Experimental results on 3n and the near-future experiments on multi-neutron states at RIBF

Studies of multineutron systems have been interesting and fascinating topics in recent nuclear physics. The findings of the 4n peaks in the ⁴He(⁸He,⁸Be)4n and ⁸He(p,pα)4n reactions sparked hot debates from both theoretical and experimental perspectives. However, thus far, a comprehensive explanation for the origin of these peaks has not been obtained. In this presentation, we will present two of new experimental approaches on multineutron systems recently performed and planned at RIBF.

 First, we introduce our experimental study on 3n systems. Experimental data on 3n can provide fundamental tests of our understanding of multineutron systems. The ³H(t,³He)3n reaction at intermediate energies is an ideal spectroscopic tool of 3n. With this reaction we can produce 3n in a low-momentum transfer condition under well-established reaction mechanism. One of the challenges of this experiment was to develop a thick tritium target. We collaborated with the tritium facility at University of Toyama and fabricated a Ti-³H target with approximately 3-mg/cm2 tritium thickness and total radioactivity of 1.6 TBq. With this target we realized the ³H(t,³He)3n measurement at 170 MeV/u using the SHARAQ spectrometer. The results of this experiment will be shown.

 Second, we explain a next generation multineutron experiment planned using SAMURAI spectrometer. By means of the knockout reactions on helium isotopes in inverse kinematics, we can observe various multineutron systems with neutron numbers up to 6. Using large acceptance recoil detector array TOGAXSI and massive neutron detector walls, we will obtain missing mass and invariant mass spectra for these multineutron systems in the same setup. The overview and outlook of this project will be explained in the presentation.