1 / 27

D.M. Hamby and A.T. Farsoni Nuclear Engineering and Radiation Health Physics

A System for Simultaneous Beta and Gamma Spectroscopy and its Application to Nuclear Non-Proliferation. D.M. Hamby and A.T. Farsoni Nuclear Engineering and Radiation Health Physics College of Engineering Oregon State University Corvallis, Oregon. Beta Spectroscopy.

stew
Download Presentation

D.M. Hamby and A.T. Farsoni Nuclear Engineering and Radiation Health Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A System for Simultaneous Beta and Gamma Spectroscopy and its Application to Nuclear Non-Proliferation D.M. Hamby and A.T. Farsoni Nuclear Engineering and Radiation Health Physics College of Engineering Oregon State University Corvallis, Oregon

  2. Beta Spectroscopy • Typically for beta dosimetry • Open- and closed-window spectral stripping • Solid-state, scintillators, thin plastics • 20-yr history

  3. Gamma Spectroscopy • Very common • Simple to complex • Solid-state, scintillators • High/low resolution

  4. Scintillator Response The light output from most scintillators can be represented as a simple exponential decay. The current pulse from the PM-tube anode is: where t is the scintillator light decay time and Q is the total collected charge Plastic τ = 2.4 nsec NaI (Tl) τ = 230 nsec

  5. Rise-Time Distribution Phoswich Detector Phoswich Detectors • The combination of dissimilar scintillators optically coupled to • a single PM tube (phosphor sandwich) *Usuda, S. and others, “Phoswich detectors for simultaneous counting of α-, β (gamma )-rays and neutrons” 1997.

  6. Digital SpectrometersAdvantages • Pulse processing algorithm is easy to edit • The algorithm is stable and reliable, no thermal noise or other fluctuations • No bulky analog electronics • Post-processing ability • More cost-effective • Effects, such as pile-up, can be corrected or eliminated at the processing level • Signal capture and processing can be based more easily on coincidence criteria between different detectors or different parts of the same detector

  7. Simultaneous Beta/Gamma Spectrometer A digital phoswich detection system capable of simultaneous spectroscopy with minimal cross-talk.

  8. Triple-Layer Phoswich Design Aluminized Mylar (6 mm) CaF2(Eu) (1.5 mm) NaI(Tl) (25.4 mm) 76.2 mm PMT BC-400 (1.5 mm) Quartz Optical Window (2.0 mm)

  9. Electron & Photon Energy Deposition MCNP modeling for detector optimization. Simulated detector response from different monoenergetic electrons in BC400. Simulated detector response from 1.0 MeV gamma-rays in the three scintillation layers.

  10. Interaction Scenarios Phoswich Detector Scenario # CaF2 NaI:Tl BC400 1 2 3 4 5 6 7

  11. Radiation Transport StudyBeta and Gamma Discrimination * Total probabilities are calculated for 1.0 MeV photon/electron events. Events with energies less than 10 keV were excluded as electronic noise.

  12. Data Acquisition System

  13. 12-bit, 100 MHz Digital Pulse Processor ADC Preamplifier Input signal from anode USB Port FPGA Output signal to oscilloscope DAC

  14. Data Acquisition SystemPulse Processing Algorithm Four parameters, Baseline, P, M1 and M2 are used for analyzing the anode pulses. Fast-Ratio (FR) = (P – M1) / P Slow-Ratio (SR) = (M1 - M2) / M1 Sums A and B used for calculating the energy absorption in each layer of the phoswich detector.

  15. Experimental ResultsMeasurements using the Phoswich/DPP - Energy Calibration Beta particles (Emax) from 14C and 99Tc were used for BC400 calibration. The 662 keV and 1332 kev photopeaks, respectively from 137Cs and 60Co, were used for NaI(Tl) calibration. The Compton edge and photopeak of 137Cs were used for CaF2(Eu) calibration. 99Tc 137Cs + 60Co 137Cs Compton Edge at 477 keV Emax = 292 keV Photopeak at 1332 keV Photopeak at 662 keV Photopeak at 1172 keV Photopeak at 662 keV 14C Emax =156 keV

  16. Experimental ResultsMeasurements using the Phoswich/DPP- Anode Signal Pulses Signal Pulses from 90Sr/90Y Signal Pulses from 137Cs

  17. Experimental ResultsMeasurements using the Phoswich/DPP- Real-Time and Simultaneous Beta/Gamma Spectroscopy Pure Beta Source: 99Tc

  18. Experimental ResultsMeasurements using the Phoswich/DPP - Real-Time and Simultaneous Beta/Gamma Spectroscopy (Beta-shielded) Gamma Source: 137Cs

  19. Experimental ResultsMeasurements using the Phoswich/DPP - Real-Time and Simultaneous Beta/Gamma Spectroscopy Mixed Beta/Gamma Field: 99Tc + 137Cs

  20. Experimental ResultsMeasurements using the Phoswich/DPP - Response to Gamma Sources (beta-shielded) Percentage of events and simultaneous beta/gamma energy spectra from (a) 137Cs and (b) 60Co (a) (b) 137Cs 60Co FWHM (662 keV) ~ 6.7%

  21. Experimental ResultsMeasurements using the Phoswich/DPP - Response to Pure Beta Sources Percentage of events and simultaneous beta/gamma energy spectra from (a)14C, (b) 99Tc and (c) 90Sr/ 90Y (a) (b) (c) 14C 90Sr/ 90Y 99Tc

  22. Radioxenon Decay Productsenergy in units of keV Isotope 131m 133 133m 135 bmax 346 901 g 164 81 233 250 c.e. 12945 199 214 X ray 30 31 30 31 (b, g) or (ce, X) Double Coincidence (b, ce, X) Triple Coincidence

  23. Dual Phoswich for Coincidence CountingUtilizing both light coincidence and signal coincidence Sample CaF2 Out Sig Sig PMT 1 NaI PMT 2 HV HV In Quartz Coupling Sleve BC400

  24. 133mXe CoincidenceProbability: 0.115 199 keV c.e. 30 keV Ka X-ray

  25. 133Xe Triple CoincidenceProbability: 0.017 45 keV c.e. 346 keV bmax 31 keV Ka X-ray

  26. Conclusions on Simultaneous Spectroscopy • Prototype digital simultaneous beta/gamma spectrometer • Customized digital pulse processor (12-bit, 100 MHz) • Optimization through particle transport simulation (MCNP) • Gamma resolution as low as 6.7% (@ 662 keV) • < 2% false positives • Better discrimination at lower energies • Double/Triple coincidence detection • High selectivity

More Related