163 research outputs found
Kinetic Modeling of Photodegradation of Water-Soluble Polymers in Batch Photochemical Reactor
Synthetic water-soluble polymers, well-known refractory pollutants, are abundant in wastewater effluents since they are extensively used in industry in a wide range of applications. These polymers can be effectively degraded by advanced oxidation processes (AOPs). This entry thoroughly covers the development of the photochemical kinetic model of the polyvinyl alcohol (PVA) degradation in UV/H2O2 advanced oxidation batch process that describes the disintegration of the polymer chains in which the statistical moment approach is considered. The reaction mechanism used to describe the photo-degradation of polymers comprises photolysis, polymer chain scission, and mineralization reactions. The impact of operating conditions on the process performance is evaluated. Characterization of the polymer average molecular weights, total organic carbon, and hydrogen peroxide concentrations as essential factors in developing a reliable photochemical model of the UV/H2O2 process is discussed. The statistical moment approach is applied to model the molar population balance of live and dead polymer chains taking into account the probabilistic chain scissions of the polymer. The photochemical kinetic model provides a comprehensive understanding of the impact of the design and operational variables
Shell model calculations of stellar weak interaction rates: I. Gamow-Teller distributions and spectra of nuclei in the mass range A=45-65
Electron capture and beta-decay rates on nuclei in the mass range A=45-65
play an important role in many astrophysical environments. The determination of
these rates by large-scale shell model calculations is desirable, but it
requires to reproduce the Gamow-Teller strength distributions and spectra of
the pf shell nuclei. We show in this paper that large-scale shell model
calculations, employing a slightly monopole-corrected version of the wellknown
KB3 interaction, fulfill these necessary requirements. In particular, our
calculations reproduce the experimentally available GT+ and GT- strength
distributions and the nuclear halflives, and describe the nuclear spectra
appropriately.Comment: 11 pages, 5 figure
Meson-exchange enhancement in first-forbidden -transitions: the case of K and Ca
The - decay of K and Ca have been investigated with the main motive of determining more accurately the first-forbidden - branches, in particular the rank-zero, J = 0, -transitions. K and Ca have been produced by fragmentation of U and Ti targets respectively, with a 1 GeV proton beam and subsequent on-line mass separation. For K, -ray spectroscopy, as well as delayed neutron spectroscopy by time of flight, were carried out to obtain a detailed decay scheme to 20 (bound and unbound) levels in Ca. The level structur e of Ca can be compared to recent calculations which incorporate 1p1h excitations from the f shell. The first-forbidden transition K(0)Ca(0) g.s. has been evaluated for the first time by a direct measurement of - and - activities. Its importance (61.0 7.4) is interpreted as an effect of the meson-exchange current (MEC) l eading to an enhancement factor of 62(5) in comparison with the value predicted by shell-model calculations using the impulse approximation. For the CaK decay, chemical selec tive production was obtained through separation of the molecular ion CaF without contamination by isobars. In these conditions, the measurement of very weak -branches, at a level of 10 decays, could be made and a limit, at the 2-confidence level, has been obtained for the 0 0 branch to the level at E = 2993 keV (I < 0.0046). Imp lications of these results on the general trend of meson-exchange enhancements of first-forbidden transitions within the framework of the spherical shell model are discussed
Measurement of fast and thermal neutron flux from the d + D reaction using the activation method
LPSC-acc ;
Spectroscopy of by decay: sd-fp shell gap and single-particle states
The decays were studied at the CERN on-line mass separator ISOLDE by and measurements, in order to corroborate thelow-level description of and to obtain the first information on the level structure of the N=21 isotope . Earlier observed lines in decay were confirmed and new gamma transitions following both beta decay and -delayed neutron emission were established. The first level scheme in , including three excited states at 910, 974 and 2168 keV, is consistent with and for the first two states respectively. Beta-decay half-life of ms and beta-delayed neutron branching value were measured unambiguously. The significance of the single-particle energy determination at N=21, Z=14, for assessing the effective interaction in sd-fp shell-model calculations, is discussed and illustrated by predictions for different n-rich isotopes
Proton instability of Rb
The steps of territorial intelligence are based on the emergence of new fashions of exchange within the territory . It acts thus on the territorial visibility and hustles the places of strategic reflexion; by doing this, it takes part within the country, to make move the bond sociétal. This paper subjects a posture of collection and mutualisation of information within the territory
-decay half-life of Kr: a bridge nuclide for the rp-process beyond A = 70
The -decay half-life of Kr has been measured for the first time at the ISOLDE PSB Facility at CERN. Mass separated Kr ions were produced by 1 GeV proton induced spallation reactions in a Nb foil. The measured half-life is 57(21) ms. This value is consistent with the half-life calculated assuming a pure Fermi decay, but is clearly lower than the value used in a recent rp-process reaction flow calculation. The result shows that the reaction flow via two-proton-capture of Se is 2.5 times faster than previously calculated assuming an astrophysical temperature of 1.5 GK and a density of 10g/cm
- decay of the proton-rich T nucleus, Kr
- decay of the T = - 1/2 nuclide Kr has been studied at the ISOLDE PSB Facility at CERN. Kr ions were produced in spallation reactions in a Nb foil using the 1 GeV proton beam and studied by means of -delayed proton, - and -ray spectroscopy. The half-life and the -decay energy of Kr were determined using the decay of protons and positrons. These results: T = 100 ± 3 ms and = 10 ± 0.32 MeV and the first observation of the b-branch to the 207 keV level in Br makes the extension of the systematics of Gamow-Teller matrix elements of mirror nuclei up to A = 71 possible. Gamow-Teller strength of the same magnitude as that of the -shell mirror nuclei is observed for the ground state transition
- decay of the M=-1 nucleus Zn studied by selective laser ionization
- decay of Zn has been studied for the first time. A new laser ion-source concept has been used to produce mass-separated sources for and - spectroscopy. The half-life of Zn was determined to be 86(18) ms. Comparisons are made with previous data from charge-exchange reactions. Our Gamow-Teller strength to the 1 state at 1051 keV excitation in Cu agrees well with the value extracted from a recent (He, t) study. Extensive shell-model calculations are presented
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