Design of back-streaming white neutron beam line at CSNS

Area of Science:

• Nuclear Physics
• Materials Science
• Particle Physics

Background:

• Construction of a novel white neutron beam line utilizing back-streaming neutrons from a spallation target at the China Spallation Neutron Source (CSNS).
• Development of various spectrometers for the Back-n beam line, specifically designed for nuclear data measurements.
• CSNS is a significant facility for advanced scientific research in China.

Purpose of the Study:

• To detail the physical design and characteristics of the Back-n white neutron beam line.
• To optimize neutron beam properties, including energy spectrum, flux, time structure, beam spots, and in-hall background.
• To support diverse applications, particularly precise nuclear data measurements, using a broad neutron energy range.

Main Methods:

• Utilizing a sophisticated collimation system and a neutron dump for beam line design.
• Comprehensive analysis of neutron beam characteristics: energy spectrum, flux, and time structure.
• Optimization of neutron beam spots and reduction of in-hall background radiation.

Main Results:

• The Back-n beam line covers a wide neutron energy range from 1 eV to 100 MeV.
• Achieved key beam properties at Endstation#2 (80m from target): neutron flux of 10^6 n/cm^2/s, time resolution of a few parts per mille, and low in-hall background (approx. 0.01/cm^2/s for neutrons and gamma).
• The facility is slated for commissioning in late 2017.

Conclusions:

• The Back-n beam line represents China's first high-performance white neutron source.
• It is poised to become one of the leading white neutron sources globally.
• The facility will significantly advance nuclear data measurements and related scientific research.