核分裂のとらえどころのない分裂中性子を追跡するためにサミットを使用する研究者たち(Researchers use Summit to track down nuclear fission’s elusive scission neutron)

2024-10-23 オークリッジ国立研究所(ORNL)

＜関連情報＞

• https://www.ornl.gov/news/researchers-use-summit-track-down-nuclear-fissions-elusive-scission-neutron
• https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.242501

核分裂におけるネック破裂と分裂中性子 Neck Rupture and Scission Neutrons in Nuclear Fission

Ibrahim Abdurrahman, Matthew Kafker, Aurel Bulgac, and Ionel Stetcu
Physical Review Letters  Published 12 June 2024
DOI:https://doi.org/10.1103/PhysRevLett.132.242501

Abstract

Just before a nucleus undergoes fission, a neck is formed between the emerging fission fragments. It is widely accepted that this neck undergoes a rather violent rupture, despite the absence of unambiguous experimental evidence. The main difficulty in addressing the neck rupture and saddle-to-scission stages of fission is that both are highly nonequilibrium processes. Here, we present the first fully microscopic characterization of the scission mechanism, along with the spectrum and the spatial distribution of scission neutrons (SNs), and some upper limit estimates for the emission of charged particles. The spectrum of SNs has a distinct angular distribution, with neutrons emitted in roughly equal numbers in the equatorial plane and along the fission axis. They carry an average energy around 3±0.5  MeV for the fission of ²³⁶U, ²⁴⁰Pu, and ²⁵²Cf, and a maximum of 16–18 MeV. We estimate a conservative lower bound of 9%–14% of the total emitted neutrons are produced at scission.