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AGATA Collaboration(Kaya, L. et al), & Gadea, A. (2018). High-spin structure in the transitional nucleus Xe-131: Competitive neutron and proton alignment in the vicinity of the N=82 shell closure. Phys. Rev. C, 98(1), 014309–19pp.
Abstract: The transitional nucleus Xe-131 is investigated after multinucleon transfer in the Xe-136 + Pb-208 and Xe-136 +U-238 reactions employing the high-resolution Advanced gamma-Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and as an elusive reaction product in the fusion-evaporation reaction Sn-124(B-11) ,p3n)Xe-131 employing the High-efficiency Observatory for gamma-Ray Unique Spectroscopy (HORUS) gamma-ray array coupled to a double-sided silicon strip detector at the University of Cologne, Germany. The level scheme of Xe-131 is extended to 5 MeV. A pronounced backbending is observed at (h) over bar omega approximate to 0.4 MeV along the negative-parity one-quasiparticle vh(11/12)(alpha = -1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations employing the PQM130, SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in Xe129-132 provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the pi 0h(11/2) orbital is found to be decisive for the description of the observed backbending phenomenon.
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AGATA Collaboration(Vogt, A. et al), & Gadea, A. (2017). High-spin structures in Xe-132 and Xe-133 and evidence for isomers along the N=79 isotones. Phys. Rev. C, 96(2), 024321–14pp.
Abstract: The transitional nuclei Xe-132 and Xe-133 are investigated after multinucleon-transfer (MNT) and fusionevaporation reactions. Both nuclei are populated (i) in Xe-136 + 2(08P)b MNT reactions employing the highresolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe-136 + Pt-198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te-130(alpha, xn) Xe134-xn fusion-evaporation reaction employing the HORUS gamma-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the J(pi) = (7(-)) and (10+) isomers in Xe-132 and above the 11/2(-) isomer in Xe-133. The results are compared to the high-spin systematics of the Z = 54 as well as the N = 78 and N = 79 chains. Furthermore, evidence is found for a long-lived (T-1/2 >> μs) isomer in Xe-133 which closes a gap along the N = isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.
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AGATA Collaboration(Kaya, L. et al), & Gadea, A. (2019). Isomer spectroscopy in Ba-133 and high-spin structure of Ba-134. Phys. Rev. C, 100(2), 024323–18pp.
Abstract: The transitional nuclei Ba-134 and Ba-133 are investigated after multinucleon transfer employing the high-resolution Advanced GAmma Tracking Array coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and after fusion-evaporation reaction at the FN tandem accelerator of the University of Cologne, Germany. The J(pi) = 19/2(+) state at 1942 keV in Ba-133 is identified as an isomer with a half-life of 66.6(20) ns corresponding to a B(E1) value of 7.7(4) x 10(-6) e(2) fm(2) for the J(pi) = 19/2(+) to J(pi) = 19/2(-) transition. The level scheme of Ba-134 above the J(pi) = 10(+) isomer is extended to approximately 6 MeV. A pronounced backbending is observed at h omega = 0.38 MeV along the positive-parity yrast band. The results are compared to the high-spin systematics of the Z = 56 isotopes. Large-scale shell-model calculations employing the GCN50:82, SN100PN, SNV, PQM130, Realistic SM, and EPQQM interactions reproduce the experimental findings and elucidate the structure of the high-spin states. The shell-model calculations employing the GCN50:82 and PQM130 interactions reproduce alignment properties and provide detailed insight into the microscopic origin of this phenomenon in transitional Ba-134.
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AGATA Collaboration(Rezynkina, K. et al), Gadea, A., & Perez-Vidal, R. M. (2022). Structure of As-83, As- 85, and As-87: From semimagicity to gamma softness. Phys. Rev. C, 106(1), 014320–14pp.
Abstract: The structure of As-83,As- 85, and As-87 have been studied in fusion-fission reaction( 238)U+9Be. Fission fragments were identified in mass and atomic number using the VAMOS++ spectrometer and the coincident gamma rays were detected in the gamma-ray tracking array AGATA. New transitions in 83As and 85As are reported and placed in the level schemes. A level scheme of the excited states in 87As is proposed for the first time. The data are interpreted in frame of large-scale shell-model calculations, SU3 symmetries, and beyond mean-field frameworks. A spherical regime at magic number N = 50 is predicted and the location of the proton g9/2 orbital is proposed for the first time. Development of collectivity in a prolate deformed, gamma-soft regime in the open shell cases 85As and 87As, most neutron-rich isotopes beyond N = 50, is concluded. Data and theoretical calculations give confidence to a relatively high extrapolated excitation energy about 4 MeV of the 9/2+ state in 79Cu, one proton above 78Ni.
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AGATA Collaboration(John, P. R. et al), & Gadea, A. (2014). Shape evolution in the neutron-rich osmium isotopes: Prompt gamma-ray spectroscopy of Os-196. Phys. Rev. C, 90(2), 021301–6pp.
Abstract: The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.
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