First experimental measurement of spin splitting and evidence for a second 0+ state in No152102254
Abstract
Background: Due to its large production cross section, No254 is the most-studied nucleus in the transfermium region and has been the “pioneer” nucleus in many different types of studies ranging from in-beam and decay γ-ray spectroscopy to γ-ray calorimetry. No254 is a well-deformed nucleus. At low excitation energy, the spins (I), parities (π), and excitation energies of three rotational bandheads are known: the 0+ ground state; a two-quasiproton Iπ=3+ state at an excitation energy of 987 keV, which decays promptly to the ground-state rotational band; and a long-lived 8− state at 1297 keV, whose microscopic configuration is still under debate. Purpose: This paper reexamines the electromagnetic decay of the long-lived 8− state in No254 using the enhanced sensitivity to the detection of internal conversion electrons of the GABRIELA detector array installed at the focal plane of the recoil separator SHELS at the Joint Institute for Nuclear Research in Dubna. Methods: No254 nuclei were produced in fusion-evaporation reactions between Ca48 ions and the atoms of Pb208 targets. The evaporation residues of interest were separated from the background of other reaction products by the recoil separator SHELS and transported to the GABRIELA decay station where the γ as well the internal-conversion decay from the 8− isomer could be jointly observed for the first time. Standard spectroscopy techniques together with a Geant4-assisted analysis of the spectroscopic data were used to establish the decay scheme of the 8− isomer. Results: The observed γ ray and internal-conversion-electron singles and coincidence spectra have revealed new decay branches from the 8− isomer as well as new states lying below it. A 4+ state has been established at 1203 keV above the ground sate. The presence of a 2− octupole phonon state could also be suggested at 1114 keV. The spectrum of detected internal-conversion electrons has uncovered the existence of an intense electric monopole (E0) contribution stemming from the decays of one or more states lying below the 3+ state. These findings are discussed in the light of quasiparticle random-phase approximation (QRPA) based on the finite-range D1M Gogny force and a new extension of the discrete nonorthogonal shell model including a variation-after-projection approach. Conclusions: The newly identified 4+ state is interpreted as the unfavored angular momentum coupling of two protons occupying the same single-particle configurations as the protons forming the previously known 3+ state. The two states form what is called a Gallagher-Moskowski doublet. This interpretation is supported by both the QRPA and shell-model calculations. The energy difference between the 3+ and 4+ states provides the first experimental measurement of spin splitting between two quasiproton states in the actinide region. The excess E0 strength evidenced by the internal-conversion-electron spectrum is attributed to the decay of members of a second 02+ rotational band lying at 884 keV above the ground state, which is weakly populated in the decay of the 3+ band. Remarkably, a 02+ state is obtained at 859 keV above the ground state in the new shell-model description of No254, which also reproduces the sequence and electromagnetic-decay properties of the ground-state and 3+ rotational bands.
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BibTeX
@article{forge2026first,
title = {{First experimental measurement of spin splitting and evidence for a second 0+ state in No152102254}},
author = {M. Forge and O. Dorvaux and A. Lopez-Martens and K. Kessaci and B.J.P Gall and K. Hauschild and D.D Dao and F. Nowacki and S. Péru and Z. Asfari and R. Chakma and A. Yeremin and M.L Chelnokov and V. Chepigin and A. Isaev and I.N Izosimov and D. Katrasev and A.A Kuznetsova and O.N Malyshev and R. Mukhin and A.G Popeko and Yu. Popov and B. Saylaubekov and A. Svirikhin and E.A Sokol and M.S Tezekbayeva and N. Zamyatin and Julien Piot},
journal = {Physical Review C},
year = {2026},
month = aug,
doi = {10.1103/qnyn-h7jt},
url = {https://hal.science/hal-05733648v1},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - JOUR
TI - First experimental measurement of spin splitting and evidence for a second 0+ state in No152102254
AU - M. Forge
AU - O. Dorvaux
AU - A. Lopez-Martens
AU - K. Kessaci
AU - B.J.P Gall
AU - K. Hauschild
AU - D.D Dao
AU - F. Nowacki
AU - S. Péru
AU - Z. Asfari
AU - R. Chakma
AU - A. Yeremin
AU - M.L Chelnokov
AU - V. Chepigin
AU - A. Isaev
AU - I.N Izosimov
AU - D. Katrasev
AU - A.A Kuznetsova
AU - O.N Malyshev
AU - R. Mukhin
AU - A.G Popeko
AU - Yu. Popov
AU - B. Saylaubekov
AU - A. Svirikhin
AU - E.A Sokol
AU - M.S Tezekbayeva
AU - N. Zamyatin
AU - Julien Piot
PY - 2026
DA - 2026/08/13
JO - Physical Review C
DO - 10.1103/qnyn-h7jt
UR - https://hal.science/hal-05733648v1
AB - Background: Due to its large production cross section, No254 is the most-studied nucleus in the transfermium region and has been the “pioneer” nucleus in many different types of studies ranging from in-beam and decay γ-ray spectroscopy to γ-ray calorimetry. No254 is a well-deformed nucleus. At low excitation energy, the spins (I), parities (π), and excitation energies of three rotational bandheads are known: the 0+ ground state; a two-quasiproton Iπ=3+ state at an excitation energy of 987 keV, which decays promptly to the ground-state rotational band; and a long-lived 8− state at 1297 keV, whose microscopic configuration is still under debate. Purpose: This paper reexamines the electromagnetic decay of the long-lived 8− state in No254 using the enhanced sensitivity to the detection of internal conversion electrons of the GABRIELA detector array installed at the focal plane of the recoil separator SHELS at the Joint Institute for Nuclear Research in Dubna. Methods: No254 nuclei were produced in fusion-evaporation reactions between Ca48 ions and the atoms of Pb208 targets. The evaporation residues of interest were separated from the background of other reaction products by the recoil separator SHELS and transported to the GABRIELA decay station where the γ as well the internal-conversion decay from the 8− isomer could be jointly observed for the first time. Standard spectroscopy techniques together with a Geant4-assisted analysis of the spectroscopic data were used to establish the decay scheme of the 8− isomer. Results: The observed γ ray and internal-conversion-electron singles and coincidence spectra have revealed new decay branches from the 8− isomer as well as new states lying below it. A 4+ state has been established at 1203 keV above the ground sate. The presence of a 2− octupole phonon state could also be suggested at 1114 keV. The spectrum of detected internal-conversion electrons has uncovered the existence of an intense electric monopole (E0) contribution stemming from the decays of one or more states lying below the 3+ state. These findings are discussed in the light of quasiparticle random-phase approximation (QRPA) based on the finite-range D1M Gogny force and a new extension of the discrete nonorthogonal shell model including a variation-after-projection approach. Conclusions: The newly identified 4+ state is interpreted as the unfavored angular momentum coupling of two protons occupying the same single-particle configurations as the protons forming the previously known 3+ state. The two states form what is called a Gallagher-Moskowski doublet. This interpretation is supported by both the QRPA and shell-model calculations. The energy difference between the 3+ and 4+ states provides the first experimental measurement of spin splitting between two quasiproton states in the actinide region. The excess E0 strength evidenced by the internal-conversion-electron spectrum is attributed to the decay of members of a second 02+ rotational band lying at 884 keV above the ground state, which is weakly populated in the decay of the 3+ band. Remarkably, a 02+ state is obtained at 859 keV above the ground state in the new shell-model description of No254, which also reproduces the sequence and electromagnetic-decay properties of the ground-state and 3+ rotational bands.
SN - 2469-9985
SN - 2469-9993
ER -