MEASUREMENTS OF THE PHOTOABSORPTION CROSS-SECTION OF DIVALENT ATOMS

The photoabsorption cross-sections of magnesium, calcium, strontium, a nd zinc were measured in the vacuum ultraviolet region by using either the synchrotron radiation source in Hsinchu, Taiwan, Republic of Chin a or a discharge lamp as a continuum background source. Samples were c onfined within a heatpipe oven, and the atom number densities were det ermined by the temperature profile distributed along the heatpipe. The relative cross-sectons of the measured autoionization series were in agreement with those reported for thermionic diode measurements, excep t for certain spectral details. The cross sections at corresponding io nization thresholds were 2.3, 1.2, 4.5, and 0.5 Mb for magnesium, calc ium, strontium, and zinc, respectively.