143 research outputs found
Prediction of the thermal release of transactinide elements (112 ≤ Z ≤ 116) from metals
Metallic catcher foils have been investigated on their thermal release capabilities for future superheavy element studies. These catcher materials shall serve as connection between production and chemical investigation of superheavy elements (SHE) at vacuum conditions. The diffusion constants and activation energies of diffusion have been extrapolated for various catcher materials using an atomic volume based model. Release rates can now be estimated for predefined experimental conditions using the determined diffusion values. The potential release behavior of the volatile SHE Cn (E112), E113, Fl (E114), E115, and Lv (E116) from polycrystalline, metallic foils of Ni, Y, Zr, Nb, Mo, Hf, Ta, and W is predicted. Example calculations showed that Zr is the best suited material in terms of on-line release efficiency and long-term operation stability. If higher temperatures up to 2773K are applicable, tungsten is suggested to be the material of choice for such experiment
Adsorption interaction of carrier-free thallium species with gold and quartz surfaces
The adsorption interactions of thallium and its compounds with gold and quartz surfaces were investigated. Carrier-free amounts of thallium were produced in nuclear fusion reactions of alpha particles with thick gold targets. The method chosen for the studies was gas thermochromatography and varying the redox potential of the carrier gases. It was observed that thallium is extremely sensitive to trace amounts of oxygen and water, and can even be oxidized by the hydroxyl groups located on the quartz surface. The experiments on aquartz surface with O2, He, H2 gas in addition with water revealed the formation and deposition of only one thallium species - TlOH. The adsorption enthalpy was determined to be Δ HSiO2ads(TlOH) = −134±5kJ mol−1. Aseries of experiments using gold as stationary surface and different carrier gases resulted in the detection of two thallium species - metallic Tl (H2 as carrier gas) and TlOH (O2, O2+H2O and H2+H2O as pure carrier gas or carrier gas mixture) with Δ HAuads(Tl) = −270±10kJ mol− and Δ HAuads(TlOH) = −146±3kJ mol−1. These data demonstrate a weak interaction of TlOH with both quartz and gold surfaces. The data represent important information for the design of future experiments with the heavier homologue of Tl in group 13 of the periodic table - element 113 (E113
Structure and Spatial Distribution of Ge Nanocrystals Subjected to Fast Neutron Irradiation
The influence of fast neutron irradiation on the
structure and spatial distribution of Ge nanocrystals (NC)
embedded in an amorphous SiO2 matrix has been
studied. The investigation was conducted by means of
laser Raman Scattering (RS), High Resolution
Transmission Electron Microscopy (HR-TEM) and X-ray
photoelectron spectroscopy (XPS). The irradiation of GeNC samples by a high dose of fast neutrons lead to a
partial destruction of the nanocrystals. Full reconstruction
of crystallinity was achieved after annealing the radiation
damage at 800
0
C, which resulted in full restoration of the
RS spectrum. HR-TEM images show, however, that the
spatial distributions of Ge-NC changed as a result of
irradiation and annealing. A sharp decrease in NC
distribution towards the SiO2 surface has been observed.
This was accompanied by XPS detection of Ge oxides and
elemental Ge within both the surface and subsurface
regio
Gas chromatography of indium in macroscopic and carrier-free amounts using quartz and gold as stationary phases
The chemical investigation of E113 is likely to become soon feasible. The determination of chemical properties of carrier-free amounts of the lighter homologues of element 113, especially indium and thallium, allows designing experimental set-ups and selecting experimental conditions suitable for performing these studies. Here, we present investigations of the interaction of indium species with quartz and gold surfaces. Deposition temperatures as well as enthalpies of adsorption were determined for indium Tdep=739±20°C (−ΔHads(In)=227±10kJ mol−1) and for indium hydroxide Tdep=250±20°C (−ΔHads(InOH)= 124±10kJ mol−1) respectively, on quartz. In case of adsorption of indium on a gold surface only a lower limit of the deposition temperature was established Tdep>980°C (−ΔHads(In)≥315±10kJ mol−1). Investigations of macroscopic amounts of indium in thermosublimation experiments at similar experimental conditions were instrumental to establish a tentative speciation of the observed indium specie
The thermal release of scandium from titanium metal - a simple way to produce pure 44Sc for PET application
The radionuclide-generator based access to radiopharmaceutical isotopes represents a valuable alternative to directly produced isotopes at particle accelerators or nuclear reactors. The 44Ti based generator is of increasing interest for the delivery of PET-radiopharmaceutical isotopes used for imaging. The product of this generator 44Sc represents with its 3.97h half-life and 94.3% positron branching[1] a very promising candidate for labeling PET radiopharmaceuticals. The long half-life of 58.9±0.3y[2] of the 44Ti assures a constant and long lasting production of the daughter nuclide. Here we present a gas phase separation method of scandium from titanium via thermal release in vacuum. Titanium foils were irradiated with 40Ar to produce scandium in multi-nucleon transfer reactions. Another production reaction used was the irradiation of titanium by neutrons from the SINQ neutron source at the Paul Scherrer Institute (PSI). The titanium metal foils containing 44mSc and 46Sc were heated up for time periods of 15 and 60min to temperatures between 900°C and 1500°C in vacuum. Thus, release properties of scandium from titanium under these conditions were studied. The released scandium was collected on tantalum foils and could be rinsed of with concentrated nitric acid resulting in carrier free scandium nitrate solutions. From the experimental results optimum release conditions are suggeste
Evidence for Intrinsic Redshifts in Normal Spiral Galaxies
The Tully-Fisher Relationship (TFR) is utilized to identify anomalous
redshifts in normal spiral galaxies. Three redshift anomalies are identified in
this analysis: (1) Several clusters of galaxies are examined in which late type
spirals have significant excess redshifts relative to early type spirals in the
same clusters, (2) Galaxies of morphology similar to ScI galaxies are found to
have a systematic excess redshift relative to the redshifts expected if the
Hubble Constant is 72 km s-1 Mpc-1, (3) individual galaxies, pairs, and groups
are identified which strongly deviate from the predictions of a smooth Hubble
flow. These redshift deviations are significantly larger than can be explained
by peculiar motions and TFR errors. It is concluded that the redshift anomalies
identified in this analysis are consistent with previous claims for large
non-cosmological (intrinsic) redshifts.Comment: Accepted for publication at Astrophysics&Space Science. 36 pages
including 8 tables and 7 figure
A Radio Survey of Seven Southern X-ray Luminous Clusters of Galaxies
The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38
GHz to survey seven southern Abell clusters of galaxies with high X-ray
luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters
have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis
Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio
sources within the Abell circles centred on their X-ray centroids. We compare
their identification fractions, emitted 1.38-GHz and optical powers, radio
spectral indices and radial variation in projected source density with those of
the radio-selected samples of Slee et al. (1998). We compare our fractional
radio luminosity function with that of the radio-selected samples of Ledlow and
Owen (1996) and Slee et al. (1998). Three significant differences are noted
between X-ray and radio-selected samples of clusters; (1) the X-ray sample has
an excess of flat-spectrum radio sources; (2) the fractional radio luminosity
function for the FR I sources in the X-ray selected sample is much steeper,
implying that fewer of their cluster galaxies become hosts for the stronger FR
I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray
selected sample. The average excess projected density of radio sources near our
cluster centres is approx. 5 times the background source density.Comment: 24 pages, 8 figures, plus 6 figures to be published online only;
accepted to appear in MNRA
Dependence of Star Formation Activity On Stellar Mass and Environment From the Redshift One LDSS-3 Emission Line Survey (ROLES)
Using the sample from the \it Redshift One LDSS3 Emission line Survey \rm
(ROLES), we probe the dependence of star formation rate (SFR) and specific star
formation rate (sSFR) as a function of stellar mass and environment as
defined by local galaxy density, in the CDFS field. Our spectroscopic sample
consists of 312 galaxies with , corresponding to stellar mass
\log(M_*/M_{\sun})>8.5, and with [OII] derived star-formation rates
SFR>0.3M_{\sun}/yr, at . The results have been
compared directly with the Sloan Digital Sky Survey Stripe 82 sample at
. For star-forming galaxies, we confirm that there is
little correlation between SFR and density at . However, for the
lowest mass galaxies in our sample, those with
\log(M_*/M_{\sun})<10, we find that both the median SFR and specific SFR {\it
increase} significantly with increasing local density. The "downsizing" trend
for low mass galaxies to be quenched progressively later in time appears to be
more pronounced in moderately overdense environments. Overall we find that the
evolution of star-formation in galaxies is most strongly driven by their
stellar mass, with local galaxy density playing a role that becomes
increasingly important for lower mass galaxies.Comment: MNRAS accepte
STAGES: the Space Telescope A901/2 Galaxy Evolution Survey
We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey
(STAGES). STAGES is a multiwavelength project designed to probe physical
drivers of galaxy evolution across a wide range of environments and luminosity.
A complex multi-cluster system at z~0.165 has been the subject of an 80-orbit
F606W HST/ACS mosaic covering the full 0.5x0.5 (~5x5 Mpc^2) span of the
supercluster. Extensive multiwavelength observations with XMM-Newton, GALEX,
Spitzer, 2dF, GMRT, and the 17-band COMBO-17 photometric redshift survey
complement the HST imaging. Our survey goals include simultaneously linking
galaxy morphology with other observables such as age, star-formation rate,
nuclear activity, and stellar mass. In addition, with the multiwavelength
dataset and new high resolution mass maps from gravitational lensing, we are
able to disentangle the large-scale structure of the system. By examining all
aspects of environment we will be able to evaluate the relative importance of
the dark matter halos, the local galaxy density, and the hot X-ray gas in
driving galaxy transformation. This paper describes the HST imaging, data
reduction, and creation of a master catalogue. We perform Sersic fitting on the
HST images and conduct associated simulations to quantify completeness. In
addition, we present the COMBO-17 photometric redshift catalogue and estimates
of stellar masses and star-formation rates for this field. We define galaxy and
cluster sample selection criteria which will be the basis for forthcoming
science analyses, and present a compilation of notable objects in the field.
Finally, we describe the further multiwavelength observations and announce
public access to the data and catalogues.Comment: 29 pages, 22 figures; accepted to MNRAS. Full data release available
at http://www.nottingham.ac.uk/astronomy/stage
The STAGES view of red spirals and dusty red galaxies: Mass-dependent quenching of star-formation in cluster infall
We investigate the properties of optically passive spirals and dusty red
galaxies in the A901/2 cluster complex at redshift ~0.17 using restframe
near-UV-optical SEDs, 24 micron IR data and HST morphologies from the STAGES
dataset. The cluster sample is based on COMBO-17 redshifts with an rms
precision of sigma_cz~2000 km/sec. We find that 'dusty red galaxies' and
'optically passive spirals' in A901/2 are largely the same phenomenon, and that
they form stars at a substantial rate, which is only 4x lower than that in blue
spirals at fixed mass. This star formation is more obscured than in blue
galaxies and its optical signatures are weak. They appear predominantly in the
stellar mass range of log M*/Msol=[10,11] where they constitute over half of
the star-forming galaxies in the cluster; they are thus a vital ingredient for
understanding the overall picture of star formation quenching in clusters. We
find that the mean specific SFR of star-forming galaxies in the cluster is
clearly lower than in the field, in contrast to the specific SFR properties of
blue galaxies alone, which appear similar in cluster and field. Such a rich red
spiral population is best explained if quenching is a slow process and
morphological transformation is delayed even more. At log M*/Msol<10, such
galaxies are rare, suggesting that their quenching is fast and accompanied by
morphological change. We note, that edge-on spirals play a minor role; despite
being dust-reddened they form only a small fraction of spirals independent of
environment.Comment: Accepted for publication in MNRA
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