We propose to measure double differential cross-sections (with respect to angle and energy of emitted neutrons) for three-body (3B) photodisintegration of 3He. This project will produce the first photodisintegration cross-section data measured using a liquid 3He target. These measurements are made possible by the use of a state-of-the-art cryogenic liquid target recently developed at HIγS. The double differential data will be integrated to obtain total cross-section data at each of seven circularly polarized gamma-ray beam energies: 15, 18, 22, 26, 30, 35, and 40 MeV. This project is motivated by the need for high accuracy cross-section data to verify the effective nucleon-nucleon (NN) and three-nucleon (3N) interactions used in ab-initio few-nucleon calculations. For example, these measurements will provide the highest accuracy total cross-section data for photodisintegration of 3He. Also, these data are needed to calculate total photo-absorption cross sections, which are critical for the normalization of spin-dependent cross sections measured in sum-rule studies. An example being the Gerasimov-Drell-Hearn (GDH) Sum-Rule measurements performed at HIγS.
The experiment technique is based on the detection of the emitted neutrons in an array of liquid organic scintillators separated by 22.5° at polar angles from 22.5° to 157.5° relative to the gamma beam axis. The differential neutron energy spectrum will be measured at each angle. The differential cross-section angular distribution will be determined at each beam energy to a systematic uncertainty of less than ±5% and to a statistical uncertainty of less than ±2% at each angle. This experiment is scheduled to run during the first quarter of 2023.