A Review of Emerging Gamma Detector Technologies for Airborne Steven Bell ANSRI Dublin 2015 12-14 January Radiation Monitoring
Airborne radiation Particulates: sub-μm to sub-mm contaminated with fission products (e.g. 137 Cs and other volatile species) Gases: 3 H, 14 C, 85 Kr, 133 Xe Background radon/thoron and progeny Inhalation of radioactive airborne particulates (aerosols) and gases pose a serious health risk Emissions from nuclear facilities must be monitored National early warning networks provide extra layer of monitoring
Airborne radiation measurement Airborne particulates: Continuous monitoring with in-situ detector and static or moving filter High volume sampling with large area filter Alpha, beta and gamma emissions can be measured Air gamma dose: Typically measured with GM tube
Radioactive aerosol generation facility Facility required to test and calibrate air monitors Particulate sizes: 0.3 μm and 4 μm polystyrene microspheres Isotopes: 239 Pu, 137 Cs, 99m Tc (alpha, beta, gamma) Controlled background of 222 Rn and progeny
MetroERM Metrology for radiological early warning networks in Europe National early warning networks provide near real time measurements to allow governments to respond during emergency situations Measurements of ambient dose rate and airborne radionuclide activity concentrations Accurate, coherent and complete data is required Outcomes: optimisation and harmonisation of measurements New technology is key to achieving outcomes
EURDEP Network European Radiological Data Exchange Platform (EURDEP)
EPA Network, Ireland Gamma dose measured near UCD campus over the last week (ave. ~0.1 μsv/hr) Geiger-Muller tube Environmental Protection Agency, Ireland - http://www.epa.ie/radiation/monassess/mapmon
Evaluation of gamma spectrometers Factors of interest: Energy resolution Detection efficiency Lower detection limit Operation with increasing background (radon etc.) Background rejection/discrimination Cost & practicality (available off the shelf?)
Scintillators Material NaI(Tl) CsI(Tl) SrI 2 LaBr 3 (Ce) CeBr 3 B 4 G 3 O 12 Gd 2 SiO 5 Z 11,53 55,53 38,53 57,35 58,35 83,32,8 64,14,8 ρ (g.cm -3 ) 3.67 4.51 4.59 5.08 5.18 7.13 6.71 Light yield (γ/mev) Emission λ Peak (nm) Decay time (ns) Refractive index Available size Notes 38,000 65,000 80,000 63,000 45,000 8,000 9,000 415 540 435 360 370 480 440 230 680 (64%) 3,340 (36%) 1,000-5,000 16 17 300 (90%) 60 (10%) 60 (90%) 400 (10%) 1.85 1.80 1.85 1.9 2.3 2.15 1.85 Large Large 1 x 1 3 x 3 2 x 2 Large Large Hygroscopic, after glow Columnar structure Hygroscopic Hygroscopic, internal activity Hygroscopic, lower internal activity Rugged, internal activity Radiation hard
Cherepy et al., 2012 Lawrence Livermore National Laboratory Energy resolution
A fast signal allows high rates (not of interest) and good timing resolution This is of interest Timing resolution allows coincidence measurements to be made With knowledge of the decay scheme, coincidence measurements can be used to identify specific radionuclides and reject background events Requirements of decay scheme: Fast detectors? E γ > ~100 kev, short lifetime of intermediate state and high probability of γ-emission (low internal conversion coefficient)
Coincidence measurements Simple coincidence set up Multichannel digitiser
Chernobyl Accident IAEA Report Inert gases Krypton-85 10.72 a 33 PBq Xenon-133 5.25 d 6,500 PBq Volatile elements Tellurium-129m 33.6 d 240 PBq Tellurium-132 3.26 d 1,150 PBq Iodine-131 8.04 d 1,760 PBq Iodine-133 20.8 h 910 PBq Caesium-134 2.06 a 47 PBq Caesium-136 13.1 d 36 PBq Caesium-137 30.0 a 85 PBq Refractory elements (including fuel particles) Zirconium-95 64.0 d 84 PBq Molybdenum-99 2.75 d 72 PBq Cerium-141 32.5 d 84 PBq Cerium-144 284 d 50 PBq Neptunium-239 2.35 d 400 PBq Plutonium-238 87.74 a 0.015 PBq Plutonium-239 24065 a 0.013 PBq Plutonium-240 6537 a 0.018 PBq Plutonium-241 14.4 a 2.6 PBq Plutonium-242 376000 a 0.00004 PBq Curium-242 18.1 a 0.4 PBq Elements with intermediate volatility Strontium-89 50.5 d 115 PBq Strontium-90 29.12 a 10 PBq Ruthenium-103 39.3 d 168 PBq Ruthenium-106 368 d 73 PBq Barium-140 12.7 d 240 PBq Other Silver-110m Antinomy-125 Cobalt-60 Uranium-237 Lanthanum-140 249.8 d 2.758 a 5.27 a 6.749 d 1.679 d
Cs-134 LNHB Library www.nucleide.org/ddep_wg/d DEPdata.htm 796 kev 605 kev
Regan et al., 2013 Precision lifetime measurements using LaBr3 detectors with stable and radioactive beams EPJ Web of Conferences, 63, 01008 Example: 152 Eu
Regan et al., 2013 Precision lifetime measurements using LaBr3 detectors with stable and radioactive beams EPJ Web of Conferences, 63, 01008 Example: 152 Eu
Summary MetroERM is a pan-european project with the aim of harmonising the measurement and interpretation of data during radiological early warning events NPL are committed to investigating new and existing technology for the measurement of gamma-emitting airborne radioactive particulates with a strong interest in coincidence measurements We aim to use the radioactive aerosol generation system to test commercially available gamma spectrometers for their suitability for these purposes
Involvement? Would you like to..become involved with the project?.provide detectors for comparison? Contact: steven.bell@npl.co.uk
The National Measurement System delivers world-class measurement science & technology through these organisations Questions?