14C Emission Research Articles

14C, δ 13C and total C content in soils around a Brazilian PWR nuclear power plant

Nuclear power plants release 14C during routine operation mainly as airborne gaseous effluents. Because of the long half-life (5730 years) and biological importance of this radionuclide (it is incorporated in plant tissue by photosynthesis), several countries have monitoring programs in order to quantify and control these emissions. This paper compares the activity of 14C in soils taken within 1 km from a Brazilian nuclear power plant with soils taken within a reference area located 50 km away from the reactor site. Analyses of total carbon, δ 13C and 137Cs were also performed in order to understand the local soil dynamics. Except for one of the profiles, the isotopic composition of soil organic carbon reflected the actual forest vegetation present in both areas. The 137Cs data show that the soils from the base of hills are probably allocthonous. The 14C measurements showed that there is no accumulation due to the operation of the nuclear facility, although excess 14C was found in the litter taken in the area close to power plant. This indicates that the anthropogenic signal observed in the litter fall has not been transferred yet to the soil. This study is part of an extensive research programme in which other samples including air, vegetation and gaseous effluents (taken in the vent stack of the Brazilian nuclear power reactors Angra I and II) were also analyzed. The present paper aimed to evaluate how 14C emissions from the nuclear power plant are transferred and stored by soils present in the surroundings of the reactor site. This is the first study concerning anthropogenic 14C in soils in Brazil.

Regulation of Intra-S Phase Checkpoint by Ionizing Radiation (IR)-dependent and IR-independent Phosphorylation of SMC3

Structure maintenance of chromosome 1 (SMC1) is phosphorylated by ataxia telangiectasia-mutated (ATM) in response to ionizing radiation (IR) to activate intra-S phase checkpoint. A role of CK2 in DNA damage response has been implicated in many previous works, but the molecular mechanism for its activation is not clear. In the present work, we report that SMC3 is phosphorylated at Ser-1067 and Ser-1083 in vivo. Ser-1083 phosphorylation is IR-inducible, depends on ATM and Nijmegen breakage syndrome 1 (NBS1), and is required for intra-S phase checkpoint. Interestingly, Ser-1067 phosphorylation is constitutive and is not induced by IR but also affects intra-S phase checkpoint. Phosphorylation of Ser-1083 is weakened in cells expressing S1067A mutant, suggesting interplay between Ser-1067 and Ser-1083 phosphorylation in DNA damage response. Consistently, small interfering RNA knockdown of CK2 leads to attenuated phosphorylation of Ser-1067 as well as intra-S phase checkpoint defect. Our data provide evidence that phosphorylation of a core cohesin subunit SMC3 by ATM plays an important role in DNA damage response and suggest that a constitutive phosphorylation by CK2 may affect intra-S phase checkpoint by modulating SMC3 phosphorylation by ATM.

Carbon radioactivity of 223Ac and a search for nitrogen emission

A very intense 227Pa source was produced in order to study the possible 14C and 15N spontaneous emission from 223Ac. After the irradiation of a hemispherical, highly efficient array of nuclear track detectors, about 350 Carbon events were found leading to a branching ratio with respect to alpha decay B = 3.2 10−11. Comparison with other 14C emitters allows the study of the influence of even-odd effects on cluster radioactivity.

Biodiesel effects on particulate radiocarbon ( 14C) emissions from a diesel engine

The relative amount of 14C in a sample of atmospheric particulate matter (PM), defined as percent modern carbon (pMC), allows the Environmental Protection Agency (EPA) to infer the fraction of PM derived from anthropogenic pollution sources. With increased use of biofuels that contain 14C, the main assumption of the two-source model, that 14C is solely derived from biogenic emissions, may become invalid. The goal of this study was to determine the 14C content of PM emitted from an off-highway diesel engine running on commercial grade biodiesel. Tests were conducted with an off-highway diesel engine running at 80% load fueled by various blends of soy-based biodiesel. A dilution tunnel was used to collect PM 10 emissions on quartz filters that were analyzed for their 14C content using accelerator mass spectrometry. A mobility particle sizer and 5-gas analyzer provided supporting information on the particle size distribution and gas-phase emissions. The pMC of PM 10 aerosol increased linearly with the percentage of biodiesel present in the fuel. Therefore, PM emissions resulting from increased combustion of biodiesel fuels will likely affect contemporary 14C apportionment efforts that attempt to split biogenic vs. anthropogenic emissions based on aerosol- 14C content. Increasing the biodiesel fuel content also reduced emissions of total hydrocarbons (THC), PM 10 mass, and particulate elemental carbon. Biodiesel had variable results on oxides of nitrogen ( NO x ) emissions.

The separation of Pa from a Th target by means of ion exchange chromatography

An ion-exchange method is presented to separate the radioisotope 227Pa from a Th target after bombardment with 66 MeV protons. Several sources of 227Pa were prepared to be used as generators of 223Ac, concluding the first stage (or radiochemistry stage) of an exotic radioactive decay experiment to determine whether the emission of 14C and 15N clusters is observed in the decay of 223Ac. The second stage (or nuclear physics stage) of the experimental investigation involves the search for tracks of 14C and 15N clusters in solid-state nuclear track detectors exposed to the emissions from these sources. While the nuclear physics stage is still in progress, we report here on the completed radiochemistry stage and the development work. As the half-life of 227Pa is relatively short (38.3 minutes) it was imperative to perform the necessary chemical separation of this radioisotope as well as the preparation of dry sources as quickly as possible. By means of the methods developed, the period from the end of bombardment (EOB) of a Th target until completion of a dry source, could be kept below two half-lives of 227Pa. The resulting source strengths were sufficient for the purposes of the nuclear physics part of the investigation.

Approaches for Reducing Carbon-14 Stack Emissions from Korean CANDU® Nuclear Power Plant

Relatively high carbon-14 emissions, which occurred at Wolsong Nuclear Power Plant during 1998 and 1999, made the site staff to implement several operational improvements: (1) restriction of the maximum in-service time of moderator ion exchange (IX) resin columns to 80 days, (2) discontinuation of the practice of re-using ‘used’ IX resin columns for removing the gadolinium nitrate at star-up, and (3) reduction of the frequency and volume of the moderator cover gas purging through increased O2 additions to the cover gas. In this way, the emission rates returned to normal levels during the remainder of 1999 and 2000. To optimize the use of the moderator IX resin column, the special surveillance was carried out at Wolsong Unit 3. This showed that only the 14C stack emission data were a practical indicator for exhaustion of IX resin column. From this data, a criterion was derived: IX resin column can be put in service for 100 days unless a 14C emission rate higher than about 20GBq-month-1 (0.4Ci-month-1) takes place for two consecutive weeks. Finally it was suggested that using a portable 14C scrubber could benefit for reducing the 14C stack emissions, especially those due to leakage of the moderator cover gas.

Approaches for Reducing Carbon-14 Stack Emissions from Korean CANDU Nuclear Power Plant

Relatively high carbon-14 emissions, which occurred at Wolsong Nuclear Power Plant during 1998 and 1999, made the site staff to implement several operational improvements: (1) restriction of the maximum in-service time of moderator ion exchange (IX) resin columns to 80 days, (2) discontinuation of the practice of re-using ‘used’ IX resin columns for removing the gadolinium nitrate at star-up, and (3) reduction of the frequency and volume of the moderator cover gas purging through increased O2 additions to the cover gas. In this way, the emission rates returned to normal levels during the remainder of 1999 and 2000. To optimize the use of the moderator IX resin column, the special surveillance was carried out at Wolsong Unit 3. This showed that only the 14C stack emission data were a practical indicator for exhaustion of IX resin column. From this data, a criterion was derived: IX resin column can be put in service for 100 days unless a 14C emission rate higher than about 20GBq-month-1 (0.4Ci-month-1) takes place for two consecutive weeks. Finally it was suggested that using a portable 14C scrubber could benefit for reducing the 14C stack emissions, especially those due to leakage of the moderator cover gas.

New measurement of exotic decay of 225Ac by 14C emission

The branching ratio of 225 Ac decay by emission of 14 C was remeasured under improved experimental conditions by using a radioactive source produced at the ISOLDE mass-separator at CERN and a nuclear track detector technique. The result, B=λ14C/λα = (4.5±1.4) 10 -12 , is consistent with the anomalously high value obtained in the 1993 experiment thus confirming the importance of nuclear structure effects in this exotic decay.

Radiological impact of an intense fusion economy

The radiological impact of an intense fusion economy, a 1000 GW operating capacity for a 1000 years, were investigated regarding the isotopes 14C and tritium. Both isotopes participate in global material cycles, the carbon and the water cycle. If a retention time of 10 000 years is assumed for the stored waste, 14C emissions from the repositories dominate the radiation impacts. While the cumulated collective doses over a long term period are rather high and according to the discount rate selected would lead to significant external costs, the individual doses are small compared with the doses associated with the natural background radiation.

Alpha and exotic decays to 210Pb daughter states

Abstract Many of the low-lying states of 214Po and 224Ra are well described in terms of 210Pb + α and 210Pb+14C cluster models, respectively. In these models, non-central forces mix configurations involving different excited states of the core and cluster orbits. Such mixing provides a mechanism for hindered cluster decay to several core (daughter nucleus) states, and its strength can be determined from the spectrum of the parent nucleus. Taking into account this mixing, we obtain both a close reproduction of the energy levels of the parent nucleus and a good description of the half-lives for α-decay from the ground state of 214Po to the lowest three states of 210Pb. Similarly, the low-lying spectrum of 224Ra and the exotic decay half-life for 14C emission populating the ground state of 210Pb are both well described. However, our prediction for exotic decay to the first excited state of 210Pb suggests that its observation is beyond current experimental capabilities.

Radiocarbon Dispersion around Canadian Nuclear Facilities

Canadian deuterium uranium (CANDU) pressurized heavy-water reactors produce 14C by neutron activation of trace quantities of nitrogen in annular gas and reactor components (14N(n,p)14C), and from 17O in the heavy water moderator by (17O(n,α)14C). The radiocarbon produced in the moderator is removed on ion exchange resins incorporated in the water purification systems; however, a much smaller gaseous portion is vented from reactor stacks at activity levels considerably below 1% of permissible derived emission limits. Early measurements of the carbon speciation indicated that >90% of the 14C emitted was in the form of CO2. We conducted surveys of the atmospheric dispersion of 14CO2 at the Chalk River Laboratories and at the Pickering Nuclear Generating Station. We analyzed air, vegetation, soils and tree rings to add to the historical record of 14C emissions at these sites, and to gain an understanding of the relative importance of the various carbon pools that act as sources/sinks within the total 14C budget. Better model parameters than those currently available for calculating the dose to the critical group can be obtained in this manner. Global dose estimates may require the development of techniques for estimating emissions occurring outside the growing season.

Carbon radioactivity of 221Fr and 221Ra and the hindered decay of exotic odd- A emitters

By using glass detectors in 4π geometry we measured the spontaneous emission of carbon clusters from two sources of 221Fr and 221(Ra + Fr) produced at the on-line mass-separator ISOLDE at CERN, and obtained branching ratios λ cl/λ α = (8.79 ± 1.14) × 10 −13 and (1.15 ± 0.91) × 10 −12 for 221Fr and 221Ra respectively. Such results exhibit a one-order-of-magnitude hindrance in respect to even-even father nuclei having the same penetrability for 14C emission.

Radiochemistry and the fine structure of radioactive cluster emission

A simple cluster model has shown itself to be outstandingly successful in describing the half-lives for emission of heavy fragments ranging from 14C to 32Si from heavy even-even nuclei. However, its predictions for the half-lives of similar decays from odd-even nuclei are systematically below the corresponding measured values or lower limits set by experiment. In view of recent experimental results on the 223Ra → 209Pb + 14C system, we suggest that many of the exotic decays of odd-even nuclei so far observed, or searched for, may be proceeding preferentially to low-lying excited states of the daughter nucleus. We show that all the discrepancies between our model predictions and the presently available data for 14C and 24Ne emission would be consistently removed if this should prove to be the case. An opportunity to extract nuclear structure information from exotic decay measurements would thus be available.

Nuclear structure effects in the exotic decay of 225Ac via 14C emission

By using a 225Ac source produced at the electromagnetic separator Isolde we collected on our track-recording glass detectors 305 14C events from the radioactive decays of 225Ac and its daughter 221Fr and obtained, for 225Ac, a branching ratio B( 14C/α) = (6.0 ± 13) × 10 −12 . Our result suggests that such a decay from an odd proton nucleus is dominated by transition to the ground or to the first excited state of daughter nucleus.

Measurements of 14C from nuclear power plants with the AMS technique

One of the most important radionuclides spread from nuclear power plants to be surroundings is 14C because of its long half-life and its incorporation in living organisms. To measure the emission of 14C in the ventilation air from the stacks is difficult, not only because it is a pure β-emitter but also because the ventilation air normally contains much higher activity concentrations of noble gases and activation products. These problems can be overcome if the activity concentration of 14C can be measured with accelerator mass spectrometry (AMS). Air samples have been taken from the stack of the Swedish nuclear power station Forsmark 1. An automatic sampler for continuous sampling for up to 14 days has been constructed. For measurements with the AMS technique only about 10 mg of carbon is needed, this corresponds to 0.050 m3 of air, which makes this method favourable considering the several m3 which are needed for on-line sampling for β-spectrometry. The first measurements show that the activity concentration in stack air is about 15–20 Bq/m3.

Nuclear data sheets for A = 215,219,223,227

This publication presents evaluated spectroscopic data and corresponding level schemes from radioactive decay and nuclear reaction studies for all nuclei with mass numbers A=215, 219, 223, and 227. Nuclei with mass number A=215 have spherical shape, and their nuclear structure has been interpreted in terms of the shell model. Nuclei with mass number A=219 belong to a transitional region, with spherical, quadrupole, and possibly, octupole deformations, and those with mass numbers A=223 and 227, to newly studied regions of deformations (pure quadrupole coexisting with possible octupole). Because deformations are small in these regions, nuclear states are no longer fully characterized by single Nilsson orbitals. This terminology, however, is used throughout this evaluation to label states rather than to accurately describe their nature. Highlights of this publication include the emission of 14C by 223Ra, discovered by Rose and Jones (84Ro30), and its fine structure, measured by Brillard et al. (89Br34). This constitutes a new mode of decay and provides additional arguments for configuration assignments. They further include the first set of nuclear levels in 215Fr, 215Ra, and 215Ac, determined from in—beam γ-ray spectroscopic measurements. Two major publications have been extensively used in this evaluation: the theoretical paper “Reflection—asymmetric Rotor Model of Odd—A ≈219–229 Nuclei” by Leander and Chen (88Le13), which presents a calculation of single—particle state properties by the coupling of shell—model states to a reflection—asymmetric rotor core; and the review paper “Intrinsic States of Deformed Odd—A Nuclei in the Mass Regions (151≤A≤193) and (A≥221)” by Jain et al. (90Ja11), which gives the systematics and assignments of single—particle states in such mass regions. These evaluations for A=215, 219, 223, and 227 supersede the earlier ones by C. Maples: 77Ma29, Nuclear Data Sheets 22, 207 (1977); 77Ma30, Nuclear Data Sheets 22, 223 (1977); 77Ma31, Nuclear Data Sheets 22, 243 (1977); and 77Ma32, Nuclear Data Sheets 22, 275 (1977).

14C radioactivity decay by 14C emission of different isotopes of radium

14C radioactivity decay by 14C emission of different isotopes of radium

Can we obtain nuclear structure information from exotic decays of heavy nuclei?

A simple cluster model has shown itself to be outstandingly successful in describing the half-lives for emission of heavy fragments ranging from 14C to 32Si from heavy even-even nuclei. However, its predictions for the half-lives of similar decays from odd-even nuclei are systematically below the corresponding measured values or lower limits set by experiment. In view of recent experimental results on the 223Ra → 209Pb + 14C system, we suggest that many of the exotic decays of odd-even nuclei so far observed, or searched for, may be proceeding preferentially to low-lying excited states of the daughter nucleus. We show that all the discrepancies between our model predictions and the presently available data for 14C and 24Ne emission would be consistently removed if this should prove to be the case. An opportunity to extract nuclear structure information from exotic decay measurements would thus be available.

Can we obtain nuclear structure information from exotic decays of heavy nuclei?

A simple cluster model has shown itself to be outstandingly successful in describing the half-lives for emission of heavy fragments ranging from 14C to 32Si from heavy even-even nuclei. However, its predictions for the half-lives of similar decays from odd-even nuclei are systematically below the corresponding measured values or lower limits set by experiment. In view of recent experimental results on the 223Ra → 209Pb + 14C system, we suggest that many of the exotic decays of odd-even nuclei so far observed, or searched for, may be proceeding preferentially to low-lying excited states of the daughter nucleus. We show that all the discrepancies between our model predictions and the presently available data for 14C and 24Ne emission would be consistently removed if this should prove to be the case. An opportunity to extract nuclear structure information from exotic decay measurements would thus be available.

Resolution of metabolic columns by a double-label 2-DG technique: interdigitation and coincidence in visual cortical areas of the same monkey

A double-label modification of the 2-deoxyglucose (DG) technique uses both 3H-2-DG and 14C-2-DG and allows for metabolic activity engaged by 2 distinct experimental conditions to be dissociated throughout the brain of a single subject. In the present study, we used this double-label method to examine the relationship between metabolic columns subserving the 2 eyes in cortical visual areas V1 and V2. The left and right eye's ocular dominance columns were separately activated in the same monkey to demonstrate that the double-label 2-DG method can resolve metabolic differences at the level of the cortical column. In 2 monkeys, 14C-2-DG was injected first and one eye was occluded while the other eye was visually stimulated for 30 min. Then 3H-2-DG was injected, and the occluder was switched so that the alternate eye was stimulated with the same pattern for 30 min. Autoradiographs depicting the 2 labels separately were obtained by exploiting the differential sensitivity of X-ray film and Ultrofilm to 3H and 14C emissions and by applying a radioactivity-subtraction algorithm to pairs of digitized images of the same section (Friedman et al., 1987). Columnar regions of increased activity were evident throughout V1, excepting the representations of the optic disk and monocular crescent. Superimposition of the 3H and 14C images from the same sections demonstrated that columns of increased 3H label were interdigitated with columns of increased 14C label in V1. In contrast, bands of increased 3H-2-DG uptake in extrastriate area V2 were largely coincident with the bands of increased 14C-2-DG uptake. These results illustrate the value of the double-label 2-DG technique for studying fluctuations of metabolic activity under different experimental conditions in the same subject. In the present example, the demonstration that ocular dominance columns are interdigitated in V1, whereas metabolically active bands are coincident in V2, would not have been fully appreciated by comparing 2-DG labeling across separate animals.