First investigation of prompt neutrons from spontaneously fissioning isomers produced in multinucleon transfer reactions

Sailaubekov B. Svirikhin A.I. Devaraja H.M. Isaev A.V. Mukhin R.S. Bychkov M.A. Chelnokov M.L. Chepigin V.I. Danilkin V.D. Izosimov I.N. Kalandarov S.A. Katrasev D.E. Kuznetsova A.A. Malyshev O.N. Popeko A.G. Popov Y.A. Sokol E.A. Teymurov E. Tezekbayeva M.S. Ulanova I.I.
January 2026 Elsevier B.V.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
2026 #872

This work presents the first experimental results on prompt neutron multiplicities from short-lived spontaneously fissioning isomers produced in the multinucleon transfer (MNT) reaction of ²⁶Mg + ²³⁸U. The observed prompt neutron multiplicity distribution yields an average neutron number of ν¯ = 2.65 ± 0.20 and a variance of σ_ν² = 1.4. The half-life of the spontaneously fissioning products was determined to be T_1/2=5.3_−0.4^+0.5μs. The shape of the multiplicity distribution of prompt fission neutrons was restored using the Tikhonov regularization technique and is characterized by a symmetrical distribution. Among the known spontaneous fission isomers, ^{239 m}Pu and ^{243 m}Am exhibit half-lives and prompt neutron multiplicities that agree with the measured values within uncertainties. GEF model estimates yield ν¯ = 2.54 ± 0.20 for ^{239 m}Pu and ν¯ = 2.91 ± 0.20 for ^{243 m}Am, with the former showing slightly better agreement. Whether the activity arises from a single isomer or a mixture of both remains unresolved, as the current data do not allow for a clear separation of their contributions. Further high-statistics measurements, including fission fragment total kinetic energy and gamma-ray spectroscopy, are required for unambiguous identification of the fissioning nucleus.

Multinucleon transfer reaction , Prompt neutrons , Spontaneous fission isomers

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Joint Institute for Nuclear Research, Dubna, 141980, Russian Federation
Institute of Nuclear Physics, Almaty, 050032, Kazakhstan
L.N. Gumilyov Eurasian National University, Astana, 010008, Kazakhstan

Joint Institute for Nuclear Research
Institute of Nuclear Physics
L.N. Gumilyov Eurasian National University

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