Bruker M1 MISTRAL, Руководство пользователя

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Functional Principles
M1 ORA/MISTRAL
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Fig. 3 Schematic working principle of a silicon drift detector (SDD)
3.3 Digitalization and Channel Allocation
In order to enable software based element identification and quantitative analysis, the measured
electronic pulses which are a measure for the energies of the detected photons have to be
translated into a digital spectrum (see Fig. 4).
The amplified analog signals from the detector are converted to digital pulses by an analog-digital-
converter (ADC). Those pulses are analyzed by a multi-channel-analyzer (MCA). For that purpose,
the measured energy range is divided into sections, the so-called channels of the MCA
1
. The MCA
looks for each incoming pulses’ height and increments the counter of the channel attributed to this
specific height by 1. The resulting spectrum shows how many pulses were counted into individual
channels.
Since, however, the channels correspond to energy intervals and the height of a pulse is
proportional to the energy of the detected photon, the obtained spectrum displays the number of
incident photons versus their respective energies, i.e. the digitized XRF spectrum,
Which channel corresponds to what specific energy has to be assigned by the software after an
energy-channel-calibration.
1
If, for example, an energy range of 40 keV is measured with a detector with 4000 channels, one
channel corresponds to an energy interval of 10 eV, i.e. the channel 2000 gives the energy range
from 19.090 keV to 19.999 keV and the 2001
st
channel is allocated to the energies from
20.000 keV to 20.009 keV.