James R. DeVoe

The Optogalvanic Effect

Every scientist since Albert Einstein has been taught about the photoelectric effect (1), by which photons more energetic than the binding energy of the outer electrons on the surface of a material are capable of producing ionization. The production of ions by collisional processes in plasmas is a familiar phenomenon as well (2). With the benefits of hindsight, it is therefore reasonable to postulate a hybrid ionization process for free atoms or molecules in a plasma, whereby the outer electron is promoted to the ionization potential by a sequence of collisional and optical excitations (3) utilizing discrete electronic energy states as “stepping stones.” One would expect the presence of photons tuned to a transition to increase the ionization rate in such a system.

Three-Dimensional Atomic Spectra in Flames Using Stepwise Excitation Laser-Enhanced Ionization Spectroscopy

Stepwise excitation laser-enhanced ionization spectroscopy utilizes two independently tunable dye lasers to populate high-lying excited states of atoms in flames. Two atomic resonances are required, with the upper level of the first-step transition coinciding with the lower level of the second-step transition. Efficient population of a high-lying atomic level is achieved, from which a high rate of collisional ionization can take place. The double-resonance aspect of such excitation adds an extra dimension of spectroscopic selectivity to the measurement. A computer-controlled dual-wavelength LEI spectrometer, including a Fizeau wave-meter for wavelength verification, is used to record three-dimensional spectra–ionization signal as a function of both first- and second-step wavelengths. Examples illustrate the accuracy advantage accorded by the three-dimensional survey.

Simultaneous determination of copper and zinc in human lung tissue by neutron activation analysis.

Abstract This paper presents a split-standard technique for estimating the chemical yields of rapid two-step radiochemical separation procedures which have been applied to the Cu64 and Zn60m isotopes produced in 125 mg portions of dried human lung samples as the result of 30-minute irradiations in a thermal neutron flux of 1013 n/cm2-sec. The separated radioactivities were counted by using a 400-channel pulse-height analyzer and a 5-inch by 4-inch single NaI(Tl) crystal. The relative standard deviations for a set of five replicate determinations were 2.9% for copper and 5.7% for zinc.