Introduction
1.1 General Introduction into Gamma Spectroscopy
The main application of gamma spectroscopy is to measure the radiation emitted from
decaying radionuclides and from this conclude on the type and quantity of isotopes
present. In most cases, the gamma radiation is most suitable to distinguish between
different radioisotopes. Gamma radiation consists of photons, similar as light. But whereas
the typical photon energy for visible light is 1eV (1.6*10
-19
Joule) the gamma photon
energy from radioactive decay is much higher and typically between 3keV and 3MeV. For
measuring this gamma radiation a suitable detector is needed. This can be a
semiconductor detector, which converts an absorbed photon directly into a small charge
quantity. Or it can be a scintillation detector, which converts an absorbed photon into
visible light, which is then converted by a photomultiplier into a charge. After the
preamplifier, which is usually integrated within the detector, the charge appears as voltage
step on the output signal, see also figures 6 and 7.
The task of the multi-channel analyzer is now to measure the amplitude of these voltage
steps with best possible accuracy and make a histogram of all measured amplitude
values. This is called pulse height analysis (PHA) mode.
The second most important operation mode is to record count rate in dependence of time,
using defined time channels. This is called multichannel scaling (MCS) mode. Various
other measurement modes are possible and described later in this manual.
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