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cal basis of calorimetry, optional modes of operation, and kinds of processes to be measured. Calorimeters for reacting systems and their principles are described: bomb calorimeters, continuous-flow gas-combustion calorimeters, solution calorimeters and microcalorimeters. Calorimeters for nonreacting systems are described: including isothermal (Bunsen) calorimeter, isoperibol calorimeter, adiabatic calorimeter (low temperature and medium temperature), receiving calorimeter (using conventional furnace or levitation), high-sneed calorimeter, and modulation calorimeter. Trends are discussed. A reading list of 19 entries and a bibliography of 96 entries are provided. 18331. Ausloos, P., Lias. S. G., Proton affinity of dichlorocar. bene, J. Am. Chem. Soc. 100, No. 14, 4594-4595 (July 5, 1978).

Key words: dichlorocarbene; heat of formation; ionmolecule reactions; proton affinity; proton transfer reaction.

18334. Durst, R. A., Sources of error in ion-selective electrode

potentiometry, Chapter 5 in lon-Selective Electrodes in Analytical Chemistry, H. Freiser, Ed., Vol. I, 311-338 (Plenum Publishing Corp., New York, NY, 1978).

Key words: electrodes; electrodes, ion-selective; electrodes, reference; errors; ion-selective electrodes; sensors, chemi

cal; standards. While the advantages and unique features of ion-selective electrodes are widely known and anpreciated, the potential sources of error are numerous and the analyst must be aware of these pitfalls in order to be able to minimize their effects. The causes of these errors are almost as varied as the sensors and samples, but several common sources can be identified: interferences, and/or fouling of the indicator electrode, sample matrix effects, reference electrode instability, and improper calibration of the measurement system. These sources of error are discussed in some detail with suggestions for overcoming or minimizing the nroblems and their analytical effects.

These sensors can be a useful and convenient means for the analysis of wide variety of ionic, molecular and gaseous species, but only if the sources of error are recognized and eliminated. More than any other modern analytical technique, ion-selective electrode potentiometry require sound knowledge of solution chemistry in order to achieve maximum effectiveness.

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It is demonstrated that the recently reported value for the proton affinity of CCl, determined through the well known bracketing technique is too high by approximately 14 kcal/mole. The assignment of a value for this proton affinity was based on the observation or nonobservation of proton transfer from CCl2H* to selected bases of known proton affinity (CCLH* + B → CCl2 + BH*). It is shown that in some experiments described in the recent study, exothermic proton transfer reactions were in competition with energetically more favorable reaction channels which strongly predominated, usually to the exclusion of proton transfer. This letter expands our earlier exhaustive study of proton transfer and competing reactions of CCl4H* to include the bases used by Levi, Taft, and Hehre (J. Am. Chem. Soc. 99, 8454 (1977)). All reaction channels as well as rate constants have been determined, and some of our earlier measurements have been refined.

18335. Hudson, R. P., NBS standards for pressure, tempera

ture, and humidity, (Proc. Air Quality Meteorology and Atmospheric Ozone, Boulder, CO, July 31-Aug. 6, 1977), Am. Soc. Testing Mater. Spec. Tech. Publ. 653, A. L. Morris, R. C. Barras, Eds., pp. 13-26 (1978).

Key words: humidity; ozone; pressure; standards; temperature; vacuum.

18332. Ausloos, P., Lias, S. G., Reactions of NO,* and solvated

NO,* ions with aromatic compounds and alkanes, Int. J. Chem. Kinet. X, 657-667 (1978).

Key words: aromatic substitution; association ions; charge transfer, ethyl nitrate; ion-molecule reactions.

A summary is presented of the metrological activities in the Heat Division of the National Bureau of Standards, covering the calibration and other service activities in temperature, pressure,

and humidity, together with a description of some representative examples of related current research and developmental work.

18336. Kusuda, T., Use of simulation models of buildings in as

sessing energy conservation strategies, Proc. Symp. Energy Conservation Strategies in Buildings: Comfort, Acceptability, and Health, New Haven, CT, Jan. 25, 1978, J. A. J. Stolwijk, Ed., pp. 143-156 (J. B. Pierce Foundation Laboratories, Hartford, CT, 1978).

Key words: heating and cooling load; hybrid computer; NBSLD; thermal comfort.

The rate constants and modes of reaction of NO,* and CH,ONO,NO,* with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and subsitution reactions (NO,+ M → MO+ + NO; C,H,O NO,NO,+ + M → MNO* + C,H,ONO,) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C,H,ONO,NO,* ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO,* and C,H,ONO,. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C,H,ONO,NO,* ions, on the energetics of the competing charge transfer process. Both NO,* and C,H,ONO,NO,* undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k(collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO,

A comprehensive treatment of building heat transfer processes is employed by the National Bureau of Standards Heating and Cooling Load Calculation program NBSLD to study the effect of various building parameters upon the resulting heating and cooling load and thermal comfort of occupants, in order to evaluate energy conservation strategies. The basis of the computation is the detailed solution of simultaneous heat balance equations at all of the interior surfaces of a room or space. Transient heat conduction through the exterior walls and in the interior structures is handled by using conduction transfer functions. The use of heat balance equations, although more time consuming than the conventional load calculation procedures, avoids the vagueness and uncertai ies inherent in the latter. In addition, it is more accurate for a specific building design. Also mentioned in this paper is use of a hybrid computing system whereby simultaneous transfer of air, moisture and heat in and through the building can be studied more efficiently than by the conventional digital computer.

18333. Unassigned.

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18337. Lias, S. G., Ausloos, P., Ionization energies of organic compounds by equilibrium measurements, J. Am. Chem. Soc. 100, No. 19, pp. 6027-6034 (1978).

Key words: aromatic compound; charge transfer equilibria; entropy change; ion cyclotron resonance; ionization ener

sy. The determination of the equilibrium constants for a number of charge transfer equilibria has generated a scale of relative values of AGo for the charge transfer reactions. The factors contributing to ASo for these reactions were elucidated by carrying out experimental determinations of the entropy changes for some of the equilibria. The values of AH° were used to generate a scale of relative ionization energies of 41 organic compounds and NO. Standardization of the scale using the spectroscopically determined values of the ionization potentials of NO, benzene, and furan was accomplished by calculating the relationship between adiabatic ionization potentials and the "enthalpies of ionization" measured in these experiments. The spectroscopically determined IPs of six of the compounds were reproduced in this way, thus verifying the technique. 18338. Lindstrom, R. M., Fleming, R. F., Optimized measure

ment of aluminum in high-purity silicon, Proc. Nuclear Methods in Environmental and Energy Research, Columbia, MO, Oct. 10-13, 1977, pp. 90-98 (Technical Information Center, U.S. Department of Energy, Washington, DC, 1978).

Key words: activation analysis; cadmium ratio; east neutron reactions; interfering nuclear reactions; optimization of

analysis; silicon; trace analysis. Measurement of small quantities of aluminum in silicon of semiconductor or solar grade is complicated by production of 28 Al by an (np) reaction on the matrix, in competition with the (ny) reaction on the trace aluminum sought. In selecting the optimum irradiation facility, the conflicting requirements of high thermal flux for the greatest signal and of low fast flux for the smallest interference must be balanced. The present work outlines a simple experimental procedure for assessing and correcting for interferences. No explicit knowledge of fast fluxes or cross sections is required; these are often poorly known. The procedure is generally applicable to other cases of competing reactions.

→ CH2 + HCL (or H + CI)

CHCI + H2 (or 2H) At 163.3 nm, process (1) is almost exclusively responsible for the photodecomposition. However, at shorter wavelengths processes (2), (3) and (4) increase while process (1) decreases in importance. At all wavelengths these four processes account for a total quantum yield of 0.75-1.0. 18341. Armstrong, R. W., Wu, C. C., Farabaugh, E. N., Crystal

subgrain misorientations via X-ray diffraction microscopy, Adv. X-Ray Anal. 20, 201-206 (1977).

Key words: Al2O.; Berg-Barrett; Lang; misorientation con

trast; x-ray topography; Zn. The “misorientation contrast" which occurs at boundaries marking the relative displacement of adjacent subgrain reflections in x-ray diffraction images is shown by a stereographic projection method of analysis to be useful for deciphering X-ray images obtained by the Berg-Barrett and Lang techniques. Experimental results are given for subgrain structures observed in Zn and Al2O, crystals.

18342. Carpenter, B. S., Mapping and detecting elements selec

tively by the Nuclear Trace Technique, Proc. Int. Conf. on Nuclear Methods in Environmental and Energy Research, Columbia, MO, Oct. 10-13, 1977, pp. 136-143 (Available as Department of Energy CONF-771072 from National Technical Information Service, Springfield, VA 22161, 1978).

Key words: alpha tracks; biomedical; boron; fission tracks; geochronology; geology; lithium; nitrogen; silicon devices; trace analysis; uranium.

The nuclear track technique (NTT) has been routinely used to determine trace concentrations of uranium, boron and lithium in a variety of matrices, as well as macro-concentrations (e.g. > 500 mg/g) of nitrogen in steels and biological materials. In addition to the trace element determinations, the NTT has found significant applications in geology as a viable method for geochronology and geothermometry. Aside from the analytical and geological applications, the NTT is being used to micromap the location, distribution and behavior of dopants, such as boron, lithium, oxygen and uranium, in various materials. This is particularly the case in the semiconductor and biomedical areas, since no convenient long lived radioactive nuclides of these elements exist.

18339. Peavy, B. A., A note on response factors and conduction

transfer functions, (Proc. Symp. American Society of Heating and Air-Conditioning Engineers Annual Meeting, Atlanta, GA, Jan. 29-Feb. 2, 1978), ASHRAE Trans. 84, Pt. 1, 688690 (1978).

Key words: computer time; conduction-transfer functions;

dynamic heat transfer; thermal response factors. The thermal response factor technique for calculating dynamic heat conduction through walls, floors, and roofs is utilized in many computer programs for determining building heating and cooling loads. Considerable computation time and computer memory space are devoted to the use of this technique, and it is advantageous to reduce the time and space required.

Reduction in computation time and computer memory space can be achieved by the use of the zeroth through fifth-order conduction-transfer functions. Computation time be reduced by about one-half, and it is possible to reduce the memory space to one-fourth of that presently used in the computer program NBSLD. 18340. Shold, D. M., Rebbert, R. E., The photochemistry of methyl chloride, J. Photochem. 9, 499-517 (1978).

Key words: chloride; methyl; methyl chloride; photochemistry.

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18343. Gills, T. E., Gallorini, M., Greenberg, R. R., The deter

mination of selected toxic elements in biological matrices using radiochemical activation analysis, Proc. 3d Int. Conf. on Nuclear Methods in Environmental and Energy Research, Columbia, MO, Oct. 10-13, 1977, pp. 597-609 (Available as Department of Energy CONF-771072 from National Technical Information Service, Springfield, VA 22161, 1978).

Key words: radiochemical; selectivity; sensitivity; toxic ele

ments. Neutron activation analysis, coupled to improved or modified radiochemical procedures, was used in the analysis of several selected toxic elements in biological matrices. These procedures proved effective in achieving maximum sensitivities

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and accuracies for the following elements: Hg, Se, As, Sb and Cd. This paper describes the application of these radiochemical procedures and their use at the National Bureau of Standards in the Standard Reference Material certification program. 18344. Schenck, P. K., Mallard, W. G., Travis, J. C., Smyth,

K. C., Absorption spectra of metal oxides using optogalvanic spectroscopy, J. Chem. Phys. 69, No. 11, 5147-5150 (Dec. 1, 1978).

Key words: light absorption; metal oxides; molecular ab

sorption; opto-galvanic spectroscopy; uv irradiation. The absorption spectra of neutral flame species may be detected by measuring current changes induced by photon irradiation at wavelengths corresponding to electronic transitions. This paper presents the first results using this optogalvanic spectroscopy to study molecular absorption. Numerous transitions have been detected for ScO, YO, and LaO in the 360630 nm wavelength region. The most extensive data have been obtained for Lao, where we observe a total of at least four electronic states and 18 sequences. Five of the sequences have not been seen in previous emission studies.

18348. Barnes, J. D., Assessing permeation performance of in

dustrial plastic shipping containers, Proc. 36th Annual Technical Conf. Society of Plastics Engineers, Washington, DC, Apr. 24-27, 1978, pp. 824-826 (Society of Plastics Engineers, Greenwich, CT, 1978).

Key words: compatibility; permachor; permeation; plastic

containers; polyethylene; standards. This paper presents a proposal for a standards-based measurement system for predicting the permeation performance of industrial plastic shipping containers. The scheme is based on early work which demonstrates that there is a systematic way (known as the “permachor") to characterize the tendency of a given molecular species to permeate polyethylene. It is possible to establish a scale for calibrating a permachor measuring system and to establish standardized conditions for making the measurements.

If such a system were operational, it would be expected that the measurements required to establish compatibility between a lading and a shipping container could be carried out more economically and with greater confidence. The number of holding tests of individual ladings in large shipping containers would also be much reduced under the proposed scheme.

18345. Tippet, J. C., Chang, D. C., A new approximation for

the capacitance of a rectangular coaxial-strip transmission line, IEEE Trans. Microwave Theory Tech., pp. 602-604 (Sept. 1976).

Key words: EMC measurements; radiation resistance;

rectangular coax; shielded strip line; TEM cell. The method of conformal transformation is used to obtain the exact capacitance of a rectangular-coaxial-strip transmission line. An approximate form, which includes the edge-interaction capacitance of the strip, is obtained and is shown to reduce in an appropriate limit to a form obtained by other authors.

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18346. Hellwig, H., Evenson, K. M., Wineland, D. J., Time,

frequency and physical measurement, Phys. Today, pp. 23-30 (Dec. 1978).

Key words: atomic clocks; frequency standards; frequency synthesis; fundamental constants; length standards; physical measurement systems; review article; speed of light; time

standards. Frequency, time, and wavelength measurements of precision have been brought about by fundamental advances in spectroscopy. These include: Sub-Doppler techniques, the stabilized laser, and the extension of direct frequency measurements to the near infrared region of the spectrum. In fact, significant changes in our system of physical measurements are taking place. This article attempts to focus on several of these developments, which, we feel, are likely to substantially impact many areas of science, technology and physical measurement.

18349. Becker, D. A., Environmental sample banking-research

and methodology, Proc. Symp. on Trace Substances in Environmental Health-X, Columbia, MO, June 8-10, 1976, D. D. Hemphill, Ed., pp. 353-359 (University of Missouri, Columbia, MO, 1976).

Key words: analytical techniques; contamination; environ

ment; retrospective; sample storage; trace analysis. The National Bureau of Standards (NBS), in cooperation with the Environment Protection Agency and the National Science Foundation, is engaged in research program establishing methodology for environmental sample banking. This program is aimed toward evaluating the feasibility of a Na. tional Environment Specimen Bank (NESB).

The capability for retrospective chemical analyses to evaluate changes in our environment would provide useful information. Much of this information could not be obtained using data from previously analyzed samples. However, to assure validity for these stored samples, they must be sampled, processed and stored under rigorously evaluated, controlled and documented conditions. Such conditions must also be specific for the various components of interest.

The program currently under way in the NBS Analytical Chemistry Division has 3 main components. The first is an extension survey of available literature concerning problems of contamination, losses and storage. The components of interest include trace elements, pesticides, other trace organics (PCBs, plasticizers, etc.), radionuclides and microbiological species. This survey has been completed and the limited and often contradictory information will be outlined. An important output of this effort has been the development of suggested “guidelines" for sampling, cleaning and storage techniques. These guidelines are being circulated through the scientific community for comment and suggestions.

The second component is an experimental evaluation of contamination and losses during sampling and sample handling. Of particular interest here is research into container cleaning methodology for trace elements, with respect to adsorption, desorption, leaching and partial dissolution by various sample matrices.

The third component of this program is an evaluation of existing methodology for long-term sample storage. Techniques under investigation include lyophilization, low-temperature (oxygen-plasma) ashing, air drying and freezing (at -20 °C and at -70 °C), including evaluation of an optimum storage container for the different trace substances.

18347. Himes, V. L., Hubbard, C. R., Mighell, A. D., 3a,6a

dimethylglycouril (3a, 6a-dihydro-3a,6a-dimethylimidazo (4,5dJimidazole-2,5(14,6H)-dione}, Acta Cryst. B34, 3102-3104 (1978).

Key words: biomedical standard; diacetylurea; molecular

structure; urea; urea determination; x-ray diffraction. C.HN,O,, M, = 170.17, orthorhombic, Cmcm, a = 7.357 (2), b = 10.836 (5), c = 10.180 (6) Å; 2 = 4, De = 1.389, Dm = 1.39 g cm-> (flotation); final R = 0.040 (463 reflections with 1> 301). Crystallographic symmetry requires the molecule to have point symmetry 2mm. In the molecule are two planar fivemembered rings with a 65.0° angle between the plane normals of the rings. Each molecule is hydrogen bonded to four neighboring molecules by eight N-H...O hydrogen bonds 100_0 = 2.869 (2) Å).

This program is a concerted effort to bring together many aspects of sampling, sample handling and storage. The results seem to be useful not only for sample banking purposes but to the general trace substance analytical community as well.

NBS's role in traceability to national standards for automated test equipment (ATE) is described. The meaning of traceability vis-a-vis ATE is discussed.

18350. Becker, D. A., LaFleur, P. D., LeRoy, A., Spontaneous

deposition radiochemical separation for platinum determination in biological materials, Proc. Int. Nuclear and Atomic Activation Analysis Conf. and Nineteenth Annual Meeting on Analytical Chemistry in Nuclear Technology, Gatlinburg, TN, Oct. 14-16, 1975, 1 page (American Nuclear Society, Hinsdale, IL, 1976).

Key words: biological materials analysis; environmental materials analysis; neutron activation analysis; noble metals analysis; platinum determination; radiochemical separation;

spontaneous deposition technique. The use of platinum and possibly other noble metals in motor vehicle emission control systems has recently been made public. The method developed and described is capable of quantitatively determining gold, platinum, and palladium in a wide variety of biological and environmental matrices. Th analytical procedure entails wet-ashing with nitric-perchloric acids with carriers, redissolving the residuc in aqua regia, and then plating out on silver metal powder. This technique is also currently being evaluated for possible use in simultaneous determination of additional noble metals.

18355. Ehrlich, M., Soares, C. G., Jackson, B., Lanoue, P., In

fluence of source configuration on spectral composition of gamma-ray beams from «Co teletherapy units, Int. J. Appl. Radiat. Isot. 29, 741-747 (1978).

Key words: atomic number; cobalt-60 photons; configuration; plug; scattered photons; sleeve; source capsule;

source pellets; spacer; spectra; spectrometry. Measurements were made of the photon spectra of simulated Co teletherapy beams. Various source configurations and source environments of practical interest were employed for this purpose. The sources consisted of activated cobalt pellets packed into steel capsules. Several combinations of capsule diameters and heights of pellet layers were used. The spacer materials filling the remaining capsule volume were chosen to be of high, intermediate, or low atomic number. The capsules could be inserted, one at a time, into a compartment of either tungsten or brass, simulating the central section of popular commerical "Co teletherapy units. There also was some choice in the atomic number of the structural elements holding the capsules in place in the compartment. The largest contribution of scattered photons was found to occur when the materials close to the source pellets had atomic numbers in the vicinity of 30.

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18351. Biétry, J., Sacré, C., Simiu, E., Mean wind profiles and

change of terrain roughness, J. Struct. Div., Am. Soc. Civ. Eng. 104, No. ST10, Proc. Paper 14099, 1585-1593 (Oct. 1978).

Key words: aerodynamics; boundary layer; loads (forces);

roughness; structural analysis; tall buildings; wind pressure. Information is presented on the wind structure in established flow over terrains with various roughness characteristics (open water, open terrain, suburban terrain, towns, centers of large cities). Based on recent results of theoretical and experimental meteorological studies a simple procedure is then proposed, enabling the designer to assess the effect upon the mean wind profile of a roughness change upwind of the structure under consideration. The procedure, which is approximate but adequate for structural engineering purposes, is then illustrated in a numerical example.

18356. Nyyssonen, D., Optical linewidth measurements on wafers, SPIE Semin. Proc. 135, 115-119 (1978).

Key words: mensuration; microdensitometry; microlithog. raphy; micrometrology; microscopy; partially coherent

imaging. An optical scanning microscope system for accurate measurement of linewidth on wafers is described. The development of this system in both theory and experiment parallels the treatment of transmitted light measurements on see-through photomasks as previously described. Threshold equations for determining edge location have been developed which include corrections for

phase. In reflected light, the wavelength dependence of these parameters due to thin film interference requires a much narrower spectral bandwidth. In addition, other light losses dictate the use of laser illumination. Control of the spatial coherence of the laser is discussed. A comparison of theoretical and experimental results is given along with a comparison of reflected and transmitted light mea. surements.

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18352. Bowman, R. C., Jr., Carter, G. C., Chabre, Y., Nuclear

magnetic resonance studies of diffusion in FeTIH, Proc. 2d Int. Congress on Hydrogen in Metals, Paris, France, June 611, 1977, 8 pages (Pergamon Press, Paris, France, 1977).

Key words: diffusion; energy; hydrides; hydrogen storage;

nuclear magnetic resonance; nuclear spin relaxation. Proton NMR of FeTiH, has been studied for x values in the B and y hydride phases. Knight shifts, linewidths, spin-lattice relaxation times, and spin-spin relaxation times have been measured and a temperatute of sudden hydrogen loss has been observed. Activation energies have been deduced from these measurements.

18353. Unassigned.

18357. Watson, R. E., Bennett, L. H., Electron factors in the

occurrence of sigma and structurally related transition metal alloy phases, Scr. Metall. 12, 1165-1170 (1978).

Key words: alloy phases; electronegativity; electron factors; electron vacancies; Laves phase; sigma phase; transition

metal. The sigma phase, a complex structure occurring in many transition metal systems, is of considerable practical and theoretical interest. Its presence can cause a normally ductile high performance steel or superalloy to embrittle and fail in service. There are a number of structurally related phases, some of which have properties which are of interest for other reasons. For example, the A15 structure includes the highest transition temperature superconductors, such as Nb Sn, while the CaCu, structure includes LaNis which is an excellent hydrogen storage alloy, and SmCo, which is an extremely useful hard magnet. The stability of the o phase has generally been discussed in terms of electron and size factors. This note concentrates on the role of electron factors, and uses a pair of

18354. Belanger, B. C., The role of NBS in truceability to na

tional standards for advanced measurement systems, Proc. Industry/Joint Services Automatic Test Conf. and Workshop on Advanced Test Technology Management and Support, San Diego, CA, Apr. 3-7, 1978, pp. 295-296 (National Security Industrial Association, Washington, DC, 1978).

Key words: automated test equipment; measurement assurance; traceability.

electronic coordinates derived from fundamental microscopic theory for a structural map of these alloy systems. 18358. Berger, M. J., Planned compilation of stopping power

and range data, Proc. Sixth Symp. on Microdosimetry, Brussels, Belgium, May 22-26, 1978, J. Booz and H. G. Ebert, Eds., I, 639-649 (Harwood Academic Publishers, Ltd., London, England, 1978).

Key words: a-particles; electrons; heavy ions; international commission on radiation units and measurements; protons;

stopping power. In recent years there has been a steady accumulation of new information about the penetration of charged particles through matter. The ICRU has appointed a committee that is charged with the task of digesting this new information and of preparing an up-to-date compilation of stopping-power and range data for electrons, protons and heavy ions, with emphasis on the needs of medical physics and radiobiology. The purpose of this talk is to indicate the plans, priorities and initial activities of the committee, and to discuss some recent development in stopping-power research which will facilitate the committee's task. 18359. Callcott, T. A., Arakawa, E. T., Ederer, D. L., Emission and absorption x-ray edges of Li, Phys. Rev. B 16, No. 12, 5185-5192 (Dec. 15, 1977).

Key words: core hole lifetime; core hole relaxation; K xray absorption spectrum; K x-ray emission spectrum; many

body effects; rhonon interactions. The K x-ray emission edge of Li is measured between 85 and 490 K and analyzed to obtain the temperature dependences of the edge position and of a Gaussian edge-broadening function. Full width at half-maximum edge widths range from 0.22 0.05 eV at 85 K to 0.38 + 0.05 eV at 440 K. Edge positions shift from 54.81 + 0.02 eV at 85 K to 54.86 + 0.02 eV at 440 K and to 54.91 1 0.02 eV after melting. Emission and absorption spectra measured with the same spectrometer establish a 0.10 + 0.02 eV separation between the emission and absorption edges. These results are compared with recent theories describing incomplete lattice relaxation about the core hole. We conclude that for a core-hole lifetime of 0.016 to 0.030 eV the theories give a satisfactory explanation of the premature peak in the emission spectra. We suggest also that phonon-core-hole interactions provide the dominant edge-broadening mechanism, and that many-body effects are small.

In elastic scattering the scattered neutron energy is known (if the angular distribution is known) and there are no gamma rays. For (n, charged particle) reactions with cross sections given to known final states the second term is zero and the third term is determined by the cross section. In other reactions, such as (n,n' a) (n,n' p), and (n,n' 3a), the kerma factor is very sensitive to information about the outgoing neutron energy (direct reaction versus boil-off reaction), and to the final states assumed (i.e. energy carried off by gamma rays). We will discuss some “global” assumptions made in kerma factor calculations-uniform assumptions based on reasonable nuclear physics used when specific data is not available. In the case of secondary particle spectra, the above simplifying relation usually does not work since energy distributions of all secondary charged particles are needed. Here the choice of nuclear reaction mechanisms is crucial. Examples will be given of alternatives and choices made for specific nuclides.

In the higher energy regions where evaluated cross sections are not available, there are several ways to go. One is essentially an extrapolation of data at lower energies using what guides (total cross sections, optical model calculations) are available. A second method is the use of optical model and nuclear statistical model cross sections to produce the complete set of data needed. A third model is the use of the Intranuclear Cascade Model (INC). Results of some of these methods will be compared.

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18361. Cavallo, L., Ehrlich, M., Hutchinson, J. M. R., Tracea

bility in ionizing radiation measurements systems, Proc. Int. Symp. on National and International Standardization of Radiation Dosimetry, Atlanta, GA, Dec. 5-9, 1977, IAEA-SM222/18, 1, 65-87 (International Atomic Energy Agency, Vienna, Austria, 1978).

Key words: dose; ionizing; radioactivity; standards; testing;

traceability. There are many demands for traceability to the national radiation measurements systems (NRMS) stemming from groups such as the regulatory agencies, state health laboratories, commercial suppliers of radioactive materials and their customers, hospitals and their patients. The United States National Bureau of Standards supervises and administers measurements assurance programmes for radiation therapy departments, the radiopharmaceutical industry, federal agencies charged with radiation and radioactivity monitoring and surveillance, and for manufacturers and users of radioactivity standards, and administers to the radioactivity measurements assurance programme of the College of American Pathologists. These efforts are described and the results are tabulated.

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18360. Caswell, R. S., Coyne, J. J., Influence of nuclear data

on calculations of neutron energy deposition, Proc. Third Symp. on Neutron Dosimetry in Biology and Medicine, Neuherberg/München, Federal Republic of Germany, May 23-27, 1977, G. Burger and H. G. Ebert, Eds., pp. 29-43 (Commission of the European Communities, DirectorateGeneral, Scientific and Technical Information Management, Bâtiment Jean Monnet, Luxembourg, 1978).

Key words: kerma factors; neutron cross section; neutron energy deposition; nuclear data; nuclear reactions; secon

dary particle spectra. It is often assumed that if one has a set of evaluated neutron cross sections such as ENDF/B-IV, that it is then possible to determine physical properties of the neutron energy deposition process, such as kerma factors and secondary particle spectra, unambiguously. While this is true for some elements, it is not true for others. In the case of kerma factor calculations, nart of the calculational problem caused by lack of data can be side-stepped by use of the relation: (kerma) (energy available )-(energy carried off by secondary neutrons)-(energy carried off by gamma rays). In all cases the energy available is known.

18362. Durst, R. A., Potential pitfalls in the use of ion-selective

electrode-reference electrode pairs, Paper in Theory, Design, and Biomedical Applications of Solid State Chemical Sensors, op. 155-163 (CRC Press, Inc., West Palm Beach, FL, 1978).

Key words: electrodes, errors; electrodes, ion-selective; electrodes, reference; ion-selective electrodes; reference

electrodes; sensors, chemical. lon-selective electrodes have demonstrated unique features for the measurement of a variety of ionic and gaseous species. While the advantages of these electrodes are widely known and appreciated, it is usually not until one is actually using these sensors that the problems and pitfalls become apparent and may result in serious errors and considerable aggra

tion. The causes of these problems are almost as varied as the sensors and the samples, but several common sources can be identified: interferences and/or fouling of the electrode, sample matrix effects, reference electrode instability, and improper calibration of the measurement system. These pitfalls are discussed in

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