A survey was initiated to depict and compare the present activity levels in pulp mill liquors from various mill locations. The 137Cs levels in pulp mill liquors were compared with the mill location and the deposition pattern of the Chernobyl fallout and nuclear weapons fallout. The large input of wood (about 2500 m3 per day) to an average Nordic Kraft mill and the relatively long-term retention time for radiocesium in the Kraft mill recovery cycle enables representative sampling of substances directly related to the activity concentration in wood.
In the paper are presented results of potassium, uranium, thorium and radium measurements performed on the natural marine sediment sample SD-N-1/2 in the framework of the IAEA-organized worldwide intercomparison exercise. Analytical methods applied in this exercise were evaluated for performance and significance of the observed discrepancies are discussed in the light of statistical and operative criteria. Possible sources of error have been identified in alpha and gamma spectrometric measurements and suggestions are given about how to avoid them. Well characterized reference materials based on natural matrices have been shown helpful in achieving better data comparability in low level measurements of environmental radioactivity.
A new method of227Ac determination is based on total sample decomposition, followed by preconcentration as oxalate and hydroxides, and purification from thorium isotopes and rare earths on ion-exchange columns with nitric acid. The actinium is electroplated on stainless-steel discs with near 100% yield from a water/propanol medium and measured by alpha spectrometry.225Ac is used as a yield monitor. An immediate first count gives overall tracer recovery (typically around 80%). A second count two months later gives a sensitive measure of227Ac through its decay products at 5.5–6.1 MeV. Analysis of reference samples gave satisfactory results.
A radiochemical procedure followed by alpha spectrometry has been developed for the determination of237Np present at low activity concentrations in seawater. The analytical procedure is based on concentration of actinides from 1800 1 sea water samples by hydroxide precipitations. Neptunium is isolated by ion exchange, fluoride precipitation and extraction with TTA (thenoyltrifluoroacetone). As a radiochemical yield determinant239Np or235Np is used. Neptunium is electroplated onto stainless steel discs before alpha-spectrometry for about 10 days. The procedure allows for sequential separation of plutonium, americium, technetium and radiocaesium together with neptunium. The radiochemical yield for neptunium is only 20–50%, but the procedure has been applied with success on several samples contaminated with237Np at fallout or close to fallout levels.
A field experiment study was performed at the rural site of South-East Lithuania. The main tasks of the study included an
evaluation of the peculiarities of partition of239Pu in soluble (239Pu(NO3)4,239PuCl3) and insoluble (239PuO2) forms in soddy and forest soil horizons. The results of durable experiments (418 and 326 days) have shown that from 44.1%
to 92.2% of239Pu of investigated chemical forms were accumulated in the top (0–5 cm) soil layer. Some share (5.7–39.2%) of plutonium from
studied chemical forms was found in the 5–20 cm layers of studied soil samples (columns). Obtained distribution of plutonium
in soil layers may be attributed to the consideration that the migration rate to the soil depth for plutonium is 0.1–1.0 cm·y−1 but for some part of plutonium 10 times higher migration rate is characteristic as well. Plutonium transfer factor (TF) to
the grassland plants was calculated, the values ranged from 10−2 to 10−1.
Evidence for the presence of111Ag in Chernobyl fallout at Monaco is given. This fission radionuclide has not been previously reported in Chernobyl fallout. Peak values were as high as 1.9 Bq m–3. Arguments are presented that the observed110mAg content in the fallout originated from volatilisation of silver neutron flux monitors in the reactor rather than production by other nuclear reactions.
The environmental contamination of transuranics following the Palomares accident in 1966 (Southern Spain) has been continuous monitored on land and scientific programs are still running. The study of the land to sea transfer of the contamination started in 1986, focussed on the depositional history recorded in marine sediments. At the continental shelf, south of the mouth of the Almanzora river, enhanced levels of plutonium and americium were found which could be related to the accident. Additional analysis of marine sediments, collected far from the impact point, showed the presence of a hot particle. The study of the chronology of this sediment core and the isotopic ratios are given in this paper to assess the origin and pathway of the particle. The route of this particle was found to be the aerial transfer at the time of the accident.
The deposition of transuranium elements in Sweden following the Chernobyl accident was investigated through the analysis of carpets of lichen-and moss-samples and also air-filters and precipitation. The impact of transuranium elements was small compared to that of radiocesium. The deposition of239+240Pu was, as for other actinides, inhomogeneously distributed and ranged from 0.1% to 100% of the inventory in 1986 from nuclear detonation tests. The activity ratio of239+240Pu/137Cs was between 10–3 and 10–6 in comparison to 10–2 for nuclear test fallout. The activity ratios of241Pu,242Cm,238Pu,243+244Am and239+240Pu were about 86, 14, 0.47, 0.14, and 0.13 respectively, but large variations were observed. The results from Sweden were compared with those found in South Finland, Denmark and Southern Europe. The deposition over Scandinavia originated from the initial explosion at Chernobyl, which contained relatively higher amounts of actinide elements than the second emission, which occurred a few days later and was a result of actions taken to bring the fire under control.
Authors:S. Ballestra, G. Barci, E. Holm, J. Lopez and J. Gastaud
This paper describes a radiochemical method for the determination of99Tc in large volumes of rain, river and seawater. The procedure is based on the reduction of technetium to the +4 oxidation state with potassium disulfite in a slightly acidic medium, followed by iron hydroxide precipitation. After oxidation to the +7 oxidation state, the technetium fraction is purified with iron hydroxide and calcium carbonate precipitations. Technetium (+7) is extracted with TBP (xylene) in 3M H2SO4, back extracted in 2M NaOH or ammonia, and the electrodeposition is made in 2M NaOH or H2SO4/NH4OH medium at pH 5–6. The radiochemical yield is determined by gamma counting of the 140 keV gamma ray from99Tcm.99Tc is counted on an anti-coincidence shielded GM-gas flow counter. The purity of the99Tc plated samples is checked by alpha and beta spectrometry using surface barrier detectors and by gamma spectrometry on Ge(HP) detector. The radiochemical yield of 50–150 l water samples is around 20–60%.
Authors:C. Greis, A. Düker, B. Allard, P. Roos and E. Holm
Fresh water from Lake Svartsjön, Sweden, was collected and four fractions were prepared: (1) adsorption on DEAE, (2) flocculation
with Ca2+, (3) co-precipitation with Fe hydrous oxide and (4) co-precipitation with Mn hydrous oxide. The plutonium level in the lake
is 65 fg/l (222 μBq/l), measured by ICP-QMS and ICP-SFMS. Pronounced accumulation in fractions (1) (34%) and (2) (66%), combined
with observed levels of organic matter indicate that plutonium is predominantly associated with organic matter. Measurements
of isotopic ratios indicate that 77% of the plutonium originates from weapons testing and the remaining appears to originate
from the Chernobyl accident.