X-Ray Spectrometric Characteristics of Potassium Acid Phthalate Crystals

The x-ray diffraction characteristics of potassium acid phthalate (KAP) crystals have been measured with a vacuum two-crystal x-ray spectrometer using a flowing-gas proportional counter as a detector. The values of resolving power, percent reflection, and coefficient of reflection as determined from the (1, −1) position rocking curves are reported for the wavelengths between 1.54 Å (Cu Kα) and 23.7 Å (O Kα). These crystals offer spectral resolving powers from 2000 to 4000 and from 3 to 40% reflection in the soft x-ray wavelength region. On the basis of these measurements, the crystals will serve as suitable diffracting elements in that range.