<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>β</mi></math>-spectrum shapes of first-forbidden transitions with <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Δ</mi><msup><mi>I</mi><mi>π</mi></msup><mo>=</mo><msup><mn>0</mn><mo>−</mo></msup></mrow></math> in <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi>Rb</mi><mprescripts></mprescripts><none></none><mn>92</mn></mmultiscripts></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi>Cs</mi><mprescripts></mprescripts><none></none><mn>142</mn></mmultiscripts></math> decays

G. A. Alcalá; A. Algora; M. Estienne; M. Fallot; V. Guadilla; A. Beloeuvre; W. Gelletly; R. Kean; A. Porta; S. Bouvier; J.-S. Stutzmann; E. Bonnet; T. Eronen; D. Etasse; J. Agramunt; J. L. Tain; H. Garcia Cabrera; L. Giot; A. Laureau; J. A. Victoria; Y. Molla; A. Jaries; L. Al Ayoubi; O. Beliuskina; W. Gins; M. Hukkanen; A. Illana; A. Kankainen; S. Kujanpää; I. Moore; I. Pohjalainen; D. Pitman; A. Raggio; M. Reponen; J. Romero; J. Ruotsalainen; M. Stryjczyk; A. Tolosa; V. Virtanen

doi:10.1103/zvdk-57bt

$β$ -spectrum shapes of first-forbidden transitions with $Δ I^{π} = 0^{-}$ in ${}^{92}{Rb}$ and ${}^{142}{Cs}$ decays

G. A. Alcalá ^1,*, A. Algora ^1,2,†, M. Estienne ³, M. Fallot³, V. Guadilla ^3,4, A. Beloeuvre³, W. Gelletly ⁵, R. Kean³, A. Porta ³ et al.

S. Bouvier³, J.-S. Stutzmann³, E. Bonnet ³, T. Eronen⁶, D. Etasse⁷, J. Agramunt¹, J. L. Tain ¹, H. Garcia Cabrera ^1,8, L. Giot³, A. Laureau³, J. A. Victoria ⁹, Y. Molla ³, A. Jaries ⁶, L. Al Ayoubi ⁶, O. Beliuskina ⁶, W. Gins⁶, M. Hukkanen⁶, A. Illana ^6,10, A. Kankainen ⁶, S. Kujanpää ⁶, I. Moore ⁶, I. Pohjalainen ⁶, D. Pitman ^6,11, A. Raggio ⁶, M. Reponen ⁶, J. Romero^6,12, J. Ruotsalainen⁶, M. Stryjczyk ^6,13, A. Tolosa ^6,14, and V. Virtanen⁶

¹Instituto de Física Corpuscular, CSIC-Universitat de València, E-46980 Paterna (València), Spain
²HUN-REN Institute for Nuclear Research (ATOMKI), H-4001 Debrecen, Hungary
³SUBATECH, CNRS/IN2P3, IMT Atlantique, Nantes Université, F-44307 Nantes, France
⁴Faculty of Physics, University of Warsaw, 02-093 Warsaw, Poland
⁵Department of Physics, University of Surrey, Guildford GU27XH, United Kingdom
⁶Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
⁷LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-Caen, France
⁸Universidad Europea de Madrid, Department of Biosciences, Faculty of Biomedical and Health Sciences, E-28670 Madrid, Spain
⁹Instituto de Física Corpuscular, CSIC-Universitat de València, E-46071 València, Spain
¹⁰Grupo de Física Nuclear, EMFTEL, and IPARCOS, Universidad Complutense de Madrid, CEI Moncloa, E-28040 Madrid, Spain
¹¹Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
¹²Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United Kingdom
¹³Institut Laue-Langevin, 71 Avenue des Martyrs, F-38042 Grenoble, France
¹⁴European Organization for Nuclear Research (CERN), Geneva, Switzerland

^*Contact author: galcala@ific.uv.es
^†Contact author: algora@ific.uv.es

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Phys. Rev. C 114, 014319 – Published 16 July, 2026

DOI: https://doi.org/10.1103/zvdk-57bt

Abstract

The electron spectra of the $β$ decays of ${}^{92}{Rb}$ and ${}^{142}{Cs}$ , key contributors to the reactor antineutrino spectrum, were measured at the IGISOL facility using radioactive beams of high isotopic purity. The shapes of the measured $β$ spectra were compared with various $β$ -shape models, including first-forbidden correction factors for $Δ I^{π} = 0^{-}$ ground-state to ground-state transitions. Comparisons with previous experimental results are also provided. The shapes of the newly measured $β$ spectra are well reproduced employing feedings extracted from total absorption gamma spectroscopy measurements.

Physical Review C

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$β$ -spectrum shapes of first-forbidden transitions with $Δ I^{π} = 0^{-}$ in ${}^{92}{Rb}$ and ${}^{142}{Cs}$ decays

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β-spectrum shapes of first-forbidden transitions with ΔIπ=0− in Rb92 and Cs142 decays

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$β$ -spectrum shapes of first-forbidden transitions with $Δ I^{π} = 0^{-}$ in ${}^{92}{Rb}$ and ${}^{142}{Cs}$ decays