Myron H. Miller

Comparison of Measured and Predicted Conditions behind a Reflected Shock

Measured thermodynamic conditions behind reflected shocks in a gas‐driven diaphragm shock tube are compared to Rankine‐Hugoniot predictions. Pressures of the shock‐heated neon, which contained small concentrations of spectroscopic additives, were measured by quartz transducers. Temperatures (9000‐13 000°K) were simultaneously measured spectroscopically by line reversal and absolute emission techniques, while electron densities were measured by the broadening of the Balmer line Hβ. The temperature has been measured to an accuracy of ±1.5%, while electron densities have been determined with an accuracy of ±10%. Pressure measurements attained accuracies of ±5%. The consistency of the data indicates that a homogeneous local thermodynamic equilibrium model is an adequate description of the shock‐heated gas. The state measurements, compared with the real gas Rankine‐Hugoniot predictions, show significant departures. Predicted temperatures are typically 3% ± 10% higher than those measured. The predicted electron...

Relative Transition Probabilities for Krypton

Relative transition probabilities of the more prominent Kr i and Kr ii lines have been measured using a gas-driven shock tube as a spectroscopic source. Results for 22 Kr i lines (4200 < λ < 8500 A) and 33 Kr ii lines (4000< λ <5300 A) have estimated reliabilities of 8–50%. The data are compared with other measurements and with theoretical calculations.

Experimental Transition Probabilities for Neon i

Absolute transition probabilities of 35 visible and near-infrared neon lines were measured spectroscopically using a gas-driven shock tube. The absolute A values were measured with accuracies of 20%–40% by a variety of techniques. Absolute and relative results are compared with earlier experiments and with theoretical predictions.

Experimental transition probabilities for neutral and singly ionized tungsten

Relative A values of 131 W i and 116 W ii lines were measured in emission using a gas-driven shock tube as the spectroscopic source. Estimated accuracy of the relative data (3150–5600 A) for each ionization stage is 6–50%. The ratio of ionic-to-neutral line strengths was determined within 30%. Wavelengths of 40 tungsten lines (3400–5300 A) prominent in 1-eV plasmas, but not reported heretofore, were measured with typical reliability of ±0.2 A. Experimental W i line strengths are compared with data of Corliss and Bozman and trends of disagreement are examined.

A new method of absolute intensity calibration

Abstract The transition probability and Stark profile of Hα are the standards for a new method of absolute intensity calibration. This new method utilizes the interaction between the radiation from a fast flash lamp and hydrogen atoms in a thermal shock tube plasma. Although it is not essential for purposes of intensity calibration, the data can be used to measure the temperature of the shock tube plasma. The optical path used for the calibration is the same as that which is subsequently used to collect spectroscopic data. The general technique is applicable to any spectral region.

Relative transition probabilities for silicon.

Relative transition probabilities for visible Si atom lines, noting disagreement with LS coupling predictions and solar Si abundance determination

Atomic spectroscopy with the shock tube

The application of the shock tube to transition probability measurements is discussed, with particular attention to determination of the thermodynamic state of the radiating gas. Specific examples from earlier work on the spectrum of neutral chromium and from current measurements for light atoms clarify the need for redundant temperature determinations and illustrate the value of a new technique of data analysis which circumvents the sensitive dependence of level populations on temperature.

A thermally insensitive technique for measuring atomic transition probabilities.

Abstract Atomic transition probabilities, particularly when measured in emission, are often critically dependent upon the temperature ascribed to the light source. This paper describes a new experimental method which imparts little or no temperature sensitivity to A-values obtained with conventional light sources. While it is conceptually simple and requires no innovations to standard laboratory instrumentation, this method should improve both the precision and accuracy of measured A-values.

Relative transition probabilities of cobalt

Relative transition probabilities are measured for Co i and Co ii, a gas-driven shock tube being used as the spectroscopic light source. Results for 139 Co i lines (3940 < λ < 6640 A) and 11 Co ii lines (3840 < λ < 4730 A) are estimated to have reliabilities 8–50%. The results are compared with other experimental data.

Stark Broadening of UV Nickel Lines

Widths of Stark broadened Ni I Lines in the spectral range of 3000 A–4000 A have been measured using a gas driven shock tube as a spectroscopic source. Electron densities were determined using measured pressure and temperature data. Within the density range 6 × 10 16 cm -3 to 12 × 10 16 cm -3 the observed widths were linear functions of the electron density. There was no apparent correlation of observed widths with neutral density. Van der Walls broadening was presumed to be negligible because we observed narrow lines which should have had the same Van der Walls widths as computed with a classical theory as some of the wide lines we observed. In this way we were able to attribute almost all of the observed broadening to the Stark effect. The experimental results were compared with results of calculations of Stark broadening parameters using the program developed by Cooper and Oertel. The measured widths were about a factor three larger than the theoretical predictions. A part of this discrepancy is probably due to the fact that only LS allowed interactions were considered in the broadening calculations and possible incomplete classifications.