IDS Collaboration(Andel, B. et al), Algora, A., & Nacher, E. (2021). New beta-decaying state in Bi-214. Phys. Rev. C, 104(5), 054301–13pp.
Abstract: A new beta-decaying state in Bi-214 has been identified at the ISOLDE Decay Station at the CERN-ISOLDE facility. A preferred I-pi = (8(-)) assignment was suggested for this state based on the beta-decay feeding pattern to levels in Po-214 and shell-model calculations. The half-life of the I-pi = (8) state was deduced to be T-1/2 = 9.39(10) min. The deexcitation of the levels populated in Po-214 by the beta decay of this state was investigated via gamma-gamma coincidences and a number of new levels and transitions was identified. Shell-model calculations for excited states in Bi-214 and Po-214 were performed using two different effective interactions: the H208 and the modified Kuo-Herling particle interaction. Both calculations agree on the interpretation of the new beta-decaying state as an I-pi = 8 – isomer and allow for tentative assignment of shell-model states to several high-spin states in Po-214.
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Kuhn, K. et al, & Nacher, E. (2021). Experimental study of the nature of the 1(-) and 2(-) excited excited states in Be-10 using the Be-11(p, d) reaction in inverse kinematics. Phys. Rev. C, 104(4), 044601–10pp.
Abstract: The nature of the 1(-) and 2(-) excited states in Be-10 is studied using the Be-11(p, d) transfer reaction in inverse kinematics at 10A MeV at TRIUMF ISAC-II, in particular to assess whether either of them can be considered as an excited halo state. The angular distributions for both states are extracted using deuteron-gamma( )coincidences and analyzed using a transfer model taking into account one-step and two-step processes. A good fit of the angular distributions is obtained considering only the one-step process, whereby an inner p(3/2) neutron of Be-11 is removed, leaving the halo neutron intact. Higher-order processes however cannot be rejected. The small spectroscopic factors extracted suggest that the structure of both states is not uniquely halo-like, but rather display a more complex configuration mixing cluster and halo structures. Further insights are limited, as this experiment specifically probed the halo-like (but not cluster-like) Be-11 (1/2(+)) circle times (nu p(3/2))(-1) configuration in both states.
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Brunet, M. et al, & Nacher, E. (2021). Competition between allowed and first-forbidden beta decays of At-208 and expansion of the Po-208 level scheme. Phys. Rev. C, 103(5), 054327–13pp.
Abstract: The structure of Po-208 populated through the EC/beta(+) decay of At-208 is investigated using gamma-ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed. rays which have been (re)assigned a position. The level scheme is compared to shell model calculations. Through this analysis approximately half of the beta-decay strength of At-208 is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations. This mass region provides an excellent testing ground for the competition between allowed and first-forbidden beta-decay calculations, important for the detailed understanding of the nucleosynthesis of heavy elements.
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Rubio, B., Gelletly, W., Algora, A., Nacher, E., & Tain, J. L. (2017). Beta decay studies with total absorption spectroscopy and the Lucrecia spectrometer at ISOLDE. J. Phys. G, 44(8), 084004–25pp.
Abstract: Here we present the experimental activities carried out at ISOLDE with the total absorption spectrometer Lucrecia, a large 4 pi scintillator detector designed to absorb a full gamma cascade following beta decay. This spectrometer is designed to measure beta-feeding to excited states without the systematic error called Pandemonium. The set up allows the measurement of decays of very short half life. Experimental results from several campaigns, that focus on the determination of the shapes of beta-decaying nuclei by measuring their beta decay strength distributions as a function of excitation energy in the daughter nucleus, are presented.
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Magro Hernandez, R. M., Muñoz-Noval, A., Briz, J. A., Murias, J. R., Espinosa-Rodríguez, A., Fraile, L. M., et al. (2024). Iodine-substituted hydroxyapatite nanoparticles and activation of derived ceramics for range verification in proton therapy. J. Mat. Chem. B, 12, 12030–12037.
Abstract: Osteosarcoma is a radioresistant cancer, and proton therapy is a promising radiation alternative for treating cancer with the advantage of a high dose concentration in the tumor area. In this work, we propose the use of iodine-substituted hydroxyapatite (IHAP) nanomaterials to use iodine (127I) as a proton radiation tracer, providing access to range verification studies in mineralized tissues. For this purpose, the nanomaterials were synthesized at four iodine concentrations via hydrothermal synthesis. The materials were characterized via different microstructural techniques to identify an optimal high iodine concentration and pure apatite phase nanomaterial. Finally, such pure IHAP powders were shaped and irradiated with proton beams of 6 and 10 MeV, and their activation was demonstrated through subsequent decay analysis. The materials could be integrated into phantom structures for the verification of doses and ranges of protons prior to animal testing and clinical proton therapy treatments of tumors located deep under combined soft and calcified tissues. Iodine-substituted hydroxyapatite nanomaterials were synthesised via hydrothermal process to use iodine (127I) as a proton radiation reporter with a view in hard tissue phantoms for proton therapy.
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Morfouace, P. et al, Benlliure, J., Cortina-Gil, D., & Nacher, E. (2025). An asymmetric fission island driven by shell effects in light fragments. Nature, 641, 339–344.
Abstract: Nuclear fission leads to the splitting of a nucleus into two fragments(1,2). Studying the distribution of the masses and charges of the fragments is essential for establishing the fission mechanisms and refining the theoretical models(3,4). It has value for our understanding of r-process nucleosynthesis(5,6), in which the fission of nuclei with extreme neutron-to-proton ratios is pivotal for determining astrophysical abundances and understanding the origin of the elements(7) and for energy applications(8,9). Although the asymmetric distribution of fragments is well understood for actinides (elements in the periodic table with atomic numbers from 89 to 103) based on shell effects(10), symmetric fission governs the scission process for lighter elements. However, unexpected asymmetric splits have been observed in neutron-deficient exotic nuclei(11), prompting extensive further investigations. Here we present measurements of the charge distributions of fission fragments for 100 exotic fissioning systems, 75 of which have never been measured, and establish a connection between the neutron-deficient sub-lead region and the well-understood actinide region. These new data comprehensively map the asymmetric fission island and provide clear evidence for the role played by the deformed Z = 36 proton shell of the light fragment in the fission of sub-lead nuclei. Our dataset will help constrain the fission models used to estimate the fission properties of nuclei with extreme neutron-to-proton ratios for which experimental data are unavailable.
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Zhang, G. et al, Algora, A., Nacher, E., Orrigo, S. E. A., Perez-Vidal, R. M., & Rubio, B. (2025). Approaching 100Sn: Structural evolution in 98,100Cd via lifetime measurements. Phys. Lett. B, 863, 139378–7pp.
Abstract: The lifetimes of low-lying excited states below the 8(+) seniority isomer were directly measured using fast timing detectors in the neutron-deficient isotopes Cd-98,Cd-100. This experiment was conducted with the DEcay SPECtroscopy (DESPEC) setup at GSI, where the ions of interest were produced via a fragmentation reaction and identified using the FRagment Separator (FRS) before being implanted in the AIDA active stopper system, and the gamma rays emitted during the de-excitation of isomeric states were detected by the LaBr3 FATIMA Array. The newly deduced values for the reduced transition probabilities were compared with shell-model calculations using different interactions and effective charges. The results indicate that, while Cd-98 aligns well with a seniority scheme description, in Cd-100 the transition strengths among low-lying states are not fully reproduced, and the nature of these states remains an open problem within the present theoretical description. Ultimately, a key element in the description of this region, crucial for nuclear physics and astrophysics, appears to be the proton-neutron term of the nuclear effective interaction.
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R3B Collaboration(Ponnath, L. et al), & Nacher, E. (2024). Measurement of nuclear interaction cross sections towards neutron-skin thickness determination. Phys. Lett. B, 855, 138780–6pp.
Abstract: The accuracy of reaction theories used to extract properties of exotic nuclei from scattering experiments is often unknown or not quantified, but of utmost importance when, e.g., constraining the equation of state of asymmetric nuclear matter from observables as the neutron-skin thickness. In order to test the Glauber multiple-scattering model, the total interaction cross section of C-12 on carbon targets was measured at initial beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The measurements were performed during the first experiment of the newly constructed (RB)-B-3 (Reaction with Relativistic Radioactive Beams) experiment after the start of FAIR Phase-0 at the GSI/FAIR facility with beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The combination of the large-acceptance dipole magnet GLAD and a newly designed and highly efficient Time-of-Flight detector enabled a precise transmission measurement with several target thicknesses for each initial beam energy with an experimental uncertainty of +/- 0.4%. A comparison with the Glauber model revealed a discrepancy of around 3.1% at higher beam energies, which will serve as a crucial baseline for the model-dependent uncertainty in future fragmentation experiments.
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Jungclaus, A., Doornenbal, P., Acosta, J., Vaquero, V., Browne, F., Cortes, M. L., et al. (2024). Position of the single-particle 3/2- state in 135Sn and the N = 90 subshell closure. Phys. Lett. B, 851, 138561–5pp.
Abstract: The decay of excited states of the nucleus Sn-135, with three neutrons outside the doubly-magic Sn-132 core, was studied in an experiment performed at the Radioactive Isotope Beam Factory at RIKEN. Several gamma rays emitted from excited Sn-135 ions were observed following one-neutron and one-neutron-one-proton removal from Sn-136 and Sb-137 beams, respectively, on a beryllium target at relativistic energies. Based on the analogy to 133Sn populated via one-neutron removal from Sn-134, an excitation energy of 695(15) keV is assigned to the 3/2(-) state with strongest single-particle character in 135Sn. This result provides the first direct information about the evolution of the neutron shell structure beyond N = 82 and thus allows for a crucial test of shellmodel calculations in this region. The experimental findings are in full agreement with calculations performed employing microscopic effective two-body interactions derived from CD-Bonn and N3LO nucleon-nucleon potentials, which do not predict a pronounced subshell gap at neutron number N=90. The occurrence of such a gap in Sn-140, i.e., when the 1f(7/2) orbital is completely filled, had been proposed in the past, in analogy to the magicity of Ca-48, featuring a completely filled 0f(7/2) orbital one harmonic oscillator shell below.
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Yue, Z. et al, Algora, A., & Nacher, E. (2024). Magnetic moments of thallium isotopes in the vicinity of magic N=126. Phys. Lett. B, 849, 138452–7pp.
Abstract: The magnetic dipole moments (mu) of Tl-209(g)(N =128) and Tl-207(m)(N = 126) have been measured for the first time using the in -source laser resonance -ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with >207. The self -consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μfor 1/2(+) thallium ground states, as well as μfor the 11/2(-) isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for mu(Tl-g , I-pi = 1/2(+)). It is shown that beyond mean-field contributions tocannot be neglected at least for thallium isotopes with I-pi = 1/2(+).
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