Incorporated into NORAN System 7 software is the PROZA quantitative analysis correction program, which provides superior results. In quantitative analysis, after reference peaks have been fitted to the unknown spectrum, the counting rate of each peak is converted to a weight percent for that element. The conversion requires correction for the x-ray intensity of each element given the influence of other elements in the fit.

These corrections account for changes in x-ray intensity due to:

• Differences between elements in the production of x-rays in the sample          
• Differential absorption by other elements    
• Fluorescence induced in other elements

Approximations for the correction are provided by a matrix correction routine based on ZAF, Bence-Albee, or Thermo NORAN's exclusive PROZA method.

PROZA is a mathematical procedure used to calculate quantitative analysis corrections for the atomic number, absorption, and fluorescence (ZAF) effects in multi-element samples.

This procedure characterizes x-ray intensity as a function of depth in a sample and gives accurate approximations for depths ranging from monolayers to several microns. It is an excellent method of characterizing thin film samples.

The characteristic curve describing the relationship between depth in a microvolume and x-ray intensity looks like the following curve:

The curve shows a noticeable deviation from a true Gaussian shape. The deviation comes from the region near the sample surface, where the ionization is restricted due to electron beam collimation by the sample. As the electron beam penetrates deeper into the sample, spreading occurs because of electron scattering, and at the same time ionization efficiency increases. The level of emitted x-rays increases until the beam reaches the depth of maximum ionization. After the peak, the x-ray emission curve decreases, assuming a Gaussian shape:

The PROZA method describes the depth distribution of x-rays generated within the microvolume with exceptional accuracy.

The PROZA method requires a description of the sample and analysis condition, including:

• Elemental composition
• Accelerating voltage
• Take-off angle

With this information, the x-ray emission due to each element in the sample is calculated, and can be displayed in graphical form.

PROZA provides superior results when light elements are present in the microvolume. This is because low energy x-rays detected from these elements orignate nearer to the surface than do the higher energy x-rays of heavier elements, and the absorption effects in the near surface region are ignored in a ZAF approach. The precision of the PROZA curve shape near the surface makes it the premier light element microvolume analysis technique.