CCD or photomultiplier for spectrometer?

 

A registering system of spectrometer may be made with CCD or with photomultipliers. Spectrometers with CCD are not expensive, have small sizes and can measure intensity in a wide area of spectrum. But their accuracy and sensitivity are not very good.

Distribution of intensity of a spectral line along Rowland circle is approximately shown above, where D is the gap width for the spectrometer with photomultipliers. Intensity of a spectral line can be defined by its maximum or by the area bounded by the line of intensity.

 

 

The screenshot of spectrum that is shown above is made by the widespread spectrometer with CCD. Below is shown the same site of spectrum that is presented by the increased scale of wave length. Obviously the maximum and the area of the line can be defined only approximately.

 

 

Approximation by fitting curve can made the picture more beautiful but accuracy of analysis becomes not so better. The blooming (spread of charges to the next pixels) may lead to even greater errors. For example, if matrix correction of calibration for the spark spectrometer was made correctly, the relative error of analysis for spectrometer with photomultipliers may be 3 -7 percents for most elements. Error for spectrometer with CCD is usually several times more.

 

Spectrometers with photomultipliers can operate for many years, and photomultipliers can be easily replaced. The lifetime of CCD is much shorter and they are not replaced. Usually they are utilized together with spectrometer.