Photon‐Counting Spectrometer for Attenuation Measurements in the Soft X‐Ray Region

A grazing incidence spectrograph, originally designed for photographic registration, is modified for the purpose of making attenuation measurements at selected wavelengths in the 100–300 A region. The modifications over previous procedures include: (1) the introduction of an open multistage Cu‐Be electron multiplier for the purpose of comparing intensities by counting photons; (2) the use of the characteristic valence emission bands of the light metals as sources of incident radiation. The photomultiplier is mounted on an arm attached to a spindle whose axis is normal to the base plate and passes through the Rowland circle at the selected wavelength. Defining slits, placed between the grating and entrance window of photomultiplier, limit the spectral band used in irradiating the absorbers. The latter are placed in the diffracted beam at the position of ``least confusion'' and may be rotated independently about the common vertical axis of the spindle, thus varying the angle at which the incident beam strikes the surface of the sample. Various tests indicate that the source intensity and detector sensitivity are adequate for the attainment of satisfactory counting rates. In conjunction with the particular sources referred to, the photon‐counting scheme makes it possible to improve materially the precision of existing attenuation measurements.