G. Barci-Funel

Sedimentation rates in Lake Chapala (western Mexico): possible active tectonic control

Abstract Lake Chapala, a major natural freshwater reservoir, belongs to the watershed of the Rio Lerma, which originates from the Mexico City area, 450 km eastwards. The east–west-trending Lake Chapala basin is located on the active tectonic feature Citala rift. Sediments of cores collected in the lake were studied for their 210Pb, 226Ra, 137Cs and 239–240Pu activities in order to evaluate sedimentation rates. Profiles of magnetic susceptibility allowed stratigraphic correlations to be made since some fine levels display more or less high susceptibility values. This allows an average sediment accumulation rate to be calculated. The sediment accumulation rate was calculated assuming that, the activity at the interface of a defined site is constant in the course of time, since any global decrease or increase in the rates could not be observed. The direct flux of atmospheric 210Pb was evaluated from the inventory in a horizontal soil: 0.25–0.3 dpm g−1. Except from two cores at the west, the fluxes to sediment were higher than the direct atmospheric flux. The sedimentation rates temporal variations along the cores seem to be mainly related to annual precipitation changes, with rates lower during the dryness epochs (1945–1957 and 1979–1991). The rates measured in the western part of the lake range approximately from 1 to 2 mm year−1. The lowest rates in the central and eastern areas are higher than 2.4–2.5 mm year−1 and exceed 3.5 mm year−1 (0.066 g cm−2 year−1) near the Rio Lerma prodelta. As the lake is not deeper eastward than westward, it can be suggested that relative subsidence, related to the active tectonic framework, compensates the higher sedimentation rate.

Reinvestigation of the decay of the long-lived odd-odd 176Lu nucleus

Abstract The decay of the naturally occuring 176Lu nucleus has been reinvestigated using coaxial and planar HPGe detectors. Energy and intensity values of the three main γ rays are given with an improved precision. The 401.04-keV γ-ray was measured in single γ-spectra and its intensity I = 0.48% was deduced. The 176Lu half life was measured using a 133Ba standard γ-activity source mixed with the Lu2O3 sample, found to be T 1 2 = (3.73 ± 0.05)×10 10 years. A revised 176Lu decay scheme has been derived.

Study of the transfer of radionuclides in trees at a forest site

The transfer of radionuclides such as 137Cs and 90Sr from soil to trees (conifers) was studied in a forest area, the Boreon massif, 30 km north of Nice in South Eastern France. This area has been highly contaminated after the Chernobyl accident. Besides the γ-emitting fission products, the α-emitters 238Pu and 239+240Pu and the pure β-emitter 90Sr were measured in different parts of the studied trees (roots, branches, twigs, etc.). As has already been reported by other authors, the radionuclide activities in the tree rings are not correlated with the fallout deposition. They were found varying according to the sap flux in the tree and higher in sapwood than in heartwood. For cesium the root absorption was found to be lower than the atmospheric deposition. Soil-to-plant concentration factors were calculated for 137Cs, 90Sr and 239+240Pu.

One step ion exchange process for the radiochemical separation of americium, plutonium and neptunium in sediments

A radiochemical separation is presented for americium, plutonium and neptunium from sediment samples by using an unique anionic exchange process. An oxidation-reduction step was introduced in the classical procedure of the radiochemical determination of transuranic elements in order to control the valence of the separated elements.

Radioanalytical determination of actinides and fission products in Belarus soils

Alpha emitting actinides such as plutonium, americium or curium were measured by alpha-spectrometry after radiochemical separation. The short range of alpha-particles within matter requires, after a pre-concentration process, a succession of isolation and purification steps based on the valence states modification of the researched elements. For counting, actinides were electrodeposited in view to obtain the mass-less source necessary to avoid self-absorption of the emitted radiations. Activity concentrations of gamma-emitting fission products were calculated after measurement with high purity germanium detectors (HPGe). These different methods were used to analyse soils sampled in the Republic of Belarus, not far from the Chernobyl nuclear plant.

Plutonium, americium and cesium records in sediment cores from Blelham Tarn, Cumbria (UK)

Abstract238Pu, 239-240Pu, and 241Am were measured, by α-counting after radiochemical separation, in two lake sediment cores. The profiles of these transuranics were compared to those of the fission product 137Cs. Datation of nuclear events and data on behavior of the studied elements were deduced.

Radionuclides in macro algae at Monaco following the Chernobyl accident

Samples of macro algae,Codium tomentosum (green),Corallina mediterranea (red),Sphaerococcus coronopifolius (red) andDictyota dichtoma (brown), were collected off Monaco during 1984 and 1988 and analyzed for gamma-emitting radionuclides and transuranium elements. Due to the Chernobyl accident, increased radioactivity in the atmosphere at Monaco was recorded on 30 April 1986 with maximal activity concentrations on 2–3 May. The maximal activity concentrations in sea water occurred on 5–6 May and in the algae on 11 May. The decrease of activity concentrations can be described after May 11 as a single exponential relationship, where elimination rates for different radionuclides and different species specific to the environment can be calculated.The elimination rates thus observed correspond to mean residence times between 70 and 370 days corrected for physical decay. The concentration factors were also estimated and the highest values were found for131I,129Tem, and 110 Agm and lowest for radiocaesium and140Ba. The red algaeSphaerococcus coronopifolius showed generally higher concentration factors than green and brown algae.Regarding transuranium elements, a theoretical contribution from the Chernobyl accident can be made but only242Cm was detected in the algae above previous levels before the accident, due to the relatively small fallout of transuranics.

Sequential radiochemical separations from Alpine Wetland soils (Boréon, France) with emphasis on 90Sr measurement

A radiochemical procedure to extract plutonium, americium and strontium from soils is presented. Strontium was separated from americium and plutonium fraction at the beginning of the method to increase the Sr recovery. The studied soils coming from an Alpine wetland site contain a big amount of iron which was eliminated by an oxalate precipitation before the column step. The hydroxide precipitation should be made by adding iron of known quantity to avoid interference. The procedure was validated by reference soils from IAEA. Plutonium-238, 239, 240, 241Am, 90Sr and 137Cs activities are given and some isotopic ratios are calculated in order to know the origin of the radionuclides.

Indirect determination of241Pu activity in soils using low energy photon spectrometers

Actinides activity levels deposited after the Chernobyl accident on the coastal Mediterranean area at Monaco have been recently measured (1). The values obtained are low. However, our γ-measurements on humic soils from the southern Alps revealed high137Cs level contamination areas and urged us to evaluate241Pu activity levels. The indirect determination of241Pu was based on the γ-activity measurement of the241Am in situ ingrown.

Simultaneous detection of short-lived 201Tl, 99Tcm and 131I isotopes in sewage sludge using low energy photon spectrometry

Abstract The low-energy photon spectrometry has been applied to measure the activity concentration of radionuclides in sludge samples from the sewage treatment plant in Nice city. Short-lived 201 Tl, 99 Tc m and 131 I isotopes which are currently used in nuclear medicine were detected at levels included between 1 and 250 Bq/kg. 134 Cs and 137 Cs due to the Chernobyl fallout are also detected.