ments of lithiumlike ionization rate coefficients are compared to calculations of the ground-state ionization-rate coefficient and the total-ionization-rate coefficient.

18503. Schoenwetter, H. K., A high-speed low-noise 18-bit digital-to-analog converter, IEEE Trans. Instrum. Meas. IM27, No. 4, 413-417 (Dec. 1978).

Key words: A/D converters; D/A converters; data acquisition; data converters; dynamic measurements; settling time. An 18-bit digital-to-analog converter (DAC) with a full-scale current output of 100 mA and a compliance voltage range of 12 V has been designed for use as a precision voltage output DAC. The output noise and settling time of the new design are considerably lower than obtainable from conventional design approaches. An accurate method of measuring settling time also is described.

18504. Siedle, A. R., Velapoldi, R. A., Erickson, N., Surface formation of cuprous benzotriazole, Inorg. Nucl. Chem. Lett. 15, No. 14, 33-36 (1979).

Key words: benzotriazole; charge transfer; copper; luminescence; microspectrofluorimetry; photoluminescence; spectrofluorimetry; surface analysis; tetrazole.

Intense, visible luminescence, attributed to charge transfer excited states, was observed in Cu(I) complexes of benzotriazole but not in the Cu(II) analogues. Microspectrofluorimetry was used to characterize cuprous benzotriazole, a surface phase formed from bulk copper and benzotriazole in dichloromethane.

18505. Souders, T. M., A bridge circuit for the dynamic characterization of sample/hold amplifiers, IEEE Trans. Instrum. Meas. IM-27, No. 4, 409-413 (Dec. 1978).

Key words: amplifier, sample/hold; bridge circuit; circuit bridge; dynamic characterization of sample/hold amplifier. A transformer bridge technique is described for measuring the dynamic performance of sample/hold amplifiers (S/H's). The technique accurately measures dynamic gain errors, signal delay, aperture time delay and jitter, and acquisition time. These parameters are of particular importance to simultaneous data acquisition. The bridge is self-calibrating, and the voltage and time resolution are primarily limited only by the oscilloscope which serves as a detector.

18506. Sugar, J., Kaufman, V., Identification of 5g and 6g terms and revised ionization energies in the Yb__4ƒ1⁄4nl isoelectronic sequence, J. Opt. Soc. Am. 69, No. 1, 141-143 (Jan. 1979).

Key words: energy levels; hafnium; ionization energies; lutetium; osmium; rhenium; tantalum; tungsten; wavelengths; ytterbium.

The 5f-5g transitions in Lu II through Os VIII and the 5f-6g transitions in Hf iv through W vi were identified and used to redetermine the ionization energies of Yb 11, Lu m, W vi, Re VII, and Os vII. Complete line-lists and energy levels are given for the one-electron spectra Hf iv, W vi and Os VIII.

18507. Sugar, J., Lucatorto, T. B., Mcllrath, T. J., Weiss, A. W., Even-parity autoionizing states in neutral sodium (350400 Å), Opt. Lett. 4, No. 4, 109-111 (Apr. 1979).

Key words: autoionizing states; laser-excitation technique; neutral sodium; sodium, neutral.

A recently developed laser-excitation technique has been used in the first photoabsorption studies of the even-parity 2p 3s3p and 2p33s4p autoionizing levels of Na I. The observed

level values are compared, where applicable, with those previously obtained by ejected-electron spectroscopy of collisionally excited Na, and the identifications are confirmed by ab initio calculations.

18508. Wiese, W. L., Younger, S. M., Theoretical simulation of beam foil decay curves for resonance transitions of heavy ions, J. Phys. 2, No. 40, Cl-146-Cl-148 (Feb. 1979).

Key words: atomic decay curve simulation; atomic transition probabilities; beam-foil spectroscopy; cascades in atomic decay; exponential fitting; Kr VIII.

We have made a theoretical study of the influence of cascades on heavy ion beam-foil lifetimes, concentrating on the resonance line of Kr VIII. Using theoretical data for the lifetimes and initial populations of excited states, we have constructed decay curves simulating beam-foil excitation conditions. The theoretical decay curve producing the best fit with experimental decays yielded the same lifetime as the experiments when subjected to the same cascade analysis, but customary exponential fitting techniques were not able to extract the theoretical primary lifetime actually used in its construction. 18509. Piermarini, G. J., Forman, R. A., Block, S., Viscosity measurements in the diamond-anvil pressure cell, Proc. 6th AIRAPT Int. High Pressure Conf., Boulder, CO, July 25-29, 1977, pp. 860-864 (Plenum Press, New York, NY, 1979).

Key words: diamond-anvil; glass transition; high pressure; hydrostaticity; liquids; pressure cell; viscosity.

The viscosity of liquids can be measured in the diamondanvil pressure cell utilizing a falling-ball method and the ruby technique for pressure measurement. The pressure dependence of the viscosity of a 4:1 mixture (by volume) of methanol:ethanol has been determined. The accuracy of the technique has been estimated from measurements made on a fluid of known viscosity.

18510. Kessler, E. G., Jr., Jacobs, L., Schwitz, W., Deslattes, R. D., Precise y-ray energies from the radioactive decay of 170Tm and 100Yb, Nucl. Instrum. Methods 160, 435-437 (1979).

Key words: crystal diffraction; gamma-ray energies; thulium; ytterbium.

Precise energy values for ten standard y-ray reference lines produced in the radioactive decay of 170Tm and 18Yb have been measured relative to an optical standard. These measurements, which have an uncertainty of about 0.5 ppm for the more intense lines, provide precise y-ray standards in the 63307 keV range. Measurements on 100Yb lines constrained by the Ritz principle satisfy the combination principle within the measurement uncertainty.

18511. Han, C. C., McCrackin, F. L., Molecular weight and polydispersity measurements of polystyrene by quasielastic light scattering, Polym. 20, 427-432 (1979).

Key words: diffusion; diffusion coefficient; light scattering; polydisperse; polydispersity; polystyrene; quasielastic light scattering; SRM-706; standard reference material.

The molecular weight and polydispersity of a polydisperse polystyrene sample was measured by quasielastic light scattering. The molecular weight distribution of the polymer was represented by the Schultz distribution. The weight average molecular weight and polydispersity of distribution was adjusted until the quasielastic light scattering spectra calculated for the distribution agreed with the measured spectra. The calculation was repeated using the logarithmic normal distribution for the polymer. The calculated value of the weight average molecular

weight is accurate and insensitive to the assumed molecular distribution function. However, the calculated values of the polydispersity are only of fair accuracy. Thus quasielastic light scattering gives values of the weight average molecular weight at least as accurate as elastic light scattering and gives a crude estimate of the polydispersity of the polymer.

18512. Brown, D. W., Lowry, R. E., The radiation-induced copolymerization of tetrafluoroethylene and styrene at high pressure, J. Polym. Sci. 17, 759-768 (1979).

Key words: copolymerization; polymerization; pressure; radiation; styrene; tetrafluoroethylene.

The

of

radiation-induced copolymerization tetrafluoroethylene (A) and styrene (B) was studied in bulk and in perfluorotoluene at 22 °C at autogenous pressure and 260 and 510 MPa. The reactivity ratio for addition to A-ended radicals, r, is effectively zero at the two lower pressures and is in the range 0.002-0.008 at 510 MPa. The other reactivity ratio, r, is 6 at autogenous pressure and also at 260 and 510 MPa if the A content of the charge is less than 50%. If the A content is greater than 95%, rg appears to be 100 at pressures of 260 and 510 MPa. The apparent variation in r cannot be explained by invoking a penultimate unit effect for B-ended radicals. Polymerization rates scatter somewhat, but all rates are quite small when the A content of the charge is in the range 95-99.8%. Polymers containing as much as 66% A appear to be inherently benzene soluble but frequently contain some gel because of radiation-induced crosslinking after their formation. No very high polymers were formed that contained more than a few percent A, even at high pressure. Features that complicated the study were immiscibility of the liquid monomers, extreme variation of the monomer-copolymer compatibility with charge composition, and freezing of B at high pressure.

18513. Anderson, W. E., Davis, R. S., Petersons, O., Moore, W. J. M., An international comparison of high voltage capacitor calibrations, IEEE Trans. Power Appar. Syst. PAS-97, No. 4, 1217-1223 (July/Aug. 1978).

Key words: calibration; Clausius-Mossotti equation; compressed-gas capacitor; high voltage; standards; sulfur-hexafluoride.

The suitability of a commercially available, compressed-gasinsulated, high voltage capacitor for precise measurement of ac voltages has been examined by national laboratories in the U.S.A. and Canada. The voltage, temperature, and pressure dependences and the mechanical stability of the capacitor were determined. It was found that by taking proper precautions the device is competitive with other methods. As a result of this research, it was also found that high voltage capacitance measurements at the two laboratories involved are in agreement.

18514. Bright, R. G., Technical developments of domestic fire detectors, (Proc. Int. Fire, Security and Safety Exhibition and Conf., London, England, Apr. 24-28, 1978), Fire Surveyor Mag. 74, 9-16 (Aug. 1978).

Key words: detection; fires; home fires; residential smoke detectors; smoke detectors.

A review of some of the more significant technical developments in residential smoke detectors, in the past four years is presented. In addition, some of the problems experienced, as well as forecasts of possible future technical developments, are also given.

18515. Castor, J. I., Lamers, H. J. G., An atlas of theoretical P Cygni profiles, Astrophys. J. Suppl. Ser. 39, No. 4, 481-511 (Apr. 1979).

Key words: line profiles; P-Cygni lines; radiative transfer; resonance lines; stars; stellar winds.

An atlas of theoretical P Cygni-type line profiles is presented. The profiles are calculated assuming resonance scattering and using the Sobolev approximation. The expanding envelope is characterized by two functions; the optical depth ↑ (v) and the velocity law v(r). The velocity law, the process of line formation, and the accuracy of the theoretical line profiles are discussed. The effect of collisional excitation is discussed and is found not to be important in most UV resonance lines, except in a star with a very high rate of mass loss and a small wind velocity. We describe a simple procedure to correct for the presence of underlying photospheric profiles, and show that the simple addition of the calculated P Cygni profile and photospheric profile can give very wrong results. We also describe a fairly simple procedure for calculating the shape of partly overlapping doublet lines. The accuracy of the information that can be derived from a comparison between observed and theoretical P Cygni profiles is discussed critically.

18516. Collins, L. A., Norcross, D. W., Schmid, G. B., Electron collisions with highly polar molecules: Integrated and momentum transfer cross sections and conductivity integrals for KOH and CSOH, J. Phys. B 12, No. 6, 1019-1030 (1979).

Key words: cross sections; electron collisions; molecules; momentum-transfer; polar molecules; scattering theory.

We report close-coupling calculations of the total integrated and momentum transfer cross sections for the scattering of electrons from KOH and CSOH in the energy range 0.01 to 10 eV. A cut-off dipole potential is used to account for the longrange interaction. We nominally chose the cut-off radius R. such that the potential has a minimum in the vicinity of the nucleus nearest to the centre-of-mass (COM) of the molecule. No explicit account is taken of the short-range interactions. The results for the total integrated and momentum transfer cross sections exhibit oscillations about a mean value, with an amplitude of approximately 1% and 10%, respectively, of the mean. The choice of a different value for R, in additional calculations for KOH led to results for the mean value and amplitude which were virtually identical for k2 ◄ 1/(2R)2. A simple semi-quantitative understanding of this behaviour is presented in the context of Fabrikant's effective-range theory (ERT). This leads to concise analytical expressions for the velocity-averaged momentum transfer cross section and mobility that also oscillate within an envelope not greater than that of the momentum transfer cross section itself, and are very insensitive to the choice of Re. We also present analytical expressions for the interaction parameters (conductivity integrals) which may be used for calculating electrical properties of gas mixtures according to the popular algorithm of Demetriades and Argyropoulos. A comparison of the predictions of our expressions with the previous best estimates for these parameters as reported by Spencer and Phelps is given.

18517. Davis, S., Assessment of fire hazards from furniture, Proc. Int. Fire, Security and Safety Exhibition and Conf., IFSSEC 78, London, England, Apr. 24-28, 1978, 30 nages (Victor Green Publ. Ltd., London, England, 1978).

Key words: bedding; beds; compartment fires; firesafety engineering; fire tests; health care facilities; hospitals; mattresses; prisons.

A test program was conducted to assess the hazards of institutional mattresses when subjected to a sustained flaming ignition source. This report gives results on full-scale room burns of ten different mattress types. Tenability and rapid flame spread notential criteria were applied in a hazard assessment which showed a wide range of behavior among mattresses now being used in institutions.

18518. Dodge, W. R., Hayward, E., Moscati, G., Wolynec, E., Electrodisintegration of 238U, Phys. Rev. C 18, No. 5, 24352437 (Nov. 1978).

Key words: electrodisintegration; proton spectrum; ternary fission; a-particles; a-spectrum; 238U.

A search has been made for a-particles that might stem from an isoscalar E2 giant resonance in 238U near 9 MeV. Using 40 MeV electrons the spectra of protons and a-particles emitted in the electrodisintegration of 238U were measured. Peaks in the proton spectrum indicated that the target has an oxygen contamination. The less intense a-spectrum contains a-particles resulting from the electrodisintegration of "O, a group that probably stems from ternary fission, and a higher energy feature which may be attributed to the electrodisintegration of U. The integrated 238U(e,a) cross section is less than 1% of a recently suggested value.

18519. Filliben, J. J., Dataplot-An interactive system for graphics, Fortran function evaluation, and linear/non-linear fitting, Proc. 1978 Statistical Computing Section of the American Statistical Association, San Diego, CA, Aug. 14-17, 1978, pp. 344-353 (American Statistical Association, Washington, DC, 1978).

Key words: computing system; dataplot; fitting; graphics; interactive graphics; regression; software; transformation. Dataplot is a high-level language that was developed in response to data analysis problems encountered at the National Bureau of Standards. The language is very powerful, very flexible, and very fast to use-especially in an interactive environment. The system combines the best features of the 3 kernal operations of data analysis—graphics (continuous or discrete), data transformations, and linear/non-linear fitting into one language. Many of the features in dataplot are singularly unique and unmatched by any other interactive system in existence. Features of the system include: Interactive fortran expression evaluation for transformations plotting/fitting, continuous/discrete plots, single/multi-trace plots, single/multi-function plots, labelled/unlabelled plots, linear/log-scale plots, linear/non-linear fittings, interactive analyses, subset analysis, distributional summary plots, data analysis plots, control charts, probability plots, (24 distributions), times series plots, complex demodulation plots, exact rational function fitting, least squares smoothing, random number generation (24 distributions), data manipulation capabilities, probability function calculations, elementary statistics (18 statistics), format-free I/O, diversible graphics output, and a desk calculator mode.

18520. Hayward, E., The electrodisintegration of Ni, Proc. 4th Seminar on Electromagnetic Interactions of Nuclei at Low and Medium Energies, Moscow, USSR, Dec. 13-15, 1977, pp. 125139 (1979).

Key words: electric quadrupole; electrodisintegration; electron energy; giant resonance; virtual photons; 58Ni.

The electrodisintegration of 58Ni into protons and a-particles has been studied. The yield curves as a function of electron energy have been obtained and a few points measured with a Tantalum radiator interposed. Using the electric dipole and electric quadrupole virtual photon spectra, these yields can be interpreted as resulting from compact El and E2 giant resonances. Alpha particle emission is the dominant mode of decay of the isoscalar E2 resonance at 16.5 MeV, while the protons are emitted only by the electric dipole giant resonance at 19 MeV. This technique represents a powerful new tool for determining giant resonance multipolities.

18521. Hayward, E., Nuclear elastic scattering of photons, Proc. 4th Seminar on Electromagnetic Interactions of Nuclei at Low

and Medium Energies, Moscow, USSR, Dec. 13-15, 1977, pp. 185-199 (1979).

Key words: coherent scattering; Delbrück scattering; elastic scattering; giant resonance; tensor polarizability; Thomson scattering.

Nuclear elastic scattering in the energy region of the electric dipole giant resonance is reviewed. The interference of the coherent nuclear scattering with Rayleigh, Delbrück, and nuclear Thomson scattering is pointed out. The tensor polarizability of the deformed and vibrational nuclei is pointed out and the results of the experiments that use neutron capture y-rays and Ge(Li) detectors are summarized.

18522. Hayward, E., Dodge, W. R., Patrick, B. H., Some experiences using a positron annihilation beam, Nucl. Instrum. Methods 159, 289-299 (1979).

Key words: positron annihilation-in-flight; quasi-monoenergetic photons; sodium iodide spectrometer; 15.1 MeV branching ratio.

The NBS positron annihilation-in-flight facility is described, along with the procedure for the calibration of the positron beam energy. Details are also given of a large NaI(T1) spectrometer used with the annihilation photon beam. Response functions of this spectrometer for photons of 15 and 31 MeV have been measured using a photon tagging scheme based on the detection of the annihilation photons in coincidence. The variation in response function caused by the presence of absorbers in front of the spectrometer has been investigated. The response function measured at 15 MeV is compared with that obtained by resonance fluorescence of the 15.1 MeV level in 12C and, from the latter data, the branching ratios for the decay of the 15.1 MeV level to the ground state and the excited states at 4.44 and 7.66 MeV have been extracted.

18523. Horton, W. S., An examination of five preferred orientation functions, Carbon 17, 153-155 (1979).

Key words: Bacon function; Bragg function; Ergun function; graphite materials; Lorentz function; preferred orientation function; pyrolitic graphite; Ruland function; x-ray diffraction.

Five functions for describing the preferred orientation of graphite-like materials were examined. Their relative behavior for various degrees of orientation were compared, particularly with respect to the ease of discriminating among them experimentally. The results obtained when data were fitted by a nonlinear least squares method were used for a practical comparison. It was found that a constant term is required to allow for base line effects and some unoriented material. For careful evaluation of functions it is necessary to assume that the angle for maximum x-ray reflection intensity was set with some error. Among the five functions compared, the Bragg function fitted the comparison data best. However, if zero slope is required 90° away from the reference axis, this function is ineligible. In that case the Bacon and Ergun functions were equally good. Systematic trends in some of the data were related to sample preparation. The standard deviation for measuring the orientation parameter by fitting a function in this manner was from 0.4 to 3%.

18524. Johnson, C. R., Leighton, F. T., Robinson, H. A., Sign patterns of inverse-positive matrices, Linear Algebra and Appl. 24, 75-83 (1979).

Key words: Hadamard product; inverse-positive matrix; matrix sign patterns; positive matrix.

We identify the sign patterns which occur among the real, nonsingular, entrywise nonzero matrices whose inverses are entrywise positive.

18525. Kaiserlik, J., Berger, H., McGogney, C., Timber pilings: Maintenance and inspection summary of a panel discussion, Proc. 4th Nondestructive Testing of Wood Symp., Vancouver, WA, Aug. 28-30, 1978, pp. 155-159 (Washington State Univ., Engineering Extension Service, Pullman, WA, 1979).

Key words: acoustics; bridges; creosote; harbor facilities; inspection; maintenance; marine borers; nondestructive testing; pilings; timber.

The panel discussion concerned with maintenance and inspection of timber pilings attracted about 100 people (including ten who registered only for this event) to a lively evening session. Timber pilings are used in bridge structures and for harbor and navigational facilities. The topic for discussion was the inspection and maintenance of these pilings in order to prevent failures such as the collapse of the Coos Bay bridge in Oregon in 1977 due to damage caused by marine borers.

18526. La Villa, R. E., Double-vacancy transitions in the copper KB, emission spectrum, Phys. Rev. A 19, No. 2, 717-720 (Feb. 1979).

1.3

Key words: copper Kß; double vacancy; emission spectrum; Hartree-Fock calculations; x-ray emission.

The B' and B" satellites in the measured Cu Kẞ1,3 emission spectrum are shown to be due to the double-vacancy transitions 1s3p 3d13D→ 1s23p53d1.3PDF. This assignment is consistent with an earlier analysis of a highly resolved Cu Ka1,2 spectrum. The M, and M, level widths are estimated to be 1.68 eV, in agreement with 2.0±0.3 eV and 1.6 ± 0.3 eV, respectively, from photoelectron spectroscopy, and a calculated width of 2.0 eV. Comparison of the calculated double-vacancy transition array with the neighboring elements 30 ≤ Z ≤ 32 suggest a similar identification to the B' and 8" satellites in their KB1.3 spectra.

18527. Klose, J. Z., Mean life of the 4s 2S1/2 resonance level in Al 1, Phys. Rev. A 19, No. 2, 678-681 (Feb. 1979).

Key words: Al 1; aluminum; delayed coincidence; ƒ-value; imprisonment; laser; lifetime; mean life; oscillator strength. The mean life of the 4s 2S1/2 resonance level in Al 1 has been measured at seven different vapor densities using a tunable dye laser for excitation and a method of delayed coincidence for detection. The lifetime values, obtained by exciting the level with radiation at the resonance wavelength of 3944.01 Å and observing its decay by means of the transition at 3961.52 Å, increase with increasing vapor density. This vapor-density dependence was interpreted as being due to the imprisonment of the 3962-Å radiation. Imprisonment theory at low densities was applied to the experimental data to yield the following results: T = 6.78 ± 0.06 ns, ₤3944 = 0.115 ± 0.001, and ƒ3982 = 0.116 ± 0.001. Experimental and theoretical results of other workers are presented for comparison with the results of the present work.

18528. Linsky, J. L., Haisch, B. M., Outer atmospheres of cool stars. I. The sharp division into solar-type and non-solar-type stars, Astrophys. J. 229, No. 1, L27-L32 (Apr. 1, 1979).

Key words: emission lines, stars; late-type stars; stellar chromospheres; stellar coronae; stellar winds; ultraviolet spectra.

IUE short-wavelength (1175-2000 Å) spectra of late-type stars clearly indicate two separate and distinct groups of stars. The solar-type group shows spectral lines formed at tempera

tures of 5×103-2 × 105 K, indicative of chromospheres, transition regions, and by implication unseen coronae at hotter temperatures. The non-solar-type group shows lines formed at temperatures no hotter than 10,000-20,000 K, indicative of chromospheres only. We interpret this acute change in character of the outer atmospheres of stars on either side of the sharp dividing line between the two groups as due either to the absence of hot material resulting from the rapid onset of large stellar winds, a hypothesis recently suggested on theoretical grounds by Mullan, or to very low transition-region densities, as suggested by a model stellar wind corona we have calculated for Arcturus.

18529. McAuliff, R. C., Lentner, K. J., Moore, W. J. M., Schuster, G., An international comparison of power measurements at 120 V, 5 A, and 60 Hz, IEEE Trans. Instrum. Meas. 27, No. 4, 445-449 (Dec. 1978).

Key words: electro-dynamic wattmeters; energy measurements; energy standards; international comparisons; metrology; power measurements; precise electrical measurements; TDM wattmeters; thermal wattmeters; transfer standards.

An international comparison of ac power measurements between metrology laboratories at the Physikalisch-Technische Bundesanstalt-Institut Berlin, (PTB(IB)), the Electrosystems Division of the National Bureau of Standards (NBS), and the Division of Electrical Engineering at the National Research Council of Canada (NRC(EE)) is described. The three calibration systems, each of different design and developed independently, are discussed, and estimates of the systematic uncertainties are given. The transfer standard was a recently developed thermal wattmeter of high stability. No laboratory differed by more than 15 parts per million (ppm) from the average, with reference to apparent power at unity and 0.5 power factors, lead, and lag. This is consistent with the error limits estimated by each of the participants.

18530. McCrackin, F. L., Monte Carlo calculations of the number of ways to pack nonoverlapping rods on a square lattice, J. Chem. Phys. 69, No. 12, 5419-5423 (Dec. 15, 1978).

Key words: configurations of rods; Monte Carlo; orientation entropy; packing of rods; square lattice; theories of liquid crystals.

The number of configurations of nonoverlapping rods on a square lattice is computed for various packing fractions and orientations of the rods. From the number of configurations, the entropies of the configurations are computed and compared with the results of approximate formulas of DiMarzio that are much used in statistical-mechanical theories of liquid crystals. For rods of three lattice sites, our calculations and Dimarzio's formulas agree to within 0.5% for packing fractions less than 0.5. Some calculations for rods of ten lattice sites also showed good agreement.

18531. Naegele, D., Yoon, D. Y., Broadhurst, M. G., Formation of a new crystal form (a,) of poly(vinylidene fluoride) under electric field, Macromolecules 11, Nb. 6, 1297-1298 (Dec. 1978).

Key words: phase change piezoelectric polymers; polarization; polyvinylidene fluoride; x-ray diffraction; a phase. Polyvinylidene films were prepared in the a crystal form by stretching at 145 °C. The x-ray diffraction spectra of films which were subjected to an electric field of 1500 kV/cm at room temperature were compared to those of films which were not subjected to changes are consistent with the assumption that the electric field changes the normally anti polar a phase into a polar phase having the same chain conformation and unit cell dimensions.

18532. Olsen, H. A., Maximon, L. C., Effect of resonance scattering in the high frequency limit of bremsstrahlung, Phys. Lett. 69A, No. 2, 90-92 (Nov. 27, 1978).

Key words: atomic screening effects; bremsstrahlung high frequence limit; bremsstrahlung spectrum tip; continuum x rays; Coulomb field; non-relativistic bremsstrahlung.

It is shown that the resonances in the bremsstrahlung cross section close to the high-frequency limit found experimentally by Liefield et al. can be explained as final state resonance scattering.

18533. Russell, T. J., Maxwell, D. B., Reimann, C. T., Buehler, M. G., A microelectronic test pattern for measuring uniformity of an integrated circuit fabrication technology, (Proc. Government Microcircuit Application Conf., Monterey, CA, Nov. 1978), Solid State Tech. 22, No. 2, pp. 71-74 (Feb. 1979).

Key words: bipolar process; contact resistor; cross bridge sheet resistor; electrical alignment resistor; integrated circuits; linewidth; photolithography; sheet resistance; silicon; test pattern; test structure; TTL.

Dopant density, device and circuit parameters, and randomfault densities across a wafer are important considerations in integrated circuit processing. The application of process validation wafers to evaluate silicon fabrication technologies is being studied in terms of the uniformity of these parameters across the wafer. This concept is illustrated by measurements of selected test structures on the NBS-7 test pattern which was designed to assess a junction-isolated transistor-transistor logic process. Use of this pattern for identifying fabrication nonuniformities is demonstrated by means of wafer maps of values of key parameters.

18534. Schubert, E., Schuck, A., Jung, K., Geltman, S., Triple differential cross sections for the electron impact ionization of helium at 35 eV collision energy, J. Phys. B 12, No. 6, 967978 (1979).

Key words: angular; Born approximation; correlations; electron impact; electrons; helium; ionization; secondary.

In a coincidence experiment with coplanar geometry, angular correlations of the two outgoing electrons have been studied for the ionisation of helium atoms by electrons with an impact energy 10.5 eV above the first ionisation threshold. The measured angular dependencies of the triple differential cross section are compared with calculated results of the Coulomb-projected Born approximation including exchange. The measured data as well as the calculated ones do not show the features that have been found at medium and high impact energies. The momentum transfer Ko looses its importance as a means of classification. For these low-energy collisions the amplitudes of direct scattering, exchange scattering and electron capture are of similar size and only the direct scattering amplitude has the momentum transfer vector Koa as a symmetry axis (in the Born approximation). Therefore the angular dependence of the triple differential cross section are no longer symmetrical with respect to the momentum transfer. Rapid variations of the angular distributions for different scattering angles 0, of one of the two outgoing ionisation electrons indicate interference of the different scattering amplitudes. Moreover, the measurements demonstrated that the angular correlations for fixed scattering angle, are independent of the ratio of the energies of the two emerging electrons. All other predictions of threshold theories are not valid in this energy range.

18535. Wolynec, E., Dodge, W. R., Hayward, E., Decay modes of giant resonances in 5aNi, Ni, and 62Ni, Phys. Rev. Lett. 42, No. 1, 27-30 (Jan. 1, 1979).

18537. Peacock, R. D., A review of fire incidents related to wood-burning appliances, Proc. Wood-Heating Seminar IV, Portland, OR, Mar. 21-24, 1979, pp. 43-66 (Wood Energy Institute, Camden, ME, 1979).

Key words: accident investigations; chimneys; coal; creosote; fire departments; fire safety; heating equipment; maintenance; stoves; wood.

As a part of the Department of Energy program to advance the technology for the utilization of fuelwood as an alternate energy source for applications ranging from single-family dwellings to apartment complexes and small industries, a review is presented for fire incidents and fire deaths attributable to wood-burning appliances. Initiated to establish accident patterns and to determine the risks involved with the use of woodburning equipment, the survey represents a compilation of approximately 11,800 fire incidents including injuries and deaths associated with solid fuel burning appliances.

18538. Sweger, D. M., Travis, J. C., An application of infrared lasers to the selective detection of trace organic gases, Appl. Spectrosc. 33, No. 1, 46-51 (1979).

Key words: CO2 laser; derivative spectra; infrared analysis; spectral coincidences; Stark modulation; Stark spectroscopy; trace gas analysis.

For molecules possessing a permanent electric dipole moment the Stark effect may be used to perturb the molecular energy levels and to "tune" some absorption lines into coincidence with fixed frequency lasers. The same perturbation may also be used to modulate the absorption and allow the use of sensitve ac detection techniques. In this paper we report quantitative results for four organic gases of industrial importance: vinyl chloride, vinylidene chloride, acrylonitrile, and methanol. All have overlapping absorption bands in the CO, laser region. Because of the modulation techniques used, the observed signal as a function of electric field is the first derivative of the absorption line profile, and the peak-to-peak intensity of the derivative is the measured analytical signal. The analytical curve is a straight line over several orders of magnitude in concentration. In all cases, parts per million or sub-parts per million concentrations of the gases in air and/or nitrogen have been measured using a CO, laser. The paper will include a discussion of interferences and selectivity of the technique.