Guadilla, V. et al, Algora, A., Tain, J. L., Agramunt, J., Jordan, D., Monserrate, M., et al. (2022). Total absorption gamma-ray spectroscopy of the ss decays of Y-96gs,Y-m. Phys. Rev. C, 106(1), 014306–14pp.
Abstract: The ss decays of the ground state (gs) and isomeric state (m) of Y-96 have been studied with the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the 8(+) isomeric state from the 0(-) ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The ss-intensity distributions of both decays have been independently determined. In the analyses the deexcitation of the 1581.6 keV level in Zr-96, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the ss-detector efficiency, influencing the ss-intensity distribution obtained. Our results for Y-96gs (0(-)) confirm the large ground state to ground state ss-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to 96.6(-2.1)(+0.3) % of the total ss intensity. Given that the decay of Y-96gs is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of Y-96m (8(+)), previously undetected ss intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption gamma-ray spectroscopy measurements of ss decays with highly fragmented deexcitation patterns. Y-96m (8(+)) is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average ss and gamma energies differ significantly from the previous values in evaluated databases. The discrepancy is far above the previously quoted uncertainties. Finally, we also report on the successful implementation of an innovative total absorption gamma-ray spectroscopy analysis of the module-multiplicity gated spectra, as a first proof of principle to distinguish between decaying states with very different spin-parity values.
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Nacher, E., Rubio, B., Algora, A., Cano-Ott, D., Tain, J. L., Gadea, A., et al. (2016). Observations of the Gamow-Teller resonance in the rare-earth nuclei above Gd-146 populated in beta decay. Phys. Rev. C, 93(1), 014308–13pp.
Abstract: The rare-earth region of the nuclear table around the quasi-doubly magic nucleus Gd-146 is one of the very few places in which the Gamow-Teller (GT) resonance can be populated in beta decay. The appropriate technique to study such a phenomenon is total absorption spectroscopy, thanks to which one can measure the B(GT) distribution in beta-decay experiments even when it is very fragmented and lies at high excitation energy in the daughter nucleus. Results on the GT resonance measured in the beta decay of the odd-Z, N = 83 nuclei Tb-148, Ho-150, and Tm-152 are presented in this work and compared with shell-model calculations. The tail of the resonance is clearly observed up to the limit imposed by the Q value. This observation is important in the context of the understanding of the “quenching” of the GT strength.
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IDS Collaboration(Stryjczyk, M. et al.), & Nacher, E. (2023). Simultaneous gamma-ray and electron spectroscopy of 182,184,186Hg isotopes. Phys. Rev. C, 108(1), 014308–20pp.
Abstract: Background: The mercury isotopes around N = 104 are a well-known example of nuclei exhibiting shape coex-istence. Mixing of configurations can be studied by measuring the monopole strength rho^2(E0), however, currently the experimental information is scarce and lacks precision, especially for the I^pi -> I^pi (I not = 0) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in 182,184,186Hg, and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in 182,184,186Hg were populated in the & beta; decay of 182,184,186Tl, produced at ISOLDE, CERN and purified by laser ionization and mass separation. The & gamma;-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes.Results: In total, 193, 178, and 156 transitions, including 144, 140, and 108 observed for the first time in a & beta;-decay experiment, were assigned to 182,184,186Hg, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an E0 component. Extracted branching ratios allowed the sign of the interference term in 182Hg as well as & rho;2(E 0; 0+2 & RARR; 0+1 ) and B(E2; 0+2 & RARR; 2+1 ) in 184Hg to be determined. By means of electron-electron coincidences, the 0+3 state was identified in 184Hg. The experimental results were qualitatively reproduced by five theoretical approaches, the interacting boson model with configuration mixing with two different parametrizations, the general Bohr Hamiltonian, the beyond mean-field model, and the symmetry-conserving configuration-mixing model. However, a quantitative description is lacking. Conclusions: The presence of shape coexistence in neutron-deficient mercury isotopes was confirmed and evidence for the phenomenon existing at higher energies was found. The new experimental results provide important spectroscopic input for future Coulomb excitation studies.
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Briz, J. A., Borge, M. J. G., Rubio, B., Agramunt, J., Algora, A., Deo, A. Y., et al. (2022). Clarifying the structure of low-lying states in Br-72. Phys. Rev. C, 105(1), 014323–17pp.
Abstract: The spins and parities of low-lying states in 72Br populated in the beta decay of 72Kr have been studied via conversion electron spectroscopy. The measurements were carried out at ISOLDE using a miniorange spectrometer with Si(Li) and HPGe detectors for electrons and gamma ray detection. Results of the conversion coefficients corresponding to transitions deexciting 12 levels in 72Br are reported. The multipolarities of the transitions are deduced and the spins and parities of the levels involved are discussed. From the multipolarities of the most intense transitions to the ground state, the spin and parity of the 72Br ground state have been definitely established as 1+. The spin of the 101.2-keV isomeric state is determined to be 3-. The level scheme is compared with mean-field and shell-model calculations and oblate deformation for the 72Br ground state is deduced. No E0 transitions have been found in 72Br. E0 transitions in the neighboring isobaric nuclei, 72Se and 72Ge, have also been studied.
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Perez-Cerdan, A. B., Rubio, B., Gelletly, W., Algora, A., Agramunt, J., Nacher, E., et al. (2013). Deformation of Sr and Rb isotopes close to the N = Z line via beta-decay studies using the total absorption technique. Phys. Rev. C, 88(1), 014324–15pp.
Abstract: A study of the Gamow-Teller strength distributions B(GT) in the beta decay of Sr-78 and Rb-76,Rb-78 has been made using a total absorption spectrometer (TAS). Following the success in deducing the sign of the deformation for Sr-76, a similar approach is adopted for Sr-78 based on a comparison of the measured B(GT) with quasiparticle random-phase approximation calculations. This work confirms its previously expected prolate deformation in the ground state. Conclusions about the structure of the odd-odd Rb-76,Rb-78 isotopes have been drawn based on their measured B(GT) distributions.
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IDS Collaboration(Benito, J. et al), & Nacher, E. (2020). Detailed spectroscopy of doubly magic Sn-132. Phys. Rev. C, 102(1), 014328–18pp.
Abstract: The structure of the doubly magic Sn-132(50)82 has been investigated at the ISOLDE facility at CERN, populated both by the beta(-) decay of In-132 and beta(-)-delayed neutron emission of In-133. The level scheme of Sn-13(2) is greatly expanded with the addition of 68 gamma transitions and 17 levels observed for the first time in the beta decay. The information on the excited structure is completed by new gamma transitions and states populated in the beta-n decay of In-133. Improved delayed neutron emission probabilities are obtained both for In-132 and In-133. Level lifetimes are measured via the advanced time-delayed beta gamma gamma(t) fast-timing method. An interpretation of the level structure is given based on the experimental findings and the particle-hole configurations arising from core excitations both from the N = 82 and Z = 50 shells, leading to positive- and negative-parity particle-hole multiplets. The experimental information provides new data to challenge the theoretical description of Sn-132.
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IDS Collaboration(Benito, J. et al), & Nacher, E. (2024). Detailed structure of 131Sn populated in the β decay of isomerically purified 131In states. Phys. Rev. C, 110(1), 014328–19pp.
Abstract: The excited structure of the single-hole nucleus 131 Sn populated by the beta – decay of 131 In was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited nu h 11 / 2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyv & auml;skyl & auml;. The level scheme of 131 Sn was notably expanded with the addition of 31 new gamma-ray transitions and 22 new excited levels. The gamma-emitting excited levels above the neutron separation energy in 131 Sn were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in 131 Sn and the beta-decaying 131 In state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct beta feeding to the 3/2+ / 2 + ground and 11/2- / 2 – isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in log ft for first-forbidden transitions observed in previous studies, and to determine the beta-delayed neutron decay probability (Pn) P n ) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in 131 Sn was performed in this work. A short T 1 / 2 = 18(4)-ps value was measured for the 1/2+ / 2 + neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M 1 behavior for the nu 3 s – 1 1/2 / 2 -> nu 3 d – 13 / 2 transition. The measured half-lives of high-energy states populated in the beta decay of the (21/2+) / 2 + ) second isomeric state ( 131 m 2 In) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic 132 Sn.
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R3B Collaboration(Boillos, J. M. et al), & Nacher, E. (2022). Isotopic cross sections of fragmentation residues produced by light projectiles on carbon near 400A MeV. Phys. Rev. C, 105(1), 014611–13pp.
Abstract: We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C-12, N-14, and O-13-16,O-20,O-22 projectiles impinging on a carbon target at kinetic energies of near 400A MeV, most of them for the first time, with the R B-3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.
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IDS Collaboration(Stryjczyk, M. et al), & Nacher, E. (2020). Decay studies of the long-lived states in Tl-186. Phys. Rev. C, 102(2), 024322–9pp.
Abstract: Decay spectroscopy of the long-lived states in Tl-186 has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The a decay from the low-spin (2(-)) state in Tl-186 was observed for the first time and a half-life of 3.4(-0.)(4)(+0.5) s was determined. Based on the alpha-decay energy, the relative positions of the long-lived states were fixed, with the (2(-)) state as the ground state, the 7((+)) state at 77(56) keV, and the 10((-)) state at 451(56) keV. The level scheme of the internal decay of the Tl-186(10((-))) state [T-1/2 = 3.40(9) s], which was known to decay solely through emission of 374-keV gamma-ray transition, was extended and a lower limit for the beta-decay branching b(beta) > 5.9(3)% was determined. The extracted retardation factors for the gamma decay of the 10((-) )state were compared to the available data in neighboring odd-odd thallium isotopes indicating the importance of the pi d(3/2) shell in the isomeric decay and significant structure differences between Tl-184 and Tl-186.
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Caballero, L., Rubio, B., Kleinheinz, P., Yates, S. W., Algora, A., Dewald, A., et al. (2010). Two-phonon octupole excitation in Gd-146. Phys. Rev. C, 81(3), 031301–4pp.
Abstract: Based on experimental evidence from the Sm-144(alpha,2n) reaction, the 3484.7- keV 6(+) state in Gd-146 is identified as the highest-spin member of the 3(-) circle times 3(-) two-phonon octupole quartet. A previously unknown gamma line of 1905.8 keV and E3 character feeding the 3(-) octupole state has been observed. These results represent the first observation of a 6(+) -> 3(-) -> 0(+) cascade of two E3 transitions in an even-even nucleus and provide strong support for the interpretation of the 6(+) state as a two-phonon octupole excitation.
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