Primary Isotopes Research Articles

Origin of mafic microgranular enclaves from the Late Triassic Cuojiaoma granitic pluton: Implications for the tectonic evolution of the Yidun arc belt, eastern Tibetan Plateau

In-situ U-Pb ages and Hf-O isotopes of zircon are frequently used to study the petrogenesis of mafic microgranular enclaves (MMEs) in granitoids. However, whether zircons in MMEs have recorded the primary isotopes of their host MMEs is still questionable. In this study, MMEs and host granites from the Cuojiaoma granitic pluton in the Triassic Yidun arc belt, eastern Tibetan Plateau, are studied. LA-ICP-MS zircon U-Pb dating of studied MMEs yields an age of 213 ± 2 Ma. Model calculations indicate that the whole-rock composition of the MMEs was different from the melt composition from which the zircon grains grew. The MMEs crystallized during magma mixing based on analyses of zircon trace element and Zr-Hf isotopes. None of zircons in this study have recorded the primary isotope signature of the mafic endmember of MMEs because they are different from the host granite in terms of zircon morphology, ɛHf values and ΔQFM. The Zr isotopic data demonstrate open-system magmatic crystallization for the host granite and that magma mixing for MMEs play key role in controlling Zr isotopic variations. Initial 87Sr/86Sr ratios of An-rich plagioclase crystals in groundmass from MMEs range from 0.7027 to 0.7058, which are significantly lower than host granites (0.7080 – 0.7089). The lowest initial 87Sr/86Sr ratios (0.7027 – 0.7028) are also lower than arc volcanic rocks and similar to a depleted mantle. Combined with previous studies, we propose that MMEs were generated during post-collision extension by mixing of mafic magma of Xiaxiaoliu basalt and felsic magma from host granite.

Measurement of the electron affinity of lead and its isotope shifts

Isotope shifts in electron affinities are sensitive to both electron correlations and interactions of the electrons and nucleus, providing new opportunities to better understand complex atoms and ions. Here, the authors use midinfrared photodetachment threshold spectroscopy of lead negative ions to measure the differences in the electron affinities of the primary isotopes 206, 207, and 208 that can provide benchmark tests for advanced atomic theory calculations.

Effects of thermal annealing on water content and δ18O in zircon

AbstractPrimary water and oxygen isotope composition are important tools in tracing magma source and evolution. Metamictization of zircon due to U-Th radioactive decay may introduce external secondary water to the crystal, thereby masking the primary water and oxygen isotope signature. Recently, Raman-based screening has been established to select the low-degree metamict zircons. However, such an approach may not be appropriate for ancient samples, in which nearly all zircons are metamict. It was reported that thermal annealing can potentially heal crystals and retrieve primary water content and δ18O information from metamict zircons, given the weaker hydrogen bond of secondary water than that of primary water. Heating experiments at temperatures of 200–1000 °C over a period of 2–10 h reveal that annealing can effectively recover primary water and oxygen isotopes from metamict zircons. Primary water in crystalline and metamict zircons remains intact when heated at <700 °C, while secondary water can be effectively expelled from metamict zircons when heated at 600 °C for >4 h, which represent the optimal annealing treatment condition. Hydrothermally altered zircon is an exception. It only yields the minimum estimate of its primary water contents at 600 °C over a period of >4 h, probably due to partial primary water loss during metamictization for hydrothermal zircons. Moreover, the proportion of low-δ18O (<4.7‰) zircon grains that may be influenced by secondary water dropped from ~21% at <600 °C to ~9% when annealed at >700 °C. This study therefore provides the basis for applying zircon water and δ18O proxies to geologically ancient samples.

The origin of mafic microgranular enclaves in granitoids: Insights from in situ Sr isotope of plagioclases and Zr-Hf isotopes of zircons

Mafic microgranular enclaves (MMEs) are common in many granitoid plutons and their origin is crucial for understanding the petrogenesis and tectonic setting of their hosts. Most previous workers have studied MMEs by using in situ zircon U-Pb and Hf-O isotopes. However, whether the zircons in the MMEs recorded the primary isotopes of their host MMEs is not well constrained. Here, two MMEs from the Daocheng (DC-2) and Dongcuo (HZS-3) granitic plutons, as well as their host granites, in the Triassic Yidun arc belt, eastern Tibetan Plateau, were studied. The MMEs have zircon U-Pb ages of 219 ± 3 Ma and 225 ± 3 Ma respectively, similar to their host granites. They also have similar or slightly depleted zircon Lu-Hf isotopes to their host granites. Furthermore, zircons from the Dongcuo pluton have indistinguishable Ti-in-zircon temperatures (Tzr) and Th/U ratios from those of their host granites, whereas zircons from the Daocheng pluton have higher Tzr values and Th/U ratios than those of their host granites. Model calculations indicate that the whole-rock composition of the studied MMEs was different from the melt composition from which the zircon grains grew. Additionally, zircon from Daocheng sample DC-2 has larger variations of Zr stable isotopes than its host granite, whereas those of Dongcuo sample HZS-3 have lower δ94/90ZrIPGP-Zr values than its host granite. Previous study suggests that early crystallized zircons will have lighter Zr isotopes. Thus, based on our new data, we propose that zircons from Dongcuo were actually xenocrysts that formed at an early stage in the granitic magma chamber, whereas those from Daocheng crystallized during magma mixing. Thus, none of the zircons in this study have recorded the primary isotopes of the MMEs. In addition, there are also many An-rich plagioclase crystals in the MMEs from both localities and the initial 87Sr/86Sr ratios of these plagioclases are quite heterogeneous. Both of the samples (DC-2 and HZS-3) record three peaks of 0.7078, 0.7064 and 0.7030, and 0.7087, 0.7096 and 0.7105, respectively, which record the primary Sr isotopes of the MMEs, as well as details of the interaction between the mantle-derived and crust-derived magmas. The lowest initial 87Sr/86Sr ratio peak was lower than the arc volcanic rocks but similar to those of MORBs in the Jinshajiang suture zone of the area. Therefore, the primary magma of the MMEs was likely derived from a depleted mantle source. We propose that in situ Sr isotopes of An-rich plagioclase and Zr isotopes of zircon can be powerful tools in deciphering the petrogenesis of MMEs. To simply use the zircon Hf-O isotopes to constrain the primary composition of MMEs is not adequate for determining their origin.

Current progress on ion driver LINAC-100 development for the new rare isotope facility DERICA at JINR

A new ambitious facility DERICA (Dubna Electron—Rare Ion Collider fAcility) was proposed recently in worldwide collaboration. A number of accelerators for various scientific applications will be built for this project and among them a driver-accelerator LINAC-100 capable of accelerating high-intensity beams of primary stable isotopes up to 100 MeV u−1. This paper contains current results on one of the LINAC-100 versions R&D: parameters of the front-end RFQ section, analysis on the stripper sections and optimal stripping energies,the layout of the superconducting part of LINAC-100 and Uranium beam dynamics simulation results.

Biochemical Characterization of the Mycobacterium smegmatis Threonine Deaminase.

The biosynthesis of branched-chain amino acids or BCAAs (l-isoleucine, l-leucine, and l-valine) is essential in eubacteria, but mammals are branched-chain amino acid auxotrophs, making the enzymes in the pathway excellent targets for antibacterial drug development. The biosynthesis of l-isoleucine, l-leucine, and l-valine is very efficient, requiring only eight enzymes. Threonine dehydratase (TD), a pyridoxal 5'-phosphate (PLP)-dependent enzyme encoded by the ilvA gene, is the enzyme responsible for the conversion of l-threonine (l-Thr) to α-ketobutyrate, ammonia, and water, which is the first step in the biosynthesis of l-isoleucine. We have cloned, expressed, and biochemically characterized the reaction catalyzed by Mycobacterium smegmatis TD (abbreviated as MsIlvA) using steady-state kinetics and kinetic isotope effects. We show here that in addition to l-threonine, l-allo-threonine and l-serine are also used as substrates by TD, and all exhibit sigmoidal, non-Michaelis-Menten kinetics. Curiously, β-chloro-l-alanine was also a substrate rather than an inhibitor as expected. The enzymatic activity of TD is sensitive to the presence of allosteric regulators, including the activator l-valine or the end product feedback inhibitor of the BCAA pathway in which TD is involved, l-isoleucine. Primary deuterium kinetic isotopes are small, suggesting Cα proton abstraction is only partially rate-limiting. Solvent kinetic isotopes were significantly larger, indicating that a proton transfer occurring during the reaction is also partially rate-limiting. Finally, we demonstrate that l-cycloserine, a general inhibitor of PLP-dependent enzymes, is an excellent inhibitor of threonine deaminase.

The impact of the Cretaceous–Paleogene (K–Pg) mass extinction event on the global sulfur cycle: Evidence from Seymour Island, Antarctica

The Cretaceous–Paleogene (K–Pg) mass extinction event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69–65.5 Ma) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69 Ma), with some fluctuations that could be related to increased pyrite burial during the ‘mid-Maastrichtian Event’. This is followed by an enigmatic +4‰ increase in δ34SCAS during the late Maastrichtian (68–66 Ma), culminating in a peak in values in the immediate aftermath of the K–Pg extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater δ34S of 3–4‰ suggests that a global decline in organic carbon burial related to collapse in export productivity, also impacted the sulfur cycle via a significant drop in pyrite burial. Box modelling suggests that to achieve an excursion of this magnitude, pyrite burial must be reduced by >15%, with a possible role for a short term increase in global weathering rates. Recovery of the sulfur cycle to pre-extinction values occurs at the same time (∼320 kyrs) as initial carbon cycle recovery globally. These recoveries are also contemporaneous with an initial increase in local alpha diversity of marine macrofossil faunas, suggesting biosphere-geosphere links during recovery from the mass extinction. Modelling further indicates that concentrations of sulfate in the oceans must have been 2 mM, lower than previous estimates for the Late Cretaceous and Paleocene and an order of magnitude lower than today.

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay.

The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW_{th} reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective ^{239}Pu fission fractions F_{239} from 0.25 to 0.35, Daya Bay measures an average IBD yield σ[over ¯]_{f} of (5.90±0.13)×10^{-43} cm^{2}/fission and a fuel-dependent variation in the IBD yield, dσ_{f}/dF_{239}, of (-1.86±0.18)×10^{-43} cm^{2}/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the ^{239}Pu fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes ^{235}U, ^{239}Pu, ^{238}U, and ^{241}Pu. Based on measured IBD yield variations, yields of (6.17±0.17) and (4.27±0.26)×10^{-43} cm^{2}/fission have been determined for the two dominant fission parent isotopes ^{235}U and ^{239}Pu. A 7.8% discrepancy between the observed and predicted ^{235}U yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.

How to Produce a Reactor Neutron Spectrum Using a Proton Accelerator

A method for reproducing the neutron energy spectrum present in the core of an operating nuclear reactor using an engineered target in an accelerator proton beam is proposed. The protons interact with a target to create neutrons through various (p,n) type reactions. Spectral tailoring of the emitted neutrons can be used to modify the energy of the generated neutron spectrum to represent various reactor spectra. Through the use of moderators and reflectors, the neutron spectrum can be modified to reproduce many different spectra of interest including spectra in small thermal test reactors, large pressurized water reactors, and fast reactors. The particular application of this methodology is the design of an experimental approach for using an accelerator to measure the betas produced during fission to be used to reduce uncertainties in the interpretation of reactor antineutrino measurements. This approach involves using a proton accelerator to produce a neutron field representative of a power reactor, and using this neutron field to irradiate fission foils of the primary isotopes contributing to fission in the reactor, creating unstable, neutron rich fission products that subsequently beta decay and emit electron antineutrinos. A major advantage of an accelerator neutron source over a neutron beam from a thermal reactor is that the fast neutrons can be slowed down or tailored to approximate various power reactor spectra. An accelerator based neutron source that can be tailored to match various reactor neutron spectra provides an advantage for control in studying how changes in the neutron spectra affect parameters such as the resulting fission product beta spectrum.

Method of fission product beta spectra measurements for predicting reactor anti-neutrino emission

The nuclear fission process that occurs in the core of nuclear reactors results in unstable, neutron-rich fission products that subsequently beta decay and emit electron antineutrinos. These reactor neutrinos have served neutrino physics research from the initial discovery of the neutrino to today׳s precision measurements of neutrino mixing angles. The prediction of the absolute flux and energy spectrum of the emitted reactor neutrinos hinges upon a series of seminal papers based on measurements performed in the 1970s and 1980s. The steadily improving reactor neutrino measurement techniques and recent reconsiderations of the agreement between the predicted and observed reactor neutrino flux motivates revisiting the underlying beta spectra measurements. A method is proposed to use an accelerator proton beam delivered to an engineered target to yield a neutron field tailored to reproduce the neutron energy spectrum present in the core of an operating nuclear reactor. Foils of the primary reactor fissionable isotopes placed in this tailored neutron flux will ultimately emit beta particles from the resultant fission products. Measurement of these beta particles in a time projection chamber with a perpendicular magnetic field provides a distinctive set of systematic considerations for comparison to the original seminal beta spectra measurements. Ancillary measurements such as gamma-ray emission and post-irradiation radiochemical analysis will further constrain the absolute normalization of beta emissions per fission. The requirements for unfolding the beta spectra measured with this method into a predicted reactor neutrino spectrum are explored.

Experimental reconstruction of primary hot isotopes and characteristic properties of the fragmenting source in heavy-ion reactions near the Fermi energy

The characteristic properties of the hot nuclear matter existing at the time of fragment formation in the multifragmentation events produced in the reaction $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon are studied. A kinematical focusing method is employed to determine the multiplicities of evaporated light particles, associated with isotopically identified detected fragments. From these data the primary isotopic yield distributions are reconstructed using a Monte Carlo method. The reconstructed yield distributions are in good agreement with the primary isotope distributions obtained from AMD transport model simulations. Utilizing the reconstructed yields, power distribution, Landau free energy, characteristic properties of the emitting source are examined. The primary mass distributions exhibit a power law distribution with the critical exponent, $A^{-2.3}$, for $A \geq 15$ isotopes, but significantly deviates from that for the lighter isotopes. Landau free energy plots show no strong signature of the first order phase transition. Based on the Modified Fisher Model, the ratios of the Coulomb and symmetry energy coefficients relative to the temperature, $a_{c}/T$ and $a_{sym}/T$, are extracted as a function of A. The extracted $a_{sym}/T$ values are compared with results of the AMD simulations using Gogny interactions with different density dependencies of the symmetry energy term. The calculated $a_{sym}/T$ values show a close relation to the symmetry energy at the density at the time of the fragment formation. From this relation the density of the fragmenting source is determined to be $\rho /\rho_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature of fragmenting source are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 3.4) MeV$ and $T=(4.9 \pm 0.2)$ MeV.

Primary isotope yields and characteristic properties of the fragmenting source in heavy-ion reactions near the Fermi energy

For central collisions of $^{40}$Ca $+ ^{40}$Ca at 35 MeV/nucleon, the density and temperature of a fragmenting source have been evaluated in a self-consistent manner using the ratio of the symmetry energy coefficient relative to the temperature, $a_{sym}/T$, extracted from the yields of primary isotopes produced in antisymmetrized molecular dynamics (AMD) simulations. The $a_{sym}/T$ values are extracted from all isotope yields using an improved method based on the Modified Fisher Model (MFM). The values of $a_{sym}/T$ obtained, using different interactions with different density dependencies of the symmetry energy term, are correlated with the values of the symmetry energies at the density of fragment formation. Using this correlation, the fragment formation density is found to be $\rho/\rho_0 = 0.67 \pm 0.02$. Using the input symmetry energy value for each interaction temperature values are extracted as a function of isotope mass $A$. The extracted temperature values are compared with those evaluated from the fluctuation thermometer with a radial flow correction.

Experimental reconstruction of excitation energies of primary hot isotopes in heavy ion collisions near the Fermi energy

The excitation energies of the primary hot isotopes in multifragmentation events are experimentally reconstructed in the reaction system 64Zn + 112Sn at 40 MeV/nucleon. A kinematical focusing method is employed to evaluate the multiplicities of the evaporated light particles associated with isotopically identified fragments with 3≤Z≤14. Angular distributions of the velocity spectra of light charged particles and neutrons associated with trigger isotopes are examined. A moving source fit is used to separate the kinematically correlated particles, evaporated from the parents of the detected isotopes, from the uncorrelated particles originating from other sources. The latter are evaluated experimentally relative to those in coincidence with the Li isotopes. A parameter, k, is used to adjust the yield of the uncorrelated particles for different trigger isotopes. For each experimentally detected isotope, the multiplicities, apparent temperatures, and k values for n, p, d, t, and α particles are extracted. Using the extracted values, the excitation energies of the primary hot isotopes are reconstructed employing a Monte Carlo method. The extracted excitation energies are in the range of 1 to 4 MeV/nucleon but show a significant decreasing trend as a function of A for a given Z of the isotopes. The results are compared with those of antisymmetrized molecular dynamics (AMD) and statistical multifragmentation model (SMM) simulations. While some of the experimental characteristics are predicted partially by each model, neither simulation reproduces the overall characteristics of the experimental results. © 2013 American Physical Society.

Mantle source heterogeneity for South Tyrrhenian magmas revealed by Pb isotopes and halogen contents of olivine-hosted melt inclusions

Nineteen olivine-hosted melt inclusions from seven volcanoes (Etna, Stromboli, Vulcano, Ustica, Alicudi, Marsili and Vavilov) from the southern Italy region were analyzed for abundances of major, trace, and volatile elements, along with Pb isotope ratios (207Pb/206Pb, 208Pb/206Pb and 206Pb/204Pb). The systematics of primary volatile (in particular F and Cl) compositions and Pb isotopes identify three main geochemically distinct mantle sources for this region: (1) a component with radiogenic Pb (207Pb/206Pb=0.780) and low volatile element abundances typified by the Etnean melt inclusions, (2) a component with moderately radiogenic Pb (207Pb/206Pb=0.798) and high volatile abundance mainly associated with Sommata magmas, and (3) a component with moderate volatile abundances associated with a MORB-like 207Pb/206Pb (0.830).The variation of F/Nd and Pb isotopes among the southern Italy melt inclusions reflects mixing between a slightly modified depleted mantle (DMM–EMII mixture) and radiogenic (HIMU-like) mantle components expressed in Pb isotope space, superimposed by slab-derived metasomatic components represented by F/Nd (F/Nd>30).

Power law behavior of the isotope yield distributions in the multifragmentation regime of heavy ion reactions

Isotope yields have been analyzed within the framework of a Modified Fisher Model to study the power law yield distribution of isotopes in the multifragmentation regime. Using the ratio of the mass dependent symmetry energy coefficient relative to the temperature, $a_{sym}/T$, extracted in previous work and that of the pairing term, $a_{p}/T$, extracted from this work, and assuming that both reflect secondary decay processes, the experimentally observed isotope yields have been corrected for these effects. For a given I = N - Z value, the corrected yields of isotopes relative to the yield of $^{12}C$ show a power law distribution, $Y(N,Z)/Y(^{12}C) \sim A^{-\tau}$, in the mass range of $1 \le A \le 30$ and the distributions are almost identical for the different reactions studied. The observed power law distributions change systematically when I of the isotopes changes and the extracted $\tau$ value decreases from 3.9 to 1.0 as I increases from -1 to 3. These observations are well reproduced by a simple de-excitation model, which the power law distribution of the primary isotopes is determined to $\tau^{prim} = 2.4 \pm 0.2$, suggesting that the disassembling system at the time of the fragment formation is indeed at or very near the critical point.

Impact of the Detailed Fission Source Distribution on IRIS Shielding Analyses

International Reactor Innovative and Secure (IRIS) is an advanced pressurized water reactor with an integral primary system. It features an integral reactor vessel surrounded by a spherical steel containment 25 m in diameter. Both deterministic and Monte Carlo methods are used to characterize its radiation environment. This paper focuses on the generation of the neutron fission source that is employed as the fixed source in radiation transport calculations. To facilitate radiation shielding analysis, a technique is proposed to synthesize fission source data from the IRIS depletion history into an average and a limiting (maximum) source distribution. The average source preserves the time-integrated, spatially dependent fission neutrons and is suitable for evaluation of long-term irradiation effects, such as the radiation damage on the reactor vessel. The maximum source gives a bounding fission neutron distribution that is suitable for calculation of the maximum instantaneous dose to the personnel. Spatial and spectral effects are also taken into consideration in the source representation. Pinwise axial distributions of the neutron fission source and the associated contribution from primary fissionable isotopes have been generated to allow evaluation of neutron leakage in the critical regions, such as at the core periphery. Less detailed assemblywise axial distributions are also made available to simplify their implementation in the MCNP and TORT models. A comparison of the results obtained with the latter distributions against the reference results (employing the most detailed distribution) will show the impact of simplifications and help identify strategic features and locations where preserving the detailed information is beneficial for meeting specific shielding objectives.The judicious postprocessing and interpretation of the fission source distribution proposed by this approach make the subsequent radiation analysis practical while retaining the critical details needed to achieve high accuracy.

The Selectivity of Charged Phenyl Radicals in Hydrogen Atom Abstraction Reactions with Isopropanol

The vertical electron affinity is demonstrated to be a key factor in controlling the selectivity of charged phenyl radicals in hydrogen atom abstraction from isopropanol in the gas phase. The measurement of the total reaction efficiencies (hydrogen and/or deuterium atom abstraction) for unlabeled and partially deuterium-labeled isopropanol, and the branching ratios of hydrogen and deuterium atom abstraction, by using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, allowed the determination of the selectivity for each site in the unlabeled isopropanol. Examination of hydrogen atom abstraction from isopropanol by eight structurally different radicals revealed that the preferred site is the CH group. The selectivity of the charged phenyl radicals correlates with the radical's vertical electron affinity and the reaction efficiency. The smaller the vertical electron affinity of a radical, the lower its reactivity, and the greater the preference for the thermodynamically favored CH group over the CH3 group or the OH group. As the vertical electron affinity increases from 4.87 to 6.28 eV, the primary kinetic isotope effects decrease from 2.9 to 1.3 for the CD group, and the mixture of primary and alpha-secondary kinetic isotopes decreases from 6.0 to 2.4 for the CD3 group.

Antiprotons and Cosmic‐Ray Propagation in the Galaxy

Based on our three-dimensional cosmic-ray (CR) propagation model, we study the behavior of CR antiprotons (CR---> 's), and compare our numerical results with recent experimental data, particularly those obtained by the BESS group. There is a common perception that diffusion-reacceleration models produce too low a --> flux below 5 GeV. However, we find that the BESS data are compatible with a model including the reacceleration process in the energy region 1 GeV, if we adopt Galactic parameters that reproduce the CR data for primary components (protons, helium, etc.), secondary components (B, sub-Fe), and CR isotopes (10Be,26Be, etc.). This indicates that most CR---> 's are secondary products of collisions between CRs and the interstellar medium (ISM) gas. However, because of poor statistics, we could not confirm whether or not BESS data with energies less than 1 GeV are consistent with those expected from other CR components, even taking the modulation effect into account. Nevertheless, it is important to determine the intensity of CR---> 's expected from the rich CR data now available, for studies of --> 's of cosmological origin, such as the evaporation of primordial black holes and/or the annihilation of supersymmetiric dark matter particles.

Primary Consumer Stable Nitrogen Isotopes as Indicators of Nutrient Source

Non-point source loading of nitrogen and phosphorus is a primary cause of eutrophication of inland waters, although the diffuse and variable nature of nutrient inputs makes it difficult to trace and identify nutrient pathways. Stable nitrogen isotope values (delta15N) in aquatic biota are thought to reflect anthropogenic nutrient inputs, and they may be a promising tool fortracing nutrient sources in watersheds. We measured delta15N of aquatic consumers from a suite of 27 Danish lakes spanning a range of trophic states (oligotrophic to eutrophic) and land uses (forest, urban, agriculture). Primary consumer delta15N values (PCdelta15N) varied more than 14% among lakes. Models of PCdelta15N were developed from limnological, nitrogen loading, and nitrogen source variables using an information-theoretic approach (Akaike's Information Criteria, AIC). Models based on land use/ land cover performed best, indicating that elevated delta15N is not only associated with high nitrogen loading, but is also reflective of nitrogen source. Urban and agricultural land use in the watershed, and particularly within the riparian buffer areas, was quantitatively linked to elevated biotic delta15N.

Towards exotic nuclei via binary reaction mechanism

Assuming a binary reaction mechanism, the yield of isotopes near the heaviest $N=Z$ neutron-deficit nucleus ${}^{100}\mathrm{Sn}$ is studied with a microscopic transport model. The large influence of nuclear shell structure and isotope composition of the colliding nuclei on the production of exotic nuclei is demonstrated. It is shown that the reaction ${}^{54}{\mathrm{F}\mathrm{e}+}^{106}\mathrm{Cd}$ seems to be most favorable for producing primary exotic Sn isotopes which may survive if the excitation energy in the entrance reaction channel is less than about 100 MeV. In the case of large differences in the charge (mass) numbers between entrance and exit channels the light fragment yield is essentially fed from the decay of excited primary heavier fragments. The existence of optimal energies for the production of some oxygen isotopes in the binary mechanism is demonstrated for the ${}^{32}{\mathrm{S}+}^{197}\mathrm{Au}$ reaction.