SOFT X-RAY PHYSICS, (ANGSTROM)/(X-UNIT).

The purpose of this research was an experimental determination of the ratio of milli-Angstrom units to X-units, which involves the relationship of a number of fundamental physical constants. In order to accomplish this, a grazing incidence vacuum spectrograph was employed, using a Rowland circle of 21 ft or 6.5 m radius. With an angle of incidence of 59 minutes of arc, this instrument covered with high dispersion the wavelength region from 5A to 110A. The experimental procedure was then to photograph on one photographic plate a characteristic X-ray emission line, namely the K alpha line of aluminum at about 8.3A, and the equivalent Lyman-alpha, -beta lines of stripped beryllium, BeIV, occurring at 76 and 64A, respectively. Since the Al K alpha line is known accurately in X-units, and since the hydrogen-like emission lines from the Be can be calculated accurately in milli-Angstrom units, it is therefore possible to obtain from the position of all of these lines on one and the same photographic plate a value for the ratio of milli-Angstrom units to X-units. Author