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Dismantling nuclear power plants entails the production of a large amount of contaminated (or potentially contaminated) material whose disposal is of crucial importance. Most of the end products have to be stored in special repositories but it can happen that some of them are slightly contaminated or not contaminated at all, making it possible to free release them. One possible approach to free release measurements uses Large Clearance Monitors, chambers surrounded by plastic scintillation detectors that allow a decision about the clearance of waste packages up to 1000 kg. Due to the composite nature of the detectors in a Large Clearance Monitor, it is easy to imagine that one can apply 3D imaging algorithms to localize radioactive sources inside a waste package. In this work we will show how a special algorithm that maximizes the conditional informational entropy allows decisions about the clearance of portions of the sample., Comment: 15 pages

Two peak area estimation methods in gamma-ray spectrometry, the total peak area (TPA) and the background step function (BSF) methods are re-considered first. For least-squares (LS) peak fitting then, a new net peak area uncertainty model is established. It results in a new function f B replacing a TPA method internal design factor. This allows applying the TPA-related decision threshold (DT) and detection limit (DL) formulae, based on ISO 11929(2010), also for peak fitting. Linear LS adapted to Poisson counting data is suggested to derive f B values for a single peak and different combinations of background shape components including a fitted BSF. f B is then adapted to penalized non-linear fitting including Poisson maximum likelihood estimation by MC simulations. Within the DL iteration the f B method is much faster than with non-linear re-fitting. The fitted peak area uncertainty can be safely modeled for peak areas up to 10 DT which is sufficient for DL calculations. The extension for peak multiplets is indicated.

Regarding cod as sea food for human consumption and as bio indicator of the marine eco system, this study is the first approach to combine the analysis of organic and inorganic contaminants and radionuclides in cod muscle as well as PCDD/Fs and dl-PCBs in its livers from the same fishing areas. Concentrations of 1-hydroxypyrene, PCDD/Fs, PCBs, cesium-137 (Cs-137), cadmium and lead were determined in individual or pooled samples over a wide geographic area, including Greenland Seas, Barents Sea, North and Baltic Sea. Highest concentrations were found in samples from the Baltic Sea, lowest in the pristine areas of the Barents Sea and Greenland. Levels of contaminants in cod muscle were found to be far below the established EU maximum levels (ML), regardless of which fishing grounds. In contrast to this, most cod liver samples from the North and Baltic Sea showed PCDD/F and PCB contents exceeding the ML. In addition, new background assessment criteria (BAC) for 1-hydroxypyrene in cod of 4.6 ng mL(-1) bile and for Cs-137 a BAC of 0.16 Bq kg(-1) wet weight are proposed to be included in the European Marine Strategy Framework Directive for cod from the Northeast Atlantic.

It is shown how a generalized evaluation of a large variety of environmental radioactivity measurements, without and with using linear unfolding, can be performed with a single program, UncertRadio (UR). Using a function parser allows deriving numerical partial derivatives for ISO GUM compatible uncertainty propagation. The evaluation within UR is extended to include ISO 11929 decision thresholds and detection limits. Alternatively, propagation of distributions with MC simulation is included. Part I gives an overview considering evaluations without using linear unfolding.

It is shown how a generalized evaluation of a large variety of environmental radioactivity measurements, without and with using linear unfolding, can be performed with a single program, UncertRadio (UR). Using a function parser allows deriving numerical partial derivatives for ISO GUM compatible uncertainty propagation. The evaluation within UR is extended to include ISO 11929 decision thresholds and detection limits. Alternatively, propagation of distributions with MC simulation is included. Part I gives an overview considering evaluations without using linear unfolding.

Fillet samples of marine fish collected from the East/West Greenland currents (GC) and from the Baltic Sea (BS) have been investigated by gamma-ray spectrometry within the regular German monitoring programme. In samples of the second half of 2011, 134Cs traces have been detected that are suggested to originate from the Fukushima fallout that was deposited in March/April 2011 over the northern North Atlantic and accumulated by fish. The radionuclide 134Cs (half-life 2 yr) was indeed detected with quite small activities at about 0.0036 Bq kg−1 w.w. Existing box models describing the transport of Cs within seawater boxes of the northeast Atlantic allowed for estimation of 134Cs contributions from other sources, i.e. from the Chernobyl fallout and from discharges by the two major European nuclear reprocessing plants; both were negligible around Greenland, while for the Chernobyl fallout a small 134Cs background contribution to BS fish was estimated. Model results confirmed the level of 134C measured in BS fish and showed its maximum to have occurred in winter 2011/2012 followed by a continuous decrease. It was also determined that 134Cs activity, but not that of 134Cs, showed a significant negative correlation with sampling depth (150–400 m) of GC fish; this strengthens our Fukushima fallout assumption. As a result, the Fukushima fallout in these sea areas only marginally enhanced (GC: 4%; BS: 0.1%) pre-Fukushima levels of individual dose rates received by human fish consumers; the addition was around 0.001 μSv following the consumption of 10 kg of fish per year, which is not expected to cause concern according to present guidelines for radiation protection.

A deterministic code was developed for the calculation of true coincidence summing correction factors and has been incorporated into the EFFTRAN tool. The approach is aimed at the analysis of extended samples measured on p-type HPGe detectors in environmental gamma-ray spectrometry and was verified against the results of a state-of-the-art full Monte Carlo code. The two sets of results matched on average within 1%. Our code requires no measurements in addition to a standard full-energy-peak calibration, has a very short run time and takes into account the spatial variation of the efficiency across the sample volume. The EFFTRAN code is free software, available from the authors on request.

Environmental surveillance of Sr-89 and Sr-90 following an accident or incident with fission material is particularly important. Most analytical strategies require at least two measurement procedures – one to determine Sr-89 and the other to determine Sr-90 indirectly by measuring the daughter Y-90. However, the Sr-89 and Sr-90 can be determined simultaneously and independently of the state of the Sr-90/Y-90 equilibrium by liquid scintillation counting. Modern LSCs allow the recording of scintillation spectra which facilitates the setting of energy regions for optimal counting of a particular radionuclide. The yield was determined by gamma spectrometry of the tracer Sr-85 added in known activity to the sample prior to analysis. This tracer is not present in nuclear fallout. In the event of a nuclear accident, however, the pressure on gamma-spectrometric capacity may limit the capability to carry out the Sr yield determination by this method.

Ages of golden redfish ( Sebastes marinus ) and deep-sea redfish ( S. mentella ) in the Northeast Atlantic were determined by measurement of natural radioisotopes in their otoliths. Using samples from S. marinus around Iceland as well as S. mentella off East Greenland and in the Irminger Sea, 226 Ra and 210 Pb activities in otolith cores, pooled by fish length groups, were measured by alpha-spectrometry. The ratio of these isotopes provided radiometric ages for the investigated 20 samples, which in general corresponded well with the expected radioactive ingrowth curves and with annulus-derived age estimates for fish of the same length group. Radiometric ages of S. marinus with 10–55 cm body length ranged from 3 to 31 years, while S. mentella from East Greenland (17–35 cm) exhibited radiometric ages of 8–15 years, and S. mentella from the Irminger Sea (26–45 cm) showed a range of 15–41 years. A slight tendency towards an underestimation of ages by annulus counts could be inferred from the comparison with the derived radiometric ages. Considerable differences between ageing methods were found for Icelandic S. marinus over 40 cm length and pelagic S. mentella from the deeper layers of the Irminger Sea, indicating problematic annulus-derived age estimation for these groups. This study confirms slow growth and high longevity of Northeast Atlantic redfish and delivers the first radiometric age validation for S. marinus .

Different algorithms exist that can be applied to the calculation of the effects of true coincidence summing in gamma-ray spectrometry. Some of these, however, are not capable of reproducing the count rates in all the pure sum peaks that a spectrum may contain. A recursive, easy-to-implement deterministic algorithm has been developed that overcomes this shortcoming.

It is shown how the decision threshold, the detection limit and the limits of a coverage interval - summarily called the characteristic limits - and, in addition, the best estimate and the associated standard uncertainty of a non-negative radiation measurand are to be calculated by using the Monte Carlo (MC) method in ionising-radiation measurements. The limits are mathematically defined by means of quantiles of the Bayesian distributions of the possible measurand values. The MC induced uncertainties of the limits and typical problems connected with MC application are also treated. The paper can serve as a bridge between the ISO Guide to the Expression of Uncertainty in Measurement (GUM), Supplement 1 applying the MC method and ISO/FDIS 11929 (at present in preparation) dealing with the characteristic limits. As an illustration, a net count rate measurand, being the difference of a gross and a background count rate, is treated theoretically and numerically. More complex examples deal with the wipe test for surface contamination and with a linear multi-channel spectrum unfolding.