127 research outputs found
Measurement of fast and thermal neutron flux from the d + D reaction using the activation method
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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
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
-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
Proton instability of Rb
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- 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
Study of Intermediate-spin States of Y-98
The nuclear structure of the odd–odd nucleus 98Y has been re-investigated
by observing prompt γ rays emitted following the proton-induced fission
of a 238U target, using the JUROGAM-II multidetector array. New highspin
decays have been observed and placed in the level schemes using triple
coincidences. The experimental level energies and γ-decay patterns are
compared to GICM and QPRM calculations, assuming that this neutronrich
N = 59 isotone is spherical at low energies and prolate deformed at
intermediate spins.Web of Science47391691
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