335 research outputs found
Exploring the multi-humped fission barrier of 238U via sub-barrier photofission
The photofission cross-section of 238U was measured at sub-barrier energies
as a function of the gamma-ray energy using, for the first time, a
monochromatic, high-brilliance, Compton-backscattered gamma-ray beam. The
experiment was performed at the High Intensity gamma-ray Source (HIgS) facility
at beam energies between E=4.7 MeV and 6.0 MeV and with ~3% energy resolution.
Indications of transmission resonances have been observed at gamma-ray beam
energies of E=5.1 MeV and 5.6 MeV with moderate amplitudes. The triple-humped
fission barrier parameters of 238U have been determined by fitting EMPIRE-3.1
nuclear reaction code calculations to the experimental photofission cross
section.Comment: 5 pages, 3 figure
Diffuse Radio Emission from Galaxy Clusters
In a growing number of galaxy clusters diffuse extended radio sources have
been found. These sources are not directly associated with individual cluster
galaxies. The radio emission reveal the presence of cosmic rays and magnetic
fields in the intracluster medium (ICM). We classify diffuse cluster radio
sources into radio halos, cluster radio shocks (relics), and revived AGN fossil
plasma sources. Radio halo sources can be further divided into giant halos,
mini-halos, and possible `intermediate' sources. Halos are generally positioned
at cluster center and their brightness approximately follows the distribution
of the thermal ICM. Cluster radio shocks (relics) are polarized sources mostly
found in the cluster's periphery. They trace merger induced shock waves.
Revived fossil plasma sources are characterized by their radio steep-spectra
and often irregular morphologies. In this review we give an overview of the
properties of diffuse cluster radio sources, with an emphasis on recent
observational results. We discuss the resulting implications for the underlying
physical acceleration processes that operate in the ICM, the role of
relativistic fossil plasma, and the properties of ICM shocks and magnetic
fields. We also compile an updated list of diffuse cluster radio sources which
will be available on-line http://galaxyclusters.com. We end this review with a
discussion on the detection of diffuse radio emission from the cosmic web.Comment: To appear in Space Science Reviews, 56 pages, 31 figures; For
associated data see http://galaxyclusters.co
In-beam fast-timing measurements in 103,105,107Cd
Fast-timing measurements were performed recently in the region of the
medium-mass 103,105,107Cd isotopes, produced in fusion evaporation reactions.
Emitted gamma-rays were detected by eight HPGe and five LaBr3:Ce detectors
working in coincidence. Results on new and re-evaluated half-lives are
discussed within a systematic of transition rates. The states in
103,105,107Cd are interpreted as arising from a single-particle excitation. The
half-life analysis of the states in 103,105,107Cd shows no change in
the single-particle transition strength as a function of the neutron number
Deep LOFAR observations of the merging galaxy cluster CIZA J2242.8+5301
Previous studies have shown that CIZA J2242.8+5301 (the 'Sausage' cluster, z = 0.192) is a massive merging galaxy cluster that hosts a radio halo and multiple relics. In this paper, we present deep, high-fidelity, low-frequency images made with the LOw-Frequency Array (LOFAR) between 115.5 and 179 MHz. These images, with a noise of 140 μJy beam- 1 and a resolution of θbeam = 7.3 arcsec × 5.3 arcsec, are an order of magnitude more sensitive and five times higher resolution than previous low-frequency images of this cluster. We combined the LOFAR data with the existing Giant Metrewave Radio Telescope (GMRT) (153, 323, 608 MHz) and Westerbork Synthesis Radio Telescope (WSRT) (1.2, 1.4, 1.7, 2.3 GHz) data to study the spectral properties of the radio emission from the cluster. Assuming diffusive shock acceleration (DSA), we found Mach numbers of Mn=2.7{}_{-0.3}^{+0.6} and Ms=1.9_{-0.2}^{+0.3} for the northern and southern shocks. The derived Mach number for the northern shock requires an acceleration efficiency of several percent to accelerate electrons from the thermal pool, which is challenging for DSA. Using the radio data, we characterized the eastern relic as a shock wave propagating outwards with a Mach number of Me=2.4_{-0.3}^{+0.5}, which is in agreement with MeX=2.5{}_{-0.2}^{+0.6} that we derived from Suzaku data. The eastern shock is likely to be associated with the major cluster merger. The radio halo was measured with a flux of 346 ± 64 mJy at 145 MHz. Across the halo, we observed a spectral index that remains approximately constant (α ^{145 MHz-2.3 GHz}_{{across ˜ 1 Mpc}^2}=-1.01± 0.10) after the steepening in the post-shock region of the northern relic. This suggests a generation of post-shock turbulence that re-energies aged electrons
The prototype of radioactive ion source
The design and experimental results of the RIB source prototype are presented. A source will have the container of ²³⁵U compounds heated up to 2200-2500°C. Vapors of uranium fission obtained when the ion source is irradiated by the high-energy neutron flux, are then ionized and extracted from the source. In the experiments with the prototype loaded by ¹²C the source working temperature 2700°C was reached, the carbon ion current 10 nA was obtained. The total operation time of more than 100 hours with no performance degradation was demonstrated
Study of the threshold anomaly effect in the reaction 7 Li+ 208 Pb at energies around the Coulomb barrier
The elastic scattering in the reaction7Li+208Pb was investigated in the bombarding energy range from 25 to39 MeV. The real and imaginary parts of the optical potential were analyzed by using a phenomenological potential. A dispersion relation analysis is presented in order to investigate the threshold anomaly effect. It is concluded that7Li has an intermediate behavior between the tightly bound nuclei suchas16O and the loosely bound nuclei such as6Li where the lack of the threshold anomaly is unambiguously observed.Reaction cross sections are also extracted from the elastic scattering data and its comparison with the ones of other systems has been performed to draw hints on the effect of the breakup channel
Fast-timing measurements in 95,96Mo
Half-lives of the 19/2+ and 21/2+ states in 95Mo and of the 8+ and 10+ states
in 96Mo were measured. Matrix elements for yrast transitions in 95Mo and 96Mo
are discussed.Comment: Proceedings of XIX International School on Nuclear Physics, Neutron
Physics and Applications, Varna, Bulgaria, 2011, 5 pages, 6 figure
Abell 746: A highly disturbed cluster undergoing multiple mergers
We present deep \textit{XMM-Newton}, Karl Jansky Very Large Array, and
upgraded Giant Metrewave Radio Telescope observations of Abell 746, a cluster
that hosts a plethora of diffuse emission sources that provide evidence for the
acceleration of relativistic particles. Our new \textit{XMM-Newton} images
reveal a complex morphology of the thermal gas with several substructures. We
observe an asymmetric temperature distribution across the cluster: the southern
regions exhibit higher temperatures, reaching 9\,keV, while the northern
regions have lower temperatures (), likely due to a complex
merger. We find evidence of four surface brightness edges, of which three are
merger-driven shock fronts. Combining our new data with the published
LOw-Frequency ARray observations has unveiled the nature of diffuse sources in
this system. The bright northwest relic shows thin filaments and high degree of
polarization with aligned magnetic field vectors. We detect a density jump,
aligned with the fainter relic to the north. To the south, we detect
high-temperature regions, consistent with shock-heated regions and density jump
coincident with the northern tip of the southern radio structure. Its
integrated spectrum shows a high-frequency steepening. Lastly, we find that the
cluster hosts large-scale radio halo emission. The comparison of the thermal
and nonthermal emission reveals an anticorrelation between the bright radio and
X-ray features at the center. Our findings suggest that Abell 746 is a complex
system that involves multiple mergers.Comment: 21 pages, 13 figures, submitted to Ap
CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources
We present a CO(1–0) survey for cold molecular gas in a representative sample of 13 highz
radio galaxies (HzRGs) at 1.4 <z< 2.8, using the Australia Telescope Compact Array.
We detect CO(1–0) emission associated with five sources: MRC 0114-211, MRC 0152-209,
MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1–0) luminosities are in the
range L
CO ∼ (5–9) × 1010 K km s−1 pc2. For MRC 0152-209 and MRC 1138-262, part of the
CO(1–0) emission coincides with the radio galaxy, while part is spread on scales of tens of
kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two
systems is MH2 ∼ 6 × 1010 M� (MH2/L
CO = 0.8). For the remaining three CO-detected sources,
the CO(1–0) emission is located in the halo (∼50-kpc) environment. These three HzRGs are
among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold
molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright
sources. In all three cases, the CO(1–0) is aligned along the radio axis and found beyond the
brightest radio hotspot, in a region devoid of 4.5 µm emission in Spitzerimaging. The CO(1–0)
profiles are broad, with velocity widths of ∼1000–3600 km s−1. We discuss several possible
scenarios to explain these halo reservoirs of CO(1–0). Following these results, we complement
our CO(1–0) study with detections of extended CO from the literature and find at marginal
statistical significance (95 per cent level) that CO in HzRGs is preferentially aligned towards
the radio jet axis. For the eight sources in which we do not detect CO(1–0), we set realistic
upper limits of L
CO ∼ 3–4 × 1010 K km s−1 pc2. Our survey reveals a CO(1–0) detection rate
of 38 per cent, allowing us to compare the CO(1–0) content of HzRGs with that of other types
of high-z galaxies
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