolution. The relationship between the measured brightness temperature and radar-estimated rain rate is examined at the frequencies between 10-92 GHz. At both 34 and 92 GHz this relationship is analyzed with the 10 GHz radar reflectivity factor measured at altitudes above the freezing layer as a further constraint. The results show that frozen hydrometeors strongly scatter radiation at these frequencies, especially at 92 GHz. It was shown from a close examination of both active and passive microwave signatures that a significant scattering of radiation at frequencies 118 GHz occurred in the inner eyewall at altitudes of 3-8 km. This scattering of microwave radiation by hydrometeors in both liquid and frozen forms is discussed under the authors' current understanding of the scattering mechanism. >

Ion beams have been used for surface modification, semiconductor device fabrication and for material analysis, which makes ion-material interactions of significant importance. Ion implantation will produce new compositions near the surface by ion mixing or directly by implanting desired ions. Ions exchange their energy to the host material as they travel into the material by several different processes. High energy ions ionize the host atoms before atomic collisions transfer the remaining momentum and stop the incident ion. As they penetrate the surface, the low energy ions ionize the host atoms, but also have a significantly large momentum transfer mechanism near the surface of the material. This leads to atoms, groups of atoms and electrons being ejected from the surface, which is the momentum transfer process of sputtering. This talk addresses the acoustic waves generated during ion implantation using modulated heavy ion beams. The mechanisms for elastic wave generation during ion implantation, in the regimes where sputtering is significant and where implantation is dominant and sputtering is negligible, has been studied. The role of momentum transfer and thermal energy production during ion implantation was compared to laser generated elastic waves in an opaque solid as a reference, since laser generated ultrasound has been extensively studied and is fairly well understood. The thermoelastic response dominated in both high and low ion energy regimes since, apparently, more energy is lost to thermal heat producing mechanisms than momentum transfer processes. The signal magnitude was found to vary almost linearly with incident energy as in the laser thermoelastic regime. The time delays for longitudinal and shear waves-were characteristic of those expected for a purely thermal heating source. The ion beams are intrinsically less sensitive to the albedo of the surface.

The performance of a compact and efficient neutron generator, using the 3H(d, n) reaction and a gas target, is reported. The target is formed in a windowless, differentially pumped vessel pressurised to 7.5 Torr. An extended source of 15 MeV neutrons is produced when the target is bombarded by a 10 mA beam of 210 keV deuterons. Measurements are reported of the neutron energy spectra, neutron and gamma-ray dose rates, target lifetime and tritium handling. The neutron flux distribution of the extended target was measured and compared with the predictions of a simple beam-gas interaction model. The measured neutron source strength is 1.7 +/- 0.4 X 10(12) neutrons per second. The source output is limited by target beam current, not target power considerations.

States excited by the $^{99}\mathrm{Ru}(\ensuremath{\alpha},2n\ensuremath{\gamma})^{101}\mathrm{Pd}$, $^{88}\mathrm{Sr}(^{16}\mathrm{O},3n\ensuremath{\gamma})^{101}\mathrm{Pd}$, and $^{92}\mathrm{Zr}(^{12}\mathrm{C},3n\ensuremath{\gamma})^{101}\mathrm{Pd}$ reactions have been studied by measuring the $\ensuremath{\gamma}$-ray yield as a function of incident projectile energy, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions, and $\ensuremath{\gamma}$-ray linear polarizations. Three intense $\ensuremath{\gamma}$-ray cascades were observed. These cascades are produced by quasirotational bands built on the 5/${2}^{+}$, 7/${2}^{+}$, and 11/${2}^{\ensuremath{-}}$ intrinsic states of the nucleus. A decay scheme is given which includes states with energy up to 6488 keV and angular momentum up to 35/2. The quasirotational bands seen in $^{101}\mathrm{Pd}$ are similar to the bands in the adjacent even-even nuclei which suggests that this odd-$A$ nucleus can be described as a particle decoupled from an even-even core. A cascade of seven $\ensuremath{\gamma}$ rays in $^{102}\mathrm{Rh}$ was also observed following the $^{92}\mathrm{Zr}(^{12}\mathrm{C},p n)^{102}\mathrm{Rh}$ reaction.[NUCLEAR REACTION $^{99}\mathrm{Ru}(\ensuremath{\alpha},2n\ensuremath{\gamma})$, $E=16\ensuremath{-}24$ MeV; $^{92}\mathrm{Zr}(^{12}\mathrm{C},3n\ensuremath{\gamma})$, $E=45\ensuremath{-}56$ MeV; $^{88}\mathrm{Sr}(^{16}\mathrm{O},3n\ensuremath{\gamma})$, $E=56\ensuremath{-}64$ MeV; measured $\ensuremath{\sigma}(E)\ensuremath{\gamma}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, $\ensuremath{\sigma}(\ensuremath{\theta})\ensuremath{\gamma}$, linear $P$; deduced decay scheme, $J$, $\ensuremath{\pi}$.]

The energy level structure of 103 Pd was studied using the reactions 100 Ru(α, nγ) 103 Pd and 94 Zr( 12 C, 3nγ) 103 Pd. The experiments included the measurement of γ-ray yield as a function of incident projectile energy, γ-γ coincidence measurements, γ-ray angular distributions, and γ-ray linear polarization measurements. Two ΔI = 2 bands built on the 7 2 + and 11 1 − intrinsic states were observed. The ( 12 C, 3n) reaction was found to be much more effective than the (α, n) reaction in exciting these bands. A decay scheme is presented showing energies up to 6049 keV and spins up to 35 2 . Additional information relating to the coupling between the odd particle and the core is presented. A cascade of six γ-rays in 103 Rh was observed following the reaction 94 Zr( 12 C, p2nγ) 103 Rh.

Two components in the spontaneous-fission decay of $^{237m}\mathrm{Pu}$ have been investigated. The half-lives of the two isomers are 82 \ifmmode\pm\else\textpm\fi{} 8 nsec and 1120 \ifmmode\pm\else\textpm\fi{} 80 nsec. The production ratio of the two components was determined for three different bombarding conditions: $^{235}\mathrm{U}$ + 24-MeV $\ensuremath{\alpha}$ particles, $^{235}\mathrm{U}$ + 27-MeV $\ensuremath{\alpha}$ particles, and $^{237}\mathrm{Np}$ + 12.1-MeV deuterons. The dependence of the production ratio on angular momentum deposition for the various reactions shows that the two shape isomers differ in spin, with the short-lived component corresponding to the lower-spin state. The experimental isomer ratios are compared with statistical-model calculations. Assuming the validity of the statistical description of isomer population, and the absence of a significant $\ensuremath{\gamma}$-decay branch for the high-spin isomer, the deformation associated with shape isomerism can be deduced from isomer-spin information extracted from the present experiment and reference to the Nilsson diagram at large deformation. The deformation indicated is approximately $\ensuremath{\epsilon}=0.6$, in good agreement with theoretical estimates.

A combined analysis of absolute in-plane and $z$-axis (spin-flip) $p\ensuremath{-}\ensuremath{\gamma}$ angular correlation measurements for ${0}^{+}$-${2}^{+}$-${0}^{+}$ transitions leads to various combinations of substate cross sections, populations, and phase angles. These quantities are compared with predictions based on reaction-mechanism theories. The test is very stringent. Measurements and analyses have been carried out for $^{12}\mathrm{C}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})^{12}\mathrm{C}^{*}$(4.44 MeV) and $^{58}\mathrm{Ni}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})^{58}\mathrm{Ni}^{*}$(1.45 MeV) at ${E}_{p}=20$ MeV, and for $^{54}\mathrm{Fe}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})^{54}\mathrm{Fe}^{*}$(1.41 MeV) at ${E}_{p}=19.6$ MeV.

Proton spin-flip probabilities and differential inelastic scattering cross sections were measured over a large angular region for the following ${2}^{+}$ excitations: 4.44 MeV in $^{12}\mathrm{C}$ at 12, 13, 14, 15, and 20 MeV; 1.45 MeV in $^{58}\mathrm{Ni}$ at 9.25, 10.46, 15, and 20 MeV; 1.33 MeV in $^{60}\mathrm{Ni}$ at 10.5 and 14 MeV; and 1.34 MeV in $^{64}\mathrm{Ni}$ at 10.5 and 14 MeV. The results were analyzed in the distorted-wave Born approximation, with collective-model form factors derived from the optical-model potential. The deformed spin-dependent part of the coupling potential was of the full Thomas form, and the data are best described when ${{\ensuremath{\beta}}_{2}}^{\mathrm{SO}}g{\ensuremath{\beta}}_{2}$. Good fits are obtained for elastic polarization data (obtained elsewhere) when the depth of the spin-orbit potential is determined from spin-flip probability measurements.

The new Ion Beam Materials Laboratory (IBML) is a Los Alamos National Laboratory (LANL) resource devoted to the characterization and modification of surfaces through the use of ion beams. IBML was developed and designed in response to a large number of recognized research needs ranging from archaeology to the Strategic Defense Initiative and from basic research to semiconductor development. Most recently, the IBML has been used in research on high temperature superconductors. The IBML was dedicated in February 1987 when the 3 MV tandem accelerator reached operational status.Beginning with an existing accelerator facility built to support nuclear physics, Los Alamos researchers added materials science capability and started to demonstrate the power of ion beam techniques as they apply to many of the Laboratory's research activities. These efforts led to a growing interest in ion beams by fellow researchers and caught the attention of LANL management. By the fall of 1984, a clear grassroots case—which was supported by the Laboratory's Center for Materials Science (CMS)—was made for developing a modern ion beam facility, which included capabilities for materials modification and analysis. The $1.7-million IBML was funded with Laboratory-wide resources in the spring of 1985 and was charged with supporting Laboratory-wide programs.

An intense negative 14 C beam has been made for acceleration in the Los Alamos Scientific Laboratory's FN tandem Van de Graaff. The beam was produced from 14 C graphite with an on-axis reflection geometry in a Middleton cesium sputter source.

Proton spin-flip probability on 58Ni has been measured, and the data are adequately described by the DWBA collective model with a full Thomas spin-orbit coupling term and β2SO > β2. Predictions are found to be sensitive to the spin-orbit potential depth.

A nuclear microprobe cannot give direct information on the chemical state of an element, but the spatial distribution of elements in a specimen is often determined by the chemical history of the sample. Fuel cells and minerals are examples of complex systems whose elemental distributions are determined by past chemical history. The distribution of catalyst in used fuel cell electrodes provides direct information on the chemical stability of dispersed catalysts under operating conditions. We have used spatially resolved Rutherford backscattering to measure the migration of platinum and vanadium from intermetallic catalysts and to determine their suitability for use under the extreme operating conditions found in phosphoric acid fuel cells. Geologic materials are complex, heterogeneous samples with small mineral grains. The trace element distribution within the individual mineral grains and between different mineral phases is sensitive to the details of the mineral formation and history. The spatial resolution and sub-100-ppm sensitivity available with a nuclear microprobe open up several new classes of experiments to the geochemist. Geochemistry and electrochemistry are two areas proving particularly fruitful for application of the nuclear microprobe.

We have deposited thin films (3.5, 7.5 and 22 nm) by atomic layer deposition (ALD) using HfCl 4 and H 2 O precursors at 350 °C. Growth, thermal annealing and thermal reoxidation of the thin hafnium oxide layers under controlled ultra-dry oxygen atmosphere were studied using ion beam techniques and isotopic tracing experiments. Secondary ion mass spectroscopy (SIMS) profiling shows that the composition of deposited films is homogeneous with depth and over a large area. RBS and NRA show that the films are under-stoichiometric in oxygen and contain trace chlorine contamination, more pronounced at the film–substrate interface. After oxidation for 20 min in 100 mbar O 2 enriched to 99.9% in 18 O at 425 °C, nuclear resonance depth-profiling using the 151 keV 18 O(p,α) 15 N narrow resonance, reveals that the main process occurring is exchange between oxygen from the gas and oxygen from the film matrix. However, following a post deposition vacuum or inert gas anneal, the atomic exchange process during thermal reoxidation, in 18 O 2 , is significantly inhibited and limited to the superficial region. We assume a link between this effect and the crystallization of the films previously reported.

We show that on SiC ( 0 0 0 1 ) (the fast-oxidizing carbon face), at 1100 °C and 100 mbar, the oxide exhibits an initial fast growth regime, followed by a constant growth rate confirming previous results that oxide growth is not limited by diffusion of the oxidizing species or reaction products through the oxide. At 1100 °C, in this linear regime, the growth rate also exhibits a linear dependence with oxygen pressure. The silicon face shows sub-linear pressure dependence. A simple oxidation model is ruled out since, on both SiC faces, sequential 16O2/18O2/16O2 oxidations show that oxygen fixed in the oxide, near the SiC/SiO2 interface moves during subsequent growth.

This paper presents a methodology based on Monte-Carlo simulations of RBS spectra recorded in channeling geometry to obtain a quantitative analysis of the damage induced in zirconia single crystals irradiated with high-energy ions. The results show that the concentration of defects is almost constant at depths above $\sim$ 500 nm, with a decreasing value in the near-surface region of the crystal. The defect accumulation kinetics exhibits a saturation at a fluence of 5 $\times$ 10$^{13}$ cm$^{−2}$ and can be reproduced by assuming the formation of tracks (diameter $\sim$2 nm) by electronic excitation processes.