An intercomparison of sampling techniques for measurements of radiocaesium in upland pasture and soil

An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of¹³⁷Cs, deposition of¹³⁷Cs in three soil layers, biomass densities, concentrations of¹³⁷Cs in pasture, and activity ratios (¹³⁴Cs/¹³⁷Cs) in soil and vegetation. The determination of total deposition of¹³⁷Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other.     

Testing the reliability of non-LTE spectroscopic models for complex ions

Collisional-radiative atomic models are widely used to help diagnose experimental plasma conditions through fitting and interpreting measured spectra. Here we present the results of a code comparison in which a variety of models determined plasma temperatures and densities by finding the best fit to an experimental L-shell Kr spectrum from a well characterized, but not benchmarked, laser plasma. While variations in diagnostic strategies and qualities of fit were significant, the results generally confirmed the typically quoted uncertainties for such diagnostics of ±20% in electron temperature and factors of about two in density. The comparison also highlighted some model features important for spectroscopic diagnostics: fine structure was required to match line positions and relative intensities within each charge state and for density diagnostics based on emission from metastable states; an extensive configuration set was required to fit the wings of satellite features and to reliably diagnose the temperature through the inferred charge state distribution; and the inclusion of self-consistent opacity effects was an important factor in the quality of the fit.     

Triple differential cross sections for the double photoionization of H2

Triple differential cross sections arising from the break up of the H2 molecule by a single photon are presented. The time-dependent close-coupling technique is used to calculate differential cross sections for various geometries. Excellent agreement is found between current work and recent exterior complex-scaling calculations, confirming, for the first time, the absolute magnitude of the triple differential cross sections. Our calculations also compare favorably with recent synchrotron light source measurements.     

Physical interpretation of the "kinetic energy release" effect in the double photoionization of H(2)

A physical interpretation is given for the variation with internuclear separation of the fully differential cross section for double photoionization of H2. This effect is analyzed in a geometry where the fourbody interaction is completely probed. Excellent agreement is found between experiment and time-dependent close-coupling theory after convoluting the latter over the relevant solid angles. We show the observed variations are purely due to the epsilon(Sigma) component of the polarization vector epsilon along the molecular axis, a conclusion which is supported through calculations of the photoionization of H2(+).     

Measurement and simulations of hollow atom X-ray spectra of solid-density relativistic plasma created by high-contrast PW optical laser pulses

K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160 J on the target allow studies of interactions between the laser field and solid state matter at 10²⁰ W/cm². Intense X-ray emission of KK hollow atoms (atoms without n = 1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5 μm thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 10¹⁸ W/cm² intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation.     

Effects of topography on caesium-137 in montane peat soils and vegetation.

This study investigated the relationship between altitude and 137Cs fallout in soils and plants. The soils and plants, Calluna vulgaris, Erica cinerea and Molinia caerulea, were sampled across a transect of two valleys in north-western Ireland. The results provided evidence that greater 137Cs deposition to soils occurred at higher altitudes, and the data supported the findings of a previous investigation in the same area. A valley effect, whereby greater concentrations of 137Cs accumulated in plants on the lower altitudes of the valley floors, was shown to be significant. Deposition values for total 137Cs in soils were not correlated with plant concentrations, although a relationship between concentrations in C. vulgaris and M. caerulea was found to be statistically significant. No relationship was observed between the 137Cs from weapons fallout with that of Chernobyl origin in the 0-10 cm depth soils, although a significant correlation emerged between the same two components measured in C. vulgaris. The results suggest that existing definitions of concentration ratios and transfer factors are, for many reasons, inappropriate for studies of soil to plant transfer of 137Cs in peatland ecosystems.     

Direct analysis of laser capture microdissected endometrial carcinoma and epithelium by matrix-assisted laser desorption/ionization mass spectrometry

Direct analysis of laser capture microdissected malignant and normal endometrial epithelium using matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (MS) was able to detect a number of proteins that are overexpressed in malignant epithelial cells. A total of 16 physiologic and malignant endometrial samples were laser capture microdissected, including four proliferative and four secretory endometria, and eight endometrioid adenocarcinomas. Two of these proteins, at 10,834 and 10,843 Da, likely correspond to calgranulin A and chaperonin 10, two proteins that had previously been identified in endometrioid adenocarcinoma in whole tissue homogenate by MS analysis. Direct analysis by MALDI-MS not only confirms that these proteins are overexpressed in endometrial carcinoma, but also localizes them to the epithelial cells, the expected cancer site.     

Observation of trielectronic recombination in Be-like Cl ions

Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations.