0000000000470192
AUTHOR
José Luis Taín Enríquez
Total Absorption Spectroscopy Study of Rb-92 Decay: A Major Contributor to Reactor Antineutrino Spectrum Shape
The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. Rb-92 makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied Rb-92 decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.
Enhanced gamma-Ray Emission from Neutron Unbound States Populated in beta Decay
Total absorption spectroscopy is used to investigate the beta-decay intensity to states above the neutron separation energy followed by gamma-ray emission in Br-87,Br-88 and Rb-94. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large. intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The gamma branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For Br-87 and Br-88 the gamma branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populate…
Fine structure of the Gamow-Teller resonance revealed in the decay of Ho-150 2(-) isomer
The γ rays following the 72s 150Ho 2- Gamow-Teller β decay have been investigated with the CLUSTER CUBE setup, an array of six EUROBALL CLUSTER Ge detectors in close cubic geometry, providing a γ ray detection sensitivity of 2×10-5 per β-parent decay for γ-ray energies up to 5 MeV. The fine structure of the Gamow-Teller resonance at 4.4-MeV excitation in 150Dy has been studied. The resolved levels are compared with Shell Model predictions.
Ni-62(n,gamma) and Ni-63(n,gamma) cross sections measured at the n_TOF facility at CERN
The cross section of the Ni-62(n,gamma) reaction was measured with the time-of-flight technique at the neutron time-of-flight facility nTOF at CERN. Capture kernels of 42 resonances were analyzed up to 200 keV neutron energy and Maxwellian averaged cross sections (MACS) from kT = 5-100 keV were calculated. With a total uncertainty of 4.5%, the stellar cross section is in excellent agreement with the the KADoNiS compilation at kT = 30 keV, while being systematically lower up to a factor of 1.6 at higher stellar temperatures. The cross section of the Ni-63(n,gamma) reaction was measured for the first time at nTOF. We determined unresolved cross sections from 10 to 270 keV with a systematic un…
beta decay of Ag-97: Evidence for the Gamow-Teller resonance near Sn-100
In two complementary measurements, a cubelike array of 6 Euroball-Cluster germanium detectors and a total-absorption gamma-spectrometer were used to investigate the beta decay of 97Ag, a three proton-hole nucleus with respect to the 100Sn core. The half-life and QEC value of the decay of the 9/2+ ground state of 97Ag were determined to be 25.9(4) s and 6.98(11) MeV, respectively. A total of 603 gamma rays (578 new) was observed, and 151 levels (132 new) in 97Pd have been identified. An interesting beta-delayed gamma cascade was observed, which comprises 6 gamma-transitions with a deexcitation pattern involving an initial increase of the level spin. The Gamow-Teller (GT) beta-decay strength …
Deformation of the N = Z nucleus Sr-76 using beta-decay studies
A novel method of deducing the deformation of the N=Z nucleus 76Sr is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of QRPA calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large Total Absorption gamma Spectrometer, 'Lucrecia', newly installed at CERN-ISOLDE.
Isospin mixing in the N = Z nucleus Ge-64
The N=Z nucleus 64Ge has been investigated in two experiments using the EUROBALL III and EUROBALL IV spectrometers coupled to ancillary devices. Multipole mixing ratios, linear polarization and picosecond lifetimes for various transitions have been measured. The linear polarization results determine unambiguously the multipole character of the 5--->4+ 1665 keV transition, allowing to extract the electric dipole strength and to investigate for the first time the amount of isospin mixing implied by the presence of a forbidden E1 transition.
B(GT) strength from beta-decay measurements and inferred shape mixing in Kr-74
A total absorption spectrometer, dedicated to the study of very short-lived atomic species, has been built and installed at the CERN/ISOLDE mass separator. The beta decay of the neutron-deficient Kr-74 nucleus has been studied using this new device. The Gamow-Teller strength distribution has been observed over most of the Q(EC) window, and a total strength of 0.69(3) g(A)(2)/4pi has been measured for states with excitation energy below 3 MeV. Shape mixing in the Kr-74 ground state is inferred from a comparison of the experimental strength distribution with self-consistent, deformed, quasiparticle-random-phase-approximation calculations.