A comparison of the regular spectral transmittance scales of National Institute of Standards and Technology (USA), Institut National de Metrologie (France), National Research Council (Canada), and All-Union Research Institute for Optical and Physical Measurements (CIS) was accomplished using neutral glass filters with transmittances ranging from approximately 0.92 to 0.001. Storing the filters for almost four years produced no conclusive evidence of improvement over a previous interchange between NIST and three different national standardizing laboratories when the filters were stored for only 30 days. The agreement ranges from 0.01% to 0.3% depending on the laboratory and the filter used. The uncertainties (99.7% estimated confidence level) are generally greater than the differences between NIST and the individual laboratories. The sample-induced error contributed 20% or more of the total uncertainty except for a few cases as found in the previous comparison. This interchange, similar to the previous one, is part of an ongoing effort to obtain international standardization.

An intercomparison of the regular spectral transmittance scales of NIST, Gaithersburg, MD (USA); PTB, Braunschweig (FRG); NPL, Teddington, Middlesex (UK); and OMH, Budapest (H) was accomplished using three sets of neutral glass filters with transmittances ranging from approximately 0.92 to 0.001. The difference between the results from the reference spectrophotometers of the laboratories was generally smaller than the total uncertainty of the interchange. The relative total uncertainty ranges from 0.05% to 0.75% for transmittances from 0.92 to 0.001. The sample-induced error was large - contributing 40% or more of the total except in a few cases.

A new high-accuracy dye-laser-based system useful for measuring the spectral transmittance of filters or the spectral response of optical detectors has recently been developed at NBS. This paper describes the system and discusses the results of measurements made for purposes of comparison with a high-accuracy spectrophotometer also developed at NBS.

AbstractSets of five colored‐glass filters, identified as Standard Reference Materials 2101 through 2105 and intended for checking the performance of spectrophotometer‐integrator systems, have been issued by NBS for many years. Highaccuracy transmittance measurements were performed on a set of the colored filters designated Master Set No. 3 by using a reference spectrophotometer constructed at NBS. A comparison of the new values with the original data obtained in 1962 for Master Set No. 3 shows agreement to within the experimental uncertainties of the 1962 measurements.

A new spectrophotometer is described which has an accuracy of approximately 0.0001 transmittance units.The spectrophotometer utilizes a collimated beam in the sample area.This is accomplished by means of off -axis parabolic mirrors in the monochromator and sample compartment.Also, circular holes are used as entrance and exit apertures in the monochromator.All components of this spectrophotometer were chosen to achieve maximum accuracy.The result of this work is a "state of the art" instrument.The instru- ment was tested to evaluate its performance.Systematic errors such as detector non-linearity, stray radiant energy, and beam non-uniformity are measured.A correction for non-linearity of the photomultiplier and electronics is applied.

An electromagnetic $T$ tube was the source of a plasma used to measure line profiles of singly ionized atoms. The profiles of C II lines emitted by a plasma composed of He and C${\mathrm{O}}_{2}$ in the ratio 95:5 were scanned with a monochromator. The profile scans were accomplished by repeated firings of the T tube while advancing the monochromator in wavelength steps. Also measured was the profile of the 3934 \AA{} Ca II resonance line emitted by a plasma composed of He, ${\mathrm{H}}_{2}$, and C${\mathrm{O}}_{2}$ in the ratio 20:10:70 with Ca as an impurity. The profile of the 3889 \AA{} He I line was also measured and its halfwidth was used to determine the plasma electron density in the case of the C II lines. Likewise ${\mathrm{H}}_{\ensuremath{\alpha}}$ was used to determine the electron density in the case of the Ca II line. The experimental C II and Ca II Stark-profile half-widths were compared with the theoretically calculated values.

An experimental study is reported of the time-resolved spectrum of the plasma produced by the magnetically-driven shock wave in a T-tube. It is shown that the population densities of the excited levels of helium ions in the plasma depart from the values they would have in local thermal equilibrium. On the other hand if local thermal equilibrium is assumed and the electron temperature estimated for the intensity ratio of He II (4686Å) to He I (5876Å) then in the conditions of the experiment an error of a factor of two in the electron temperature arises. The reason for the departure from local thermal equilibrium was shown to be the rapid rate of change of the plasma conditions (especially the electron temperature). This is so great that the ionization and recombination rates, being slower, cause certain population densities to lag behind the electron density and electron temperature. These rates were found to be consistent with the rates calculated by Bates et al. in their collisional-radiative model for the ionization and recombination of hydrogen-like ions.

view Abstract Citations (11) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relative Oscillator Strengths of Some O II and O III Lines from Measurements on Shock-Heated Plasmas. Berg, H. F. ; Eckerle, K. L. ; Burris, R. W. ; Wiese, W. L. Abstract The layer of plasma behind reflected shock waves, which were produced in a T-tube filled with a helium-oxygen mixture, served as a high-temperature light source for the measurement of relative oscillator strengths of some 0 ii and 0 iii lines. Densities and temperatures were determined using the line-broadening data of some neutral and ionized helium lines as well as their relative intensities. Some relative 0 ii and 0 iii oscillator strengths were then determined by intensity measurements, using a scanning technique. The 011 results compared very well with previous work employing a high-current arc. Furthermore, for all measured oscillator strengths, theoretical values were obtained from the Coulomb approximation. The relative values from theory and experiment were found to be in satisfactory agreement. Absolute 0111 oscillator strengths could not be given with certainty due mainly to the rapid time characteristics of the source which made the establishment of an equilibrium population in the second ionization stage of oxygen uncertain. Publication: The Astrophysical Journal Pub Date: February 1964 DOI: 10.1086/147800 Bibcode: 1964ApJ...139..751B full text sources ADS |