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

X-ray mass absorption coefficients for beryllium, magnesium, aluminium, copper and silver have been measured using a 10 cm radius bent mica-crystal vacuum spectrometer. The x-ray detector was a thin plastic window, gas-flow proportional counter. An accuracy to about 1% was achieved and it appears that the commonly used values of Allen seriously undervalue the absorption in the region 7-17 Å