Bq Kg-1 Research Articles

Natural radioactivity in Italian ceramic tiles

Zircon is the mostly widely occurring zirconium-containing mineral mined commercially. Thorium and uranium may substitute for zirconium in the zircon crystal lattice. The radioactivity levels in zircon lies typically within the ranges 500–1000 Bq kg-1 for 232Th and 1000–5000 Bq kg-1 for 238U [1]. One of the most important use of zircon is as opacifier for ceramic tiles. Body of ceramic tiles is a mixture of different raw materials, including: clays, quartz materials and feldspathic materials. The body may be glazed or left unglazed. Due to the presence of zircon in the glaze or in the body, ceramic tiles can show natural activity concentration significantly higher than the average values of Earth's crust. This study contains a summary of results obtained by a survey on Italian ceramic tiles collected over three years (2005–2007). About one hundred ceramic tiles were analysed. The survey consisted of measurement of 226Ra, 232Th and 40K activity concentrations and of the gamma-index [2] and radium-equivalent [3, 4] calculation. The activity concentrations of 226Ra, 232Th and 40K result in the order of 100, 50 and 500 Bq kg-1, respectively. Gamma index and radium equivalent activity have been found well below the acceptable limit in most of the samples.

Determination of the transfer of tritium to crops fertilised with contaminated sewage sludge

Authorised discharges of radionuclides into sewers can result in contamination of the sludge, and so provide a pathway by which radionuclides can enter the foodchain. Specific data on the uptake of radionuclides from sludge amended land into crops is scarce. A study has been undertaken to generate data on tritium uptake by crops grown in soil amended with tritium contaminated sewage sludge using a range of soil types and crops common to the UK. The study was performed over two years. The concentration of tritium in soil fell throughout the study. It was therefore not possible to quantify individual soil to crop transfer in terms of conventional concentration ratios. Instead, an aggregated transfer quotient was estimated relating the concentration in the edible part of the crop in Bq kg-1 to the original amount of activity applied to the soil in Bq m-2. The values obtained were broadly similar at for all crop and soil types studied, being about 2 10-4 m2 kg-1. The observed values depend on factors such as temperature and rainfall, and so they should not be used in generalised radiological assessments. They are however indicative of the small amounts of tritium transferred to crops from amended soil.

Gamma-ray spectrometry sensor and geochemical prospecting in an area of sugar cane plantation

In this study the K, U and Th radionuclide concentrations were determined in a sugar cane plantation that received large quantities of fertilizer and gypsum. Geochemical data were obtained for the clay, iron and organic matter in the soil samples, taken from depths of 0-20 and 20-40 cm. The average radionuclide concentrations were 71 Bq Kg-1 for K; 5.97 Bq Kg-1 for U, and 11.26 Bq Kg-1 for Th, and the uranium was variable (56%). The radionuclide average concentrations for the different fertilizer compositions varied in the range of 603.5 - 8855.0 Bq Kg-1 for K; 27.3 - 684.4 Bq Kg-1 for U, and 58 - 788.5 Bq Kg-1 for Th, and it was most variable for K (53%). Gypsum average concentrations were 82.6 Bq Kg-1 for K, 641.5 Bq Kg-1 for U, and 201.7 Bq Kg-1 for Th, and it was most variable for K (46%). Average organic matter, clay and iron concentrations for both the depths were 0.71 and 0.68 %; 16.2 and 16.9 %, and 29.0 and 26.8 mg/l respectively.

DECOMMISSIONING PROCEDURES FOR AN 11 MEV SELF-SHIELDED MEDICAL CYCLOTRON AFTER 16 YEARS OF WORKING TIME

The present article describes the decommissioning of a compact, self-shielded, 11 MeV medical cyclotron. A Monte Carlo simulation of the possible nuclear reactions was performed in order to plan the decommissioning activities. In the course of the cyclotron dismantling, cyclotron components, shields, and floor concrete samples were measured. Residual activities were analyzed with a Ge(Li) detector and compared with simulation data. Doses to staff involved in the decommissioning procedure were monitored by individual TL dosimeters. The simulations identified five radioactive nuclides in shields and floor concrete: 55Fe and 45Ca (beta emitters, total specific activity: 2.29 x 10(4) Bq kg) and 152Eu, 154Eu, 60Co (gamma emitters, total specific activity: 1.62 x 10(3) Bq kg-1). Gamma-ray spectrometry confirmed the presence of gamma emitters, corresponding to a total specific activity of 3.40 x 10(2) Bq kg-1. The presence of the radioisotope 124Sb in the lead contained in the shield structure, corresponding to a simulated specific activity of 9.38 x 10(3) Bq kg-1, was experimentally confirmed. The measured dose from external exposure of the involved staff was <20 muSv, in accordance with the expected range of values between 10 and 20 muSv. The measured dose from intake was negligible. Finally, the decommissioning of the 11 MeV cyclotron does not represent a risk for the involved staff, but due to the presence of long-lived radioisotopes, the cyclotron components are to be treated as low level radioactive waste and stored in an authorized storage area.

Rapid Method for the Analysis of Plutonium Isotopes in a Soil Sample within 60 min

A rapid method for the determination of Pu isotopes in a soil sample within 60 min of starting sample pretreatment was developed. The large reduction in the analysis time was attained by the rapid and perfect digestion of the sample using an alkaline fusion method with an induction heating machine. Pu concentrations were then determined by flow injection/ICP-MS using a solid extraction resin after preconcentration by batch extraction with a chelate resin. The limits of detection for 239Pu and 240Pu were 9.2 fg and 4.3 fg, corresponding to 0.03 and 0.05 Bq kg(-1), respectively, under our analytical conditions, which satisfy the lower detection limits (0.5 Bq kg(-1) of 239Pu, and 2 Bq kg(-1) of 240Pu) required for rapid analysis techniques by the Ministry of Education, Culture, Sports, Science and Technology, Japan. This method provides a powerful and practical technique for emergency monitoring in and around nuclear facilities that handle large amounts of plutonium.

Gamaespectrometria, resistividade elétrica e susceptibilidade magnética de solos agrícolas no noroeste do estado do Paraná

Gamma-ray spectrometry, electrical resistivity, and magnetic susceptibility measurements were taken from agricultural areas near the City of Maringa, in the Northwest region of the Parana state, south Brazil, in order to characterize the spatial distribution of radionuclides (K, eU, and eTh), the apparent resistivity, and the magnetic susceptibility determined for soils. Three different types of soils are present in this agricultural area: Alfisoil, clayey texture Oxisoil, both deriving from Lower Cretaceous basalts of the Serra Geral Formation; and medium texture Oxisoil from reworked Serra Geral and Goio-Ere formations, the latter deriving from sandstones of the Upper Cretaceous Caiua Group. It could be observed that in more clayey soils both concentration of radionuclides and susceptibility values are higher than in more sandy soils, especially due to the higher adsorption in the former and to the higher availability of magnetic minerals in the latter. The average ppm and Bq Kg-1 grades for K, eU, and eTh in the areas under anthropic activity are of 1766-54.75, 0.83-10.22, and 1.78-7.27, respectively. These grades are significantly higher than those of non-occupied or non-fertilized areas (1101-34.15 K, 0.14-1.69 eU, and 1.31-5.36 eTh in ppm and Bq Kg-1, respectively.) Correlations were observed between uranium and clay, uranium and magnetic susceptibility, uranium and organic matter, and between electric resistivity and clay grades. Varied concentrations of radionuclides were also observed in different fertilizer formulations applied to soy and wheat cultures. Apparent electric resistivity values between 25 and 647 Ohm.m and magnectic susceptibility values between 0.28 e 1.10 × 10-3 SI due to clay and magnetic minerals represented important soil discrimination factors in the study area that can be incorporated as easy, low-cost soil mapping tools.

Analysis of the 40K levels in soil using gamma spectrometry

Potassium-40 was determined in soil in an area with 40,000 m² situated in the western State of Pernambuco, Brazil. For radiometric measurements, the gamma spectrometry method with a high purity germanium (HPGe) detector was used. Sampling of 78 soil samples has been performed at intervals of 25 m. The specific activities of 40K were calculated based on the photopeak of 1.46 MeV. Values from 541 to 3,572 Bq kg-1 were obtained (mean of 1,827 Bq kg-1). These values allowed the determination of the elemental concentrations as well as the absorbed dose rates in air, 1 m above the ground. The values varied from 1.7 to 11.5% (mean of 6%) and from 23.4 to 154.3 nGy h-1 (mean of 79 nGy h-1), respectively.

Evaluation of the radioactive impact of the phosphogypsum wastes used as amendment in agriculture soils

Some 3×109 kg of phosphogypsum (PG) wastes are annually generated by two fertiliser-production factories in Huelva (south-western Spain). PG has relatively high concentrations of 226 Ra and other radionuclides, with an special concern due to the 222 Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226 Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226 Ra. The drainage waters have 226 Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. Our results are suggesting that the major uranium input comes from the application of phosphate-fertiliser. No significant levels of radionuclides were found in the vegetal tissues.

Environmental radioactivity of the St. Martin's island of Bangladesh

The activity concentration of natural and anthropogenic radionuclides in soil and rock, and in benthic algae, corals and oysters across the St. Martin's island of Bangladesh were investigated together with physicochemical parameters and texture of soil with an aim of evaluating the radioecology of the island. Soil and rock samples from the twenty-two locations of the island, eleven species of benthic algae, six species of corals and two species of oysters were analyzed. The activity of 226 Ra in soil was found in the range of 7.22–103.8, in benthic algae 2.5–9.7, in coral 5.5–10 and in oyster 4.2–11.5 Bq kg-1 . The activity of 232 Th in soil was found in the range of 14.56–216, in benthic algae 1.3–12.6, in coral 4.4–15.6 and in oyster 3.2–8.4 Bq kg-1 ; and the activity of 40 K in soil was in the range of 322–732, in benthic algae 17.1–45.5, in coral 21–146 and in oyster 24–32 Bq kg-1 . The external radiation dose rate due to activity concentration of natural radionuclides in soil was assessed. The activity of anthropogenic 137 Cs was found below detection limit.

Analysis and processing of samples for a carbon-14 monitoring program at a radioactive waste storage site.

A monitoring program was undertaken to determine the levels of airborne radioactive 14CO2 in an operating waste management area, and it its vicinity. As a part of this program, alkaline microporous pellets, recently developed, were used to sample the 14CO2 in air near waste storage structures and near the waste management area. These pellets were never fully characterized for their ability to capture high levels of 14CO2, and the processing and analysis needed to be improved to provide data on recoveries and consistencies, for an eventual method validation, with independent calibrations and standards. The sample analysis scheme also had to accommodate 14CO2 levels varying from near the natural background (250 Bq kg-1 C), to potentially three to four orders of magnitude above this value, near the wastes. The porous alkaline solid pellets were used for the passive capture of airborne 14CO2 over a period of weeks, to a few months. The pellets were processed to release the captured CO2 (14CO2 and 12CO2) into a NaOH solution, which was subsequently analyzed by liquid scintillation. Processing of the pellets yielded a 14C recovery of 96.0 +/- 4.2% and a lower, but consistent total carbon recovery, i.e., 85.9 +/- 2.7 and 86.9 +/- 2.6%, for procedural blanks and standards, respectively. The detection limits for the pellet sampling and processing was sufficient to reach environmental levels. For the higher levels of 14CO2 and for 'spot' sampling, we also used air samples, pumped into a NaOH solution to trap the 14CO2. These NaOH solutions were counted directly for 14C, also by liquid scintillation. The method limits of this latter technique, although much higher than for pellet samples, also achieved the performance objective for detecting airborne 14CO2. Both sampling and processing techniques, when used together, provided sufficient flexibility to be used for low (environmental) levels and high levels, near the wastes.

Radiological study of exposure levels in El Maghara underground coal mine.

Coal is largely composed of organic matter, but it is the inorganic matter in coal minerals and trace elements that have been cited as possible causes of health, environmental and technological problems associated with the use of coal. Some trace elements in coal are naturally radioactive. These radioactive elements include uranium (U), thorium (Th) and their numerous decay products, including radium (Ra) and radon (Rn). Although these elements are less chemically toxic than other coal constituents, such as arsenic, selenium or mercury, questions have been raised concerning the possible risk from radiation. In order to accurately address these questions and to predict the mobility of radioactive elements during the coal fuel cycle, it is important to determine the specific activity, distribution and form of radioactive elements in coal. The assessment of the radiation exposure from coal burning is critically dependent on the specific activity of radioactive elements in coal and in the fly ash that remains after combustion. The El-Maghara coal mine is the only producing coal mine in Egypt. It is located in the middle of the Sinai desert about 250 km north-east of Cairo, where a coal-fired power plant is intended to be built. In this study, a pre-operational radiological baseline of the site and the occupational radiation exposures due to radon progeny in the mine were determined. The specific activities of 226Ra, 232Th and 40K in soil and coal dust samples collected along the main gallery ranges were found to be 6-22.9, 9.6-47.3 and 77-489 Bq kg-1, respectively. Soil samples collected around the mine showed concentrations of 226Ra, 232Th and 40K in the ranges 2.7-20.2, 3.2-12.6 and 14.6-201 Bq kg-1, respectively. All of the mean values of radon progeny were lower than the action levels for working places recommended in the International Commission on Radiological Protection (ICRP) 65.

A new method for determination of uranium isotopes in water, vegetation and soil by alpha spectrometry

A new and accurate method for determination of uranium isotopes ( 238 U, 234 U and 235 U) in environmental samples by alpha spectrometry has been developed. Uranium is preconcentrat ed from filtered water samples by coprecipitati on with iron (III) hydroxide at pH 9-10 using ammonia solution and the precipitate is dissolved with HN0 3 and mineralised with H 2 02 and HF; uranium in biological samples is ashed at 600 °C, leached out with Na 2 C0 3 solution and mineralised with HN0 3, HF and H 2 0 2; uranium in soil samples is melted with Na 2 C0 3 and Na 2 02 at 600 °C and leached out with HC1, HN0 3 and HF. The mineralised or leaching solution in 2 M HN0 3 is passed through a Microthene-TOPO (tri- octyl-phosphine oxide) column; after washing uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha spectrometry. The lower limits of detection of the method are 0.37 Bq kg1 (soil) and 0.22 mBq l1 (water) for 238 U and 234 U and 0.038 Bq kg1 (soil) and 0.022 mBq l1 (water) for 235 U if 0.5 g of soil and 1 litre of water are analysed. Five reference materials supplied by IAEA have been analysed and reliable results are obtained. The average uranium yields for waters, mosses, lichens and sediments are 74.5+9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7% respectively.

Effect of fertilisation and drainage intensity on the foliar radiocaesium and potassium concentrations of Scots pine on a drained peatland

This study aims at finding out the effects of fertilisation and drainage intensity on the needle 134 Cs and 137 Cs activity in Pinus sylvestris on a pine mire in Finland. The fertilisation treatments were as follows : a control, fertilised once in 1965 or fertilised twice in 1965 and 1977, with N, P and K. The potassium concentrations of the current year needles in 1990 showed severe potassium deficiency on the controls (K 3.6 mg g-1 ) and slight deficiency on the plots fertilised only once (K 4.2 mg g-1 ) but no deficiency on the plots fertilised twice (K 4.8 mg g-1 ). Fertilisation decreased the radiocaesium concentrations and amounts in the needles. The concentrations of 134 Cs were 821 in the control, 442 in the single fertilisation and 485 Bq kg-1 in the repeated fertilisation treatment, and the 137 Cs concentrations 5378, 2734 and 2104 Bq kg-1 , respectively. Drainage intensity (10-100 m) had no significant effect on the needle K concentration or radiocaesium activity.

Monitoring DNA damage in wood small-reed (Calamagrostis epigejos) plants growing in a sediment reservoir with substrates from uranium mining.

For most plant species growing in polluted areas genotoxicity assays are not available. We have studied the possibility of using the alkaline protocol of the Comet assay as a method for detecting induced DNA damage in a grass Calamagrostis epigejos, growing wild in highly polluted areas. To calibrate the Comet assay for C. epigejos, two model mutagens were applied: the monofunctional alkylating agent ethyl methanesulfonate (EMS) and gamma-rays. With increasing concentrations of EMS (0 to 10 mM, 18 h treatment at 26 degrees C) applied on excised leaves, the DNA damage, as expressed by the tail moment (TM) values, increased from 4.7 +/- 0.9 to 60.8 +/- 2.7 microns. After gamma irradiation (0 to 30 Gy) the TM value increased from 4.2 +/- 0.2 to 48.1 +/- 1.7 microns. A 24 to 72 h recovery of leaves after EMS treatment in an EMS-free medium did not result in a significant change in the induced EMS damage. By contrast, a 24 h recovery after gamma-irradiation led to a complete repair of DNA damage measurable by the Comet assay. We have measured the DNA damage in nuclei of leaves of C. epigejos plants growing in the area of a sediment reservoir with substrates from uranium mining, where the ore was exploited through leaching with sulfuric acid. The average specific activity of natural radionuclides measured in the substrate was for 226Ra = 11,818 Bq kg-1, for 232Th = 66 Bq kg-1 and for 40K = 75 Bq kg-1. No significant increase in the DNA damage in plants growing on the sediment substrate above the DNA damage in control plants was detected by the Comet assay.

Distribution of 40K, 232Th and 238U in Soils of Southern and Western Coasts of Viti Levu, Fiji

Abstract A 10 cm (diameter) x 7.5 cm NaI(Tl) gamma-ray spectrometer was used to measure the concentrations of 40K, 232Th and 238U in 50 samples of top soils of the southern and western coasts of Viti Levu, the largest island of the Republic of Fiji Islands. The average activities of 232Th, 238U and 40K in soils of this region were 2.8, 3.6 and 160 Bq kg-1, respectively. The average external gamma-dose, which is likely to be delivered to the local population in this region, is estimated to be 10.3 nGy h-1, well below the world average.

Plutonium Contamination Level and Isotopic Composition in Soils around St. Petersburg

Plutonium isotopic composition including 238Pu, 239Pu, 240Pu, and 241Pu and the Pu contamination level are determined in soils around St. Petersburg using an advanced procedure involving radiochemical separation stage followed by the α-ray spectrometric and mass spectrometric determination. The Pu specific activity in surface horizons (0-25 cm) ranges from 0.2 to 0.44 Bq kg-1. The mean 238Pu/239,240Pu activity ratio is found to be 0.033±0.007. The Pu contamination level of the surface horizon (0-25 cm) is 62±5 Bq m-2. The 238Pu/239Pu, 240Pu/239Pu, and 241Pu/239Pu isotopic ratios are (2.0±0.5)×10-4, 0.172±0.004, and 0.003±0.002, respectively. These ratios are close to the values typical of plutonium from the global radioactive fallout due to nuclear weapons tests in the atmosphere. The effect of the Chernobyl accident and regional potential contamination sources, including the Leningrad NPP, on the Pu isotopic composition and contamination level in the soil is insignificant.

Distribution of natural radioactivity in rocks from Ikogosi-Ekiti, Southwestern Nigeria and its radiological implications.

The natural radioactivity in some rock samples in Ikogosi-Ekiti, Southwestern Nigeria, has been measured using a very sensitive gamma spectroscopic system consisting of a 76 mm x 76 mm NaI(TI) scintillation detector system coupled to a versatile Canberra Series 10 plus multichannel analyzer. The average concentrations of natural radioisotopes 238U, 232Th, and 40K are 57.9 +/- 28.1 Bq kg-1, 81.6 +/- 23.8 Bq kg(-1) and 1203.1 +/- 687.2 Bq kg(-1), respectively. These average values give rise to a mean absorbed dose rate of 0.128 +/- 0.051, microGy h(-1) at a height of 1.0 m and an effective dose equivalent of 156.90 microSv (y-1). The results indicate no radiological anomaly. The data presented here will serve as a baseline survey for primordial radionuclide concentrations in rocks of the area.

Concentrations of 239Pu and 240Pu and Their Isotopic Ratios Determined by ICP-MS in Soils Collected from the Chernobyl 30-km Zone

Soil samples collected from three forest sites within the 30-km zone around the Chernobyl reactor were analyzed for 239Pu and 240Pu by ICP-MS. The average 240Pu/239Pu atom ratio in contaminated surface soil samples, values of which are scarce in the literature, was 0.408. There were almost no differences in the 240Pu/239Pu ratios between the individual samples analyzed, although the 239+240Pu levels varied very widely (i.e. from 6.3 to 1430 Bq kg-1 dry weight) depending on the distance from the reactor and on the soil layers investigated. This result corresponded to area-related activities for 239+240Pu between 1.1 kBq m-2 and 13.3 kBq m-2. It was estimated that about half of the Pu migrated from the organic layers to the underlying mineral layers. The 240Pu/239Pu ratio observed in the Chernobyl area was much higher than that attributed to weapons fallout (ca. 0.18). The high ratio was related to the high burn-up grade of the reactor fuel. The 240Pu/239Pu ratio observed might be used as a “fingerprint” in identifying the distribution of Chernobyl-derived Pu in the environment and in distinguishing it from other sources, e.g. global fallout. Relationships between the concentrations of Pu and those of 137Cs, 60Co, and 125Sb were also discussed.

Natural radioactivity and radiation exposure at the Minjingu phosphate mine in Tanzania

In this paper the results of studies on activity and ambient radiation background around the Minjingu phosphate mine in Tanzania are presented. The outdoor dose rate in air and the activity levels of samples from and outside the mine were determined by thermoluminiscent dosimeters and a gamma spectrometer system with a Hyper Pure germanium detector system respectively. The determination of activity was made for the 226Ra, 228Ra, 228Th and 40K radionuclides. High concentrations of radium-226 were observed in phosphate rock (5760±107 Bq kg-1), waste rock (4250±98 Bq kg-1), wild leaf vegetation (650±11 Bq kg-1), edible leaf vegetation (393±9 Bq kg-1), surface water (4.7±0.4 mBq l-1) and chicken feed (4±0.1 Bq kg-1) relative to selected control sites. These findings suggest a radiation health risk particularly when the samples are ingested, because the internal exposure may give rise to an effective dose exceeding 20 mSv which is the annual limit of intake of natural radionuclides recommended by the ICRP. On the other hand, the radiation dose from ambient air over five years at the phosphate mine ranges from 1375 to 1475 nGy h-1 with an average of 1415 nGy h-1. The average is about 28 times that of the global average background radiation from terrestrial sources, and about 12 times the allowed average dose limit for public exposure over five consecutive years. Future investigations on the occupancy factor, external dose rate and radon and radon progeny exposure in drinking water, buildings and activity content in the locally grown foodstuffs are proposed, for the realistic quantification of the overall exposure of workers and public at Minjingu, and remedial measures for future radiation safety.

A note on radionuclide 137Cs and 40K concentrations in Dall’s porpoises, Phocoenoides dalli, in coastal waters of Japan

Concentrations of artificial radionuclide 137Cs and natural radionuclide 4°K in Dall's porpoise, Phocoenoides dalli, from the Pacific coast of northern Japan in 1996 are presented. Concentrations of 137Cs in muscle tissue from two male Dall's porpoises were 0.153 ± 0.01 l and 0.234 ± 0.016 Bq kg-1 wetweight, and those of4°K were 104.0 ± 0.3 and 107.8 ± 0.9 Bq kg-1 wet weight, respectively. Concentration factors (CF, concentration in animal/concentration in sea water) for the two porpoises are 59 and 90 for 137Cs, respectively. These concentrations and CF values are within published ranges for marine fish in coastal waters. The CFs obtained in this study suggest that the trophic position of Dall's porpoises is similar to that of the large piscivorous fish in the marine community in coastal waters of Japan.