Physics and Engineering of Radiation Detection

13.1. Data Acquisition Chain 719

counter (see Fig.13.1.2). Note that a fast pulse counting application also requires
a fast preamplifier. The counter output can be read out by a computer for further
processing and storage.

Detector

PC

Amplifier/Shaper Fast Discriminator

Counter/Timer

Fast Preamplifier

Figure 13.1.2: Block diagram of a simple fast pulse counting system.

13.1.BEnergySpectroscopy.......................

Energy spectroscopy has been thoroughly discussed in the chapter on spectroscopy.
We saw that the best method for this kind of analysis is to use a multichannel
analyzer (MCA). A multichannel analyzer can be thought to consist of an array
of single channel analyzers with adjacent windows. It has a number of channels,
each of which corresponds to a specific range of pulse heights. A pulse with height
corresponding to one of these channels gets counted. In this way the whole spectrum
of pulse heights gets recorded by the analyzer. Since the pulse height is proportional
to the energy deposited by the incident radiation, the spectrum obtained corresponds
to the energy spectrum of the radiation. Such a spectrum is also sometimes referred
to as pulse height spectrum. The block diagram of a typical energy spectroscopy
system is shown in Fig.13.1.3.

Detector Preamplifier Amplifier/Shaper MultichannelAnalyzer PC

Figure 13.1.3: Block diagram of a simple energy spectroscopy system.

13.1.CTimeSpectroscopy........................

In some applications it is desired that the arrival time of detector pulses be precisely
recorded. For example, measurement of lifetime of atomic states requires one to
measure time of arrival of photons emitted as a result of those transitions. Such
a measurement is generally done through the so calledtime-to-amplitudeconverter
or TAC. A simple TAC device converts the time into a voltage pulse with a height
proportional to the time. The idea is to start charging (or discharging) a capacitor
at the arrival of a pulse and stop the process as soon as another pulse arrives. The
charge remaining on the capacitor is then proportional to the time. Of course this