Radiotracers are widely used for environmental monitoring and industrial applications [1-2]. In a number of these applications, a Data Acquisition System (DAQ) capable of performing simultaneous recording and analysis of a large number of gamma ray probes located in different locations is required.
The International Atomic Energy Agency (IAEA) has been using and disseminating within its Member States a system capable of handling up to twelve probes based on NaI(Tl) scintillator detectors. Each probe currently features an electronic front-end board which provides an output voltage signal proportional to the anode current and a logical signal, the latter being sent to a central unit via a coaxial cable. The central unit counts the logical pulses from the twelve probes to measure the time and location dependent radiotracer activity.
As a major improvement to the overall performance of this system, a new DAQ system has been developed and now is capable of performing multiprobe gamma spectroscopy measurements as well as counting pulses in several voltage amplitude intervals, i.e. adjustable energy Regions Of Interest (ROI).. This paper presents the design of the hardware and software of this new DAQ system.
Each probe integrates a digital pulse processing (DPP) electronic board connected through an Ethernet CAT-5 connection cables to a Power Over Ethernet (PoE) switch and a personal computer (PC/laptop);the switch is also being used to power the probes.
The DPP board is continuously sampling the voltage signal from detector and associated analog front-end board using a high-speed Analog-to-Digital Converter (ADC). The sampled signal is processed with an on-board Field ProGrammable Array (FPGA) that collects the gamma-ray energy spectra in successive intervals of time and can count the pulses in five different ROIs. Spectra and counts are sent to the central computer over an on-board Ethernet controller based on Advanced RISC Machines (ARM) core.
The FPGA firmware has been designed using Xilinx Vivado IDE. The design features two main parts: (1) Microblaze soft core processor, and (2) a set of logical blocks for signal processing. These blocks are mostly implemented as custom AXI IP cores, according to their function, and instantiated in a Vivado block design.
Slow shaping IP core is used to convert exponential signal with predefined rise and fall time, into a trapezoid pulse with user selected peaking time. The trapezoidal pulse is detected by a peak detector IP core, and then counted or its amplitude analyzed and stored in a dual port memory. There are also blocks for pile-up rejection, base line correction and dead time measurement using Gedcke-Hale live time clock.
Finally, in addition to the hardware, programs and a dedicated graphical user interface have been developed for PC/laptop to control up to 12 detectors, record, save and process their spectra, as well as show the data from the probes in real time.
Acknowledgements: The authors thank Nikola Jovalekic who has provided, under a consultancy contract with the IAEA, a valuable contribution to the development of the DAQ system presented in this paper.
 International Atomic Energy Agency, Radiotracer and Sealed Source Applications in Sediment Transport Studies, IAEA Training Course Series 59, IAEA, Vienna (2014)
 International Atomic Energy Agency, Radiotracer technology as applied to industry, Final report of a coordinated research project 1997–2000, IAEA TECDOC Series 1262, IAEA, Vienna (2001)