# Resurgence of a Nation's Radiation Science Driven by Its Nuclear Industry Needs
## 4 New and Emerging Capabilities
### Automated, Reaptable Experiments
One of the attractive features of this scheme is that the projectile nucleus is more massive than the target nucleus, meaning that the center of mass of the collision system is moving forwards when viewed in the laboratory frame of reference. As a consequence, neutrons going into 4\(\pi\) in the collision frame all go into the forward direction in the laboratory frame. The closed contours are shown in Figure 14 for the impact of \({}^{7}\)Li ions on hydrogen-rich targets. At high energies the \({}^{7}\)Li ions produce neutrons with two distinct energies in the forward direction in the laboratory frame. The higher energy peak is due to forward ejection in the collision frame, which is further boosted in the laboratory frame by the motion of the center of mass of the collision pair, as illustrated by the blue arrows in the insert to Figure 14. The lower energy peak is due to backward-ejected neutrons in the collision frame, which results in slower neutrons in the laboratory frame, as illustrated by the red arrows in the insert. As \({}^{7}\)Li ions pass through a hydrogen-rich solid target, they will progressively slow down. However, they undergo negligible scattering. As they slow, they will produce a progressively more forward pointing beam of neutrons, i.e., the cone of neutrons in the center of mass frame shown in the Figure 14 insert will progressively close down. This process is illustrated by the three lines for 19.5, 14.5, and 13.18 MeV Li-ions. Below 13.18 MeV, neutrons are no longer produced as the collision is below the production threshold for the reaction. Hence, the prediction from kinematic simulations is that for \({}^{7}\)Li ions impacting onto a thick hydrogen-rich target, no neutrons are expected below an energy of 13.18 MeV, after which an increasing yield of forward-directed neutrons will be expected along with a negligible yield of neutrons to the side of the ion beam axis. Results from the initial commissioning of our neutron beam, as shown in Figure 15, agree with these predictions. Figure 14: Simulations of examples of the kinematics available for neutron production in thin targets using the accelerators available at DCF. Each line is labelled with the collision conditions pertaining to the neutron production. The x-axis shows the angle at which neutrons would be ejected with respect to the beam axis. The corresponding neutron energy is indicated on the y-axis. Towards the bottom left of this figure, several of the lines, corresponding to the inverse kinematic \({}^{7}\)Li(p,n)\({}^{7}\)Be reaction, are shown. These lines show two values of neutron energy, although they do not cover the full angular range. This is because the reaction can produce two neutron energies in the lab frame, but it is impossible to produce neutrons at large angle, i.e., these collisions result in a directed beam. The insert illustrates the kinematics giving rise to this effect and is explained in the main text. The target used for this experiment was a simple static polymer. The below-threshold production of forward-directed neutrons and the small yield of sideward directed neutrons are probably due to interactions with impurities in the target. However, they are unimportant from the viewpoint of neutron-beam experiments. One motivation for developing a high-energy neutron beam is to explore the radiation biology of neutron irradiated cells. This is motivated by the inevitable neutron burden created in proton therapy. High-energy protons, upon entering the patient, drive the reaction \(p+{}^{16}O\to p+{}^{15}O+n\), which can produce neutrons almost up to the energy of the initial proton beam (typ > 200 MeV). This reaction has a cross section of almost 100 mb for energies above 20 MeV [63], which, combined with the high density of oxygen (mostly through a patient's water content), leads to approximately one high-energy neutron being created by every proton entering a patient during a proton therapy session.