The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in ...groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of 283112 through the alpha decay of the short-lived 287114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of 283112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Superconducting radiofrequency (SRF) cavities are vital components of particle accelerators nowadays. In order to minimise the energy dissipation, a perfect inner surface of the cavity, ...hindering the penetration of magnetic field, is required. In this work, we investigated ten planar samples differing in the surface quality of Nb film deposited on Cu substrate, and as a consequence exhibiting various levels of the first entry field,
H
en
, at which the magnetic field starts to enter the film. The observed surface defects are categorised as hills, pits and cracks. For a practical range of dimensions of these features, the factor
β
, characterising the local magnetic field enhancement, was calculated by the numerical finite-element simulations. It is expected that the local field enhancement causes a premature penetration of the magnetic field, thus lowering
H
en
. Then, for each investigated sample, the range of
β
values characterising defect type that cause the highest field enhancement, is identified and compared with the
H
en
fields. We have found that the
H
en
of the samples that contain multiple types of the surface features is indeed limited by those defects that cause the highest field enhancement. The
H
en
vs
β
dependence has shown a good match with linear fit for the set of investigated samples. Thus, the main result is that the local magnetic field enhancement, computed in a straightforward way for the most significant defects, is a strong indicator of the surface quality that is relevant for the superconducting film intended for SRF cavity application.
Abstract
In superconducting radiofrequency accelerating cavities for particle accelerators, the Nb/Cu structure is one of the alternatives to bulk Nb but R&D is required to achieve a reproducible ...performance that competes with bulk Nb. The DC entry field
H
en
and critical temperature were studied in the thin Nb films deposited by magnetron sputtering on Cu substrate. The Nb surfaces were further treated by Nd:YAG laser at four energy doses (
D
1 = 350,
D
2 = 233,
D
3 = 175 and
D
4 = 140 J cm
−2
). The superconducting properties and other characteristics obtained by atomic force microscope, scanning electron microscope and x-ray diffraction were compared before and after laser treatment. The laser treatment increased the field of first flux entry by up to 65% compared to a non-irradiated sample. The laser irradiation also led to reduction of surface roughness, improvement of the surface morphology, reduction in crystallite size and increase of lattice parameter.
GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyzer) is a detection system installed at the focal plane of the SHELS (Separator for Heavy Elements Spectroscopy) recoil ...separator for gamma and internal conversion electron spectroscopy of heavy and superheavy nuclei. GABRIELA has recently been upgraded. The characteristics of the new setup are presented using the
Geant4
Monte Carlo simulation toolkit and validated against experimental results. The impact of summing on the gamma-ray and electron detection efficiencies is discussed.
Using a thin Nb layer on Copper substrate has several advantages compared with the bulk Nb in construction of Superconducting Radiofrequency accelerating cavities (SRF) for particle accelerators. We ...were evaluating the properties of two series of Nb layers deposited on Cu substrate, mainly by determining the start of magnetic flux penetration into the sample - the first magnetic flux entry field Ben, proportional to the Bc1. The values of Ben are compared with the surface roughness and surface morphology of the Nb layers, which have a strong influence on Ben. The surfaces of the samples were also treated by Nd:YAG laser depending on laser irradiation dose. The results of Ben and surface roughness before and after laser polishing are compared.
Bulk niobium is currently the material of choice for superconducting radio frequency (SRF) cavities and is a well matured process. However, it is possible that SRF cavities could be further improved ...beyond bulk Nb by sputtering thin Nb films onto Cu cavities. Copper has a greater thermal conductivity than Nb and is also easier to machine, while sputtering films on the surface reduces the amount of Nb used to fabricate the whole cavity. However, sputtering Nb on Cu produces other issues, for example, the surface quality of the Cu affects the quality of the Nb deposited on the surface and therefore the superconducting parameters. As the Nb on the surface is not perfect, the magnetic field produced by the RF can enter the cavity earlier than expected, producing RF losses, which can in turn lead to a quench. One approach is to treat the Nb post deposition by irradiating the surface using a laser to polish the surface of the Nb and increase the surface magnetic field that the cavity can maintain while remaining in the Meissner state. A magnetic field penetration experiment designed and built at Daresbury Laboratory has been used to measure the field of full flux penetration to characterize the effect of the laser treatment on the superconducting properties of the Nb. Surface characterization and the response of the Nb in a dc magnetic field have also been performed to try and provide an explanation for the change in the superconducting properties. The results demonstrate that the laser treatment can lead to an increase in the magnetic field at which the flux penetrates from one side of the sample to the other, thus it could potentially improve the performance of Nb coated RF cavities.
The current work discusses the experimental evaluation technique for the prompt neutron multiplicity distribution (PNMD) emitted is the spontaneous fission (SF). The restoring technique for the ...detector efficiency correction is shown as well as the comparison of two regularization parameter choice methods. The shape of the PNMD helps to achieve the information according the dynamic of the SF. The work also compiles all currently published PNMDs in the transfermium (Z > 100) region and discusses their shapes, providing a physical interpretation of the distortion of these distributions.
The article discusses the magnetoelectric effect in the thickness-shear mode region in a layered structure of a piezoelectric bimorph and a magnetostrictive material. Numerical estimates according to ...the proposed theoretical model of the magnetoelectric effect in the structure of the langatate bimorph and yttrium-iron garnet show that the value of ME voltage coefficient is much higher than for the bilayer of langatate and yttrium-iron garnet.
EuroCirCol is a conceptual design study of a post-LHC, Future Circular Hadron Collider (FCC-hh) with 50 TeV of beam energy and 100 km long, which aims to expand the current energy and luminosity ...frontiers. The vacuum chamber of the FCC-hh will have to cope with unprecedented levels of synchrotron radiation power for proton colliders, dealing simultaneously with a tighter magnet aperture. Considering that the high radiation power and photon flux will release larger amounts of gas into the system, the difficulty to meet the vacuum specifications increases substantially compared with the LHC. This paper presents a study on the beam induced vacuum effects for the FCC-hh novel conditions, the different phenomena which, owing to the presence of the beam, have an impact on the accelerator’s vacuum level. It is concluded that thanks to the adopted mitigation measures the proposed vacuum system shall be adequate, allowing us to reach≤1×1015H2eq/m3with baseline beam parameters within the first months of conditioning.
Abstract
With the benefits of evenly distributed pumping, low thermal outgassing rate and low photon-/electron-/ion stimulated desorption yields, non-evaporable getter (NEG) coating has been widely ...used in particle accelerators for many years. Our earlier work has demonstrated the different thickness of Ti-Zr-V coating in the range of 0.1–1 μm affects its pumping properties. In this study, the electron stimulated desorption (ESD) yields were studied for Ti-Zr-V coating deposited from a twisted target with its thickness less than 0.5 μm, while an uncoated sample was also measured as a reference. The ESD yields for H
2
, CH
4
, CO and CO
2
were measured as a function of electron accumulated dose up to ∼2 × 10
24
e
-
/m
2
followed bakeout/activation by heating to 80, 120, 140, 180 and 250°C. After each ESD experiment the samples were full saturated with a mix of H
2
, CO and CO
2
. Both NEG coated samples demonstrate lower values in comparison to the uncoated one after heating/activation to temperatures up to 180°C for H
2
, up to 250°C for CH
4
, up to 140°C for CO and 120°C for CO
2
. The activation to 140°C is the most efficient way to reach lower pressure and avoid quick aging of the NEG coating. The thinner NEG coating provides a significantly lower ESD yield in comparison to the thicker one only after activation to 180°C, while their ESD yields are almost identical for each gas at the lower temperature.
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