Experiments on 4n using SHARAQ spectrometer*

Study of isolated multi-neutron systems is one of fundamental subjects in nuclear physics.  

Recentrly observed 4n mass spectrum by using alpha-knockout (KO) reaction from ⁸He shows a strong correlation just above the 4n threshold in addition to a contimuum with a broad bump structure[1], which is similar characteristics to the 4n mass spectrum obtained by using an exothermic double-charge exchange (DCX) reaction ⁴He(⁸He,⁸Be) at 190 A MeV[2].

Production mechanism and kinematical consideration for the DCX experiment are introduced, where an impulse nature and the recoil-less condition are emphasized.  The relevant reaction process populating a four-body continuum system taking into account the final-state interactions in the di-neutrons is discussed as well as differences and common natures in the KO reaction.

Results on a new DCX experiment with better accuracy in the 4n mass are also presented.

Reference:

[1] M. Duer et al., Nature 606, 678 (2022)

[2] K. Kisamori et al., Phys. Rev. Lett 116, 052501 (2016)