Radiation Protection Bureau of Health Canada

Ottawa, Canada

Radiation Protection Bureau of Health Canada

Ottawa, Canada
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Pan P.,Canadian Nuclear Safety Commission | Ungar R.K.,Radiation Protection Bureau of Health Canada
Journal of Environmental Radioactivity | Year: 2012

It is important to know the initial time, or zero-time, of a nuclear event such as a nuclear weapon's test, a nuclear power plant accident or a nuclear terrorist attack (e.g. with an improvised nuclear device, IND). Together with relevant meteorological information, the calculated zero-time is used to help locate the origin of a nuclear event. The zero-time of a nuclear event can be derived from measured activity ratios of two nuclides. The calculated zero-time of a nuclear event would not be complete without an appropriately evaluated uncertainty term. In this paper, analytical equations for zero-time and the associated uncertainty calculations are derived using a measured activity ratio of two nuclides. Application of the derived equations is illustrated in a realistic example using data from the last Chinese thermonuclear test in 1980. © 2011.


Zhang W.,Radiation Protection Bureau of Health Canada | Mekarski P.,Radiation Protection Bureau of Health Canada | Ungar K.,Radiation Protection Bureau of Health Canada
Applied Radiation and Isotopes | Year: 2010

A single-channel phoswich well detector has been assessed and analysed in order to improve beta-gamma coincidence measurement sensitivity of 131mXe and 133mXe. This newly designed phoswich well detector consists of a plastic cell (BC-404) embedded in a CsI(Tl) crystal coupled to a photomultiplier tube (PMT). It can be used to distinguish 30.0-keV X-ray signals of 131mXe and 133mXe using their unique coincidence signatures between the conversion electrons (CEs) and the 30.0-keV X-rays. The optimum coincidence efficiency signal depends on the energy resolutions of the two CE peaks, which could be affected by relative positions of the plastic cell to the CsI(Tl) because the embedded plastic cell would interrupt scintillation light path from the CsI(Tl) crystal to the PMT. In this study, several relative positions between the embedded plastic cell and the CsI(Tl) crystal have been evaluated using Monte Carlo modeling for its effects on coincidence detection efficiency and X-ray and CE energy resolutions. The results indicate that the energy resolution and beta-gamma coincidence counting efficiency of X-ray and CE depend significantly on the plastic cell locations inside the CsI(Tl). The degraded X-ray and CE peak energy resolutions due to light collection efficiency deterioration by the embedded cell can be minimised. The optimum of CE and X-ray energy resolution, beta-gamma coincidence efficiency as well as the ease of manufacturing could be achieved by varying the embedded plastic cell positions inside the CsI(Tl) and consequently setting the most efficient geometry. © 2010.


Zhang W.,Radiation Protection Bureau of Health Canada | Yi J.,Radiation Protection Bureau of Health Canada | Mekarski P.,Radiation Protection Bureau of Health Canada | Hoffman I.,Radiation Protection Bureau of Health Canada | And 2 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2011

In this study, a gamma-gamma coincidence spectrometry was developed and examined for environmental low-level cosmogenic 22Na monitoring purposes. The spectrometry consists of two bismuth germanate scintillators (BGO) and XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The developed spectrometry was optimized according to the considerations of output count rate and gamma peak energy resolution. This spectrometry provides a more sensitive and effective way to quantify even trace amounts of 22Na with critical detection limit of 9 mBq. A sophisticated computer simulation was also created with the goal of obtaining a better understanding of the experimental results and gamma-gamma coincidence efficiencies at different sample geometries. © 2010 Akadémiai Kiadó, Budapest, Hungary.


Zhang W.,Radiation Protection Bureau of Health Canada | Mekarski P.,Radiation Protection Bureau of Health Canada | Bean M.,Radiation Protection Bureau of Health Canada | Yi J.,Radiation Protection Bureau of Health Canada | Ungar K.,Radiation Protection Bureau of Health Canada
Pure and Applied Geophysics | Year: 2014

In this study, an optimized single-channel phoswich well detector design has been proposed and assessed in order to improve beta-gamma coincidence measurement sensitivity of xenon radioisotopes. This newly designed phoswich well detector consists of a plastic beta counting cell (BC404) embedded in a CsI (Tl) crystal coupled to a photomultiplier tube. The BC404 is configured in a cylindrical pipe shape to minimise light collection deterioration. The CsI (Tl) crystal consists of a rectangular part and a semi-cylinder scintillation part as a light reflector to increase light gathering. Compared with a PhosWatch detector, the final optimized detector geometry showed 15 % improvement in the energy resolution of a 131mXe 129.4 keV conversion electron peak. The predicted beta-gamma coincidence efficiencies of xenon radioisotopes have also been improved accordingly. © 2012 Springer Basel AG.


Zhang W.,Dalhousie University | Zhang W.,Radiation Protection Bureau of Health Canada | Chatt A.,Dalhousie University
Journal of Radioanalytical and Nuclear Chemistry | Year: 2013

In order to reduce interferences from high activities of 24Na, 56Mn, 82Br, and 38Cl as well as to improve detection limits, precision, and accuracy of measuring iodine levels in biological materials, foods and diets in particular, an epithermal instrumental neutron activation analysis (EINAA) method in conjunction with anti-coincidence (EINAA-AC) gamma-ray spectrometry was employed. The Compton scattering background in the region of the 442.9-keV photopeak of 128I was significantly suppressed by anti-coincidence counting. In order to validate the EINAA-AC method as well as to evaluate its broad applicability to diverse types of biological material, 17 NIST and IAEA reference materials containing very low to high levels of iodine as well as interfering elements were analyzed by the EINAA-AC method. The samples were irradiated in the cadmium-lined pneumatic site at a neutron flux of 2 × 1011 cm-2 s-1 of the Dalhousie University SLOWPOKE-2 Reactor (DUSR) facility for 10 or 20 min followed by 1-min decay and 30-min counting. The detection limit for iodine by EINAA-AC was improved by a factor of 2-5 compared to EINAA depending on the sample matrix and other factors, and a limit of 3-5 μg kg-1 was achieved for low-salt foods. We found the RSD to be about ±5 % above 200, increasing to ±10 % at 20, and then to greater than ±30 % at about 5 μg kg-1 iodine levels. © 2012 Akadémiai Kiadó, Budapest, Hungary.


Zhang W.,Radiation Protection Bureau of Health Canada | Ungar K.,Radiation Protection Bureau of Health Canada | Liu C.,Radiation Protection Bureau of Health Canada | Mailhot M.,Radiation Protection Bureau of Health Canada
Journal of Environmental Radioactivity | Year: 2016

A series of measurements have been recently conducted to determine the cosmic-muon intensities and attenuation factors at various indoor and underground locations for a gamma spectrometer. For this purpose, a digital coincidence spectrometer was developed by using two BC408 plastic scintillation detectors and an XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The results indicate that the overburden in the building at surface level absorbs a large part of cosmic ray protons while attenuating the cosmic-muon intensity by 20-50%. The underground facility has the largest overburden of 39 m water equivalent, where the cosmic-muon intensity is reduced by a factor of 6. The study provides a cosmic-muon intensity measurement and overburden assessment, which are important parameters for analysing the background of an HPGe counting system, or for comparing the background of similar systems. © 2016 Elsevier Ltd.


Zhang W.,Radiation Protection Bureau of Health Canada | Ungar K.,Radiation Protection Bureau of Health Canada | Stukel M.,Radiation Protection Bureau of Health Canada | Mekarski P.,Radiation Protection Bureau of Health Canada
Journal of Environmental Radioactivity | Year: 2014

In this study, a digital gamma-gamma coincidence/anticoincidence spectrometer was developed and examined for low-level cosmogenic 22Na and 7Be in air-filter sample monitoring. The spectrometer consists of two bismuth germanate scintillators (BGO) and an XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The spectrometer design allows a more selective measurement of 22Na with a significant background reduction by gamma-gamma coincidence events processing. Hence, the system provides a more sensitive way to quantify trace amounts of 22Na than normal high resolution gamma spectrometry providing a critical limit of 3mBq within a 20h count. The use of a list-mode data acquisition technique enabled simultaneous determination of 22Na and 7Be activity concentrations using a single measurement by coincidence and anticoincidence mode respectively. © 2014 Elsevier Ltd.


Zhang W.,Dalhousie University | Zhang W.,Radiation Protection Bureau of Health Canada | Chatt A.,Dalhousie University
Journal of Radioanalytical and Nuclear Chemistry | Year: 2014

An instrumental neutron activation analysis method in conjunction with anticoincidence counting (INAA-AC) gamma-ray spectrometry was developed for the determination of ppb levels of V in biological, mostly nutritional, reference materials containing varying amounts of salt. The method involved irradiation in the Dalhousie University SLOWPOKE-2 reactor facility at a fission neutron flux of 5 × 1011 cm-2 s-1 for 1 min, decay for 1 min, and counting for 10 min. In order to fully investigate the extent of improvement that can possibly be obtained for V determination by INAA-AC, a theoretical term called the analytical figure of merit was developed and applied to 16 National Institute of Standards and Technology and International Atomic Energy Agency reference materials. The overall background around the 1,434.1-keV photopeak of 52V was reduced by a factor of 5-10 for several materials in the anticoincidence counting mode. The detection limits were lowered by factors of 3-5 in INAA-AC (0.61-9.4 μg kg-1) compared to conventional INAA (1.9-79 μg kg-1) in samples with varying ratios of Na/V (0.24-1,000), Cl/V (0.12-1,827), Al/V (7.45-115) and Mn/V (1.84-66.9) making rapid and reliable V measurements possible at sub-ppb levels without any chemical separation. © 2013 Akadémiai Kiadó, Budapest, Hungary.


Zhang W.,Radiation Protection Bureau of Health Canada | Chen J.,Radiation Protection Bureau of Health Canada | Ungar K.,Radiation Protection Bureau of Health Canada | Cooke M.,Radiation Protection Bureau of Health Canada
Journal of Environmental Radioactivity | Year: 2015

In this study, the aerosol activity concentrations of 210Pb at 28 Canadian radiological monitoring stations from 2009 to 2013 were analyzed. The results show that the ratio of 210Pb winter average concentration to summer average concentration increases with increasing latitude. This could be used to evaluate the transport of pollutants to the Arctic region such as the Arctic haze from Eurasia through long-range atmospheric transport during winter. Based on 12 years of monitoring results from the Yellowknife station that includes both 210Pb and 212Pb concentrations, the study confirms that the seasonal distribution of 210Pb to 212Pb activity concentration ratios has a significant peak in winter and a relatively low value in summer, which can be used as an indicator of the air mass flow to the Arctic. The period dominated by long-range aerosol transport and Arctic haze was estimated by fitting a Gaussian distribution function to the peak values of this ratio in winter. A peak width parameter of full width at half maximum (FWHM) allows a year by year estimate of the period of influence by long-range transport of aerosols, and this varied between 67 and 88 days in this study. The fitted Gaussian peak also shows that the season of the continental influenced air mass in Yellowknife usually starts in mid-to-late November and ends in mid-to-late April. Thus, the 210Pb to 212Pb ratio distributions may enable the determination of periods dominated by long-range aerosol transport and the scale of the Arctic haze at different latitudes. © 2014.


PubMed | Radiation Protection Bureau of Health Canada
Type: | Journal: Journal of environmental radioactivity | Year: 2016

Health Canadas Radiation Protection Bureau has identified trace quantities of (134)Cs and (137)Cs in commercially available green tea products of Japanese origin. Referenced to March 11, 2011, the activity ratio ((134)Cs/(137)Cs) has been determined to be 1:1, which supports an origin from the Fukushima Dai-ichi Nuclear Power Plant accident. The upper limits of typical tea beverage preparation conditions were applied to the most contaminated of these green tea samples to determine the proportion of radiocesium contamination that would be available for human consumption. The distribution of radiocesium among the components of the extraction experiments (water, residual tea solid, and filter media) was determined by both conventional and Compton-suppressed gamma spectroscopy. The latter aided tremendously in providing a more complete radiocesium distribution profile, particularly for the shorter-lived (134)Cs. Cesium extraction efficiencies of 64 7% and 64 5% were determined based on (134)Cs and (137)Cs, respectively. Annual, effective dose estimates from ingestion of (137)Cs and (134)Cs (1.8-3.7 Sv), arising from the consumption of tea beverages prepared from the most contaminated of these samples, are insignificant relative to both total ( 2.4 mSv) and ingested ( 0.28 mSv) annual effective doses received from naturally occurring radioactive sources. As such, there is no health concern arising from the consumption of green tea beverages contaminated with radiocesium at the levels encountered in this study.

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