10Be in Ice Cores and 14C in Tree Rings: Separation of Production and Climate Effects

Cosmogenic radionuclides are more and more used in solar activity reconstructions. However, the cosmogenic radionuclide signal also contains a climate component. It is therefore crucial to eliminate the climate information to allow a better interpretation of the reconstructed solar activity indices. In this paper the method of principal components is applied to 10Be data from two ice cores from opposite hemispheres as well as to 14C data from tree rings. The analysis shows that these records are dominated by a common signal which explains about 80% of the variance on multi decadal to multi millennial time scales, reflecting their common production rate. The second and third components are significantly different for 14C and 10Be. They are interpreted as system effects introduced by the transport of 10Be and 14C from the atmosphere where they are produced to the respective natural archives where they are stored. Principal component analysis improves significantly extraction of the production signal from the cosmogenic isotope data series, which is more appropriate for astrophysical and terrestrial studie

Testing of Large Diameter Fresnel Optics for Space Based Observations of Extensive Air Showers

The JEM-EUSO mission will detect extensive air showers produced by extreme energy cosmic rays. It operates from the ISS looking down on Earth's night time atmosphere to detect the nitrogen fluorescence and Cherenkov produce by the charged particles in the EAS. The JEM-EUSO science objectives require a large field of view, sensitivity to energies below 50 EeV, and must fit within available ISS resources. The JEM-EUSO optic module uses three large diameter, thin plastic lenses with Fresnel surfaces to meet the instrument requirements. A bread-board model of the optic has been manufactured and has undergone preliminary tests. We report the results of optical performance tests and evaluate the present capability to manufacture these optical elements

Simulating ice core 10Be on the glacial–interglacial timescale

10Be ice core measurements are an important tool for paleoclimate research, e.g., allowing for the reconstruction of past solar activity or changes in the geomagnetic dipole field. However, especially on multi-millennial timescales, the share of production and climate-induced variations of respective 10Be ice core records is still up for debate. Here we present the first quantitative climatological model of the 10Be ice concentration up to the glacial–interglacial timescale. The model approach is composed of (i) a coarse resolution global atmospheric transport model and (ii) a local 10Be air–firn transfer model. Extensive global-scale observational data of short-lived radionuclides as well as new polar 10Be snow-pit measurements are used for model calibration and validation. Being specifically configured for 10Be in polar ice, this tool thus allows for a straightforward investigation of production- and non-production-related modulation of this nuclide. We find that the polar 10Be ice concentration does not immediately record the globally mixed cosmogenic production signal. Using geomagnetic modulation and revised Greenland snow accumulation rate changes as model input, we simulate the observed Greenland Summit (GRIP and GISP2) 10Be ice core records over the last 75 kyr (on the GICC05modelext timescale). We show that our basic model is capable of reproducing the largest portion of the observed 10Be changes. However, model–measurement differences exhibit multi-millennial trends (differences up to 87% in case of normalized to the Holocene records) which call for closer investigation. Focusing on the (12–37) b2k (before the year AD 2000) period, mean model–measurement differences of 30% cannot be attributed to production changes. However, unconsidered climate-induced changes could likely explain the model–measurement mismatch. In fact, the 10Be ice concentration is very sensitive to snow accumulation changes. Here the reconstructed Greenland Summit (GRIP) snow accumulation rate record would require revision of +28% to solely account for the (12–37) b2k model–measurement differences

Cross Section Measurements Using the Zero Degree Detector

The Zero Degree Detector (ZDD) is an instrument that has been used in accelerator exposures to measure the angular dependence of particles produced in heavy ion fragmentation experiments. The ZDD uses two identical layers of pixelated silicon detectors that make coincident measurements over the active area of the instrument. The angular distribution of secondary particle produced in nuclear interactions for several heavy ions: and target materials will be presented along with performance characteristic of the instrument

Kinetic and Spectroscopic Characterisation of Highly Reactive Methanesulfonates. Leaving Group Effects for Solvolyses and Comments on Geminal Electronic Effects Influencing SN_N1 Reactivity

Highly reactive methanesulfonates (mesylates, ROMs) have been prepared from 1-phenylethanol. cyclohex-2-en-1-ol, diphenylmethanol and p-methoxybenzyl alcohol by treatment with methanesulfonyl chloride and triethylamine in dichloro- or trichloro-methane at - 20 to 0 °C. The mesylates. characterised in solution by $^1$H and $^{13}$C NMR at -20 °C, were obtained in satisfactory purity (ca. 95%) in cold solutions but they decomposed by reaction with chloride, triethylamine or the parent alcohol. Rate constants for solvolyses in aqueous acetone and aqueous ethanol have been determined by a fast response conductimetric method. Product selectivities for solvolyses of pmethoxybenzyl mesylate in aqueous ethanol and methanol at 0 °C have been determined by HPLC. From additional new or Iiterature kinetic data for solvolyses of corresponding bromides. chlorides and p-nitrobenzoates (OPNB). Br/CI. OMs/Br and OMs/OPNB rate ratios were calculated; the results are consistent with electronic effects stabilising the carbocationic transition states and increasing OMs/Br rate ratios for these SN 1 solvolyses; none of the evidence supports a geminal electronic effect on Br/CI rate ratios (e.g. caused by stabilisation of the initial state in pmethoxybenzyl chloride). Steric effects on ester /halide rate ratios for solvolyses of tertiary substrates are confirmed. Relative rates over a 10$^{16}$ range for ester and halide leaving groups are evaluated for solvolyses of 1-phenylethyl substrates in 80% ethanol-water. updating previous work by Noyce et al. (1972)