A High-Brightness, Electron-Based Source of Polarized Photons and Neutrons

A compact and comparatively inexpensive system that is practical for universities is described based on a low-energy, electron storage ring with at least one undulator based oscillator to store photons. If the oscillator cavity length is relativistically corrected to be an harmonic of the ring circumference (LC=βLRn=nB with nB the number of bunches), higher-energy, secondary photons from Compton backscattering may become significant. Then, besides synchrotron radiation from the ring dipoles and damping wigglers as well as undulator photons, there are frequency upshifted Compton photons and photoneutrons from low Q-value targets such as Beryllium (Qn=-1.66) or Deuterium (Qn=-2.22 MeV). For 100 MeV electron bunches, an adjustable-phase, planar, helical undulator can be made to produce circularly polarized UV photons having a fundamental εγ1=11.1 eV. If these photons are stored in a multimode, hole-coupled resonator they produce a Compton endpoint energy up to εγ2=1.7 MeV. When incident on a Be conversion target these secondary photons make unmoderated, epithermal neutrons having mean energy εn= 24.8 6.8 keV from the two-body reaction Be9+γ!n+Be8(!2α)with negligible, residual radioactivity. The system is shown in Fig. 1. Oscillator Cavity Dump 11eV Undulator Small Storage Ring (3rd Order Achromat) RF Be Target epithermal neutrons