also be used to frequency lock a laser to a transition frequency of a substance in a gas discharge cell.

19719. Petersen, F. R., Evenson, K. M., Jennings, D. A., Scalabrin, A., New frequency measurements and laser lines of optically pumped 12CH3OH, IEEE J. Quantum Elec. QE-16, No. 3, 319-323 (Mar. 1980).

Key words: carbon dioxide laser; laser frequency measurements; new 12CH3OH laser lines; optically pumped FIR lasers; relative power output of CH3OH laser lines.

The frequencies of 70 optically pumped CW FIR 12CH3OH laser lines have been measured relative to stabilized CO2 lasers. Fifteen new laser lines together with the relative output powers and polarizations for most of the 104 known lines pumped by laser lines in the normal 9 and 10 μm bands of 12C16O2 are also reported.

19720. Mucha, J. A., Evenson, K. M., Jennings, D. A., Ellison, G. B., Howard, C. J., Laser magnetic resonance detection of rotational transitions in CH2, Chem. Phys. Lett. 66, No. 2, 244-247 (Oct. 1, 1979).

Key words: CH2; laser; magnetic resonance; rotational transitions.

Laser magnetic resonance spectra observed at 163.0 μm have been identified as pure rotational transitions in the ground electronic state (3B,) of the methylene radical. The identification was based on the observation of hyperfine spin triplets and by isotopic substitutions involving deuterium and 13C as well as other chemical and spectroscopic evidence. A low-pressure flame produced by reacting discharged fluorine with methane was found to be an excellent new spectroscopic source of ground-state CH, radicals.

19740. Baer, T., Kowalski, F. V., Hall, J. L., Frequency stabilization of a 0.633-μm He-Ne longitudinal Zeeman laser, Appl. Opt. 19, No. 18, 3173-3177 (Sept. 15, 1980).

Key words: stabilized laser; wavelength standards; Zeeman laser.

A new method of stabilizing the output frequency of a HeNe laser in a longitudinal magnetic field has been developed. With simple modifications to a standard He-Ne laser tube we obtain a frequency stability of < 1 MHz (< 10-9) for an averaging time of 1 sec and a long term (5 months) frequency reproducibility of ~+1 MHz.

19759. Huie, R. E., Herron, J. T., Braun, W., Tsang, W., Chlorine isotope enrichment in CO2 TEA laser photolysis of CF2Cl2, Chem. Phys. Lett. 56, No. 1, 193-196 (May 15, 1978).

Key words: chlorine isotopes; isotope separation; laser chemistry.

A number of lines from a CO, TEA laser were used to photolyze CF2Cl2. Enrichment of the 35C1 and 37Cl isotopes in the molecular chlorine formed during the photolysis was observed using a mass spectrometer. Maximum enrichment was about 1.8. The dependence of enrichment on wavelength, reactant concentration, inert gas pressure, and the presence of SiF is reported. Of particular interest is the persistence of significant enrichment at pressures up to several hundred torr (≈105 Pa). Aside from the practical significance of this enrichment at high pressures, it suggests that there are important contributions from isotopically specific interactions after the laser pulse. 19775. Pence, W. H., Leone, S. R., New atomic and molecular lasers and their application to the study of collision physics, Proc. Int. Conf. on Physics of Electronic and Atomic Collisions,

ICPEAC 1979, Kyoto, Japan, Aug. 29-Sept. 4, 1979, pp. 773785 (North Holland Publ. Co., Amsterdam, The Netherlands, 1979).

Key words: calcium; collision physics; dimer lasers; energy transfer; lasers.

New atomic and molecular lasers can be used in a variety of ways to elucidate mechanisms and rates of inelastic collision processes. Examples are given whereby specific energy transfer processes are discovered and studied by laser diagnostic mea

surements.

19790. Wells, J. S., Petersen, F. R., Maki, A. G., Heterodyne frequency measurements with a tunable diode laser-CO2 laser spectrometer: Spectroscopic reference frequencies in the 9.5μm band of carbonyl sulfide, Appl. Opt. 18, No. 21, 35673573 (Nov. 1, 1979).

Key words: carbonyl sulfide; OCS calibration frequencies; OCS reference frequencies; TDL-CO2 heterodyne measurements; TDL reference frequencies; tunable diode laser. The frequencies of twelve carbonyl sulfide absorption lines near 9.5 μm have been measured by means of a heterodyne frequency measuring technique, which uses a frequency stabilized CO2 laser and a tunable diode laser. The diode laser was locked to the peak of each OCS absorption line by means of a first derivative frequency lock procedure. In addition to lines in the 020-000 band, measurements also include some nearby OCS hot band features as well as lines in isotopically enriched samples of OC34S, O13CS, and 18OCS. These measurements are part of an effort to provide frequency standards for the calibration of tunable IR laser devices.

19799. Drullinger, R. E., Wineland, D. J., Laser cooling of ions bound to a Penning trap, (Proc. Fourth Int. Conf. RottachEgern, Fed. Rep. of Germany, June 11-15, 1979), Paper in Laser Spectroscopy, H. Walther and K. W. Rothe, Eds., IV, 66-72 (Springer-Verlag, New York, NY, 1979).

Key words: atomic clocks; atomic spectroscopy; Doppler effects; frequency standards; ion storage; laser cooling; laser spectroscopy; radiation pressure.

MgII ions which are confined in a room temperature Penning trap have been cooled to ≤ 0.5 K by scattering photons which are nearly resonant with the 3s2S1/2 → 3p2P3/2 transition. The magnesium loaded into the trap has a natural isotopic abundance consisting of ~80% 24Mg, and ~10% each 25Mg and 26Mg. The 24Mg is radiatively cooled and it subsequently cools the 25.26Mg by long range Coulomb collisions. This allows the use of a "cooling ion" being used in conjunction with a more complex species of spectroscopic interest.

Experiments using two lasers are reported where one laser is fixed in frequency and provides the cooling source and the other laser is swept in frequency. By monitoring the scattered light from the second laser, an optical spectrum of MgII ions is obtained. Because the Doppler width of the cooled ions is reduced, the three isotopic lines are clearly resolved.

19822. Santoro, R. J., Semerjian, H. G., Emmerman, P. J., Goulard, R., Shabahang, R., Multiangular absorption measurements in a methane diffusion jet, (Proc. Symp. of the 178th Meeting of the American Chemical Society, Washington, DC, Sept. 9-14, 1979), Chapter 36 in Laser Probes for Combustion Chemistry, D. R. Crosley, Ed., ACS Symp. Series 134, pp. 427-433 (American Chemical Society, Washington, DC, 1980).

Key words: absorption measurement; combustion measurements; convolution algorithm; diffusion jet; laser diagnostics; reconstruction algorithm; tomography.

A multiangular absorption approach is used to measure the concentration profile of methane across a diffusion jet. The results have been used to assess the applicability of tomography to gas phase species analysis. Comparisons of the center line concentration and jet position have shown excellent agreement with the known experimental values. The effect of the number of angles for which data is obtained has also been addressed and found to agree with previous analytical studies.

19836. Ehrlich, D. J., Osgood, R. M., Jr., Turk, G. C., Travis, J. C., Atomic resonance-line lasers for atomic spectrometry, Anal. Chem. 52, No. 8, 1354-1356 (July 1980).

Key words: atomic resonance laser; atomic resonance-line laser; flame spectrometry; laser enhanced ionization; optogalvanic effect; photodissociation laser.

Atomic resonance-line lasers based on photodissociation of metal-halide molecules have important implications for spectrochemical analysis. Analytical curves of growth and limits of detection have been obtained by laser enhanced ionization (LEI) for two (Tl and Na) of the eight atomic resonance line lasers which have been demonstrated to date. The fixed frequency lasers offer a significant simplicity advantage over tunable dye lasers. In addition, the presence of additional atomic laser lines permits the excitation of high energy electronic levels by means of sequential excitation. Such twowavelength excitation demonstrated by the Na LEI result reported here, has important implications for both selectivity and sensitivity. Although general applicability will depend on further development of the lasers, they are presently appropriate for many special, dedicated applications.

Low Temperature Science and Engineering

TN1029. The thermodynamic properties of helium II from 0 K to the lambda transitions, R. D. McCarty, Nat. Bur. Stand. (U.S.), Tech. Note 1029, 64 pages (Dec. 1980) SN003-00302280-2, $3.75.

Key words: computer program; deviation plots; equation of state; helium II; mathematical model; superfluid; thermodynamic properties.

The equation of state of He-II is modeled by an equation of state explicit in pressure as a function of density and temperature. The equation of state is divided into three regions of temperature 0 to .8 K; .8 to 1.2 K and 1.2 to the lambda temperature for which similar functional forms are used with different adjustable parameters. The combined functions are valid over the entire PT range of the superfluid and may be used for all classical thermodynamic properties. Comparisons between calculated and experimental data are presented. A computer program for calculation of thermodynamic properties (PVT, isochoric heat capacity, isobaric heat capacity, internal energy, enthalpy, entropy, and velocity of sound) is included.

NBSIR 80-1633. Materials studies for superconducting machinery coil composites, J. W. Ekin, M. B. Kasen, D. T. Read, R. E. Schramm, R. L. Tobler, and A. F. Clark, 162 pages (Nov. 1979). Order from NTIS as PB80-212202, $14.00.

Key words: critical current; fiberglass/epoxy composite; mechanical properties; niobium-tin; niobium-titanium; strain; superconducting coil composite; superconducting wire.

The physical properties of a superconducting coil composite are studied to accurately predict the coil behavior under operating conditions. Emphasized in this third interim report are studies on the effect of stress and strain on the critical current of superconducting wires. The report also includes data on

several fiberglass/epoxy support structures for the coil and its dewar. Preliminary results are also given for the effect of stress on small superconducting composite rings used to model the full sized coil behavior. A summary of the program results to date is included.

19673. Read, D. T., McHenry, H. I., Steinmeyer, P. A., Thomas, R. D., Jr., Metallurgical factors affecting the toughness of 316L SMA weldments at cryogenic temperatures, Weld. J.: Res. Suppl. 59, No. 4, 104S-113S (Apr. 1980).

Key words: cryogenic; delta ferrite; ferrite content; fracture; mechanical properties; stainless steel; strength; toughness; welds.

The effects of delta ferrite content, ferrite morphology, carbon content, and sensitization on the fracture toughness and tensile properties of AWS E316L and E316 shielded metal arc (SMA) weldments at 295, 76, and 4 K were investigated. Ten SMA test welds were evaluated, eight made with E316L and two with E316 electrodes. In four of the welds, the delta ferrite content was controlled over the ferrite number range of 0 to 11 through slight variations in the chemical compositions of the electrode coatings. In three of the welds, the ferrite morphology was varied in 8% ferrite welds deposited using the same electrode by varying heat input, preheat, and interpass temperature. One E316 weld with low ferrite content (FN 1.3) and the baseline welding parameters was used to assess the effect of carbon content. The two remaining welds were made with a low cooling rate to study sensitization in the low-ferrite, low (E316L) and regular (E316) carbon welds. Part of the E316 weld was deliberately sensitized at 675 °C (357 °F) for 24 hours.

All of the weldments had excellent toughness at room temperature. However, at 76 K only the E316L weld with low ferrite had acceptable (to ASME standards) toughness. Large decreases in toughness at 76 and 4 K were related to increasing ferrite content. Decreases in Charpy impact energy at 76 K were also related to coarsened ferrite morphology caused by reduced cooling rates, to increased carbon content, and to the sensitization heat treatment. The tensile yield strength increased with ferrite content, especially at 4 K. The effects of ferrite content on the ultimate tensile strength and the ductility were generally minor.

19761. Jones, M. C., Cool-down of superconducting power transmission lines with single phase helium, Cryogenics 20, No. 3, 139-145 (Mar. 1980).

Key words: conservation equations; cool-down; numerical solutions; superconducting transmission lines.

Numerical solutions of the one-dimensional conservation equations of fluid flow are given for the problem of the cooldown of superconducting power transmission cables. By including the continuity and momentum conservation equations, both time dependent and spatially dependent mass flow may be treated. The equations are applied to specific designs in which one stream of helium fills the bore of a cable while a second fills the space between the outside of the cable and an enclosing pipe. Both co-current flow and counter flow are treated with a variety of boundary conditions. Temperature profiles as a function of time, and total cool-down times are given.

Mathematical and Statistical Methods

19773. Olver, F. W. J., Whittaker functions with both parameters large: Uniform approximations in terms of parabolic cylinder functions, Proc. R. Soc. Edinburgh 86A, 213-234 (1980).

Key words: asymptotic expansions; confluent hypergeometric functions; error bounds; parabolic cylinder functions; turning points; Whittaker functions.

Asymptotic approximations are derived for the Whittaker functions Wk.u(2), Mk.u(2), Wik.iu(iz) and Mik.iu(iz) for large positive values of the parameter μ that are uniform with respect to unrestricted values of the argument z in the open interval (0,∞), and bounded real values of the ratio k/μ. The approximations are in terms of parabolic cylinder functions, and in most instances are accompanied by strict error bounds.

The results are derived by application of a recentlydeveloped asymptotic theory of second-order differential equations having coalescing turning points, and an extension of the general theory of equations of this kind is also included.

19778. Rosenblatt, J., Chayes, F., Trochimczyk, J., An algebraic explanation of closure correlation among the coefficients of a principal component, Annual Report 1977-78 to The Carnegie Institution of Washington Year Book 77, pp. 901-902 (Dec. 1978).

Key words: chemical petrology; closure correlation; principal components analysis; statistics.

In chemical petrology, especially in the study of the distribution of essential constituents, the data matrix is a table of percentages resulting in (well-known) negative covariances among major constituents. Principal components analysis has been used for characterization of such arrays. This note considers a "data" matrix consisting of a set of experimental estimates of the leading principal component obtained from a set of tables of percentages; there will be negative covariances among the elements of the estimates.

Measurement Science and Technology:

Physical Standards and Fundamental Constants 19685. Soulen, R. J., Jr., Marshak, H., The establishment of a temperature scale from 0.01 K to 0.05 K using noise and 60Co y-ray anisotropy thermometers, Cryogenics 22, No. 7, 408412 (July 1980).

Key words: cryogenic temperature scale; Josephson junction; noise thermometry; nuclear orientation; thermometry; 60CoCo y-ray anisotropy thermometry.

We report here on our latest intercomparison of the Josephson junction noise thermometer and 60 Co y-ray anisotropy thermometer from 0.01 K to 0.05 K. These results show both thermometers are in agreement to better than 0.5%. This is an improvement over our previous data and is due mainly to better temperature control and advances in instrumentation.

19709. Jennings, D. A., Petersen, F. R., Evenson, K. M., Direct frequency measurement of the 260 THz (1.15 μm) 2oNe laser: And beyond, (Proc. Fourth Int. Conf. on Laser Spectroscopy, Rottach-Egern, Fed. Rep. of Germany, June 11-15, 1979), Paper in Laser Spectroscopy, H. Walther and K. W. Rothe, Eds., IV, 41-48 (Springer-Verlag, New York, NY, 1979).

Key words: frequency; He-Ne laser; nonlinear optics; visible frequencies; 1.15 μm.

Absolute frequency measurement has been extended to the visible spectrum with the measurement of the strong 1.15 μm laser line in 20Ne at 260 THz and lines in iodine at twice this frequency. The 260 THz frequency was synthesized in nonlinear crystals of CdGeAs, and AgASS, from stabilized CO2 lasers and the 1.5 μm laser line in 20Ne. The visible frequencies

were synthesized by generating the second harmonic of the 260 THz radiation with a LiNbO3 crystal. The absolute frequencies of ten hyperfine components of 1271, near 520 THz were measured.

19777. Risley, A., Jarvis, S., Jr., Vanier, J., The dependence of frequency upon microwave power of wall-coated and buffergas-filled gas cell Rba frequency standards, J. Appl. Phys. 51, No. 9, 4571-4576 (Sept. 1980).

Key words: cavity pulling; frequency stability; microwave power dependence; optical pumping; Rb frequency standards; wall coating.

Previous studies of a commercial passive gas cell Rb87 frequency standard showed a strong dependence of the output frequency VR upon the microwave power Pul. A major conclusion of that work was that the dependency of VR upon Put was due to a line inhomogeneity effect. The line inhomogeneity interpretation suggested that substituting a wall coating for the usual buffer gas would reduce the dependence upon P. As a part of the present work, a wall coating (a form of paraffin) was used and a reduction of this dependence by a factor of 100 was obtained. The present work has led to a more convincing theoretical demonstration of the line inhomogeneity effect. The paper discusses some of the details of the analytical procedure. There are certain major requirements that a wall coating would have to satisfy if it is to be superior to the usual buffer gas, and these are discussed in the text. The advantages demonstrated by the present work indicate that further studies are warranted to determine if an improved standard could be built based on a wall coating.

19814. Koch, W. F., The value of the Faraday via 4aminopyridine, (Proc. Atomic Masses and Fundamental Constants, East Lansing, MI, Sept. 18-21, 1979), Paper in Atomic Masses and Fundamental Constants, J. A. Nolen, Jr., and W. Beneson, Eds., 6, 157-172 (Plenum Publ. Corp., New York, NY, 1980).

Key words: coulometry; Faraday constant; 4-aminopyride. In 1833, Michael Faraday of the Royal Institution in London formulated the laws of electrolysis revealing the relationship between electric current, time, and chemical equivalent weight (mole). Translated into mathematical terms, this relationship can be expressed: mole = (1/F) ƒ o' i dt. The constant of proportionality, F, has of course been named the Faraday constant and its value is the subject of this presentation.

At the last meeting (AMCO-5), preliminary results were reported on the determination of the Faraday constant by way of coulometric titration of 4-aminopyridine performed at lowa State University. Additional titrations of the same material have since been conducted at the National Bureau of Standards, taking advantage of improved standards of mass, time, voltage and resistance. A reappraisal of the error analysis has also been undertaken in light of further evidence and is reported herein.

Detailed accounts of experimental procedures, instrumentation and data treatment are well documented and need not be repeated here. However, a brief review of the experiment may prove helpful to the following discussion.

19898. Deslattes, R. D., The Avogadro constant, Ann. Rev. Phys. Chem. 31, 435-461 (1980).

Key words: atomic masses; fundamental constants; mole; precision measurement.

This review of the Avogadro Constant is prepared in response to an invitation from the Editor of the Annual Reviews of Physical Chemistry. It attempts to deal with some aspects of the history in this field of certain conceptual problems and the present state of experimental measurement.

Measurement Science and Technology:

Policy and State-of-the-Art Surveys

NBSIR 78-1583. Standardization and measurement services in Indonesia, H. S. Peiser, N. J. Raufaste, R. C. Sangster, B. M. Gutterman, and P. M. Odar, 344 pages (Sept. 1979). Order from NTIS as PB80-166267, $18.00.

Key words: calibration; development; Indonesia; industrialization; instrumentation; less developed country; metrology; standardization; Third World.

At the request of the Indonesian State Minister for Research and Technology, the National Bureau of Standards conducted a two-week survey of standardization and measurement systems in support of industrialization. Financial support was shared between the Agency for International Development and the Government of Indonesia. Coordination by the Lembaga Ilmu Pengetahuan Indonesia (Indonesian Institute of Sciences) and the U.S. National Research Council was provided. There were six topics of specialization: (1) Food and Food Safety, (2) Building and Construction, (3) Quality Control in Industry, (4) Safety Standards, (5) Calibration, Instrumentation, and Metrology, and (6) Industrial Measurement Techniques. In the executive summary the appraisal of the existing systems for standardization and measurement is coupled with recommendations. A background section is followed by one with the Indonesian specialists' assessments of needs and opportunities. The itinerary details about 80 visits and discussions of team members, and there is a concluding section with general remarks. Indonesia has immense human and natural resources. With a capable infrastructure in standardization and measurement (among other requirements), development could become rapid and very successful.

Mechanics: Design, Testing, and Measurement NBSIR 80-2073.2. Guidelines for exchangeable APT data packages. APT part programmer's manual, B. M. Smith, 24 pages (June 1980). Order from NTIS as AD-A092929, $6.50.

Key words: APT; automation; computer aided manufacturing; NC machining; NC programming; numerical control; part programming.

A method of APT programming and postprocessor design has been developed which permits more efficient data preparation for numerical control (NC) machine tools and then allows this data to be quickly and easily exchanged among different NC machines. This is accomplished through rigorous specification of the APT post-processor language based upon new ANSI standards for APT plus a comprehensive definition of the machining functions which should result from the use of each APT language statement. Individual post-processors are modified to process each statement in the same manner. The concept was successfully demonstrated in production by processing a single APT data package on three different milling-drilling type machine tools. A 23% increase in NC manufacturing efficiency is projected. This document describes the APT post-processor language used, including the syntax and semantics of each statement. It also defines the default conditions under which the post-processor and machine tool operator accomplish the desired function in the absence of the automatic feature.

NBSIR 80-2073.3. Guidelines for exchangeable APT data packages. APT postprocessor specifications, B. M. Smith, 15 pages (June 1980). Order from NTIS as AD-A092933, $5.00.

Key words: APT; automation; computer aided manufacturing; NC machining; NC Programming; numerical control; part programming; software specifications.

A method of APT programming and postprocessor design has been developed which permits more efficient data preparation for numerical control (NC) machine tools and then allows this data to be quickly and easily exchanged among different NC machines. This is accomplished through rigorous specification of the APT postprocessor language based upon new ANSI standards for APT plus a comprehensive definition of the machining functions which should result from the use of each APT language statement. Individual postprocessors are modified to process each statement in the same manner. This document sets forth minimum specifications for the procurement of APT Postprocessors consistent with the standardized postprocessing language concept. It is expected that these specifications will be used in future machine tool procurements. The concept was successfully demonstrated in production by processing a single APT data package on three different milling-drilling type machine tools. A 23% increase in NC manufacturing efficiency is projected.

19665. Nagel, R. N., VanderBrug, G. J., Albus, J. S., Lowenfeld, E., Experiments in part acquisition using robot vision, (Proc. Autofact II, Robots IV Conf., Detroit, MI, Oct. 29Nov. 1, 1979), Soc. Mfg. Eng. Tech. Paper MS79-784, pp. 1-14 (Society of Manufacturing Engineers, One SME Drive, P.O. Box 930, Dearborn, MI 48128, 1979).

Key words: part manipulation; robotics; robot vision. The National Bureau of Standards (NBS) vision system is mounted on the wrist of the robot, and provides both depth and part orientation information to the robot control system. The principle components of the vision system are a solid state camera, a structured light source, and a camera interface system. In experiments performed with the NBS vision system, the robot has been able to acquire both rectilinear and curved parts. This paper reviews the hardware configuration, provides an overview of the software and describes the experiments.

Metrology: Physical Measurements

U.S. Patent 4,227,096. Microwave integrated circuit for Josephson voltage standards, L. B. Holdeman, J. Toots, and C. C. Chang, 6 pages (Oct. 7, 1980).

Key words: Josephson junctions; microstrip; microwave integrated circuit; stripline transmission line.

A microwave integrated circuit, comprised of one or more Josephson junctions and short sections of microstrip or stripline transmission line, is fabricated from thin layers of superconducting metal on a dielectric substrate. The short sections of transmission line are combined to form the elements of the circuit, and particularly, two microwave resonators. The Josephson junctions are located between the resonators, and the impedance of the Josephson junctions forms part of the circuitry that couples the two resonators. The microwave integrated circuit has an application in Josephson voltage standards. In this application, the device is asymmetrically driven at a selected frequency (approximately equal to the resonance frequency of the resonators), and a D.C. bias is applied to the junction. By observing the current-voltage characteristic of the junction, a precise voltage, proportional to the frequency of the microwave drive signal, is obtained.

U.S. Patent 4,233,107. Ultra-black coating due to surface morphology, C. E. Johnson, Sr., 6 pages (Nov. 11, 1980).

The dried substrate, coated with the electroless nickelphosphorus alloy, is then immersed in an etchant bath consisting of an aqueous solution of nitric acid, wherein the nitric acid concentration ranges from a 1:5 ratio with distilled or deionized water to concentrated, until the coated surface of the substrate develops ultra-blackness, the blackness being associated with the surface morphology as described above.

The resulting substrate, covered with the ultra-black coating is thereafter washed and dried.

The ultra-black surface, which has a spectral reflectance on the order of about from 0.5 to 1.0% at wavelengths of light of about from 320 to 2140 nanometers, finds use as a solar collector in the field of solar energy.

19646. Geist, J., Zalewski, E. F., The quantum yield of silicon in the visible, Appl. Phys. Lett. 35, No. 7, 503-506 (Oct. 1, 1979).

Key words: quantum efficiency; quantum yield; silicon; silicon photodetector; spectral response; visible.

Extremely high accuracy measurements of the internal quantum efficiency of shallow-junction silicon photodetectors were fit with various theoretical models. The internal quantum efficiency was found to be rather model independent indicating its possible use as a radiometric standard. The results of this investigation indicate that the quantum yield of silicon is unity to within a few tenths of one percent in the visible.

19675. Schaefer, A. R., Reflectance and external quantum efficiency change of a silicon photodiode after surface cleaning, Appl. Opt. 18, No. 15, 2531 (Aug. 1, 1979).

Key words: cleaning; dirt films; reflectance; silicon photodiodes.

A change in the reflectance of silicon photodiodes was observed and attributed to possible formation of an impurity coating on the detector surface. An experiment was performed to verify this hypothesis and show how the external quantum efficiency of the detector varied with the reflectance in a compensating manner such that the internal quantum efficiency remained constant.

19695. Bright, D. S., Fletcher, R. A., Chabay, I., Particle Doppler shift spectrometry. Accurate size determinations of 5-15μm aerosol, J. Phys. Chem. 84, No. 12, 1607-1611 (June 12, 1980).

Key words: aerosol; light scattering; Lorenz-Mie light scattering calculation; particle sizing; Stoke's velocity. We have improved the particle Doppler shift spectrometer (PDSS) to determine the diameter of 5-15-μm droplets to high

accuracy (±0.05 μm). The diameter is calculated from Stokes law and the gravitational settling velocity which is obtained by measuring the Doppler shift of laser light scattered at a single angle. This scattered light also shows intensity variations with diameter as predicted by Lorenz-Mie light scattering theory. Characteristic features of the plot of scattered light intensity vs. droplet diameter are used as size calibration markers. The features are a function of only the index of refraction of the aerosol material and the wavelength of the light. Our results show better agreement with Stokes law without the slip correction than with the correction.

19738. Geist, J., Silicon photodiode front region collection efficiency models, J. Appl. Phys. 51, No. 7, 3993-3995 (July 1980).

Key words: collection efficiency; quantum efficiency; silicon photodiode; surface recombination.

The minority-carrier transport equations are solved numerically for a realistic model of the front region of a UV-enhanced silicon photodiode. Surface recombination is shown to be the dominant quantum efficiency reducing mechanism. Auger recombination is shown to be almost negligible for the type of diode under investigation.

19742. Bender, P. L., Goad, C. C., Probable LAGEOS contributions to a worldwide geodynamics control network, Proc. Symp. on the Use of Artificial Satellites for Geodesy and Geodynamics and Laser Workshop, Lagonissi, Greece, May 1978, G. Veis and E. Livieratos, Eds., II, 145-161 (National Technical University, Athens, Greece, 1979).

Key words: artificial satellites; distance measurements; geodesy; geodynamics; lasers; station positions.

The need to establish a worldwide reference system for use in geodynamics is clear. We have carried out simultations on the contributions which laser range measurements to LAGEOS can make in establishing such a system. A distribution of ten fixed ranging stations was assumed for most of our calculations, with the stations located in the U.S., S. America, W. Europe, Australia and Japan. A single 7-day arc was used and measurements were assumed to be made only every 10 min., in order to avoid artificial reductions in the uncertainties due to oversampling. As is well known, the gravity field model will be the main contributor to the station coordinate uncertainties initially. However, if some of the harmonic coefficients are adjusted using the LAGEOS data, the gravity field model effects can be substantially reduced. Simulations in which we solved for all of the tesseral harmonic coefficients through degree 5 plus 20 additional terms have shown that a rms station coordinate uncertainty of 4 to 5 cm can be achieved for random range measurement errors and range biases of between 0.7 and 2 cm. The scaled GEM-10 standard deviations were used both as a priori uncertainties for the adjusted coefficients and in calculating the effects of the remaining unadjusted coefficients. When further improvements in the gravity field models have been made, it seems likely that retrospective analyses of the LAGEOS ranging data obtained in the next couple of years will be limited mainly by the atmospheric correction uncertainty and the range measurement biases, even, if the bias uncertainty is only 0.7 cm. Some comments also are made on possible procedures for maintaining a worldwide geodynamics reference system.

19745. Cezairliyan, A., Miiller, A. P., A transient (subsecond) technique for measuring heat of fusion of metals, Int. J. Thermophys. 1, No. 2, 195-215 (1980).

Key words: dynamic techniques; heat of fusion; high temperatures; melting; niobium.