Tuesday, January 14, 2014

Powerful Solution for the Emulation of Any Detection Setup

The Digital Detector Emulator is a multichannel instrument for the emulation of radiation detection systems. The algorithm is initialized by a reference pulse shape, with statistical distribution of amplitude and time. Then a statistical stream of events is generated according to the input distributions. The events can be also selectively summed together simulating the pile-up phenomenon. An arbitrarily generated noise and a baseline drift can be superimposed to each pulse.

Therefore, the instrument is not a pulse generator of recorded shapes, but it is a synthesizer of random pulses compliant with programmable statistical distributions of energy spectrum, time distribution, and pulse shape. The stream of emulated signals becomes a statistical sequence of pulses, reflecting the programmed input features (e.g. energy spectrum, time distribution, noise, signal shape, etc.). When the emulation process is reset, the kernels of generators can be either re-initialized with new random data making the sequence always different, or they can be stored to reproduce the same sequence many times.
The Digital Detector Emulator is able to emulate two different radiation sources at a time on the two output channels and to provide them either with fully independent parameters, or with some of them correlated. For example the events can be time correlated (steps of 12 ps), or a subset of events can share the same energy spectrum. It is also possible to set the channels in a master/slave configuration, where the first channel works as a trigger for the second one.

The use of digital pulse processing techniques is widely used in many fields of application of radiation measurements, for example in the pulse height analysis, in the pulse shape discrimination, in the time-to-digital and amplitude conversion, etc. Since those systems and algorithms are becoming more and more complex, it is very useful to have precise simulations of the detection and acquisition systems. This can help, for instance, in preliminary feasibility studies or in tests to understand the system response itself, as well as for later debug purposes. Another advantage is the reduction in time of radioactive source use, thus reducing the risk for the experimenter’s health.

All of this encouraged the idea of developing a digital technique to emulate the radiation signals which can resemble as much as possible the real experimental data.

Currently, there are electronic instruments able to generate analog signals with exponential shape, fixed amplitude, and exponential time distribution. Anyway, they cannot modulate the amplitude according to a given energy spectrum. This issue has been overcome by recording long sequences of events (the so called “Arbitrary Waveform Generators”), being strongly limited by the memory size, and therefore by the signal length and the counting rate.

The CAEN Digital Detector Emulator not only is able to perform such standard features, but is also able to generate an electrical signal that fully emulates real detection systems. The user can control all the signal features, providing as input the statistical distributions of energy spectrum, time distribution, and pulse shape. The output stream of events is a statistical distribution itself that emulates the input energy and time spectra.

Advanced features allow also to simulate the noise, the interferences, the pile-up, the baseline drift, and the correlations among channels. The sequence of data can be either re-initialized with new random data to have always different sequences, or with the same starting seeds to reproduce the same sequence many times. The possibility to fine control each input parameter allows to study any variation of the system and to predict the outcome of the analysis algorithms. Moreover, the user can test specific cases and push the parameters to their physics limits to test the readout electronics.

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