S. Zuberi, University of Rochester Digital Signal Processing of Scintillator Pulses Saba Zuberi, Wojtek Skulski, Frank Wolfs University of Rochester

S. Zuberi, University of Rochester Outline Description of the DDC-1 digital pulse processor. Response to scintillator pulses. Gamma-ray spectra obtained with DDC-1 Pulse Shape Discrimination and Particle ID Conclusion

S. Zuberi, University of Rochester USB processor connector FPGA JTAG connector Fast reconstruction DAC 65 MHz * 12 bits Signal OUT Signal IN Variable gain amp ADC 65 MHz * 12 bits Single Channel Prototype Digital Pulse Processor 12-bit sampling ADC, operating at 48MHz sampling rate USB interface processor, 8K internal memory Output reconstruction channel for development and diagnostic

S. Zuberi, University of Rochester DDC-1 Digital Pulse Processor

S. Zuberi, University of Rochester Response to Scintillator Pulses Fast Plastic Scintillator BC-404 –Original decay time: 1.8ns –Nyquist filter f c =20 MHz Good response to very fast pulse 1 sample = 20.8 ns Slower Scintillator Pulse: –Signal from Bicron NaI(Tl) –Effective Decay time: 0.23  s Good response to slower pulse

S. Zuberi, University of Rochester Response to scintillator pulses: Phoswich Detector CsI(Tl) crystal cosmic ray phototube teflon Bicron BC-404 FAST SLOW Fast plastic pulse clearly separated from slower decay in CsI(Tl)

S. Zuberi, University of Rochester Response to scintillator pulses: CsI(Tl) nat Thorium source:  -particle –High ionization density –Overall decay time:  s  -ray –Low ionization density –Longer overall decay time than  - particle (0.695  s for electron) Clear pulse shape dependence on type of radiation

S. Zuberi, University of Rochester Gamma Ray Spectra Signals obtained from Bicron 2” x 2” NaI(Tl) X-rays from excitation of Pb casing of detector Low energy region: – 56 Ba characteristic x-ray, 33keV, from 137 Cs decay measured –FWHM = 23.2keV High energy region : –FWHM of 662keV 137 Cs: 7.1% 60 Co 137 Cs

S. Zuberi, University of Rochester Pulse Shape Discrimination: Phoswich Thick nat Th source used with 1cm 3 CsI(Tl) + 1cm 3 Plastic detector Select events by leading-edge discriminator programmed in PC GUI Cut signals in plastic determined by FAST/SLOW Discard ADC overflow

S. Zuberi, University of Rochester Particle ID: Cs-137 & Co-60 PID = TAIL/TOTAL Compton Scattering 662keV

S. Zuberi, University of Rochester Particle ID in CsI(Tl) + phototube Distinct bands obtained for  -particles and  rays Cosmics passing through CsI(Tl) look like  rays. Energy independent PID FOM = 1.85, constant for 1 to 4 MeV FOM drops to 0.78 for 0.5 to 1 MeV Not as good as FOM E<1MeV = 1.89 obtained [1] for CsI(Tl)+ photodiode PID windows not yet optimized. Digital smoothing filter not yet applied. FOM = peak separation/  FWHM [1] W. Skulski et al, Nucl. Instr. and Meth. A 458 (2001) 759

S. Zuberi, University of Rochester Conclusion Wide range of signals handled by DDC-1, including fast plastic signals. Nyquist filter is crucial for fast pulses. NaI(Tl)  -ray spectra also show X-ray peaks at 33keV. Pulse shape discrimination demonstrated with CsI(Tl). –Energy independent PID obtained. –PID not as good as CsI+photodiode. –PID algorithms will be optimized. Applications of the DDC-1: –Algorithm development, student projects.