Decay Of 137Cs Research Articles

Assessment of secondary radioactive contamination of a decontaminated land plot located on the territory of a recreation base in a wooded area

The article presents results of a long-term (1998–2021) radiological monitoring survey of a recreation base located in a wooded area in the zone of radioactive contamination after the accident at the Chernobyl nuclear power plant. Local mechanical decontamination of the soil had been made on the territory of the base in 1997. The evaluation of the secondary radioactive contamination of the decontaminated territory was performed by comparing dynamics of the radiological situation at the treated plot and the control, nondecontaminated, part of the base according to four main criteria: 1) dose rate of gamma radiation in the air from cesium radionuclides; 2) inventory of 137Cs in soil; 3) vertical distribution of 137Cs in soil; 4) activity concentration of 137Cs in plants and fungi. In 1998, the value of the 137Cs inventory in the upper 20 cm of soil in the control part of the territory of the base and in the decontaminated plot was 930 kBq/m2 and 143 kBq/ m2, respectively. By 2015, the value of the 137Cs inventory in the control area and the decontaminated plot had significantly decreased: by 35% and 36%, respectively. A decrease in the dose rate of gamma radiation in the air at the decontaminated plot and control area proceeded at the same rate, which is currently mainly determined by the decay of 137Cs. There was a gradual self-restoration of the forest ecosystem at the plot subjected to decontamination. Activity concentration of 137Cs in biota (pine, edible mushrooms) in the treated plot was many times lower than that in the control part of the recreation base. In general, there was no significant secondary radioactive contamination of the decontaminated plot in the 24 years after the intervention.

Thirty-year simulation of environmental fate of 137Cs in the Abukuma River basin considering the characteristics of 137Cs behavior in land uses

The Fukushima Daiichi Nuclear Power Plant accident caused a radioactive contamination of deposited radionuclides, including 137Cs, on the land surface. Cesium-137 deposited on the land surface was strongly adsorbed on soil particles and was then washed off through soil erosion. Trends of temporal variation of 137Cs wash-off varied greatly depending on land use. Therefore, it is important to reflect the characteristics of 137Cs migration processes in each land use to clarify the long-term fate of 137Cs. In this study, a 30-year simulation of environmental fate of 137Cs was conducted using a distributed radiocesium prediction model, taking into account the characteristics of the 137Cs behavior in each land use. Overall, in the Abukuma River basin, the 137Cs transported into the ocean for 30 years was estimated to correspond to 4.6 % of the initial deposition in the basin, and the effective half-life of 137Cs deposited in the basin was estimated to be 3.7 years shorter (by 11.6 %) than its physical half-life. These results suggested that 137Cs deposited from the accident could still remain for decades. Based on the analysis of the 137Cs behavior in land use, in 2011, the contribution of 137Cs export to the ocean from urban lands was estimated to correspond to 70 % of the total 137Cs export. Meanwhile, from 2012 to 2040, the contribution of 137Cs export from agricultural lands was estimated to correspond to 75 % of the total 137Cs export. The reduction ratios excluding radioactive decay of 137Cs remained in areas with and without human activities for 30 years after the accident, defined as the ratios of the total outflow to the initial deposition, were estimated to be 11.5 %–17.7 % and 0.4 %–1.4 %, respectively. These results suggested that human activities enhance the reduction of 137Cs remaining in land in the past and future.

Contamination processes of tree components in Japanese forest ecosystems affected by the Fukushima Daiichi Nuclear Power Plant accident 137Cs fallout

In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with 137Cs. However, 137Cs transfer processes determining tree contamination (particularly for stem wood, a prominent commercial resource) remain insufficiently understood. We propose a model for simulating dynamic behavior of 137Cs in a forest tree–litter–soil system and applied it to contaminated forests of cedar plantation and natural oak stand in Fukushima to elucidate relative impact of distinct 137Cs transfer processes determining the tree contamination. The transfer of 137Cs to the trees occurred mostly (>99%) through surface uptake of 137Cs trapped by needles and bark during the fallout. Root uptake of soil 137Cs was several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, internal contamination of the trees proceeded through an enduring recycling (translocation) of 137Cs absorbed on the tree surface. A significant surface uptake of 137Cs through bark was suggested, contributing to 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining uptake occurred at needles) of the total uptake by the trees, although that pathway still needs to be evaluated by experimental evidence. It was suggested that the activity concentration of 137Cs in stem wood of the trees at these sites are currently (as of 2021) decreasing by ~3% per year, mainly through radioactive decay of 137Cs and partly through dilution effect from tree growth. Although further refinement of the model is recommended, for example by including tree species specific 137Cs transportation in stem, these findings provide vital information for planning of forestry reactivation in Fukushima; e.g., removal of forest floor organic layer will not reduce the tree contamination for a long term because of the 137Cs absorption via the tree surface substantially greater than root uptake of 137Cs deposited to the floor.

Chernobyl still with us: 137Caesium activity contents in seabed sediments from the Gulf of Bothnia, northern Baltic Sea

Anthropogenic radionuclides are among those human impacts, which can be seen widely in the marine and terrestrial ecosystems. Fallout from the 1986 Chernobyl nuclear power plant accident has rendered the Baltic Sea as the most polluted marine body in the world with respect to 137Cs.This research investigated sediment cores from 56 sites around the Gulf of Bothnia, Baltic Sea. Radioactivity from 137Cs in sediments has generally declined due to natural/radioactive decay of 137Cs over the last decades. However, 137Cs contents in subsurface sediments remain at elevated levels compared to pre-Chernobyl levels.The highest 137Cs activity contents in subsurface sediments (>4000 Bg kg−1) occur in coastal areas including estuaries. These areas often experience severe anthropogenic pressure. The southern Bothnian Sea, Kvarken archipelago, and southern Bothnian Bay all show elevated 137Cs values in subsurface sediments.Sedimentary 137Cs can also help constrain recent rates of sedimentation. Post-Chernobyl sedimentation rates in the Gulf of Bothnia varied from 0.1 to 4.8 cm/year with an average sedimentation rate of 0.54 cm/year.

Caesium-137 in mountain flora with emphasis on reindeer's diet – Spatial and temporal trends

The present study summarizes three decades of studies on 137Cs transfer to various species of lichens, graminoids, herbs and woody plants across a ~3000 km2 area used as mountain pasture for reindeer and other ruminants. The investigation comprised of field studies covering the period 2011–2016, and a compilation of studies and data for the preceding period (1986–2010). Altogether, more than 700 individual vegetation samples were considered. For lichens, relatively fast decrease in contamination levels was observed during the first decade after the Chernobyl fallout (ecological half-time of about 3 years). For later years there seems to be a continuous re-contamination which results in a “steady state” where time-trends are mainly governed by physical decay of 137Cs. For green plants, decline in transfer factors (TF) (i.e. the ratio between activity concentration in vegetation and activity density in soil) during the period 1986–2012 was not as pronounced as for lichens: Some species showed significant decrease with time, while others did not. 25–30 years after the Chernobyl accident, 137Cs levels in lichens and green plants were significantly dependent on the levels in soil (R2 between 0.53 and 0.57), but there were also some significant differences in transfer between sampling sites. Moreover, marked variability in TFs was found between different plant species growing at the same site, whereas such differences were not found for reindeer lichens.

Dynamics of decrease of the gamma dose rate in air in rural settlements of the Bryansk region (Russia) in the remote period after the Chernobyl accident

The aim of this study was to determine the dynamics of decrease of the dose rate of gamma radiation in air from 137Cs in typical rural locations in the remote period after the Chernobyl accident. The dose rate measurements were performed in the areas of 15 settlements of the Zlynka, Klintsy and Novozybkov districts of the Bryansk region of Russia in the period 1998–2012. After the accident in 1986, the density of contamination of the territory with 137Cs in all settlements was higher than the value of 555 kBq/m2 . Monitoring measurements of the dose rate were performed in eight locations commonly used in assessing the radiation doses to the rural population after the Chernobyl accident: 1) virgin soils (meadows) located outside settlements, 2) virgin soils located inside settlements, 3) forests, 4) arable fields, 5) kitchen gardens, 6) other ground surfaces (earthen yards next to residential buildings), 7) single-story wooden houses, 8) asphalted areas (streets, roads, courtyards next to residential buildings). The number of observation sites in individual locations ranged from 6 to 19 (a total of 103 sites). Series of measurements at individual sites were launched in the period 1998–2001 and completed in 2009–2012. On average, the duration of the series was 11.1 years. The measurements were made in the spring-autumn period annually (in some years at some sites two to three times a year) using a portable gamma-ray spectrometer-dosimeter. In the initial period of the study (1998–2001), the values of the absorbed dose rate in air from 137Cs were in the range from 40 to 2020 nGy/h. The maximum values were recorded in virgin meadows and forests, and the minimum ones were observed inside houses and over asphalted surfaces. By the end of our series of observations (2009–2012), the dose rate decreased at all sites, by an average of 33% (range 6–64%). The values of the ecological period of half-reduction of the dose rate, calculated for individual sites, ranged from 14 to 320 years and averaged 34 years (virgin soils located outside settlements), 30 years (virgin soils located inside settlements), 37 years (forests), 93 years (arable fields), 99 years (kitchen gardens), 33 years (other earth surfaces), 45 years (wooden houses), 60 years (asphalted areas). The deduced values of the rate of decrease of the dose rate of gamma radiation in the air in the surveyed locations were used to estimate the ecological period of the half-reduction of the effective external dose for rural population living in wooden houses. On average, this period was equal to 50 years. Given the radioactive decay of 137Cs, we can expect that the external dose from Chernobyl 137Cs to the rural population will decrease by approximately 4% per year. Our estimate of the rate of decrease of the external effective dose from 137Cs in the remote period after the Chernobyl accident is in agreement with the estimates that were previously given by other authors for the slow component of decreasing external doses from 137Cs to adults living in rural settlements of the Bryansk region.

Accumulation of radioactive caesium in the Japanese eel Anguilla japonica in Northeast Japan after the Fukushima nuclear accident

ABSTRACT The unpredicted nuclear accident by the Fukushima Daiichi Nuclear Power Plant (F1NPP) is a global concern for human health and ecosystems. In the present study, five-year fluctuations and accumulations of Cs, 134Cs and 137Cs in the Japanese eel were examined in Northeast Japan. The eel is one of the most important research subjects in fishery resources in Asia. The total radioactive Cs, 134Cs and 137Cs levels in the fish gradually decreased throughout the five-year study period after the F1NPP accident. A faster decay rate was found for 134Cs (10–15%) for five years after the F1NPP accident, and the decay of 137Cs (30–90%) was slower during the five years. The difference of decay rates between radiocaesiums might be explained by their different half-lives. The F1NPP derived 134Cs contamination might cease unless fresh input may be detected, and 137Cs might still be distributed and remain in the natural environment.

Зміна вмісту 137CS у корі крушини ламкої (Frangula Alnus Mill.) у вологих суборах лісів Полісся України з часу аварії на ЧАЕС

Досліджено динаміку вмісту 137Cs у корі крушини ламкої у лісах Житомирського Полісся з часу аварії на ЧАЕС (1991-2018 рр.). Відзначено істотне зменшення величини питомої активності 137Cs у корі крушини ламкої на постійних пробних площах за період спостережень (27 років) – від 4 до 38 разів, тобто темпи зниження питомої активності 137Cs у корі крушини ламкої на різних постійних пробних площах відрізняються у широких межах. Це можна пояснити особливостями екологічних умов кожної пробної площі, а також недосконалістю методичних підходів до відбору зразків. Зменшення питомої активності радіонукліда в корі крушини ламкої зумовлено: природним розпадом 137Cs у ґрунті та в самій корі; жорсткішим закріпленням радіоактивного елементу у ґрунті; зменшенням активності радіонукліда у ґрунті завдяки його надходженню до чисельних компонентів лісових біогеоценозів. Також відзначено зниження рівня щільності радіоактивного забруднення ґрунту – від 2,2 до 3,8 раза, що пояснено розпадом 137Cs, його жорсткішим закріпленням у ґрунті та переміщенням його частини до лісових рослин. Зазначено особливості методичних підходів до відбору зразків ґрунту для визначення величини щільності радіоактивного забруднення ґрунту, – враховуючи вертикальну міграцію 137Cs у нижчі шари ґрунту, тепер зразки ґрунту необхідно відбирати завглибшки 25 см (на відміну від відбору зразків ґрунту завглибшки 10 см). Виявлено сучасні рівні радіоактивного забруднення та встановлено залежність між щільністю радіоактивного забруднення ґрунту та вмістом радіонукліда а корі крушини ламкої. Простежено лінійну залежність збільшення концентрації 137Cs у корі крушини із збільшенням величини щільності радіоактивного забруднення ґрунту. Крушину ламку віднесено до рослин, які помірно накопичують 137Cs.

Quantification of dissolved and particulate radiocesium fluxes in two rivers draining the main radioactive pollution plume in Fukushima, Japan (2013–2016)

Radionuclides released by the accident at the Fukushima Daiichi Nuclear Power Plant included 137Cs (Cesium-137) and 134Cs (Cesium-134), which were deposited on land as a result of fallout and concentrated in the uppermost 2–5 cm of the soil. In this study, river monitoring was conducted for 3.5 years to quantify dissolved and particulate radiocesium fluxes in the Mano and Hiso Rivers in Fukushima Prefecture from 2013 to 2016. Total 137Cs export was estimated to be 191 GBq from the Hiso River and 26 GBq from the Mano River during the 3.5-year study. Annual particulate 137Cs export during rainfall events accounted for 90–98% of total 137Cs export. Annual dissolved 137Cs export during rainfall events accounted for 1.5–3.3% of total export. The annual sum of particulate and dissolved 137Cs exports during low-flow periods accounted for 0.6–6.5% of total export. Hence, radiocesium was redistributed mainly by transport of particulate radiocesium bound to suspended sediments. During the study period, 0.7% and 0.6% of the 137Cs initially deposited on soil were exported by the Hiso River and Mano River, respectively. The slopes of regression lines relating fine suspended sediment concentrations and particulate 137Cs concentrations in river water declined from 2013 to 2016 by 79% for the Hiso River and 83% for the Mano River. Especially noteworthy was a sharp decrease of the annual mean 137Cs concentration of SS in 2016. This decrease was much greater than the decrease that would have been expected from the physical decay of 137Cs and was probably related to changes of soil erosion processes due to heavy rainfall and the effects of decontamination efforts in 2015.

137Cs activity in Sweden after the Chernobyl Nuclear Power Plant accident in relation to quaternary geology and land use

After the Chernobyl Nuclear Power Plant accident 137Cs was deposited in Mid-Sweden, with the highest activity in Gävle municipality. We compared aerial measurements of 137Cs on the ground over time in Gävle municipality since 1986. Maps of soil types and land use were used to analyse the decrease in activity of 137Cs. A spatial pattern was identified where the reduction of activity was greater in sand than in organic soil. For land use the reduction was greater in urban areas than in forests, with agricultural land in between. Long-term external radiation from 137Cs depends not only on the physical decay of 137Cs but also indirectly on geology, and this should be considered when calculating external radiation doses to individuals in epidemiological studies.

Total cancer incidence in relation to 137Cs fallout in the most contaminated counties in Sweden after the Chernobyl nuclear power plant accident: a register-based study

ObjectivesTo determine the total cancer incidence in relation to a 5-year exposure to caesium-137 (137Cs) from the 1986 Chernobyl nuclear power plant accident.MethodsA closed cohort was defined as all individuals...

Energy and intensity of gamma-transitions in the decay of 137-Cs

Energy and intensity of gamma-transitions in the decay of 137-Cs

Comparative Study between Lead Oxide and Lead Nitrate Polymer as Gamma-Radiation Shielding Materials

In this work, the Styrene-butadiene rubber (SBR)/lead oxide and the Styrene-butadiene rubber (SBR)/lead nitrate composites were prepared as gamma-radiation shielding materials. The investigated materials were prepared with three different weight percentage of lead oxide and lead nitrate (30, 50 and 70 wt%). The mass attenuation coefficients (μm) for all composite samples were measured experimentally at 511 and 661.6 keV photon energies. The measurements were made by performing transmission experiments with a 3'' × 3'' NaI (Tl) scintillation detector, which had an energy resolution of 7% at 0.662 MeV for the gamma-rays from the decay of 137Cs. The effective atomic numbers (Zeff) and the effective electron densities (Neff) were determined experimentally. Also they were determined theoretically using the obtained μm values for the studied composites samples by WinXCom program. The obtained results show that the experimental values of the composites are found to be in a good agreement with the theoretical values. It is recognized that the mass attenuation coefficient (μm), effective atomic numbers (Zeff) and the effective electron densities (Neff) are increased in the composite samples which contain lead oxides than which contain lead nitrates. Finally, the Styrene-butadiene rubber (SBR)/lead oxide is better than Styrene-butadiene rubber (SBR)/lead nitrate polymer as gamma radiation shielding.

PERIODICITY ANALYSIS OF GAMMA RADIATION MEASUREMENTS IN THESSALONIKI, NORTHERN GREECE, IN THE PERIOD 1988-2015.

Gamma radiation measurements were performed during the last 27 y, starting from 1988, with a NaI(Tl)-based Xetex 501A radiation monitor located outside the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki in Northern Greece, and a time series was created. Measurements were also performed in the same place during 1995-98 and 2013-15 with portable high purity germanium (HPGe) detector. The total absorbed dose rate in air decreases exponentially with time. The total absorbed dose rate in air is the sum of the gamma dose rates due to (1) uranium series, (2) thorium series, (3) 40K and (4) 137Cs (due to the Chernobyl accident). In addition, a small contribution due to cosmic radiation is measured by the radiation monitor. From the time-dependence measurements with the HPGe detector, it was found that the time dependence of the absorbed gamma dose rate in air due to (1) uranium series, (2) thorium series and (3) 40K is quite constant. On the contrary, gamma dose rate due to 137Cs decreases exponentially with an effective half-life (t½) of ∼13.5 y, stronger than expected due to the natural decay of 137Cs. Time series analysis of the mean monthly total absorbed dose rate in air was performed. Fourier analysis reveals several periodicities, and applying Zhao-Atlas-Marks transform unravels the time distribution of those periodicities. There are three main discernible periodicities: 12 ± 0.2, 42.3 ± 2.9 and 53.2 ± 3.2 months. One of them is of a seasonal character (annual cycle) and can be linked to seasonal atmospheric variations and is strongly visible from 1988 to 2002 and 2008 to 2014. The other two (42.3 ± 2.9 and 53.2 ± 3.2 months) were found to be also related to meteorological parameters (air temperature), and they were very intense during the years 2002-4 when the annual periodicity was weak. Apart from the three main periodicities, there are also four others (14.7, 18.6, 21.3 and 27.3 months) with lower magnitudes; of which, three agree well with literature data periodicities in solar activity. Different possible mechanisms that can influence the gamma radiation measurements, due to solar activity, were discussed.

Production of highly-enriched 134Ba for a reference material for isotope dilution mass spectrometry measurements

Isotope dilution mass spectrometry (IDMS) is an analytical technique capable of providing accurate and precise quantitation of trace isotope abundance and assay providing measurement uncertainties below 1 %. To achieve these low uncertainties, the IDMS method ideally utilizes chemically pure “spike” solutions that consist of a single highly enriched isotope that is well-characterized relating to the abundance of companion isotopes and concentration in solution. To address a current demand for accurate 137Cs/137Ba ratio measurements for “age” determination of radioactive 137Cs sources, Idaho National Laboratory (INL) is producing enriched 134Ba isotopes that are tobe used for IDMS spikes to accurately determine 137Ba accumulation from the decay of 137Cs. The final objective of this work it to provide a homogenous set of reference materials that the National Institute of Standards and Technology can certify as standard reference materials used for IDMS. The process that was developed at INL for the separation and isolation of Ba isotopes, chemical purification of the isotopes in solution, and the encapsulation of the materials will be described.

Determining photon energy absorption parameters for different soil samples.

The mass attenuation coefficients (μs) for five different soil samples were measured at 661.6, 1173.2 and 1332.5 keV photon energies. The soil samples were separately irradiated with 137Cs and 60Co (370 kBq) radioactive point gamma sources. The measurements were made by performing transmission experiments with a 2″ × 2″ NaI(Tl) scintillation detector, which had an energy resolution of 7% at 0.662 MeV for the gamma-rays from the decay of 137Cs. The effective atomic numbers (Zeff) and the effective electron densities (Neff) were determined experimentally and theoretically using the obtained μs values for the soil samples. Furthermore, the Zeff and Neff values of the soil samples were computed for the total photon interaction cross-sections using theoretical data over a wide energy region ranging from 1 keV to 15 MeV. The experimental values of the soils were found to be in good agreement with the theoretical values. Sandy loam and sandy clay loam soils demonstrated poor photon energy absorption characteristics. However, clay loam and clay soils had good photon energy absorption characteristics.

Remote examination of radioactive wastes using γ-ray spectrometry

Places of location of some γ-ray sources on the site for temporary storage of solid radioactive wastes of SevRAO OF-2 Federal State Unitary Enterprise (Gremikha settlement, Murmansk oblast, Russia) were determined using a procedure for remote determination of radiation source coordinates with a Cartogam γ-imaging system. The γ-ray spectra from these radiation sources were recorded using the remote procedure with an ISOCS spectrometric complex. In particular, the isotope composition of γ-active containers Bet8, TK113, L18, and L20 was determined. The main technogenic γ-radiation from these objects is associated with the decay of 137Cs and, to a lesser extent, with the decay of 60Co, 152Eu, and 154Eu. For the Bet8 container, its activity content was estimated (∼1014 Bq). The dependence of the specific activity of the soil surface layer in the guard zone in front of the waste storage site on the distance from the site was determined with a 7 m step. The specific activity considerably decreases with an increase in the distance from the site (from 15–28 kBq kg−1 at a distance of 3 m to 1–2.8 kBq kg−1 at a distance of 10–24 m).

137Cs in natural ecosystem components within the 30-km impact zone of the Smolensk nuclear power plant

The accumulation and redistribution of 137Cs in natural ecosystems within the 30-km impact zone of the Smolensk nuclear power plant (SNPP) are analyzed. It is shown that the radioactive pollution of this territory is mainly due to the Chernobyl-derived radioactive fallout. However, the radioactive decay of 137Cs from the Chernobyl disaster is partly compensated for by the 137Cs technologic emission from the SNPP. The highest rate of the vertical migration of 137Cs is typical of the bog phytocenoses and deciduous forests. The components of biota may be ranked by their capacity for 137Cs accumulation as follows: higher fungi > mosses > herbs and shrubs > trees. The organisms and their parts that may serve as bioindicators of the modern radioactive contamination of the territory have been identified. These are the assimilative organs and bark of the trees, various fern species among herbs, sphagnum mosses and Pleurozium schreberi (among mosses), and Typolius felleus among higher fungi.

Recovery and purification of 4.66 TBq(126 Ci) of 137Cs from a 20-year-old spent sealed source

An attempt to recover and purify 4.66 TBq(126 Ci) of 137Cs as solution from a 20-year-old doubly encapsulated sealed source containing 137CsCl was made successfully. The primary capsule was first cut open to retrieve the secondary capsule. The top end of the secondary SS capsule was then cut to render it as an open cylinder and the 137CsCl pellet inside was dissolved in small aliquots of water. Each aliquot of the 137CsCl solution was dispensed into glass vials, sealed, assayed and stored. Barium formed during the radioactive decay of 137Cs was removed by carbonate precipitation. Chloride was removed by heating with HNO 3 and evaporation. About 91.8% of the total activity could be recovered and used subsequently for making brachytherapy sources.

Radionuclide tracing of water masses and processes in the water column and sediment in the Algerian Basin

Caesium-137 and 239,240PU were analysed in the water column along the Algerian coast. The 137Cs activity concentration in surface water increased from the west to the east from 1.6 to 3.3 mBq L −1, documenting a presence of Modified Atlantic Water (MAW) in the region. Higher concentrations observed in deep waters may be due to an intrusion of Levantine Intermediate Water (LIW), which has been carrying higher levels of 137Cs from Chernobyl accident. The 239,240Pu sub-surface concentration peaked at about 250 m water depth as a result of biogeochemical processes in the water column. The observed 239,240Pu/ 137Cs activity ratio at the surface (0.003) was significantly lower than that in global fallout (0.04). This decrease exceeds that expected from radioactive decay of 137Cs, and confirms that Pu due to its adsorption on sinking particles is more effectively removed from surface layers than is 137Cs. An increase of the 239,240Pu/ 137Cs activity ratio with depth suggests that 239,240Pu, similarly as 137Cs, should be also transported by advection to maintain the observed ratios in deep waters. An intrusion of LIW may enhance therefore both the 137Cs and 239,240Pu concentrations in deep waters. The average 238Pu/ 239+240Pu activity ratio in seawater was 0.03 ± 0.02, confirming a global fallout origin of Pu in the Algerian Basin. Caesium-137 and 239,240Pu inventories in the water column were estimated to be from 2.7 ± 0.5 kBq m −2 to 3.8 ± 0.7 kBq m −2, and from 13.8 ± 2.6 Bq m −2 to 41 ± 7 Bq m −2, respectively. The 137Cs massic activities in surface sediment were almost constant, the average activity was 9.0 ± 0.8 Bq kg −1. Sedimentation rates obtained using the 210Pb method were from 0.1 to 0.7 cm y −1, and resulting penetration depths of 137Cs in the sediment cores were from 15 to over 40 cm. The 137Cs peaks found in the sediment cores were associated with the Chernobyl accident (1986) and global fallout (1964). The 137Cs inventories in the sediment were increasing from the west (180 Bq m −2) to the east (350 Bq m −2).