Design of a new experimental setup and simulation of neutron shielding for the very-forward-angle neutron elastic scattering

Constraints on parameters of the symmetry energy are important for understanding of the nuclear many-body system which is related to various astrophysical phenomena. The symmetry energy is essential for the neutron matter, but it is less certain than the symmetric nuclear matter. It is known that there is a linear correlation between the slope parameter and neutron skin thickness δR in ²⁰⁸Pb. δR can be written as the difference of the neutron and proton rms radii. However, the uncertainty of the neutron radius in ²⁰⁸Pb is still large, while its proton radius is precisely determined by electron scattering.

Proton elastic scattering (PES) is one of the powerful probes in determining the density distributions. In the case of PES, the cross sections at very forward angles which is sensitive to the nuclear radius, are mainly caused by the Coulomb scattering. It is difficult to extract the information of the neutron radius. Therefore, we proposed an experiment of the neutron elastic scattering (NES) to precisely determine the neutron radius in ²⁰⁸Pb.

Recently, we have performed a development to measure the NES at very forward angles (4, 7 degrees) in ²⁰⁸Pb and ⁴⁰Ca. We have designed a new setup with neutron beams at 63 MeV generated by the 7Li(p,n) reaction. To distinguish between the neutron beams and the scattered neutrons, beam collimation and neutron shielding were essential. In this presentation, the details of the experimental setup and feasibility test with simulations will be discussed.