| 1. |
- Gårdestig, Magnus, 1973-, et al.
(författare)
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RadiaCopter – UAS Gamma spectrometry for detection and identification of radioactive sources
- 2011
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Ingår i: XVI Conference of the NSFS, Reykjavik Iceland, 22-25 August 2011.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With an unmanned helicopter (UAS), known as drones, equipped with a gamma spectrometer, one can achieve both a high spatial resolution and good range, and be able to approach a radioactive source closely. Linköping University, Sweden, is proposing a microdrone system that will fill a gap between man-portable measurement systems and full-sized airborne systems, complementing the car-driven measurement systems. The system may play a unique role in many of our contingency scenarios in terms of accessibility, versatility, efficiency, and is advantageous from the viewpoint of radiation protection as it can be controlled at a safe distance.
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| 2. |
- Kock, Peder, et al.
(författare)
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A deviation display method for visualising data in mobile gamma-ray spectrometry.
- 2010
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Ingår i: Applied Radiation and Isotopes. - : Elsevier BV. - 0969-8043. ; 68, s. 1832-1838
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Tidskriftsartikel (refereegranskat)abstract
- A real time visualisation method, to be used in mobile gamma-spectrometric search operations using standard detector systems is presented. The new method, called deviation display, uses a modified waterfall display to present relative changes in spectral data over energy and time. Using unshielded (137)Cs and (241)Am point sources and different natural background environments, the behaviour of the deviation displays is demonstrated and analysed for two standard detector types (NaI(Tl) and HPGe). The deviation display enhances positive significant changes while suppressing the natural background fluctuations. After an initialisation time of about 10min this technique leads to a homogeneous display dominated by the background colour, where even small changes in spectral data are easy to discover. As this paper shows, the deviation display method works well for all tested gamma energies and natural background radiation levels and with both tested detector systems.
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| 3. |
- Kock, Peder, et al.
(författare)
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A real-time statistical alarm method for mobile gamma spectrometry-Combining counts of pulses with spectral distribution of pulses
- 2012
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 681, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- A well-founded decision needs to take into account as much information from a sample as possible. In gamma spectrometry, the number of photons and their energy are the two quantities readily accessible to the physicist and both should be used in order to increase the power of a statistical test. While the problem of counts of pulses has been much studied the problem of spectral distribution of pulses has been generally overlooked. This work presents a statistical test combining tests on count rate and tests on spectral distribution. The proposed method is shown to have an acceptable false positive rate and, when compared with two other test statistics found in the literature, greater power. (C) 2012 Elsevier B.V. All rights reserved.
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| 4. |
- Kock, Peder, et al.
(författare)
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Comparison of airborne and terrestrial gamma spectrometry measurements - evaluation of three areas in southern Sweden.
- 2011
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 1879-1700 .- 0265-931X. ; 102:6, s. 605-613
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Tidskriftsartikel (refereegranskat)abstract
- The Geological Survey of Sweden (SGU) has been conducting airborne gamma spectrometry measurements of natural radioactivity in Sweden for more than 40 years. Today, the database covers about 80% of the country's land surface. This article explores the first step of putting this data into use in radioactive source search at ground level. However, in order to be able to use the airborne background measurements at ground level, SGU data must be validated against terrestrial data. In this work, we compare the SGU data with data measured by a portable backpack system. This is done for three different areas in southern Sweden. The statistical analysis shows that a linear relationship and a positive correlation exist between the air and ground data. However, this linear relationship could be revealed only when the region possessed large enough variations in areal activity. Furthermore, the activity distributions measured show good agreement to those of SGU. We conclude that the SGU database could be used for terrestrial background assessment, given that a linear transfer function is established.
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| 5. |
- Kock, Peder, et al.
(författare)
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On background radiation gradients - the use of airborne surveys when searching for orphan sources using mobile gamma-ray spectrometry
- 2014
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 1879-1700 .- 0265-931X. ; 128, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- Systematic background radiation variations can lead to both false positives and failures to detect an orphan source when searching using car-borne mobile gamma-ray spectrometry. The stochastic variation at each point is well described by Poisson statistics, but when moving in a background radiation gradient the mean count rate will continually change, leading to inaccurate background estimations. Airborne gamma spectrometry (AGS) surveys conducted on the national level, usually in connection to mineral exploration, exist in many countries. These data hold information about the background radiation gradients which could be used at the ground level. This article describes a method that aims to incorporate the systematic as well as stochastic variations of the background radiation. We introduce a weighted moving average where the weights are calculated from existing AGS data, supplied by the Geological Survey of Sweden. To test the method we chose an area with strong background gradients, especially in the thorium component. Within the area we identified two roads which pass through the high-variability locations. The proposed method is compared with an unweighted moving average. The results show that the weighting reduces the excess false positives in the positive background gradients without introducing an excess of failures to detect a source during passage in negative gradients. (C) 2013 Elsevier Ltd. All rights reserved.
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| 6. |
- Kock, Peder
(författare)
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Orphan source detection in mobile gamma-ray spectrometry - Improved techniques for background assessment
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hazardous radioactive sources out of regulatory control are referred to as orphan sources. Focussing on gamma-emitting orphan sources, this thesis describes methods that can be used in mobile gamma-ray spectrometry to perform real-time discrimination between an actual source signal and the signal due to the natural radiation background. Two categories of methods for orphan source detection are presented: visualisation and statistical hypothesis testing. Visualisation leaves the interpretation to the operator, whereas the hypothesis testing aims at answering the question: is there a signal or not? The methods are shown to work well for purely stochastic background data. The visualisation method gives a homogeneous representation of large data sets, which enhances the capability to discern significant positive deviations. The hypothesis testing method is shown to exhibit false alarms at the expected rate. Furthermore, by taking into account the spectral distribution in a hypothesis test, the power of the test was increased when compared with reference methods from the literature. Systematic background radiation variations can be disclosed by using data from airborne gamma-ray spectrometry (AGS) surveys. Validation of AGS data at the ground level by the use of terrestrial surveys yielded a strong positive correlation between the two data sets for background activity of uranium and thorium. By deriving a step function from AGS data, the systematic background variations were successfully modelled at the ground level. This approach was shown to reduce the number of excess false positives in an area with strong background gradients. In addition to random and systematic background radiation fluctuations, germanium spectrometers can have problems with microphonic noise due to the vibrations that inevitably will occur in mobile gamma-ray spectrometry. The additional noise can be expected to degrade the resolution of the detector. The level of resolution degradation was found to be 0-19%, depending on the speed of the vehicle.
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