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Early warning networks are used for detecting abnormal radioactivity levels in the environment. State-of-the-art networks are equipped with both dose rate detectors and spectrometric stations. Current networks don't automatically discriminate between radioactivity on the ground and in the air. A novel directional sensing gamma radiation detector utilizing a collimated phoswich scintillator was developed. The signals from the two scintillator materials are separated using a pulse shape discrimination. The separated signals are employed to determine the radioactivity concentrations on the ground and in the air assuming specific concentration distributions. Limitations related to imperfect directional sensing and dead time are discussed.

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A novel Compton suppression device has been developed at the Radiation and Nuclear Safety Authority of Finland to improve the sensitivity of measurements in the Gamma Laboratory. It utilizes γ-γ anticoincidence, but operates as a full coincidence system. Specific software has been developed for the sorting, visualization and analysis of list mode data produced by the multi-detector list-mode devices in the Gamma Laboratory. By utilizing the software, the coincidence data can be accessed and the true-coincidence losses of photo-peaks of multiple gamma-ray-emitting nuclides restored in the analysis. This simplifies data analysis and further increases the sensitivity of the device in low count-rate gamma spectrometry. A detailed Geant4 simulation model of the device was developed and used to optimize the device as well as to support calibrations and complex analysis tasks. The setup has been integrated to current laboratory information management system used in the Gamma Laboratory. Compton suppression reduces the continuous background seen by the high-purity germanium detector by a factor of 3-10, in addition to comparable reduction in the Compton continuum of any peaks in the spectrum. A comparison with the results of conventional gamma-ray spectrometry is presented.

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Decommissioning of nuclear facilities incurs high costs regarding the accurate characterisation and correct disposal of the decommissioned materials. Therefore, there is a need for the implementation of new and traceable measurement technologies to select the appropriate release or disposal route of radioactive wastes. This paper addresses some of the innovative outcomes of the project "Metrology for Decommissioning Nuclear Facilities" related to mapping of contamination inside nuclear facilities, waste clearance measurement, Raman distributed temperature sensing for long term repository integrity monitoring and validation of radiochemical procedures.

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An optical radon detection method is presented. Radon decay is directly measured by observing the secondary radiolumines cence light that alpha particles excite in air, and the selectivity of coincident photon detection is further enhanced with online pulse-shape analysis. The sensitivity of a demonstration device was 6.5 cps/Bq/l and the minimum detectable concentration was 12 Bq/m(3) with a 1 h integration time. The presented technique paves the way for optical approaches in rapid radon detec tion, and it can be applied beyond radon to the analysis of any alpha-active sample which can be placed in the measurement chamber.

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An approach for in situ alpha spectrometry that allows one to measure the spectra with good energy resolution at ambient air pressure has been developed recently. Here, novel equipment is introduced for in situ measurements. Neither vacuum pumps nor radiochemical sample processing are necessary. Flat and smooth surfaces are ideal sources provided that the radionuclide contamination represents a thin layer on the surface. Other sources, such as air filters or evaporation residues, are also possible. Alpha particle collimation is used to obtain good energy resolution, but the equipment can also be used without collimation. An estimation of the detection efficiency with and without collimation is given using an extended area source containing 241Am.

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A nuclear bomb particle containing 1.6 ng of Pu was investigated nondestructively with a position-sensitive α detector and a broad-energy HPGe γ-ray detector. An event-mode data acquisition system was used to record the data. α-γ coincidence counting was shown to be well suited to nondestructive isotope ratio determination. Because of the very small background, the 51.6 keV γ rays of (239)Pu and the 45.2 keV γ rays of (240)Pu were identified, which enabled isotopic ratio calculations. In the present work, the (239)Pu/((239)Pu+(240)Pu) atom ratio was determined to be 0.950 ± 0.010. The uncertainties were much smaller than in the previous more conventional nondestructive studies on this particle. Obtained results are also in good agreement with the data from the destructive mass spectrometric studies obtained previously by other investigators.

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Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where (137)Cs fallout from the Chernobyl accident is 23-45 kBq m(-2). A 3-GBq (137)Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h(-1) and data acquisition interval of 1s. Respective response for (192)Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 microSv h(-1), which gives for the activity concentration of (131)I less than 1 kB qm(-3). Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2-0.7 m(3)h(-1) at a flight speed of 70 km h(-1) depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as (239)Pu, is of the order of 0.2 Bq m(-3) or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as (137)Cs and (131)I are of the order of 1 Bq m(-3).

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