The 2-Body Photodisintegration Reaction $^{4}$He($\gamma $,n)$^{3}$He below 30 MeV

The charge-symmetric reactions $^{4}$He($\gamma $,p)$^{3}$H and $^{4}$He($\gamma $,n)$^{3}$He are of special interest in few-body physics. Although they have been studied for half a century, the data for these classical breakup reactions scatter widely. For the $^{4}$He($\gamma $,n)$^{3}$He reaction case, it is advantageous to detect the $^{3}$He particles rather than the associated neutrons. The most recent approach used a time-projection chamber [1] for the $^{3}$He detection, but these data disagree considerably from those obtained via neutron detection [2]. In an attempt to clarify the situation, we measured the cross section of the $^{4}$He($\gamma $,3He)n 2-body breakup reaction below E$\gamma $=30 MeV at TUNL's HIGS facility using high-pressure $^{4}$He/Xe gas scintillators of various composition ratios. The challenge in this approach is to separate the pulses from the low-energy $^{3}$He ions, which are not mono-energetic, from those produced by Compton scattered electrons at the low pulse-height side and those from the $^{4}$He($\gamma $,p)$^{3}$H reaction at the high pulse-height side. First results will be compared to existing data and theoretical calculations. [1] T. Shima\textit{ et al}., Phys. Rev. C\textbf{ 72}, 044004 (2005). [2] B. Nilsson \textit{et al}., Phys. Rev. C \textbf{75}, 014007 (2007).