A nearly real-time high temperature laser-plasma diagnostic using photonuclear reactions in tantalum

A method of measuring the temperature of the fast electrons produced in ultraintense laser-plasma interactions is described by inducing photonuclear reactions, in particular (gamma,n) and (gamma,3n) reactions in tantalum. Analysis of the gamma rays emitted by the daughter nuclei of these reactions using a germanium counter enables a relatively straightforward near real-time temperature measurement to be made. This is especially important for high temperature plasmas where alternative diagnostic techniques are usually difficult and time consuming. This technique can be used while other experiments are being conducted. (C) 2002 American Institute of Physics.

Characterization of a gamma-ray source based on a laser-plasma accelerator with applications to radiography

The application of high intensity laser-produced gamma rays is discussed with regard to picosecond resolution deep-penetration radiography. The spectrum and angular distribution of these gamma rays is measured using an array of thermoluminescent detectors for both an underdense (gas) target and an overdense (solid) target. It is found that the use of an underdense target in a laser plasma accelerator configuration produces a much more intense and directional source. The peak dose is also increased significantly. Radiography is demonstrated in these experiments and the source size is also estimated. (C) 2002 American Institute of Physics.

Laser generation of proton beams for the production of short-lived positron emitting radioisotopes

Protons of energies up to 37 MeV have been generated when ultra-intense lasers (up to 10(20) W cm(-2)) interact with hydrogen containing solid targets. These protons can be used to induce nuclear reactions in secondary targets to produce P-emitting nuclei of relevance to the nuclear medicine community, namely C-11 and N-13 via (p, n) and (p, alpha) reactions. Activities of the order of 200 kBq have been measured from a single laser pulse interacting with a thin solid target. The possibility of using ultra-intense lasers to produce commercial amounts of short-lived positron emitting sources for positron emission tomography (PET) is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Production of radioactive nuclides by energetic protons generated from intense laser-plasma interactions

Nuclear activation has been observed in materials exposed to the ablated plasma generated from high intensity laser-solid interactions (at focused intensities up to 2x10(19) W/cm(2)) and is produced by protons having energies up to 30 MeV. The energy spectrum of the protons is determined from these activation measurements and is found to be consistent with other ion diagnostics. The possible development of this technique for

Taxonomy and phylogeny of Osmundea (Rhodomelaceae, Rhodophyta) in Atlantic Europe

Two species of Osmundea Stackhouse (Rhodomelaceae, Rhodophyta) that occur in Atlantic Europe have been confused under the names Osmundea ramosissima (Oeder) Athanasiadis and Osmundea truncata (Kutzing) Nam et Maggs, regarded until now as a synonym of O. ramosissima, An epitype from its type locality (Stavanger, Norway) is selected for Osmundea ramosissima Athanasiadis, recognized here as a valid name for Fucus ramosissimus Oeder, nom. illeg. Details of vegetative and reproductive morphology of O. ramosissima are reported, based on material from France, the British Isles, and Helgoland. Osmundea ramosissima resembles other species of Osmundea in its vegetative axial segments with two pericentral cells and one trichoblast, spermatangial development from apical and epidermal cells (filament type), the formation of five pericentral cells in the procarp-bearing segment of the female trichoblast, and tetrasporangial production from random epidermal cells. Among the species of Osmundea, O. ramosissima is most similar to O. truncata. Both species have discoid holdfasts, secondary pit connections between epidermal cells, and cup-shaped spermatangial pits. They differ in that: (a) O. ramosissima lacks lenticular wail thickenings and refractive needle-like inclusions in medullary cells, both of which are present in O. truncata; (b) O. ramosissima has branched spermatangial filaments that terminate in a cluster of several cells, whereas in O. truncata the unbranched spermatangial filaments have a single large terminal sterile cell; and (c) cystocarps of O. ramosissima lack protuberant ostioles but ostioles are remarkably protuberant in o. truncata. Phylogenetic analyses of rbcL sequences of Laurencia obtusa (Hudson) Lamouroux and all five Atlantic European species of Osmundea, including the type species, strongly support the generic status of Osmundea. Osmundea ramosissima and O. truncata are closely related (5.2% sequence divergence) and form a well-supported clade sister to a clade consisting of O. pinnatifida (Hudson) Stack-house, O. osmunda Stackhouse and O. hybrida (A. P. de Candolle) Nam. The formation of secondary pit connections between epidermal cells is a synapomorphy for the O. ramosissima + O. truncata clade. The close relationship between species with cup-shaped spermatangial pits (Osmundea hybrida) and urn-shaped pits (Osmundea pinnatifida and Osmundea osmunda) shows that spermatangial pit shape is not an important phylogenetic character. Parsimony analysis of a morphological data set also supports the genus Osmundea but conflicts with the molecular trees in infrageneric relationships, placing O. hybrida basal within the Osmundea clade and grouping O. osmunda and O. pinnatifida but not O. truncata and O. ramosissima. A key to Osmundea species is presented.

RESURRECTION OF THE GENUS OSMUNDEA WITH AN EMENDATION OF THE GENERIC DELINEATION OF LAURENCIA (CERAMIALES, RHODOPHYTA)

Vegetative and reproductive development of some European and Californian species of Laurencia Lamouroux (Ceramiales, Rhodophyta), L. obtusa (Hudson) Lamouroux, L. spectabilis Postels et Ruprecht, L. crispa Hollenberg, L. osmunda (S.G. Gmelin) Maggs et Hommersand, L. pinnatifida (Hudson) Lamouroux and L. truncata Kutzing, is investigated on the basis of liquid-preserved and herbarium specimens. The latter five species share several features, but they differ distinctly from L. obtusa, the lectotype of the genus, in essential anatomical characters of vegetative and male reproductive structures and tetrasporangial development. In these five species each vegetative axial segment produces two rather than four pericentral cells, and spermatangial branches (filaments) are produced in apical pits of branchlets from apical and epidermal cells rather than from trichoblasts arising from axial cells. The spermatangial branches are usually branched alternately and usually terminate in a cluster of several large sterile vesicular cells, rather than being branched dichotomously and terminating in a single, or occasionally a row of two, large sterile vesicular cells as in L. obtusa. Apical spermatangial pits of fertile male branchlets (except for those in L. truncata) are pocket- (or urn)-shaped, with an ostiole-like upper opening, rather than cup- (or bowl)-shaped. In these five species tetrasporangia are produced laterally from random epidermal cells rather than abaxially from particular pericentral cells (the third and fourth ones) as in L. obtusa, and the two presporangial cover cells are aligned parallel rather than transverse to the stichidial axis in surface view. These important differences strongly suggest that L. spectabilis, L. crispa, L. osmunda, L. pinnatifida and L. truncata occupy a phylogenetically different position from L. obtusa, and lead to the conclusion that the genus Osmundea Stackhouse, which was based on 0. expansa Stackhouse, nom. illeg. (= Laurencia osmunda) and which has been a nomen rejiciendum as an earlier facultative synonym of Laurencia, should be resurrected. Emendations of the generic criteria of Laurencia and Osmundea are proposed here, and relevant nomenclatural changes for several Laurencia species are also included.

Discovery of Main-Belt Comet P/2006 VW<sub>139 by Pan-STARRS 1

The main-belt asteroid (300163) 2006 VW139 (later designated P/2006 VW139) was discovered to exhibit comet-like activity by the Pan-STARRS1 (PS1) survey telescope using automated point-spread-function analyses performed by PS1's Moving Object Processing System. Deep follow-up observations show both a short (~10'') antisolar dust tail and a longer (~60'') dust trail aligned with the object's orbit plane, similar to the morphology observed for another main-belt comet (MBC), P/2010 R2 (La Sagra), and other well-established comets, implying the action of a long-lived, sublimation-driven emission event. Photometry showing the brightness of the near-nucleus coma remaining constant over ~30 days provides further evidence for this object's cometary nature, suggesting it is in fact an MBC, and not a disrupted asteroid. A spectroscopic search for CN emission was unsuccessful, though we find an upper limit CN production rate of Q CN 100 Myr, while a search for a potential asteroid family around the object reveals a cluster of 24 asteroids within a cutoff distance of 68 m s-1. At 70 m s-1, this cluster merges with the Themis family, suggesting that it could be similar to the Beagle family to which another MBC, 133P/Elst-Pizarro, belongs.