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Digital Data Acquisition for Spectrometry with a High-resolution Diamond Detector

31.01.2011

Fast signal processing is necessary to optimally exploit the properties of commercially available detectors made of monocrystalline diamond for applications in fusion research. Digital data acquisition systems are well suited for this. Therefore, a fast current amplifier was developed and adapted to the characteristics of an existing data acquisition system. A transimpedance amplifier AD8015 of the Analog Devices company is used as the first amplification stage; it is characterised by a high bandwidth of 240 MHz and low noise. Due to the differential outputs, which contribute to low feedback on the supply lines, it is particularly well-suited for the envisaged application. The originally fixed amplification and the bandwidth were adapted to the characteristics of the digital data acquisition system in such a way that signals from diamond detectors can be measured up to a maximum energy deposition in the diamond of approx. 35 MeV.

The combination of the diamond detector, the fast current amplifier and the digital data acquisition system was thoroughly tested in PTB’s reference fields. For this purpose, monoenergetic neutrons, a high-intensity neutron field and high-energy charged particles were used. The figure shows the result of one of these measurements. In this figure, the measured pulse height spectrum (for an irradiation with 20 MeV α particles from PTB’s cyclotron) is plotted. In addition, the pulse height spectrum that was recorded with a conventional, analogue data acquisition system is shown. Although the resolution of the new system is not as good as that of an analogue data acquisition system, the achieved values are sufficient for the envisaged applications and the new data acquisition system offers the possibility to process counting rates which are higher by a factor 10 than those analogue systems can deal with. These measurements therefore confirm the basic suitability of this measuring system for high-resolution spectrometry at high counting rates.

Figure : Pulse height spectra for the irradiation of a diamond detector with 20 MeV α particles from the PTB cyclotron, measured with the new digital data acquisition in comparison with a measurement with conventional analog electronics.