Natural Decay Series Research Articles

Leaching of uranyl–silica complexes from the host metapelite rock favoring high radon activity of subsoil air: case of Castañar cave (Spain)

Castanar cave is a subterranean site with an outstanding natural environmental radioactivity. The maintaining of high radon activity of cave air and the detection of spatially anomalies of this gas in some cave emplacements, suggests that some natural geochemical processes are involved on the mobilization of radioactivity sources to cave environment, other than a simple exhalation of radon from the host-rock. The host rocks are interlaid dolostone–metapelite beds with radioactive nuclides of the three actinium, thorium and uranium decay series. In situ measurements on the spatial distribution of radioactivity, uranyl group’s luminescence and radon gas concentrations inside cave were main focus of this work to model lixiviation and deposition mechanisms of radioactive elements from the host rock to the karstic system. In addition, collected micro-samples were also analyzed by a multi-approach suite of analytical techniques: inductively coupled plasma mass spectrometry, environmental scanning electron microscopy with an attached X-ray energy dispersive system and spectral cathodoluminescence detector, thermoluminescence, Raman spectroscopy, X-ray diffraction, differential-thermal and thermogravimetry analysis, Alpha-spectrometry and Gamma-spectrometry techniques. The host metapelitic beds contain Zr(Hf)–Th(U)–Ti–P–REE phases such as zircon, xenotime-(Y), monazite-(Ce, La) and poly-metallic mineralization veins of hydrothermal origin. Carbonated host beds and speleothems show frequently chemical elements leaked from the upper host rock masses. The weathering leakage processes are favored by the existence of pyrite and limonite in the dolostone masses. The cave exhibits under UV lamps abundant hydrous silica–uranyl coatings covering carbonated speleothems with radionuclides of 238U natural decay series. The long-lived radio-nuclides of the radium radioactive decay chain are responsible of the continuous regeneration of radon gas inside cave. The experimental work was focused to identify origin and remobilization processes of radio-nuclides and their latte settlement into the cave environment associated to mineral phases of speleothems and cave deposits.

A Determination of the Concentration Level of Lead 210PB Isotope in Solid Samples for the Assessment of Radiation Risk Occuring in Coal Mines

Abstract Lead 210Pb, an element of the natural uranium radioactive decay series, is not currently considered a source of radiation risk, especially in a radiation protection system in underground mines in Poland. However, it could be a completely independent element of the radioactive series due to its physical and chemical properties. Routine measurements showed significantly higher than expected concentrations of 210Pb in underground radium rich sediments, based only on the radioactive decay law. This phenomenon implies a need of 210Pb concentration monitoring in such sediments. Nevertheless, the laboratory analysis of 210Pb by gamma radiation spectroscopy is connected with a particular hindrance, the self-attenuation of 210Pb radiation in samples. Current work describes a practical method for obtaining the self-attenuation correction factor in the case of 210Pb concentration analysis. Experimentally obtained correction factors range between 0.51–6.96 cm2/g. Neglecting this factor can cause a significant error or underestimations in radiological risk assessment.

Reaction of bentonite in low-alkali cement leachates: an overview of the Cyprus Natural Analogue Project (CNAP)

AbstractThe Cyprus Natural Analogue Project was carried out due to the requirement to support ongoing laboratory and modelling efforts on the potential reaction of the bentonite buffer with cementitious leachates in the repository engineered barrier system. Although it is known that the higher pH (12.5–13) leachates from ordinary Portland cement will degrade bentonite, it is unclear if this will also be the case for the lower pH (10–11) leachates typical of low alkali cements. Ongoing laboratory and underground rock laboratory programmes, which are currently investigating this, face the obstacle of slow kinetics and the production of short-lived metastable phases, meaning obtaining unambiguous results may take decades. It was therefore decided to implement a focussed natural analogue study on bentonite/low alkali cement leachate reactions to provide indications of the probable long-term reaction products and reaction pathways to provide feedback on the existing short-term investigations noted above and to ascertain if any critical path research and development needs to be instigated now. The results of the analyses presented here, in this short overview of the project, suggest that there has been very limited alkaline groundwater reaction with the bentonite. This is generally supported by both the geomorphological evidence and the natural decay series data which imply groundwater/rock interaction in the last 105 a.

Gamma-spectrometric analysis of high salinity fluids – how to analyze radionuclides of the thorium decay chain far from radioactive equilibrium?

Highly saline brines from a geothermal plant in Neustadt-Glewe, Germany, were investigated with respect to their radionuclide concentrations. The natural decay series in these fluids are far from radioactive equilibrium with main activity contributions from the radium isotopes (226)Ra, (228)Ra and (224)Ra. A general mathematical formulation for the coupled radionuclide activities within one decay chain is applied on the system (228)Ra…(212)Pb and tested on real samples in order to evaluate several radionuclide concentrations at the moment of sampling.

Monte Carlo based calibration of scintillation detectors for laboratory and in situ gamma ray measurements

The calibration of scintillation detectors for gamma radiation in a well characterized setup can be transferred to other geometries using Monte Carlo simulations to account for the differences between the calibration and the other geometry. In this study a calibration facility was used that is constructed from bricks of well-known activity concentrations of 40K and of radionuclides from the 238U- and 232Th-series. Transfer of the calibration was attempted to a Marinelli beaker geometry with the detector inside a lead shield and to an in situ application with the detector positioned on a sand bed. In general this resulted in good correspondence (within 5–10%) between the activity concentrations derived using the transferred calibration and activities that were derived by independent measurements. Some discrepancies were identified that were attributed to coincident summing in the natural decay series and interference of radon.

Chromatographic generator systems for the actinides and natural decay series elements

Abstract This work describes chromatographic radionuclide generator systems for the production of actinides and natural decay series elements. The generator systems begin with alpha emitting parent radioisotopes with half-lives (T 1/2) of greater than one year and produce alpha or beta emitting radioisotopes with half-lives of hours to days. Chromatographic systems were chosen to minimize radiolytic damage to chromatographic supports, preserve the parent activity for repeated use, provide high purity daughter radionuclide tracers, and to minimize or eliminate the need for evaporation of solutions of the parent or daughter nuclides. Useful secondary separations involving the daughters of the initial parent radionuclide are also described. Separation systems for 210Bi, 210Po, 211Pb, 212Pb, 223Ra, 224Ra, 225Ra, 225Ac, 227Th, 228Th, 231Th, 234Th, and 239Np are outlined in detail.

A first order assessment of the potential radiological impact of foodstuffs grown in a catchment area influenced by mining and mineral processing industries

Natural radioactivity is associated with the vast mineral resources in South Africa in such concentrations that the radionuclides from the natural uranium and thorium decay series are found to pose concern for public exposure to communities living around these areas. Consumption of water and food is usually the most important route by which natural radionuclides can enter the human body and assessment of natural radionuclide levels in different foods and diets is therefore important to estimate the intake of these radionuclides by man. Sensitive measurement of three major radionuclides (in addition to 238 U, 234 U, 232 Th, 226 Ra, 224 Ra and 223 Ra) is necessary to calculate the estimated annual dose with a high degree of certainty i.e. 230 Th, 210 Pb and 210 Po, while 231 Pa, 227 Ac and 228 Ra also require improved sensitivity. In order to evaluate the yearly dose due to an individual source at a screening level of 25 μSv/a, one is faced with a required lower limit of determination (LLD) of 0.1 to 0.5 Bq/kg for certain foodstuffs. In this study the potential radiological impact of foodstuffs grown in a catchment area influenced by mining and mineral processing industries in South Africa, was determined by measuring the natural radionuclides in a number of foodstuffs collected from the area. The radionuclides were measured by non-destructive techniques such as Instrumental Neutron Activation Analysis (INAA) and low background gamma spectrometry. The assessment of natural radionuclides in foods allowed us to evaluate the items that present the highest risk to the population, and compare this to the limits established by the National Nuclear Regulator (NNR). From the public’s point of view it is important to ensure the population that the contaminant levels in specific food as a result of mining activities, do not exceed the permissible limits. For the majority of the analysed foodstuffs, the estimated dose was less than 250 μSv/a. Overestimation of dose, due to poor measurement detection limits, was clearly indicated for some of the samples. For most of the analysed nuclides, suitable data for evaluation of the yearly dose at the screening level of 25 μSv/a was obtained by broad energy gamma analysis of ashed samples. However, nuclides such as 230 Th, 210 Po and 231 Pa has to be analysed by radiochemical separation through acid destruction of dried foodstuffs followed by individual element separations to provide suitable data with a low enough LLD not to result in an overestimation of the calculated dose.

Elements of Natural Radioactive Decay Series in Iranian Drinking Water and Cigarettes

The uranium (238U) decay series provides the most important isotopes of elements radium (226Ra), radon (222Rn), and polonium (210Po) with half-lives of about 1600 years, 3.8 days, and 140 days, respectively. Although the chemical structure of radium is very similar to calcium, the fact that it produces a radioactive gas (radon) complicates its handling in the laboratory and natural environment. In this study, we used the average concentrations of naturally occurring radionuclide 226Ra in drinking water at different parts of Iran to estimate the annual effective dose. In the other part of the study, we measured the concentrations of 210Po in Iranian cigarettes to estimate the internal intake of this radionuclide and its concentration in the lung tissues of smokers. The results indicate that the average concentration of 226Ra in Iranian drinking water was below the 100 mBq L(-1) recommended by the World Health Organization while the average concentration of 210Po and 210Pb in Iranian cigarettes was relatively high in comparison with other cigarettes found on the market.

Commentary to the paper Assessment of annual effective dose from natural radioactivity intake through wheat grain produced in Faisalabad, Pakistan

Tufail et al. [1] studied and reported the concentrations of naturally occurring radionuclides (K, Ra and Th) in wheat grains. The method that was used was gamma-ray spectroscopy. Determining the activity concentration of Th by gamma-ray spectroscopy is, however, not possible. The two gammas from Th (63.8 and 141 keV) exhibit very low intensities (0.26 and 0.02%, respectively) and cannot hence be separated from the background using the set-up described in the paper. It is, hence, probable that the authors used the gammas from thorium series radionuclides of Ac, Pb or Tl. The activity of Ac follows that of Ra whereas the activity the latter two that of Th (and/or Ra). In short, they did not measure Th. The authors listed the activity concentrations of Th in wheat reported by e.g. Scheibel et al. [2] and PieterzakFlies et al. [3] and found that ‘‘activity values for K and Th in Indian wheat grain samples are quite comparable to that of studied samples’’. This is true with respect to Scheibel et al. [2], who employed the same erroneous method in analyzing Th as the authors did. The survey carried out by Pieterzak-Flies et al. [3] is, however, rigorous and the analyzing methods used are correct. The authors failed to recognize the activity concentration reported by Pieterzak-Flies et al. [3] was expressed as mBq kg, not as Bq kg. Market basket study of K, U and Th in foods sold in Pakistan has been carried out previously by Akhter et al. [4]. The ICP-MS method used for determining Th in this study was correct and the reported values were in-line with e.g. values compiled in UNSCEAR 2000. The effective dose to Pakistani adult population from Th from all food was 0.8 lSv a which is in gross contrast to the value reported by Tufail et al. [1] which was 43.1 lSv a from wheat consumption only. I would like to point out that this commentary also applies to several other papers on this topic (that I find fruitless to list here). Regrettably, it is a common mistake to assume full equilibrium of natural decays series’ radionuclides in biological samples, such as food. Radium uptake by vegetation is much more efficient than that of actinoids. This applies also to intake by livestock. Caution must therefore be exercised when calculating results of the natural decay series.

Influence of the physico-chemical properties of Selangor soil series on the distribution coefficient (K d-value) of 226Ra

Ra is a member of the 238 U natural decay series and is one of the most important isotope to be determined among the naturally occurring nuclides in environmental samples. In order to evaluate the radiation dose from 226 Ra, it is important to know its mobility in different types of soils. The aim of the present study is to quantify the influence of physico-chemical soil properties on 226 Ra adsorption. The distribution coefficients (Kd-value) of 226 Ra in Selangor soil series samples were measured in one core, at three depth levels to evaluate the adsorbability of 226 Ra. The soil samples were spiked with 226 Ra tracer and the activities of 226 Ra in the separated phase from batch sorption test were measured by a low background but high efficiency well-type HPGe detector. Several physico-chemical soil properties were also char- acterised for each soil samples. Pearson's correlation and stepwise multiple regression test were applied at the 0.05 level of significance throughout all analysis to determine the relationships and influences between distribution coefficients (Kd-value) of 226 Ra with physicochemical soil properties for the Selangor soil series. The observed Kd value was in the range of 50.55-172.28 mL g -1 (mean: 93.20 ± 46.99 mL g -1 ). The regression showed that the highest positive correlations were observed for organic matter (OM) and cation exchange capacity (CEC) (r = 0.96**, 0.81**, respectively) with Kd-values. The results indicate that the stepwise multiple regression model incorporating the soil's OM and CEC accounts for 98% of the variability in distribution coefficients of 226 Ra.

DECSERVIS-2: A tool for natural decay series mass flow simulation

After the publication of “DECSERVIS: a tool for radioactive decay series visualisation” we have further developed our DECSERVIS software. With the new tool DECSERVIS-2 one can simulate radioactive decay chains in open systems, i.e. when the concentrations of nuclides change also due to mass flows. Decay chains can be simulated under continuous and successive nuclide mass flow events into and out from the system and in freely determined time intervals. Simulation output for the entire decay chain (nuclide activity, mass, number of nuclides, nuclide ratios) can be presented as a function of time with various graphical presentations such as solid curve and column diagrams or animation. In this paper we introduce DECSERVIS-2 and demonstrate its use with simulation examples. DECSERVIS-2 is easy to use and has been designed with an eye on the demands of teaching.

Natural radioactivity of 226Ra and 228Ra in thermal and mineral waters in Croatia

Thermal waters are known as valuable natural resources of a country. They contain certain degree of natural radioactivity attributable to the elements of the uranium and thorium natural decay series. Among these elements, the most radiotoxic and the most important is radium that exists in several isotopic forms (226Ra and 228Ra). The focus of attention was the content of radium in samples of thermal and mineral spring water from several spas in Croatia. These waters are mainly used for medical, bathing and recreational purposes, and some of them are used for drinking. Measured activity concentrations of 226Ra ranged from 87 to 6200 mBq l(-1) which, in some springs, exceed the maximal permissible level of 1 Bq l(-1) for drinking water. Measured activity concentrations of 228Ra ranged from 23 to 3480 mBq l(-1). The study showed that radium content for the investigated thermal and mineral waters is below the levels at which negative consequences would arise due to ingestion.

Determination of Polonium-210 in various foodstuffs after microwave digestion

Natural radioactivity is associated with the vast mineral resources in South Africa in such concentrations that the radionuclides from the natural uranium and thorium decay series are found to pose concern for public exposure to communities living around these areas. The radiological impact of all operations is monitored as part of the license obligations, imposed by the South African National Nuclear Regulator Act [1]. Two main pathways giving rise to significant exposures are of interest: (a) direct ingestion resulting from regular and continuous use of contaminated water for drinking purposes, and (b) regular consumption of fish and other food products harvested from and/or grown in contaminated areas. To measure the individual nuclides in foodstuffs at the required sensitivity level in order to evaluate the yearly dose due to an individual source at a screening level of 25 μSv/a, one is faced with a required lower limit of determination (LLD) of 0.1 to 0.5 Bq/kg for certain foodstuffs. For some of the nuclides this LLD can only be obtained with radiochemical separation through acid destruction of dried foodstuffs followed by individual element separations. In this study the digestion of foodstuffs in an open-vessel microwave system followed by the determination of 210Po through radiochemical separation by spontaneous deposition onto silver discs and subsequent measurement by α-spectrometry, has been evaluated. The levels of 210Po in a variety of foodstuffs were determined and the estimated dose for the adult age group, resulting from consumption was evaluated. The dose from 210Po varied from 4 to 250 μSv/a for the various foodstuffs, with the largest intake from fish (about 0.5 Bq/day). The assessment of natural radionuclides in foods allowed us to evaluate the items that present the highest risk to the population, and compare this to the limits established by the National Nuclear Regulator (NNR). Not much data of this kind is available in South Africa. However, one would need more accurate consumption/intake values to calculate the actual yearly dose and the potential radiological impact on the public.

Dose effect for South Serbians due to 238U in natural drinking water

The use of depleted uranium ammunition in South Serbia during the 1999 Kosovo conflict raised a great deal of public concern in the Balkans. Radioactivity levels of 238U in 20 wells and lake water samples were checked from the viewpoint of internal radiation exposure for South Serbian subjects. We have measured 238U concentration using inductively coupled plasma mass spectrometry, whereas thermal ionisation mass spectrometry has been used for the measurement of isotope ratios, e.g. 234U/238U and 235U/238U. The concentration of uranium in water samples varies in the range 1.37-63.18 mBq/L. 234U belongs to the 238U natural radioactive decay series, and at secular equilibrium, the abundance ratio, 234U/238U, corresponds to the ratio of their half-lives. The 234U/238U activity ratio varies in the range 0.88-2.2 and 235U/238U isotope ratio varies from 0.00698 to 0.00745. These findings indicate that uranium in water was a mixture of natural and anthropogenic origin. The annual effective dose due to 238U was estimated to be in the range 9.2 x 10(-5)-2.1 x 10(-3) mSv.

A γ-ray background model for Monte Carlo simulations

We present here a γ-ray background model for a typical urban environment. Such models are crucial for realistic evaluations of the sensitivity of nuclear detection systems. The model spectrum consists of a collection of lines and a continuum component. The details of the iterative approach used in the creation of the model are discussed. When the final model is used as the source spectrum emitted by the ground or the concrete walls surrounding a typical coaxial Ge detector, the simulated response of the detector matches the data observed in the field extremely well. The final emission spectrum is very precise, and contains features crucial in nuclear detection applications. The prominent 40K line (1460.8 keV) is clearly seen, as well as the 2615 keV peak due to Tl-208 (thorium natural decay series). The lines of 238U (1001.2 keV) and 235U (185.7 keV) are also present. We find this spectrum to be a useful tool for estimating sensitivities in our Monte Carlo modeling of several nuclear detector setups. We offer this model to the community for unlimited use, in the form of a Geant4 class or as a table of ‘intensity vs. energy’ for use with other Monte Carlo packages. We also note that the iterative procedure described here can be used for the creation of other background spectra.

Exposure of workers in a mineral processing industry in Brazil

In Brazil there are many regions where the extraction mining and processing of ores containing elements of great economical importance as tin, niobium and tantalum. Some of these ores have uranium and thorium natural decay series associated. This study was carried out in a niobium mine, where is obtained concentrates of niobates-tantalates, cassiterite and zirconite. The aim of this study is the evaluation of the occupational exposure to uranium, thorium, niobium and tin through urine bioassay data. In order to have it, 105 urine samples were analysed: 17 samples of exposed workers collected after a working day, 49 samples of exposed workers collected before a working day and 39 samples of local non-exposed people, assigned as a control group. The samples were analysed by mass spectrometry. The obtained results showed that the average concentration of Nb, Sn and U in the exposed group is statistically higher than those found in the control group indicating an occupational exposure. For Th there were no statistically difference between the exposed and the control group.

The measurement of radioactivity in Italian drinking waters

Drinking waters generally contain variable amounts of radioactivity. Many radionuclides, like 40K and those belonging to the natural decay series of 238U, 235U and 232Th, are transferred to the water from the aquifer rocks by erosion and dissolution mechanisms. In recent years, a great interest arose towards the natural radioactivity in drinking water. The European Council Directive 98/83/EC, subsequently enforced in Italian law, pushed public authorities to organize tap water surveys. Parameter values for radioactivity levels in water are given, according to World Health Organization recommendations. Maximum concentration values for radon are separately proposed in a European Commission Recommendation. For this reason, during the latest years, the Regional Environment Protection Agency (ARPA) has been performing an extensive monitoring of tap waters in the Lombardia district of Italy. Natural radioactivity content was measured to check the compliance with recent European and Italian rules. Analyses were performed by an ultra-low level scintillation counter equipped with an alpha–beta discrimination device. Specifically arranged procedures, requiring quick and easy pre-treatments, allowed to measure gross alpha and beta activity, 222Rn, 226Ra, and uranium isotopes concentrations in a relatively short time. Subsequently, more complex procedures, involving radiochemical separation of radionuclides, are currently being studied for 210Pb, 210Po and 228Ra. Method performances were carefully tested by both internal validation procedures and international intercomparison exercises. These procedures have been employed for a wide range screening in the Lombardia district in Italy. Obtained results showed that in most cases gross alpha activity was lower than the parameter value given by the cited regulations. When these values were exceeded, a more detailed survey was planned: at present three of them, in the western and south-western part of Lombardia and in the city of Milan have been carried out.

Characterization of the NIST seaweed Standard Reference Material

The National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for seaweed was developed through an interlaboratory comparison with 24 participants from 16 countries. After evaluating different techniques to calculate certified values for the radionuclides, the median method was found to be the most representative technique. The certified values were provided for 13 radionuclides and information values were given for 15 more radionuclides. Results for the natural decay series showed disequilibrium in both the uranium and thorium series.

A very long-term HPGe-background gamma spectrum

Background gamma spectra, taken with one HPGe detector between 1987 and 2003, are summed up to represent a total collect time of 1.03×10 8 s. Standard background gamma lines belonging to the natural decay series as well as more uncommon ones are identified. A high temporal variability of the background lines related to radon decay products is found in comparison with lines related to other radionuclides contained in the environment and in the structural material of the detector.

On the integrated decay and ingrowth equations used in the measurement of radioactive decay families: the general solution

In the measurement of radioactivity, a finite measurement time is employed to collect data. Usually, this time is small with respect to the half-life of the nuclide being measured and the ‘usual’ decay equations can be used to decay measured activities to a given reference time. In some applications, such as neutron activation, an integrated form of the decay equation needs to be employed as the measurement time is comparable to the half-life and using the non-integrated form introduces a significant error. This correction is well known and is used widely. For radionuclide families, such as the natural decay series of uranium and thorium or simple parent–daughter systems, no such integrated form of the decay and ingrowth series appears to have been published in the open literature. This paper sets out the general solution for integrated decay and ingrowth of sequential decay and illustrates the validity of this theoretical solution by applying it to real examples.