Reevaluation of structures in 70Se from combined conversion-electron and 𝛾-ray spectroscopy

J. Smallcombe; A. B. Garnsworthy; W. Korten; P. Singh; D. Muir; L. Próchniak6; F. A. Ali; C. Andreoiu; S. Ansari; G. C. Ball; C. J. Barton; S. S. Bhattacharjee; M. Bowry; A. D. Briscoe; R. Caballero-Folch; A. Chester; S. A. Gillespie; G. F. Grinyer; G. Hackman; J. Heery; C. Jones; B. Melon; M. Moukaddam; A. Nannini; P. Ruotsalainen; K. Starosta; C. E. Svensson; R. Wadsworth; J. Williams

doi:10.1103/PhysRevC.110.024318

Reevaluation of structures in ⁷⁰Se from combined conversion-electron and 𝛾-ray spectroscopy

J. Smallcombe^*, A. B. Garnsworthy, W. Korten, P. Singh, D. Muir, L. Próchniak6, F. A. Ali, C. Andreoiu, S. Ansari, G. C. Ball, C. J. Barton, S. S. Bhattacharjee, M. Bowry, A. D. Briscoe, R. Caballero-Folch, A. Chester, S. A. Gillespie, G. F. Grinyer, G. Hackman, J. HeeryC. Jones, B. Melon, M. Moukaddam, A. Nannini, P. Ruotsalainen, K. Starosta, C. E. Svensson, R. Wadsworth, J. Williams

^*Corresponding author for this work

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Abstract

Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near ⁷⁰Se , where no coexistence has yet been identified.

Purpose: To determine the presence or absence of any low-lying 0⁺ state in ⁷⁰Se, confirm the level structure, and interpret the nuclear deformation with theoretical models.

Methods: A combined internal-conversion-electron and 𝛾-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH).

Results: Despite a comprehensive search, no evidence was found for the existence of a 0⁺ state below 2 MeV in ⁷⁰Se . Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well.

Conclusion: ⁷⁰Se
does not have a well-defined axial shape. The 2⁺₂ state at 1601 keV resembles a quasi-𝛾 excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

Original language	English
Article number	024318
Number of pages	16
Journal	Physical Review C
Volume	110
Issue number	2
DOIs	https://doi.org/10.1103/PhysRevC.110.024318
Publication status	Published - 20 Aug 2024

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2024 07 03 Smallcombe et al Structures finalFinal published version, 2.42 MBLicence: CC BY 4.0

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Smallcombe, J., Garnsworthy, A. B., Korten, W., Singh, P., Muir, D., Próchniak6, L., Ali, F. A., Andreoiu, C., Ansari, S., Ball, G. C., Barton, C. J., Bhattacharjee, S. S., Bowry, M., Briscoe, A. D., Caballero-Folch, R., Chester, A., Gillespie, S. A., Grinyer, G. F., Hackman, G., ... Williams, J. (2024). Reevaluation of structures in ⁷⁰Se from combined conversion-electron and 𝛾-ray spectroscopy. Physical Review C, 110(2), Article 024318. https://doi.org/10.1103/PhysRevC.110.024318

@article{f7c859011231449582c7bac922321e81,

title = "Reevaluation of structures in 70Se from combined conversion-electron and 𝛾-ray spectroscopy",

abstract = "Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near 70Se , where no coexistence has yet been identified. Purpose: To determine the presence or absence of any low-lying 0+ state in 70Se, confirm the level structure, and interpret the nuclear deformation with theoretical models. Methods: A combined internal-conversion-electron and 𝛾-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH). Results: Despite a comprehensive search, no evidence was found for the existence of a 0+ state below 2 MeV in 70Se . Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. Conclusion: 70Se does not have a well-defined axial shape. The 2+2 state at 1601 keV resembles a quasi-𝛾 excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.",

author = "J. Smallcombe and Garnsworthy, {A. B.} and W. Korten and P. Singh and D. Muir and L. Pr{\'o}chniak6 and Ali, {F. A.} and C. Andreoiu and S. Ansari and Ball, {G. C.} and Barton, {C. J.} and Bhattacharjee, {S. S.} and M. Bowry and Briscoe, {A. D.} and R. Caballero-Folch and A. Chester and Gillespie, {S. A.} and Grinyer, {G. F.} and G. Hackman and J. Heery and C. Jones and B. Melon and M. Moukaddam and A. Nannini and P. Ruotsalainen and K. Starosta and Svensson, {C. E.} and R. Wadsworth and J. Williams",

year = "2024",

month = aug,

day = "20",

doi = "10.1103/PhysRevC.110.024318",

language = "English",

volume = "110",

journal = "Physical Review C",

issn = "2469-9985",

publisher = "American Physical Society",

number = "2",

}

Smallcombe, J, Garnsworthy, AB, Korten, W, Singh, P, Muir, D, Próchniak6, L, Ali, FA, Andreoiu, C, Ansari, S, Ball, GC, Barton, CJ, Bhattacharjee, SS, Bowry, M, Briscoe, AD, Caballero-Folch, R, Chester, A, Gillespie, SA, Grinyer, GF, Hackman, G, Heery, J, Jones, C, Melon, B, Moukaddam, M, Nannini, A, Ruotsalainen, P, Starosta, K, Svensson, CE, Wadsworth, R & Williams, J 2024, 'Reevaluation of structures in ⁷⁰Se from combined conversion-electron and 𝛾-ray spectroscopy', Physical Review C, vol. 110, no. 2, 024318. https://doi.org/10.1103/PhysRevC.110.024318

TY - JOUR

T1 - Reevaluation of structures in 70Se from combined conversion-electron and 𝛾-ray spectroscopy

AU - Smallcombe, J.

AU - Garnsworthy, A. B.

AU - Korten, W.

AU - Singh, P.

AU - Muir, D.

AU - Próchniak6, L.

AU - Ali, F. A.

AU - Andreoiu, C.

AU - Ansari, S.

AU - Ball, G. C.

AU - Barton, C. J.

AU - Bhattacharjee, S. S.

AU - Bowry, M.

AU - Briscoe, A. D.

AU - Caballero-Folch, R.

AU - Chester, A.

AU - Gillespie, S. A.

AU - Grinyer, G. F.

AU - Hackman, G.

AU - Heery, J.

AU - Jones, C.

AU - Melon, B.

AU - Moukaddam, M.

AU - Nannini, A.

AU - Ruotsalainen, P.

AU - Starosta, K.

AU - Svensson, C. E.

AU - Wadsworth, R.

AU - Williams, J.

PY - 2024/8/20

Y1 - 2024/8/20

N2 - Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near 70Se , where no coexistence has yet been identified. Purpose: To determine the presence or absence of any low-lying 0+ state in 70Se, confirm the level structure, and interpret the nuclear deformation with theoretical models. Methods: A combined internal-conversion-electron and 𝛾-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH). Results: Despite a comprehensive search, no evidence was found for the existence of a 0+ state below 2 MeV in 70Se . Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. Conclusion: 70Se does not have a well-defined axial shape. The 2+2 state at 1601 keV resembles a quasi-𝛾 excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

AB - Background: In the selenium isotopes various shape phenomena are present, in particular, the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near 70Se , where no coexistence has yet been identified. Purpose: To determine the presence or absence of any low-lying 0+ state in 70Se, confirm the level structure, and interpret the nuclear deformation with theoretical models. Methods: A combined internal-conversion-electron and 𝛾-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the generalized triaxial rotor model (GTRM) and the collective generalised Bohr Hamiltonian (GBH). Results: Despite a comprehensive search, no evidence was found for the existence of a 0+ state below 2 MeV in 70Se . Significant discrepancies to the previously established positive-parity-level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. Conclusion: 70Se does not have a well-defined axial shape. The 2+2 state at 1601 keV resembles a quasi-𝛾 excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

U2 - 10.1103/PhysRevC.110.024318

DO - 10.1103/PhysRevC.110.024318

M3 - Article

SN - 2469-9985

VL - 110

JO - Physical Review C

JF - Physical Review C

IS - 2

M1 - 024318

ER -

Reevaluation of structures in 70Se from combined conversion-electron and 𝛾-ray spectroscopy

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Reevaluation of structures in ⁷⁰Se from combined conversion-electron and 𝛾-ray spectroscopy