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.

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.

The role of non-protein sulphydryls in determining the chemical repair rates of free radical precursors of DNA damage and cell killing in Chinese hamster V79 cells. I

Chinese hamster V79 fibroblasts were irradiated in the gas explosion apparatus and the chemical repair rates of the oxygen-dependent free radical precursors of DNA double-strand breaks (dsb) and lethal lesions measured using filter elution (pH 9.6) and a clonogenic assay. Depletion of cellular GSH levels, from 4.16 fmol/cell to 0.05 fmol/cell, by treatment with buthionine sulphoximine (50 mumol dm-3; 18 h), led to sensitization as regards DNA dsb induction and cell killing. This was evident at all time settings but was particularly pronounced when the oxygen shot was given 1 ms after the irradiation pulse. A detailed analysis of the chemical repair kinetics showed that depletion of GSH led to a reduction in the first-order rate constant for dsb precursors from 385 s-1 to 144 s-1, and for lethal lesion precursors from 533 s-1 to 165 s-1. This is generally consistent with the role of GSH in the repair-fixation model of radiation damage at the critical DNA lesions. However, the reduction in chemical repair rate was not proportional to the severe thiol depletion (down to almost-equal-to 1% for GSH) and a residual repair capacity remained (almost-equal-to 30%). This was found not to be due to compartmentalization of residual GSH in the nucleus, as the repair rate for dsb precursors in isolated nuclei, washed virtually free of GSH, was identical to that found in GSH-depleted cells (144 s-1), also the OER remained substantially above unity. This suggests that other reducing agents may have a role to play in the chemical repair of oxygen-dependent damage. One possible candidate is the significant level of protein sulphydryls present in isolated nuclei.

A review of studies of ionizing radiation-induced double-strand break clustering

Underpinning current models of the mechanisms of the action of radiation is a central role for DNA damage and in particular double-strand breaks (DSBs). For radiations of different LET, there is a need to know the exact yields and distributions of DSBs in human cells. Most measurements of DSB yields within cells now rely on pulsed-field gel electrophoresis as the technique of choice. Previous measurements of DSB yields have suggested that the yields are remarkably similar for different types of radiation with RBE values less than or equal to1.0. More recent studies in mammalian cells, however, have suggested that both the yield and the spatial distribution of DSBs are influenced by radiation quality. RBE values for DSBs induced by high-LET radiations are greater than 1.0, and the distributions are nonrandom. Underlying this is the interaction of particle tracks with the higher-order chromosomal structures within cell nuclei. Further studies are needed to relate nonrandom distributions of DSBs to their rejoining kinetics. At the molecular level, we need to determine the involvement of clustering of damaged bases with strand breakage, and the relationship between higher-order clustering over sizes of kilobase pairs and above to localized clustering at the DNA level. Overall, these studies will allow us to elucidate whether the nonrandom distributions of breaks produced by high-LET particle tracks have any consequences for their repair and biological effectiveness. (C) 2001 by Radiation Research Society.

Low-dose hypersensitivity in Chinese hamster V79 cells targeted with counted protons using a charged-particle microbeam

The Gray Laboratory charged-particle microbeam has been used to assess the clonogenic ability of Chinese hamster V79 cells after irradiation of their nuclei with a precisely defined number of protons with energies of 1.0 and 3.2 MeV. The microbeam uses a 1-mum. silica capillary collimator to deliver protons to subcellular targets with high accuracy. The detection system is based on a miniature photomultiplier tube positioned above the cell dish, which detects the photons generated by the passage of the charged particles through an 18-mum-thick scintillator placed below the cells. With this system, a detection efficiency of greater than 99% is achieved. The cells are plated on specially designed dishes (3-mum-thick Mylar base), and the nuclei are identified by fluorescence microscopy. After an incubation period of 3 days, the cells are revisited individually to assess the formation of colonies from the surviving cells. For each energy investigated, the survival curve obtained for the microbeam shows a significant deviation below I Gy from a response extrapolated using the LQ model for the survival data above 1 Gy. The data are well fitted by a model that supports the hypothesis that radioresistance is induced by low-dose hypersensitivity. These studies demonstrate the potential of the microbeam for performing studies of the effects of single charged particles on cells in vitro. The hypersensitive responses observed are comparable with those reported by others using different radiations and techniques. (C) 2001 by Radiation Research Society.

NUCLEAR STAINING IN ALGAL HERBARIUM MATERIAL - A REAPPRAISAL OF THE HOLOTYPE OF CALLITHAMNION-DECOMPOSITUM AGARDH,J. (RHODOPHYTA)

The taxonomic importance of uninucleate vs. multinucleate vegetative cells in the Ceramiaceae is emphasized. It has been possible to make visible nuclei in old material, including type specimens, using aceto-carmine and aceto-iron-haematoxylin stains. The holotypes of Ceramium roseum and Callithamnion fasciculatum (currently known as Callithamnion roseum and Pleonosporium borreri var. fasciculatum) have uninucleate cells and belong to Aglaothamnion. In contrast, the holotype of Callithamnion decompositum, a name that has been applied to collections of at least two uninucleate taxa, has multinucleate cells; its morphological and cytological details agree with those of specimens collected in France and Ireland that were previously thought to represent an undescribed species. Female reproductive morphology (described from a thallus with gametangia in addition to tetrasporangia), in conjunction with habit and vegetative features, indicates that this species belongs to Compsothamnion (Compsothamnieae), as a third species, being distinguished from C. thuyoides and C. gracillimum by its sessile, lateral tetrasporangia. The required new combinations under Aglaothamnion and Compsothamnion are made.

UNUSUAL CHROMOSOME-NUMBER OF GRACILARIA-VERRUCOSA (GRACILARIALES, RHODOPHYTA) IN THE CAPE-GRIS-NEZ AREA, NORTHERN FRANCE

The chromosome number of Gracilaria verrucosa (Hudson) Papenfuss was estimated in numerous individuals from different populations of the Cape Gris-Nez area of Northern France. To optimize estimates and to minimize counting errors, several counts were made on the same nucleus and in different nuclei of the same individual. The haploid chromosome number was estimated in vegetative gametophytic cells and tetrasporocytic cells; the diploid number was estimated from tetrasporophytic vegetative cells. The basic haploid number was n = 17 +/- 1, whereas all other Gracilaria species for which chromosome numbers are available are reported to have n = 24. These include populations of G. verrucosa from Norway and Wales that have previously been shown to be conspecific with the Cape Gris-Nez populations by comparison of plastid DNA data. G. verrucosa is therefore one of the few red algae for which populations with different chromosome numbers are known.

A KARYOLOGICAL DEMONSTRATION OF MEIOSIS IN GELIDIUM-LATIFOLIUM (GELIDIACEAE, RHODOPHYTA) FROM IRELAND

A population of Gelidium latifolium (Greville) Bornet et Thuret (Rhodophyta) from Portstewart, County Antrim, Northern Ireland, was dominated by tetrasporophytes. When grown in culture, excised tips from 10 non-reproductive individuals all formed tetrasporangial branches. Chromosome counts in mitotic nuclei of vegetative cells from cultured tetrasporophytic apices were 58 +/- 4 chromosomes. In nuclei of dividing tetrasporocytes there were 29 +/- 2 larger bodies that were interpreted as paired meiotic chromosomes. Field-collected tetrasporophytes from Islandmagee. County Antrim. also showed approximately 29 pairs of chromosomes during meiosis in tetrasporocytes, This is the first report of meiosis in G. latifolium and the first direct demonstration of meiosis in this commercially important genus. In germinating tetraspores, the haploid nucleus initially divided prior to or during formation of the germination tube. The two daughter nuclei then underwent synchronous mitoses to form four haploid nuclei (n = 29 +/- 2), only one of which entered the germination tube. The sporeling survival rate was low, and few plants grew to maturity. The largest of these was diploid, with 55-58 chromosomes, and formed spermatangia after 14 months in culture. Other plants, which were abnormally bushy and densely branched, failed to reproduce. Since the most vigorous individual (and possibly also the other survivors) had apparently diploidized spontaneously during development, it is possible that the lack of gametophytes in the local G. latifolium population results from poor viability of haploid sporelings.

The incidences of trisomy 8, trisomy 9 and D20S108 deletion in polycythaemia vera: an analysis of blood granulocytes using interphase fluorescence in situ hybridization:an analysis of blood granulocytes using interphase fluorescence in situ hybridization

We have used interphase fluorescence in situ hybridization (IFISH) to detect trisomy 8, trisomy 9 and 20q deletion in circulating granulocytes from patients with polycythaemia vera (PV). Out of 64 PV patients, 15 (23%) exhibited an abnormality. Two patients had trisomy 9, three had trisomy 8 and 10 patients had hemizygous deletion of D20S108 (a locus in the 20q common deleted region). Aberrant nuclei ranged from 10% to 80% in these 15 cases. There was no correlation between the presence of a marker and sex, age, interval between presentation and IFISH analysis, neutrophil or platelet count or therapy. Conventional marrow cytogenetic karyotype results were available in 23 cases and there was concurrence between these and blood IFISH in 16 cases (13 normal and three with 20q/D20S108 deletion by both methods). Three patients with D20S108 deletion by IFISH were normal by previous marrow cytogenetic testing and four cases with 20q deletion by previous marrow cytogenetics had normal blood granulocytes according to IFISH. Thus, we confirm that trisomies 8 and 9 and deletion of 20q are diagnostically useful markers of PV. IFISH analysis of blood granulocytes is a practical method for detecting these markers, but as an adjunct to, not as a substitute for, conventional marrow cytogenetics.

Comparative study of the spatial relationship between nicotinamide adenine dinucleotide phosphate-diaphorase activity, serotonin immunoreactivity, and GYIRFamide immunoreactivity and the musculature of the adult liver fluke, Fasciola hepatica (Digenea, Fasciolidae)

This is the first detailed description of the nitrergic nervous system in a fluke. In this study, the authors analysed the distribution of the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reactivity in neuronal and nonneuronal tissues of the adult fluke Fasciola hepatica and compared this with the distribution of the musculature using tetramethylrhodamine isothiocyanate-phalloidin. To assess the correlation between the number of muscle cells in different parts of the fluke and the NADPH-d-stained cells, the nuclei were stained with Hoechst 333 42, which is specific for chromatin. The spatial relation between the NADPH-d-positive nerves and the 5-hydroxytryptamine (serotonin; 5-HT)-immunoreactive (-IR) and GYIRFamide-IR nervous elements was also examined. The methods complement each other. NADPH-d-positive staining occurs in both in neuronal tissue and nonneuronal tissue. Large, NADPH-d-stained neurones were localised in the nervous system. The oral and ventral suckers are innervated with many large NADPH-d-stained neurones. Ln addition, the NADPH-d staining reaction follows closely the muscle fibres in both the suckers, in the body, and in the ducts of the reproductive organs. The presence of NADPH-d activity along muscle fibres in F. hepatica and in other flatworms supports a possible myoinhibitory role for nitric oxide. Neuronal nitric oxide synthase in flatworms may form a novel drug target, which would facilitate the development of a novel anthelminthic. (C) 2001 Wiley-Liss, Inc.

Effect of positron-atom interactions on the annihilation gamma spectra of molecules

Calculations of ?-spectra for positron annihilation on a selection of molecules, including methane and its fluoro-substitutes, ethane, propane, butane and benzene are presented. The annihilation ?-spectra characterise the momentum distribution of the electron-positron pair at the instant of annihilation. The contribution to the ?-spectra from individual molecular orbitals is obtained from electron momentum densities calculated using modern computational quantum chemistry density functional theory tools. The calculation, in its simplest form, effectively treats the low-energy (thermalised, room-temperature) positron as a plane wave and gives annihilation ?-spectra that are about 40% broader than experiment, although the main chemical trends are reproduced. We show that this effective 'narrowing' of the experimental spectra is due to the action of the molecular potential on the positron, chiefly, due to the positron repulsion from the nuclei. It leads to a suppression of the contribution of small positron-nuclear separations where the electron momentum is large. To investigate the effect of the nuclear repulsion, as well as that of short-range electron-positron and positron-molecule correlations, a linear combination of atomic orbital description of the molecular orbitals is employed. It facilitates the incorporation of correction factors which can be calculated from atomic many-body theory and account for the repulsion and correlations. Their inclusion in the calculation gives -spectrum linewidths that are in much better agreement with experiment. Furthermore, it is shown that the effective distortion of the electron momentum density, when it is observed through positron annihilation -spectra, can be approximated by a relatively simple scaling factor. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Calculation of gamma spectra for positron annihilation on molecules

Calculations of gamma spectra for positron annihilation for a selection of molecules, including methane and its fluoro-substitutes, ethane, propane, butane and benzene are presented. The contribution to the ?-spectra from individual molecular orbitals is obtained from electron momentum distributions calculated using the density functional theory (DFT) based B3LYP/TZVP model. For positrons thermalised to room temperature, the calculation, in its simplest form, effectively treats the positron as a plane wave and gives positron annihilation ?-spectra linewidths that are broader (30-40%) than experiment, although the main chemical trends are reproduced. The main physical reason for this is the neglect of positron repulsion from the nuclei. We show that this effect can be incorporated through momentum-dependent correction factors, determined from positron-atom calculations, e.g., many-body perturbation theory. Inclusion of these factors in the calculation gives linewidths that are in improved agreement with experiment.

Fluorescence yields for 3lnl′ Rydberg series in ions belonging to the He isoelectronic sequence

Fluorescence yields are reported for 3lnl' Rydberg series members in He-like ions of N, O and Ne. Results are presented for singlet series members with n values between 3 and 9, i.e. up to the region of overlap with the states belonging to the 4l4l' manifold in these atoms. This data is required, for example, for the interpretation of charge-exchange experiments involving bare N, O and Ne nuclei. Fluorescence yields, averaged over all 3lnl' singlet states, larger than 50% are obtained from about n = 7.

Nonadiabatic forces in ion-solid interactions:The initial stages of radiation damage

The Born-Oppenheimer approximation is the keystone for molecular dynamics simulations of radiation damage processes; however, actual materials response involves nonadiabatic energy exchange between nuclei and electrons. In this work, time dependent density functional theory is used to calculate the electronic excitations produced by energetic protons in Al. We study the influence of these electronic excitations on the interatomic forces and find that they differ substantially from the adiabatic case, revealing a nontrivial connection between electronic and nuclear stopping that is absent in the adiabatic case. These results unveil new effects in the early stages of radiation damage cascades.

Effects of very low birthweight on brain structure in adulthood

Very-low-birthweight (VLBW) individuals are at high risk of brain injury in the perinatal period. We wished to determine how such early brain lesions affect brain structure in adulthood. Thirty-two VLBW adults (20 female, 12 male) and, 18 term, normal birthweight sibling control individuals (nine female, nine male) underwent structural MRI at a mean age of 23 years 4 months (range 17 to 33 years; SD 3.4). Images were analyzed using an automated tissue segmentation algorithm in order to estimate whole brain tissue class volumes in native space. Images were then warped to a template image in standard space. There was no significant between-group difference in whole brain, greymatter, white matter, or total cerebral spinal fluid (CSF) volumes. However, lateral ventricular volume was significantly increased by 41% in those with VLBW. The ratio of grey to white matter was also significantly increased (by 10%) in those with VLBW. Group comparison maps showed widespread changes in the distribution of grey and white matter, and relative excess of ventricular CSF, in the brains of VLBW individuals. Increased ventricular volume predicted decreased grey matter in subcortical nuclei and limbic cortical structures, and decreased periventricular white matter. We conclude that these diffuse abnormalities of grey and white matter are a consequence,of the interaction of perinatal brain injury and ongoing neurodevelopmental processes.