Isotopic Scaling Research Articles

Chronologie et enregistrements climatiques dans les dépôts travertineux du Maroc

Establish an accurate chronological frame for the climatic proxies remains an important issue. The chronology of calcitic deposits (speleothems and travertines) can be of great help for modeling the various mechanisms which control the climatic variations in Northwestern Africa in isotopic stratigraphic scale based on oxygen isotopes variations. Travertines can be dated using several methods among them the radiocarbon, uranium-series, Electron Spin Resonance and magnestratigraphy. The dating results obtained on hydrothermal or fluvial travertines taken on 24 sites spread on Moroccan territory are presented in this article. Sites in which the oldest human bearing occupations are attributed to the Middle Pleistocene are given priority. Our results show that travertines formed from Lower Pleistocene, around the Middle Plesitocene Transition (MPT), which occurred between 1.2 and 0.7Ma, and today. The second major information demonstrates that these formations grew during even or odd isotopic stages both in hydrothermal and fluvial travertines, from the beginning of Brunhes epoch thanks to palaeomagnetic data.

Projectile Fragmentation and Isotopic Scaling in a Transport Approach

We investigate projectile fragmentation using transport theory coupled with statistical decay codes for the excited primary fragments. We concentrate on isotope distributions and on an isoscaling analysis of isotope ratios to obtain information about the symmetry energy. The analysis is performed depending on the impact parameter since the thermodynamic properties of the primary fragments depend on it strongly. We compare reaction systems with different neutron and proton excess, Ar-38, Ca-40+Be-9 and Ca-48, Ca-40+Be-9 both at 140 AMeV, to investigate the range of validity of the isoscaling assumption. We find it is well-justified for isotopes which are mainly produced by the secondary decay. However, for isotopes with N or Z near the incident projectile for grazing impact parameters, the process is more direct and the distributions are not well-represented by statistical ensembles. In the range of validity, the extracted symmetry energies are generally reasonable.

Development and evaluation of a suite of isotope reference gases for methane in air

Abstract. Measurements from multiple laboratories have to be related to unifying and traceable reference material in order to be comparable. However, such fundamental reference materials are not available for isotope ratios in atmospheric methane, which led to misinterpretations of combined data sets in the past. We developed a method to produce a suite of synthetic CH4-in-air standard gases that can be used to unify methane isotope ratio measurements of laboratories in the atmospheric monitoring community. Therefore, we calibrated a suite of pure methane gases of different methanogenic origin against international referencing materials that define the VSMOW (Vienna Standard Mean Ocean Water) and VPDB (Vienna Pee Dee Belemnite) isotope scales. The isotope ratios of our pure methane gases range between −320 and +40 ‰ for δ2H–CH4 and between −70 and −40 ‰ for δ13C–CH4, enveloping the isotope ratios of tropospheric methane (about −85 and −47 ‰ for δ2H–CH4 and δ13C–CH4 respectively). Estimated uncertainties, including the full traceability chain, are < 1.5 ‰ and < 0.2 ‰ for δ2H and δ13C calibrations respectively. Aliquots of the calibrated pure methane gases have been diluted with methane-free air to atmospheric methane levels and filled into 5 L glass flasks. The synthetic CH4-in-air standards comprise atmospheric oxygen/nitrogen ratios as well as argon, krypton and nitrous oxide mole fractions to prevent gas-specific measurement artefacts. The resulting synthetic CH4-in-air standards are referred to as JRAS-M16 (Jena Reference Air Set – Methane 2016) and will be available to the atmospheric monitoring community. JRAS-M16 may be used as unifying isotope scale anchor for isotope ratio measurements in atmospheric methane, so that data sets can be merged into a consistent global data frame.

Projectile fragmentation of 40,48Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of 40,48Ca on 9Be and 181Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the 40,48Ca pair. The symmetry energy determined in this way depends on these structure effects.

Mass Fractionation Laws, Mass-Independent Effects, and Isotopic Anomalies

Isotopic variations usually follow mass-dependent fractionation, meaning that the relative variations in isotopic ratios scale with the difference in mass of the isotopes involved (e.g., δ17O ≈ 0.5×δ18O). In detail, however, the mass dependence of isotopic variations is not always the same, and different natural processes can define distinct slopes in three-isotope diagrams. These variations are subtle, but improvements in analytical capabilities now allow precise measurement of these effects and make it possible to draw inferences about the natural processes that caused them (e.g., reaction kinetics versus equilibrium isotope exchange). Some elements, in some sample types, do not conform to the regularities of mass-dependent fractionation. Oxygen and sulfur display a rich phenomenology of mass-independent fractionation, documented in the laboratory, in the rock record, and in the modern atmosphere. Oxygen in meteorites shows isotopic variations that follow a slope-one line (δ17O ≈ δ18O) whose origin may be associated with CO photodissociation. Sulfur mass-independent fractionation in ancient sediments provides the tightest constraint on the oxygen partial pressure in the Archean and the timing of Earth's surface oxygenation. Heavier elements also show departures from mass fractionation that can be ascribed to exotic effects associated with chemical reactions such as magnetic effects (e.g., Hg) or the nuclear field shift effect (e.g., U or Tl). Some isotopic variations in meteorites and their constituents cannot be related to the terrestrial composition by any known process, including radiogenic, nucleogenic, and cosmogenic effects. Those variations have a nucleosynthetic origin, reflecting the fact that the products of stellar nucleosynthesis were not fully homogenized when the Solar System formed. Those anomalies are found at all scales, from nanometer-sized presolar grains to bulk terrestrial planets. They can be used to learn about stellar nucleosynthesis, mixing in the solar nebula, and genetic relationships between planetary bodies (e.g., the origin of the Moon). They can also confound interpretations based on dating techniques (e.g., 146Sm-142Nd) when they are misidentified as isotopic variations of radiogenic origin. To summarize, there is a world to explore outside of mass-dependent fractionation whose impact is promised to expand as analytical capabilities to measure ever-subtler isotopic anomalies on ever-smaller samples continue to improve.

Будова, історія формування поверхонь вирівнювання Північно-Західного Передкарпаття

Based on the detailed geomorphological analysis of the terraces of the Dnister River, and of its tributaries, and the analysis of the sections of the terrace deposits, the main stages of the history of the Dnister valley development in the north-south Forecarpathians have been presented. Some existing and already firmly establishes opinions concerning the structure of the terraces, their extent, and the time of their formation were clarified. The paleogeographical events were correlated with the stages of the oxygen isotope scale, the paleomagnetical reference points and the paleogeographical (paleoclimatical) phases. Key words: Krasna planation surface, Loyeva planation surface, Starosilska planation surface, terrace, surface of the terrace, plinth (socle) of the terrace, alluvium, glacial deposits, absolute and relative datum levels.

Diffusion of multi-isotopic chemical species in molten silicates

Diffusion experiments in a simplified Na2O–CaO–SiO2 liquid system are used to develop a general formulation for the fractionation of Ca isotopes during liquid-phase diffusion. Although chemical diffusion is a well-studied process, the mathematical description of the effects of diffusion on the separate isotopes of a chemical element is surprisingly underdeveloped and uncertain. Kinetic theory predicts a mass dependence on isotopic mobility, but it is unknown how this translates into a mass dependence on effective binary diffusion coefficients, or more generally, the chemical diffusion coefficients that are housed in a multicomponent diffusion matrix. Our experiments are designed to measure Ca mobility, effective binary diffusion coefficients, the multicomponent diffusion matrix, and the effects of chemical diffusion on Ca isotopes in a liquid of single composition.We carried out two chemical diffusion experiments and one self-diffusion experiment, all at 1250°C and 0.7GPa and using a bulk composition for which other information is available from the literature. The self-diffusion experiment is used to determine the mobility of Ca in the absence of diffusive fluxes of other liquid components. The chemical diffusion experiments are designed to determine the effect on Ca isotope fractionation of changing the counter-diffusing component from fast-diffusing Na2O to slow-diffusing SiO2. When Na2O is the main counter-diffusing species, CaO diffusion is fast and larger Ca isotopic effects are generated. When SiO2 is the main counter-diffusing species, CaO diffusion is slow and smaller Ca isotopic effects are observed. In both experiments, the liquid is initially isotopically homogeneous, and during the experiment Ca isotopes become fractionated by diffusion. The results are used as a test of a new general expression for the diffusion of isotopes in a multicomponent liquid system that accounts for both self diffusion and the effects of counter-diffusing species.Our results show that (1) diffusive isotopic fractionations depend on the direction of diffusion in composition space, (2) diffusive isotopic fractionations scale with effective binary diffusion coefficient, as previously noted by Watkins et al. (2011), (3) self-diffusion is not decoupled from chemical diffusion, (4) self diffusion can be faster than or slower than chemical diffusion and (5) off-diagonal terms in the chemical diffusion matrix have isotopic mass-dependence. The results imply that relatively large isotopic fractionations can be generated by multicomponent diffusion even in the absence of large concentration gradients of the diffusing element. The new formulations for isotope diffusion can be tested with further experimentation and provide an improved framework for interpreting mass-dependent isotopic variations in natural liquids.

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

AbstractSince the early 1950s, the number of international measurement standards for anchoring stable isotope delta scales has mushroomed from 3 to more than 30, expanding to more than 25 chemical elements. With the development of new instrumentation, along with new and improved measurement procedures for studying naturally occurring isotopic abundance variations in natural and technical samples, the number of internationally distributed, secondary isotopic reference materials with a specified delta value has blossomed in the last six decades to more than 150 materials. More than half of these isotopic reference materials were produced for isotope-delta measurements of seven elements: H, Li, B, C, N, O, and S. The number of isotopic reference materials for other, heavier elements has grown considerably over the last decade. Nevertheless, even primary international measurement standards for isotope-delta measurements are still needed for some elements, including Mg, Fe, Te, Sb, Mo, and Ge. It is recommended that authors publish the delta values of internationally distributed, secondary isotopic reference materials that were used for anchoring their measurement results to the respective primary stable isotope scale.

Doubly Labelled Water analysis: Preparation, memory correction, calibration and quality assurance for δ2H and δ18O measurements over four orders of magnitudes

The Doubly Labelled Water (DLW) method is an established way of determining the metabolic rate in humans and animals, with the advantage that the subjects need not be confined. The method, however, needs accurate determination of both the δ(2)H and the δ(18)O isotope values over a wide range of enrichments. In this paper we describe a number of crucial steps in the process of isotope determination in body fluids. These steps include micro-distillation, correction of the measurements for sample-to-sample memory and calibration of the isotope scales over many orders of magnitudes. In contrast to several published protocols and guidelines, we also take highly enriched samples into account, as they are required for studying the metabolic rate of birds and small mammals. For our isotope scale calibration, we made a set of gravimetrically prepared, double labelled waters with known isotope values. Our quality assurance includes a scheme for easy calculation of the error propagation, leading to a reliable estimate of the analytical error in the metabolic rate. Our memory correction algorithm assumes the existence of three water "pools" that have different sizes and exchange rates with the injected samples. We show that the method can correct even huge memory signals, without the need for "true" values. With the presented building blocks, we show how to assure a reliable and accurate isotope analysis for the DLW method, both for human and for animal applications. Although our measurements have been performed using isotope ratio mass spectrometry, most of the procedures are also useful for laser spectrometry.

탄산칼슘을 이용한 이산화탄소 안정동위원소 표준시료 제작에 대한 연구

안정동위원소 질량분석기를 이용한 탄소와 산소의 동위원소비 측정은, 이산화탄소 표준기체의 동위원소 비에 대하여 그 상대적인 값을 측정함으로써 이루어진다. 따라서 실험실 표준기체는 <TEX>${\delta}^{13}C$</TEX>와 <TEX>${\delta}^{18}O$</TEX> 값의 국제 표준물질인 PDB와 V-SMOW에 대해 보정된 이산화탄소이여야 하며, 이는 국제적 자료의 비교와 검증을 위해 필수적이다. 그러나 표준기체는 제작 기간이 길며, 가격이 비싼 단점이 있고, 장기간 사용 시 실린더 내부 압력의 변화로 동위원소의 분별이 생길 우려가 크다. 따라서 본 연구는 실험실 표준기체 관리의 효율성을 높이기 위해 장기간 안정적 보관이 가능한 고체 표준물질로부터 동위원소 분별없이 순수한 이산화탄소 기체를 추출하여, 실험실 표준기체로 사용할 수 있는 방법을 제시하고자 한다. 본 논문은 Coplen et al.(1983)에 의하여 제안된 방법을 기초로 한 다량의 이산화탄소 표준 기체 제작에 초점을 두었다. 이산화탄소는 탄산칼슘과 100% 순수 인산의 반응에 의해 생성되는데, 두 물질의 반응에 필요한 실험 장치 및 실험 과정을 상세히 기술하였으며, 최적의 실험 조건 결정을 위한 다양한 분석 결과를 소개하였다. 이어 생성된 이산화탄소 기체의 추출, 정제와 포집은 자체 제작된 진공관에서 이루어졌으며, 각 단계에 대한 자세한 설명이 주어진다. 이산화탄소의 <TEX>${\delta}^{13}C$</TEX>와 <TEX>${\delta}^{18}O$</TEX> 측정은 서울대학교 기초과학교육연구 공동기기원에서 운영 중인 안정동위원소 질량분석기(VG Isotech, SIRA Series II)를 이용하여 이루어졌다. 탄산칼슘 고체 표준물질로부터 이산화탄소 기체 추출과 추출된 기체의 정제 포집 등 전체 분석과정의 정밀도 검증을 위해 동일한 Solenhofen-ori <TEX>$CaCO_3$</TEX>(< <TEX>$63{\mu}m$</TEX>) 고체 시료로 부터 15회에 걸쳐 표준기체를 제작하였고, 매회 100 mg <TEX>$CaCO_3$</TEX>을 이용하여 총 15개의 표준기체 제작이 8일에 걸쳐 이루어졌다. 이 표준기체들의 분석 표준편차(<TEX>$1{\sigma}$</TEX>)는 <TEX>${\delta}^{13}C$</TEX>의 경우 <TEX>${\pm}0.01$</TEX>‰, <TEX>${\delta}^{18}O$</TEX>는 <TEX>${\pm}0.05$</TEX>‰로 매우 높은 정밀도를 보여주었다. 이러한 분석 정밀도는 안정동위원소 질량분석기기 자체와 같은 내부 정밀도에 상응하며, 본 연구에서 제시한 실험실 표준기체 제작방법의 높은 신뢰성과 재현성을 입증하는 결과이다. 따라서 본 연구는 표준기체 보유가 어려워 정밀, 정확한 안정동위원소 분석에 어려움이 많았던 연구 분야에 자체 표준기체 제작 기술을 제공하는데 크게 기여할 것으로 생각된다. The isotope ratios of <TEX>$^{13}C/^{12}C$</TEX> and <TEX>$^{18}O/^{16}O$</TEX> for a sample in a mass spectrometer are measured relative to those of a pure <TEX>$CO_2$</TEX> reference gas (i.e., laboratory working standard). Thus, the calibration of a laboratory working standard gas to the international isotope scales (Pee Dee Belemnite (PDB) for <TEX>${\delta}^{13}C$</TEX> and Vienna Standard Mean Ocean Water (V-SMOW) for <TEX>${\delta}^{18}O$</TEX>) is essential for comparisons between data sets obtained by other groups on other mass spectrometers. However, one often finds difficulties in getting well-calibrated standard gases, because of their production time and high price. Additional difficulty is that fractionation processes can occur inside the gas cylinder most likely due to pressure drop in long-term use. Therefore, studies on laboratory production of pure <TEX>$CO_2$</TEX> isotope standard gas from stable solid calcium carbonate standard materials, have been performed. For this study, we propose a method to extract pure <TEX>$CO_2$</TEX> gas without isotope fractionation from a solid calcium carbonate material. The method is similar to that suggested by Coplen et al., (1983), but is better optimized particularly to make a large amount of pure <TEX>$CO_2$</TEX> gas from calcium carbonate material. The <TEX>$CaCO_3$</TEX> releases <TEX>$CO_2$</TEX> in reaction with 100% pure phosphoric acid at <TEX>$25^{\circ}C$</TEX> in a custom designed, evacuated reaction vessel. Here we introduce optimal procedure, reaction conditions, and samples/reactants size for calcium carbonate-phosphoric acid reaction and also provide the details for extracting, purifying and collecting <TEX>$CO_2$</TEX> gas out of the reaction vessel. The measurements for <TEX>${\delta}^{18}O$</TEX> and <TEX>${\delta}^{13}C$</TEX> of <TEX>$CO_2$</TEX> were performed at Seoul National University using a stable isotope ratio mass spectrometer (VG Isotech, SIRA Series II) operated in dual-inlet mode. The entire analysis precisions for <TEX>${\delta}^{18}O$</TEX> and <TEX>${\delta}^{13}C$</TEX> were evaluated based on the standard deviations of multiple measurements on 15 separate samples of purified <TEX>$CO_2$</TEX>. The pure <TEX>$CO_2$</TEX> samples were taken from 100-mg aliquots of a solid calcium carbonate (Solenhofen-ori <TEX>$CaCO_3$</TEX>) during 8-day experimental period. The multiple measurements yielded the <TEX>$1{\sigma}$</TEX> precisions of <TEX>${\pm}0.01$</TEX>‰ for <TEX>${\delta}^{13}C$</TEX> and <TEX>${\pm}0.05$</TEX>‰ for <TEX>${\delta}^{18}O$</TEX>, comparable to the internal instrumental precisions of SIRA. Therefore, we conclude the method proposed in this study can serve as a way to produce an accurate secondary and/or laboratory <TEX>$CO_2$</TEX> standard gas. We hope this study helps resolve difficulties in placing a laboratory working standard onto the international isotope scales and does make accurate comparisons with other data sets from other groups.

Extreme &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C depletion of CCl&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;F&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in firn air samples from NEEM, Greenland

Abstract. A series of 12 high volume air samples collected from the S2 firn core during the North Greenland Eemian Ice Drilling (NEEM) 2009 campaign have been measured for mixing ratio and stable carbon isotope composition of the chlorofluorocarbon CFC-12 (CCl2F2). While the mixing ratio measurements compare favorably to other firn air studies, the isotope results show extreme 13C depletion at the deepest measurable depth (65 m), to values lower than δ13C = −80‰ vs. VPDB (the international stable carbon isotope scale), compared to present day surface tropospheric measurements near −40‰. Firn air modeling was used to interpret these measurements. Reconstructed atmospheric time series indicate even larger depletions (to −120‰) near 1950 AD, with subsequent rapid enrichment of the atmospheric reservoir of the compound to the present day value. Mass-balance calculations show that this change is likely to have been caused by a large change in the isotopic composition of anthropogenic CFC-12 emissions, probably due to technological advances in the CFC production process over the last 80 yr, though direct evidence is lacking.

Normalization procedures and reference material selection in stable HCNOS isotope analyses: an overview

The uncertainties of stable isotope results depend not only on the technical aspects of measurements, but also on how raw data are normalized to one of the international isotope scales. The inconsistency in the normalization methods used and in the selection of standards may lead to substantial differences in the results obtained. Therefore, unification of the data processing protocols employed is highly desirable. The best performing methods are two-point or multipoint normalization methods based on linear regression. Linear regression is most robust when based on standards that cover the entire range of δ values typically observed in nature, regardless of the δ values of the samples analysed. The uncertainty can be reduced by 50% if measurements of two different standards are performed four times, or measurements of four standards are performed twice, with each batch of samples. Chemical matrix matching between standards and samples seems to be critical for δ (18)O of nitrate or δ (2)H of hair samples (thermal conversion/elemental analyser), for example; however, it is not necessarily always critical for all types of samples and techniques (e.g. not for most δ (15)N and δ (13)C elemental analyser analyses). To ensure that all published data can be recalculated, if δ values of standards or the isotope scales are to be updated, the details of the normalization technique and the δ values of the standards used should always be clearly reported.

The stable isotopic signature of biologically produced molecular hydrogen (H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;)

Abstract. Biologically produced molecular hydrogen (H2) is characterised by a very strong depletion in deuterium. Although the biological source to the atmosphere is small compared to photochemical or combustion sources, it makes an important contribution to the global isotope budget of H2. Large uncertainties exist in the quantification of the individual production and degradation processes that contribute to the atmospheric budget, and isotope measurements are a tool to distinguish the contributions from the different sources. Measurements of δ D from the various H2 sources are scarce and for biologically produced H2 only very few measurements exist. Here the first systematic study of the isotopic composition of biologically produced H2 is presented. In a first set of experiments, we investigated δ D of H2 produced in a biogas plant, covering different treatments of biogas production. In a second set of experiments, we investigated pure cultures of several H2 producing microorganisms such as bacteria or green algae. A Keeling plot analysis provides a robust overall source signature of δ D = −712‰ (±13‰) for the samples from the biogas reactor (at 38 °C, δ DH2O= +73.4‰), with a fractionation constant &amp;amp;varepsilon;H2-H2O of −689‰ (±20‰) between H2 and the water. The five experiments using pure culture samples from different microorganisms give a mean source signature of δ D = −728‰ (±28‰), and a fractionation constant &amp;amp;varepsilon;H2-H2O of −711‰ (±34‰) between H2 and the water. The results confirm the massive deuterium depletion of biologically produced H2 as was predicted by the calculation of the thermodynamic fractionation factors for hydrogen exchange between H2 and water vapour. Systematic errors in the isotope scale are difficult to assess in the absence of international standards for δ D of H2. As expected for a thermodynamic equilibrium, the fractionation factor is temperature dependent, but largely independent of the substrates used and the H2 production conditions. The equilibrium fractionation coefficient is positively correlated with temperature and we measured a rate of change of 2.3‰ / °C between 45 °C and 60 °C, which is in general agreement with the theoretical prediction of 1.4‰ / °C. Our best experimental estimate for &amp;amp;varepsilon;H2-H2O at a temperature of 20 °C is −731‰ (±20‰) for biologically produced H2. This value is close to the predicted value of −722‰, and we suggest using these values in future global H2 isotope budget calculations and models with adjusting to regional temperatures for calculating δ D values.

Isotope ratio mass spectrometry – history and terminology in brief

The history of isotope ratio mass spectrometry (IRMS) is briefly described. It is shown that the fundamental design of isotope ratio mass spectrometers has not changed since the 1940s. The basic findings concerning the natural variation of isotope abundances even date back to the 1930s. Recent improvements in the methodology mainly concern online coupling and analytical peripherals. The nature of isotopic scales necessitates a specific terminology which is unfamiliar to many analysts. However, corresponding guidelines exist that should be adopted by the anti-doping community. Currently, steroids represent the only group of compounds routinely analyzed by IRMS in doping-control. Suggestions are made in respect to a harmonized terminology concerning the nature and origins of steroids.

δ18O values of Sus scrofa blood water and bone phosphate; a marked discrepancy between domestic and wild specimens

δ¹⁸O analyses of water in the blood of domestic and wild pigs indicated that large isotopic differences exist between domestic and wild specimens of the same species (Sus scrofa) living in the same area. Similar isotopic differences are found between the δ¹⁸O(PO₄³⁻) values of bones from the two groups of animals. When δ¹⁸O values obtained from recent wild boar bones are introduced in the equation of the isotopic scale determined for domestic pigs, totally unreliable δ¹⁸O values of local meteoric water are obtained. The δ¹⁸O(PO₄³⁻) values measured in three groups of modern wild boar specimens allow the calculation of a first approximate equation which is quite different from that of domestic pigs. This isotopic scale should be accurately re-calibrated for wild animals.

Error propagation in normalization of stable isotope data: a Monte Carlo analysis

A higher analytical precision of a stable isotope ratio mass spectrometer does not automatically guarantee accurate determination of the true isotope composition (delta-value) of samples, since estimates of true delta-values are obtained from the normalization of raw isotope data. We performed both Monte Carlo simulations and laboratory experiments to investigate aspects of error propagation during the normalization of carbon stable isotope data. We found that increasing both the number of different reference standards and the number of repetitions of each of these standards reduces the normalization error. A 50% reduction in the normalization error can be achieved over the two-point normalization by either analyzing two standards four times each, or four standards two times each. If the true delta-value of a sample is approximately known a priori, the normalization error may then be reduced through a targeted choice of locally optimal standards. However, the difference in improvement is minimal and, therefore, a more practical strategy is to use two or more standards covering the whole stable isotope scale. The selection of different sets of standards by different laboratories or for different batches of samples in the same laboratory may lead to significant differences in the normalized delta-values of the same samples, leading to inconsistent results. Hence, the same set of standards should always be used for a particular element and a particular stable isotope analytical technique.

Nicotine, acetanilide and urea multi‐level 2H‐, 13C‐ and 15N‐abundance reference materials for continuous‐flow isotope ratio mass spectrometry

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the delta values of these reference materials should bracket the isotopic range of samples with unknown delta values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for delta13C and delta15N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: delta2H(nicotine) -162 to -45 per thousand, delta13C(nicotine) -30.05 to +7.72 per thousand, delta15N(nicotine) -6.03 to +33.62 per thousand; delta15N(acetanilide) +1.18 to +40.57 per thousand; delta13C(urea) -34.13 to +11.71 per thousand, delta15N(urea) +0.26 to +40.61 per thousand (recommended delta values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different delta15N values. Comparative delta13C and delta15N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials.

Surface and symmetry energies in isoscaling for multifragmentation reactions

The possibilities of modifications for symmetry and surface energy coefficients of nuclear matter at freeze-out density are investigated theoretically by means of isoscaling (isotopic scaling) on the basis of a statistical multifragmentation model. It is seen that while the isoscaling parameters as predicted by Markov chain calculations for the single sources 124Sn and 112Sn are very sensitive to the symmetry term, the surface energy variation slightly affects the isoscaling parameters in the multifragmentation region. The influence of these changes on the mean neutron to proton ratios of light fragments for 2 ⩽ Z ⩽ 10 is also shown. Comparing our results with MSU experimental data, it is confirmed that a significant reduction of the symmetry-term coefficient is found necessary to reproduce the isoscaling parameters of Z ⩽ 8 fragments.

Isospin dependent properties of asymmetric nuclear matter

AbstractThe density dependence of nuclear symmetry energy is determined from a system-atic study of the isospin dependent bulk properties of asymmetric nuclear matterusing the isoscalar and the isovector components of density dependent M3Y in-teraction. The incompressibility K ∞ for the symmetric nuclear matter, the isospindependent part K asy of the isobaric incompressibility and the slope L are all inexcellent agreement with the constraints recently extracted from measured isotopicdependence of the giant monopole resonances in even-A Sn isotopes, from the neu-tron skin thickness of nuclei and from analyses of experimental data on isospindiffusion and isotopic scaling in intermediate energy heavy-ion collisions. This workprovides a fundamental basis for the understanding of nuclear matter under extremeconditions, and validates the important empirical constraints obtained from recentexperimental data. PACS numbers : 21.65.-f, 21.30.Fe, 21.10.Dr, 26.60.Kp Key words: EoS; Symmetry energy; Incompressibility; Isobaric incompressibility.

Stratigraphic and paleopedological aspects from the Middle Pleistocene continental deposits of the southern Valdelsa Basin

A multidisciplinary approach on mainly continental carbonate deposits outcropping in the southern part of the Valdelsa Basin has allowed the recognition of two units, the Strove Synthem (STR) and the Campiglia dei Foci Synthem (CDF), both previously attributed altogether to a single indistinct sequence. The presence of a mammalian fauna suggests that the STR Synthem belongs to the Early-Middle Pleistocene, whereas the CDF Synthem is assigned to Middle Pleistocene because of its stratigraphic position. Lateral correlation with continental deposits cropping out in the adjacent Lower Valdarno Basin suggests an age not younger of the Stage 11 of the isotope scale. A paleopedological study of the soils on the synthems has distinguished two pedogenetic typologies: a Cutanic Alisol (Manganiferric) on Gleyic Vertisol for STR Synthem and a Haplic Cambisol on Rhodic Luvisol on Rhodic Nitisol for CDF Synthem. The different pedogenetic development corroborated the hypothesis of two distinct synthems. The attitude of the STR Synthem (tilted deposits) in comparison with the CDF Synthem (sub-horizontal bedding) shows that the former was affected by a tectonic phase which ended before the deposition of the latter synthem. The chronostratigraphic attribution of the two synthems allow us to tentatively relate this tectonic phase with the regional Middle Pleistocene tectonic uplift, which caused the present Northern Apennine mountain chain.