v 1Ta c m^SV Detection of mixed fields of neutron and photon radiation using 3he and new scintillation materials Aleš Jančářa & Zdeněk Kopeckýa František Cvachovec0, Jan Dressler% Martin Veškrnaab, Lukáš Džbánek a a- VF, a.s. company & ^Masaryk University, Faculty of Informatics, cUniversity of Defence Abstract The poster includes experimental measurements with 3He and the latest scintillation materials EJ-299-33 in fields of neutron and photon radiation using modern electronics which we designed. Electronic part of the measuring system is built on recently developed AD converter with very high sampling frequency (1 GHz). In the theoretical part, the Monte Carlo simulations of response characteristics of the measured scintillation materials are presented. Fast Digitizer Card The fast digitizer is based on AD converters, type ADC12D1000 by Texas Instruments, and connected to the Combo card via XGMII (10 Gigabit Media Independent Interface). The converters operate with a resolution of 12 bits and have two differential inputs with a sampling frequency 1 GHz. The output interface consists of 4 sets of 12-bit outputs. For transferring data between AD converters and PC memory the transmission protocol has been designed. Information about the measurement, and lost data, is contained within the protocol. XGMII interface between the ADC card and Combo card uses a standard Ethernet protocol. ADO channel 1 channel 2 ADC2 channel 1 channel 2 FPGA 24 GWs V-3SjgS&..> lOGb/s . Combo card .....lOGfafe.w MDIO PCIe 12Gb/s RAM Disk Figure 1: Schematic representation of the data transfer. Data transfer is limited by the the transmission capacity of the lines and buffer sizes. The internal FIFO memory of the FPGA has a size of 1536 kilobytes. In interlaced mode of AD converter and sampling frequency 2 GHz a FIFO card is able to store approximately 62 /is. This value is a maximum pulse length which ensures that data will not be lost. Measurement with 3He Proportional Detector Figure 2: The fast digitizer. The fast digitizer consists of two cards, an ADC card with converters (in the front), and a Combo card (in the back). He proportional counters are widely used as neutron detectors. It's known (see, for example, [1]) that 3He counters are capable of detecting other types of particles like photons, betas, and alphas, and that it is possible to distinguish them according to the pulse shape. We used the fast digitizer (described above) in the oscilloscope mode to verify that the typical gamma pulse has considerably smaller amplitude and longer risetime (^ 2 /is) in comparison with the typical thermal neutron pulse (~ 0.5 fjs). The experimental arrangement with 137Cs gamma source and PuBe neutron source is shown in the Fig. 4, the preamplifier, the fast digitizer and the measuring server is in the Fig. 3. Resulting pulse height spectrum is in the Fig. 5. Figure 3: The preamplifier (in the front the fast digitizer (in the back), and the measuring server (in the bottom Q. o Figure 4: Arrangement of the detector (in the middle), 137Cs source (on the left) and PuBe source on the right). Cs-137 + PuBe PuBe Cs-137 ------1 2000 3000 4000 channel 5000 6000 7000 Figure 5: Pulse height spectrum from 3He proportional detector with the 10" Bonner sphere using 137Cs source (green line), PuBe source (red line) and both sources (black line). Digital Neutron-Gamma Discrimination with Liquid and Plastic Scintillators Liquid scintillating detectors are widely used to achieve neutron - gamma discrimination due to their excellent Pulse Shape Discrimination (PSD) properties. Recently, a new class of plastic scintillating materials wih PSD properties has been developed. The availability of these new detection materials in commercial form is very recent. Eljen Technologies has manufactured a number of experimental plastic scintillator materials classed as EJ-299. The PSD properties of the new plastic scintillator EJ-299-33 and an NE-213 type scintillator has been compared by the measurement of neutron-gamma radiation emitted by a 252Cf source. EJ-299-33 detector: Cylindrical detection part: 7.62 cm (thickness) x 7.62 cm (diameter), pho-tomultiplier: HAMAMATSU R6233-01. NE-213 (BC 501A) detector: Cylindrical detection part: 5.08 cm (thickness) x 12.7 cm (diameter), photomultiplier: HAMAMATSU R1250. A PSD parameter is calculated to separate off neutron and photon events. The parameter is given by the ratio PSD = ffend pulse(t) dt t clil J0Tend pulse(ŕ) dí (1 where is an optimized beginning of the tail part of the pulse and Tencj is an optimized end point of the pulse. W 5000 2500 -1000 -500 -250 100 -50 0 500 1000 1500 2000 2500 3000 Energy [keVee] 3500 4000 Figure 6: 2D plot Energy versus PSD (EJ-299-33 0.45 0.35 0.25 Q W Q. 0.15 500 250 100 50 20 10 -5 0.05 U 500 1000 1500 2000 2500 Energy [keVee] 3000 3500 4000 Figure 7: 2D plot Energy versus PSD (Ne-213 Energy cut :120 keVee I '— FOM= 0.93626 j 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 PSD Figure 8: Figure of Merit (FOM) plot: 120 keVee Energy Cut (EJ-299-33; 450 Energy cut :120 keVee 300 - 200 150 - 100 Figure 9: Figure of Merit (FOM) plot: 120 keVee Energy Cut (NE-213; Monte Carlo Simulation of Response Matrix Monte Carlo simulations of the response matrices were performed using MCNPX 2.7.0 + MCUNED, A new interface for tracking particle events in the MPI mode has been developed. Figure 10: Detector Response Matrix Simulation EJ-299-33^ Figure 11: Detector Response Matrix Simulation NE-213^ Acknowledgment The presented work has been supported by the Technology Agency of the Czech Republic within the project SPECTRUM, No. TA01011383. References 1] T. J. Langford, C. D. Bass, E. J. Beise, H. Breuer, D. K. Erwin, C. R. Heimbach, J. S. Nico: Event Identification in 3He Proportional Counters Using Risetime Discrimination, Nuclear Instruments and Methods, Volume 717, 21 July 2013, Pages 51 57 [2] Benjamin Klopper, Natalie Cranston, Markus Aleksy, Marcel Dix: Developing portable FPGA applications, Industrial Informatics (INDIN), IEEE International Conference, 29-31 July 2013 www. vf. cz