Radioactive Isotope 14C Research Articles

Neutronic performance of 208Pb-Bi eutectic-cooled fast reactor with uranium nitride fuel (enriched 15N)

Fast reactors (FRs) require more uranium enrichment than LWRs and fuel reprocessing. The solution proposed to address these issues is to use the modified CANDLE burnup scheme on the reactor core. The use of uranium nitride (UN) as fuel was proposed because the UN fuel has several advantages, such as high melting point, high heavy metal density, and large thermal conductivity. However, using UN as a fuel can produce the radioactive isotope 14C via the reaction 14N (n, p)14C. Therefore, in this study, a neutronic analysis was performed in a modified CANDLE fast reactor employing UN and UN (enriched 15N) as fuel using SRAC. The modified CANDLE fast reactor fuelled with UN (99% 15N) has a higher keff than the UN-fuelled reactor with similar parameters. Similarly, the atomic density of fissile nuclides and power density are higher because the 15N isotope has a smaller neutron capture cross-section than the 14N isotope.

Instrumental base and abilities of the Analytical Center for Isotope Investigations of IMCES SB RAS

The available up-to-date equipment allows us to perform various research tasks using modern scientific tools. The article shows examples of how data on the composition of stable isotopes can be used in biology, environmental studies, archeology, and paleoclimatology. In addition to stable isotopes, radioactive isotopes 14C and 3H are studied. An 1220 Quantulus spectrometer-radiometer is used to determine their specific activity. Investigations on the tritium specific activity in aqueous samples and tritium water isolated from tree ring cellulose on background and anthropogenically loaded sites are carried out. An analysis of carbon specific activity allows performing radiocarbon dating of bottom sediments, peat deposits, and archaeological samples. A qualitative elemental analysis is carried out using a Hitachi TM-1000 microscope equipped with an X-ray spectral analyzer.

The 13C method as a robust alternative to 14C-based measurements of primary productivity in the Mediterranean Sea.

Due to the increasing constraints on using the radioactive isotope 14C to measure primary productivity (14C-PP), we determined the surface carbon fixation rates in the Mediterranean Sea, using the alternative stable isotope 13C method (13C-PP). Rates obtained (13C-POCp) were compared with simultaneous 14C-POCp measurements in samples of different volumes (72 mL and 1.2 L). We also tested the variation of the percentage of dissolved primary production (PER), to the total productivity using organic and inorganic filters (14C method). 13C-POCp rates ranged from 0.4, in the Ionian basin, to 1.5 mgC m−3 h−1 in the Ligurian region. These results agreed with those found with the 14C-PP in 1.2-L samples (two sample t-test, t = 1.035, df = 22, P = 0.31). However, we found that 14C-POCp rates derived from 72-mL incubations were 46% lower than those measured with 13C-PP. The discrepancy between large and small volume incubations was likely due to differences in the number of large phytoplankton cells within the community. PER values measured with silver membrane filters yielded similar results than those obtained using polycarbonate filters. Our findings showed that when the sample size is carefully chosen, the 13C-PP provide comparable results to 14C-PP even in waters of low productivity in the Mediterranean Sea.

Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)

Abstract. Carbon isotopes in the ocean are frequently used as paleoclimate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized data set, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly fewer computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example, too sluggish ventilation of the deep Pacific Ocean.

Isotope analyses of the lake sediments in the Plitvice Lakes, Croatia

Abstract The analyses of radioactive isotopes 14C, 137Cs and 210Pb, and stable isotope 13C were performed in the sediment cores, top 40 cm, taken in 2011 from karst lakes Prošće and Kozjak in the Plitvice Lakes National Park, central Croatia. Frozen sediment cores were cut into 1 cm thick layers and dried. 14C activity in both carbonate and organic fractions was measured using accelerator mass spectrometry technique with graphite synthesis. 137Cs, 210Pb, 214Pb and 214Bi were measured by low level gamma spectrometry method on ORTECHPGe detector with the efficiency of 32%. Distribution of 14C activity from both lakes showed increase of the 14C activity in the top 10–12 cm in both carbonate and organic fractions as a response to thermonuclear bomb-produced 14C in the atmosphere in the sixties of the 20th century. Anthropogenically produced 137Cs was also observed in sediment profiles. Sedimentation rates for both lake sediments were estimated based on the unsupported 210Pb activity. Different 14C activity of the carbonate fraction (63–80 pMC, percent of modern carbon) and organic fraction (82–93 pMC) is the result of geochemical and biological processes of the sediment precipitation in the lake waters. This is also confirmed by the δ 13 C values of both fractions. Carbon isotope composition, a 14 C and δ 13 C, was compared with the lake sediments from the same lakes collected in 1989 and 2003.

Radiocarbon Analysis of Carbonaceous Aerosols: Recent Developments

Carbonaceous aerosols are a major fraction of airborne particulate matter. They contribute to climate and health effects of the total aerosol burden of the atmosphere by counteracting the current trend of global warming and inducing respiratory and cardiovascular diseases, respectively. In spite of this general importance, only little is known about composition and sources of carbonaceous aerosols. Analysis of the long-lived radioactive isotope 14C (radiocarbon) is a unique source apportionment tool: it unambiguously separates fossil from non-fossil sources, as 14C has completely decayed in fossil fuels, whereas modern materials have the contemporary radiocarbon level. A novel separation method was developed for the direct determination of 14C in organic carbon (OC) and elemental carbon (EC), two sub-fractions of total carbon (TC). The implementation of a gas ion source for measurement with accelerator mass spectrometry (AMS) made 14C analysis more simple and robust. Based on this technique, all major contributions to the carbonaceous aerosol can be identified, which originate from fossil-fuel, biomass-burning and biogenic emissions. A survey of results from different field campaigns is shown.

Using the scanning electron microprobe and secondary ion mass spectrometry to locate 14C‐ and 13C‐labelled plant residues within soil aggregates

Increasing concentrations of CO2 in the atmosphere are placing emphasis on the necessity for sequestering carbon (C) into soil organic matter (SOM). By studying the interior parts of soil aggregates, a better understanding of the incorporation and sequestration of plant residue materials within these aggregates could be obtained. The location of newly added plant residues within soil aggregates may also assist in the investigation of the impact of these newly added plant materials on soil aggregation. This study investigated two different techniques for determining the location of newly added plant residues within soil aggregates by using plant materials labelled with 14C and 13C isotopes incorporated into two different soil types, Black Earth (Pellic Vertisol) and Red Clay (Chromic Vertisol). Both autoradiography combined with scanning electron microprobe analysis (14C) and secondary ion mass spectrometry (SIMS) (13C) were successfully used for detecting the presence and location of the newly added plant residues fragments within soil aggregates of both soil types. The use of labelled plant materials is essential for the study of the location of newly added plant materials within soil aggregates, and this has proven to be a useful tool for studying the impact of residue additions on soil aggregate formation. Furthermore, these methods have been shown to be useful for determining the incorporation and sequestration of C materials within soil aggregates. The development of the 13C SIMS technique could alleviate the necessity for the use of the radioactive isotope 14C in soil studies.

Using the scanning electron microprobe and secondary ion mass spectrometry to locate 14 C and 13 C labelled plant residues within soil aggregates

Increasing concentrations of CO2 in the atmosphere are placing emphasis on the necessity for sequestering carbon (C) into soil organic matter (SOM). By studying the interior parts of soil aggregates, a better understanding of the incorporation and sequestration of plant residue materials within these aggregates could be obtained. The location of newly added plant residues within soil aggregates may also assist in the investigation of the impact of these newly added plant materials on soil aggregation. This study investigated two different techniques for determining the location of newly added plant residues within soil aggregates by using plant materials labelled with 14C and 13C isotopes incorporated into two different soil types, Black Earth (Pellic Vertisol) and Red Clay (Chromic Vertisol). Both autoradiography combined with scanning electron microprobe analysis (14C) and secondary ion mass spectrometry (SIMS) (13C) were successfully used for detecting the presence and location of the newly added plant residues fragments within soil aggregates of both soil types. The use of labelled plant materials is essential for the study of the location of newly added plant materials within soil aggregates, and this has proven to be a useful tool for studying the impact of residue additions on soil aggregate formation. Furthermore, these methods have been shown to be useful for determining the incorporation and sequestration of C materials within soil aggregates. The development of the 13C SIMS technique could alleviate the necessity for the use of the radioactive isotope 14C in soil studies.

Primary productivity and calcification rate in blooms of the coccolithophoridEmiliania huxleyi(Lohmann) Hay et Mohler developing in mesocosms

Abstract Primary production and calcification rate were monitored in mesocosms with different nutrient conditions at the Marine Biological Field Station 20 km south of Bergen, Norway. The incorporation of carbon in particulate orfianic matter (POC) and of calcium in calcite was measured with the radioactive isotopes 14C and 45Ca, respectively. It appeared that under eutrophic conditions daily poe production in the algal size fraction < 10 µm eventually reached a higher level than in the < 10 µm algae, which was probably the result of size-selective grazing of the smaller algae by microzooplankton. At oligotrophic conditions the < 10 µm algae became the dominant producers. In two of the mesocosms studied blooms of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler developed. Indirect evidence shows that after culmination of the blooms both the poe content in the size fraction < 10 µm (to which E. huxleyi belongs) and the calcite content were strongly reduced. Bloom decline probably resulted fro...

In Situ-Produced Cosmogenic Isotopes in Terrestrial Rocks

In the late forties, Libby and his collaborators detected the naturally occurring radioactive isotope 14C, produced by cosmic radiation in the Earth's atmosphere (Libby 1946, Anderson et al 1 947). This marked the onset of the search for cosmic-ray-produced (cosmogenic) isotopic changes in terrestrial and extraterrestrial samples and in the cosmic rays themselves. During the four decades since Libby's discovery, some four dozen cosmo­ genic stable and radioactive isotopes in extraterrestrial samples (Reedy et al 1983) and two dozen in terrestrial samples (Lal & Peters 1 967) have been discovered. These isotopes have found applications in cosmic-ray physics (in the study of acceleration and propagation of galactic and solar cosmic rays), in solar system astrophysics (in determining the evolutionary history of meteorites, the lunar surface, and interplanetary dust particles), and in the Earth sciences (in archaeology, meteorology, glaciology and oceanography). For reviews on these topics, reference is made to Simpson (1983); Reedy et al (1983); and Lal & Peters (1967), Oeschger et al (1970), and Faure ( 1986), respectively. The process of discovery continues, pro­ pelled by advances in the techniques used to measure these isotopes. Even now, examples of new isotopic effects are being discovered, and new applications are being made of the various isotopic effects. When one looks at the history of the development of the terrestrial cosmogenic field, one observes that it grew in waves: After an idea is implemented, the field

1 Measurement of the turnover of substrates of carbohydrate and protein metabolism using radioactive isotopes

The rate of turnover of glucose or leucine can be measured in the steady state by using the radioactive isotopes 14C or 3H to 'trace' these metabolites. The tracer can either be injected or infused intravenously and its metabolism followed by monitoring levels of the tracer in blood, breath and urine. If a 14C labelled metabolite is used the oxidation rate may sometimes be determined by measuring the expiry rate of 14CO2. If the single injection technique is used the specific activity curve is fitted with an exponential function and the area under the curve calculated. Turnover rate is calculated from dose of isotope injected/area under the specific activity time curve. This technique can be used to construct a compartmental model to describe the behaviour of the metabolite. If the constant infusion technique is used, tracer is infused until a steady state level of tracer is achieved. This plateau is used to calculate the turnover of the metabolite from infusion rate of tracer/specific activity at steady state. While this latter method provides the simplest method of calculating turnover it cannot be used to model the data. The infusion technique can be used to measure changes in turnover and oxidation in the non-steady state. Tracer is infused to a steady state level and the system is then perturbed by for example, the infusion of a hormone. The changes in Ra and Rd can be determined either by using the Steele equation which assumes a single pool or by using compartmental analysis.

On the reaction mechanism of the carburization and decarburization of α‐iron in CH4/H2‐mixtures

The surface reaction of the carburization and decarburization of α‐iron in CH4/H2‐mixtures has been investigated by a method using the radioactive isotope 14C. Experimentally two different kinetic equations have been confirmed and discussed in detail: urn:x-wiley:01774832:srin00846:equation:srin00846-math-0001 In accordance to 1) the kinetic equation (1) is explained by a slow reaction: .For the kinetic equation (2) the adsorption, respectively the desorption of CH4, is considered to be the most slow partial step. The correlation of the carburization with the adsorption is supported by the relations: urn:x-wiley:01774832:srin00846:equation:srin00846-math-0003 Thus can be regarded as Ea, the activation energy of the adsorption. Its value was determined at 109 kJ/mol being equivalent to 1.1 eV, which is characteristic for a chemisorption.Further it was established, that the rate of the decarburization according to equation (2) increases with decreasing temperature, i.e. the (apparent) activation energy proved to be negative. This is explained by the fact that before its rate‐controlling desorption the CH4‐molecule first of all must be formed step‐by‐step and by the assumption that for thermodynamical reasons the surface concentration of CH4 increases very much with decreasing temperature.The range of validity of the kinetic equations (1) and (2) can be limited to each other as follows: – The kinetic law (1) is established especially at higher H2‐pressures and at surfaces with low, but effective impurities. The impurities simultaneously result in a high decline of the reaction rate. – The kinetic law (2) is valid especially at lower H2‐pressures.

Laser detection of rare radioactive isotopes. Selective enrichment of the initial state

An investigation is made of the enrichment of the initial state with atoms or ions of rare radioactive isotopes by using cw laser radiation. Estimates of the enrichment of metastable levels are obtained for 14C and 26Al atoms and 41Ca+ ions. The radioactive isotope 14C is used as an example to discuss the combination of enrichment of the initial state with multistage selective photoionization of atoms. It is shown that in this case, it is realistic to expect a selectivity higher than 1020.

Synthesis of the preparations pyrroxan and butyroxan labeled with the radioactive isotope14C

Synthesis of the preparations pyrroxan and butyroxan labeled with the radioactive isotope14C