The absorption of X-rays in the range 7-17A by Be, Mg, Al, Cu and Ag.

A 5 cm. radius Rowland circle vacuum spectrometer has been used to neasure the mass absorption coefficients of Be, Mg, A1, Cu and Ag in the wavelength range 7-17A. A mica crystal was used as the monochromator. The construction and alignment procedure for the spectrometer are described together with the operation of a thin-window gas flow proportional counting system for measurement of the incident and transmitted X-ray flux. Nordfors method for measuring the scattered X-ray background in the spectrometer and calculating the optimum counting times for a given absorber thickness has been employed throughout. The preparation and mounting of the absorbing foils is described, including the use of Polypropylene as a substrate. The experimental values are compared with those available from the literature and also with the 'Universal' curve of Jonsson. It is concluded that new measurements of mass absorption coefficients are desirable in all wavelength ranges and that Jonssons curve is seriously in error in the long wavelength region. Numerical values for mass absorption coefficients have been obtained from calculations using a screened hydrogen-like atomic model and compared with those produced experimentally. The fullness of agreement varies widely with the atomic shells but is considered to be adequate for such a treatment