Spallation Neutron Production by 0.8, 1.2 and 1.6 GeV Protons on various Targets

Spallation neutron production in proton induced reactions on Al, Fe, Zr, W, Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at the SATURNE accelerator in Saclay is reported. The experimental double-differential cross-sections are compared with calculations performed with different intra-nuclear cascade models implemented in high energy transport codes. The broad angular coverage also allowed the determination of average neutron multiplicities above 2 MeV. Deficiencies in some of the models commonly used for applications are pointed out.Comment: 20 pages, 32 figures, revised version, accepted fpr publication in Phys. Rev.

Uncertainties in measurements of leaf optical properties are small compared to the biological variation within and between individuals of European beech

The measurement of leaf optical properties (LOP) using reflectance and scattering properties of light allows a continuous, time-resolved, and rapid characterization of many species traits including water status, chemical composition, and leaf structure. Variation in trait values expressed by individuals result from a combination of biological and environmental variations. Such species trait variations are increasingly recognized as drivers and responses of biodiversity and ecosystem properties. However, little has been done to comprehensively characterize or monitor such variation using leaf reflectance, where emphasis is more often on species average values. Furthermore, although a variety of platforms and protocols exist for the estimation of leaf reflectance, there is neither a standard method, nor a best practise of treating measurement uncertainty which has yet been collectively adopted. In this study, we investigate what level of uncertainty can be accepted when measuring leaf reflectance while ensuring the detection of species trait variation at several levels: within individuals, over time, between individuals, and between populations. As a study species, we use an economically and ecologically important dominant European tree species, namely Fagus sylvatica. We first use fabrics as standard material to quantify measurement uncertainties associated with leaf clip (0.0001 to 0.4 reflectance units) and integrating sphere measurements (0.0001 to 0.01 reflectance units) via error propagation. We then quantify spectrally resolved variation in reflectance from F. sylvatica leaves. We show that the measurement uncertainty associated with leaf reflectance, estimated using a field spectroradiometer with attached leaf clip, represents on average a small portion of the spectral variation within a single individual sampled over one growing season (2.7 ± 1.7%), or between individuals sampled over one week (1.5 ± 1.3% or 3.4 ± 1.7%, respectively) in a set of monitored F. sylvatica trees located in Swiss and French forests. In all forests, the spectral variation between individuals exceeded the spectral variation of a single individual at the time of the measurement. However, measurements of variation within individuals at different canopy positions over time indicate that sampling design (e.g., standardized sampling, and sample size) strongly impacts our ability to measure between-individual variation. We suggest best practice approaches toward a standardized protocol to allow for rigorous quantification of species trait variation using leaf reflectance

Warming and elevated CO2 induced shifts in carbon partitioning and lipid composition within an ombrotrophic bog plant community

Plant carbon (C) allocation is a key process determining C cycling in terrestrial ecosystems. In carbon-rich peatland ecosystems, impacts of climate change can exert a strong influence on C allocation strategies of the dominant plant species, with potentially large implications for the peatland C budget. However, little is known about plant C allocation into various secondary biosynthetic metabolites and whether different plant species vary in C allocation strategies in response to climate change. Here, we report species-specific leaf chemistry and secondary metabolism in trees (Picea mariana and Larix laricina), shrubs (Rhododendron groenlandicum and Chamaedaphne calyculata), and Sphagnum mosses (Sphagnum angustifolium and Sphagnum magellanicum) in response to whole-ecosystem warming (+0, +2.25, +4.5, +6.75 and +9 °C) and elevated CO2 manipulation (ambient or +500 ppm) in an ombrotrophic peatland. We show that warming and elevated CO2 substantially altered leaf chemistry and cuticle composition, including increases in leaf nitrogen, shifts in lipid composition and dependence on new photosynthates, although results varied by species. Shrub species lowered the saturation of their membrane fatty acids and increased their leaf nitrogen and C concentrations, while tree species increased their wax concentrations under higher warming treatments. Using isotopic labeling to trace the fate of newly-assimilated C, we observed an unexpectedly low fraction of new C in tree and shrub species (∼50% and ∼70% respectively). This suggests the combined use of newly-assimilated and older C reserves stored in plant organs for plant functional processes and CO2 originating from peat degradation and even more so in response to warmer temperatures and elevated CO2 concentrations. Under higher temperatures, Sphagnum mosses increased their leaf nitrogen but decreased their leaf C concentrations and the fraction of experiment-derived C (by 20%); suggesting an increasing C allocation to osmotic compounds that aid in maintaining high water retention capacity, albeit at the cost of other metabolites. Our results indicate species-specific shifts in plant chemistry and cuticular lipid composition, which could strongly moderate and shape boreal peatland ecosystem response to climate change in the future

Neutron production in semiprototypic target assemblies for accelerator transmutation technology

Integral neutron production was measured by the manganese-activation technique, on targets semiprototypic of spallation-neutron-driven transmutation systems, after irradiation by 400-MeV to 2.0-GeV protons. The purpose of these experiments was to provide data to benchmark nuclear transport codes for targets irradiated by protons in this energy range, as well as to evaluate design options to maximize the production of spallation neutrons in various targets under consideration. These computer codes are used to design accelerator systems that will utilize spallation neutrons for the generation of tritium, transmutation of nuclear waste, production of radioisotopes, and other scientific investigations. Some of the targets used in this investigation were semiprototypic of the proposed Accelerator Production of Tritium target. Other targets were included to provide data to test the computational models in the codes. Total neutron production is the main factor that determines the economics of transmutation for a particular accelerator design. Comparisons of the data reported here with calculations from computer simulations show agreement to within 15% over the entire energy region for most of the targets