A New Method to Obtain Neutrons with Maxwellian Energy Distribution for Nuclear Astrophysics Study

To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides, a monoenergetic 3.4 MeV proton beam produced by the tandem-accelerator in the China Institute of Atomic Energy was utilized. The proton beam was first transmitted through a 60.5 μm aluminum foil and then impinged on a natural LiF target to produce neutron beam via 7Li(p, n)7Be reaction. The quasi-Gaussian energy distribution of protons in the LiF target resulted in neutron energy spectra that agreed with a Maxwellian energy distribution at kT=(22±2) keV, which was achieved by integrating neutrons detected within an emission angle of 65.0°±2.6° using a 6Li glass detector positioned at 65° relative to the proton beam direction. The narrow angular spread of the Maxwellian-distributed neutron beam enables direct measurement of neutron capture cross-sections for most s-process nuclides, overcoming previous experimental limitations associated with broad angular distributions.