Читать книгу Monument Future - Siegfried Siegesmund - Страница 232

Several companies market portable XRF instruments. These consist of an X-ray generating tube, typically with a rhodium target, a silicon semiconductor X-ray detector, and electronics for pulse height analysis and data storage. The output spectrum is a histogram of the X-ray photon counts per energy bin, which is roughly one eV wide. The individual elements are represented in the spectrum by their peaks at characteristics energies. For example, the Mn peaks at 5.90 keV and 6.49 keV are shown in Fig. 2. The mass of the element in the material is proportional to the number of photon counts in the peak. A suitable calibration standard is required to convert the counts data into mass, discussed in more detail below. The pXRF instrument is designed to be handheld, but for accurate measurement in the field it is preferable to mount it on a tripod to maintain a constant standoff distance.

Figure 2: Mn and Fe peaks in a pXRF spectrum of urban varnish.