Improved Apparatus for the Measurement of Absolute f-Values

Abstract

The absolute oscillator strengths of the ground state transitions of metallic elements can be determined by measuring the optical absorption from a continuous spectrum in a beam of the evaporated material. The apparatus makes use of synchronous detection for the optical signal and a pivotal microbalance for the determination of beam density. This form of microbalance does not require the usual magnetic damping and thus permits accurate measurements to be made on ferromagnetic materials.

The measurement of oscillator strengths

“…With the classical technique of atomic-beam absorption (Wessel 1949, Kopfermann andWessel 1951), the equivalent width of resonance lines is measured through an atomic beam with known column density of the absorbing levels. Since the publication of Foster's (1964) review, this technique has been employed in several laboratories to obtain absolute oscillator strengths of the resonance lines of neutral Cr, CO, Ni, Ga, Pd, Ag, In, Sn, Au and G a (Lawrence er a1 1965), of Sc I (Bell and Lyzenga 1976), Ti I (Reinke 1967, Bell et a1 1975, V I (Mie and Richter 1973), of Fe I and Cu I (Bell and Tubbs 1970a) and of Er I and Gd I (Dohnalik el a1 1979, Szynarowska andPapaj 1982). The quoted uncertainties of the results range between 1 5 % and *25%.…”

“…Figure 21 shows a schematic apparatus (Bell and Tubbs 1970b) where vapour effusing upward through the orifice of a heated crucible is defined by apertures into the form of an inverted pyramid. The equivalent widths of interest are measured with respect to a background continuum from the light beam that traverses the atomic beam horizontally (sometimes also in multiple passes).…”

“…The exact value of the total absorption was found by fitting calculated line profiles (obtained from folding the instrument function with a theoretical absorption profile). The angular aperture of the atomic beam, which appears to have been much smaller than that used in the experiments by Bell and Tubbs (1970b), was varied from measurement to measurement. The results, which have a stated accuracy of -*lo% agree within a few percent with those obtained by other methods (particularly by lifetime measurements).…”

A review of oscillator strengths for lines of Cu I

“…A thorough summary of recoent determinations of absolute values for Cu I 3247 A is given by Bell and Tubbs [1970]. Inspection of the 11 values determined since 1957 in their table 1 leaves little doubt that at present the best fvalue for 3247 A is 0.43 corresponding to log gj=-0.07.…”