Overview of Current Radioxenon Research C. Sivels 1, T. Cousins 1, S. Clarke 1, S. Pozzi 1, J. McIntyre 2, A. Prinke 2, E. Padovani 3 1 University of Michigan, Department of Nuclear Engineering and Radiological Sciences 2 Pacific Northwest National Laboratory 3 Politecnico di Milan, Department of Energy
Motivation Verification of the CTBT (CVT Thrust Area 4) The Comprehensive Nuclear-Test-Ban Treaty (CTBT) seeks to ban all nuclear testing worldwide Verification is performed by the International Monitoring System (IMS) IMS uses four technologies: Seismic Infrasound Hydro acoustic Radionuclide IMS Radionuclide Stations ctbto.org 67 radionuclide stations worldwide (red) 80 total radionuclide stations planed (grey) 25 radioxenon stations (R+) 2
Why Radioxenon? Noble gases can reach the surface even in underground explosions Radioxenon has the highest cumulative fission yield of the noble gases produced Various modes of decay Mainly interested in β-γ coincidence Triple-coincidence and anticoincidence are other measurement options 3
Radioxenon Detection Gas line to Plastic Cell Isotope Electron Energy (kev) Photon Energy (kev) 131m Xe 129 ~30 133 Xe 346 (endpoint) ~30 and 80 133m Xe 199 ~30 135 Xe 950 (endpoint) 250 Plastic Cell Radon 135 Xe γ Xe β 133 Xe NaI Cooper M.W. et al. NIM A (2007) 579:426-430 doi: 10.1016/j.nima.2007.04.092 131m Xe 133m Xe 4
Goal - Event Discrimination using Isotopic Ratios Kalinowski, M.B. et al. Pure Appl. Geophys. (2010) 167: 517. doi:10.1007/s00024-009-0032-1 5
Current Limitations to Coincidence Counting Xe-133 interference with Xe-131m and Xe-133m Radon interference The DPRK February 2016 demonstrated the low activity interference of Xe-133 for measuring metastable isotopes. Gamma (kev) Xe-131m? Beta (kev) Memory effect Xenon partially diffuses into the plastic and remains Xe-133 6
Advanced Detector Systems Improved detector systems are needed to reliably distinguish the various Xe isotopes Better resolution Better sensitivity (lower the minimum detectable activity) Alternate Materials Silicon Stilbene CZT 7
Advantages of Stilbene Better resolution than plastic Pulse shape discrimination capable (radon alphas vs xenon betas) No memory effect No backscatter effects as seen with silicon and CZT Standard plastic beta cell Prototype stilbene cell developed in collaboration with Inrad Optics 1.81 cm 4.18 cm 3.10 cm 1.80 cm Stilbene Endcap 8
Characterization of the Stilbene Cell Gamma ray deposits partial energy in both detectors through Compton scattering Experimental Setup Sum of each detector contribution equals initial gamma ray energy 9
Characterization of the Stilbene Cell Cs-137 2D Spectrum Comparison Stilbene Plastic Line represents Compton Scattering of 0.662 MeV photon Line represents Compton Scattering of 0.662 MeV photon Similar shape between two detectors but stilbene has more counts meaning it s efficiency is higher, possibly due to increase in detector volume (61%) 10
Characterization of the Stilbene Cell Preliminary Resolution Comparison Stilbene FWHM at 129 kev decreases by 33% compared to plastic Stilbene FWHM at 198 kev decreases by 12% compared to plastic 11
Preliminary Gas Measurement - Xe-127 Electron Energy (kev) Photon Energy (kev) ~24-29 203 ~24-29 375 ~110-200 29 ~110-200 57 ~112-169 ~145-203 Stilbene Plastic 12
Conclusions and Future Work Improved detector systems are needed to reliably distinguish the various Xe isotopes A prototype stilbene beta cell has been developed and characterization is underway Stilbene has been demonstrated to have an improved resolution over plastic The cell geometry will be optimized through simulation Radioxenon will be measured using stilbene and plastic to compare the performance Radon will be measured to quantify sensitivity improvements 13
QUESTIONS? 14
EXTRA SLIDES 15
Xe-127 Beta Spectrum Comparison 16
Stilbene Prototype #1 Cf-252 PSD 17
Additional Radioxenon Detection Work Anticoincidence Analysis Method Plastic detector triggers BOTH detectors trigger ONLY plastic detector triggers 18
Stilbene Prototype Comparison 19
Cs-137 Compton Scatter Technique Line sums to.662 MeV 137 Cs γ γ' Deconvolve system resolution from diagonal line 20