Electron scattering off online-produced radioactive isotopes at the SCRIT facility

The SCRIT facility is the first facility in the world designed specifically for electron scattering experiments on unstable nuclei. Last year we successfully measured the angular distribution of elastically scattered electrons from online-produced unstable nuclei 137Cs. This success marks the beginning of research into unstable nuclei using lepton probes, elementary particles that have only electromagnetic interactions, and the practical use of fixed targets for unstable nuclei will be technological innovations in unstable nuclear research.

The ion capture force from the 0.25-A electron beam in the electron storage ring stops and concentrates 10^8 externally injected target ions on the electron beam axis, forming a 10^9/cm2 thick target. That is SCRIT. The unstable nuclear ions produced by the photo-fission reaction of uranium are extracted from the ISOL system, converted into a pulsed beam by a cooler buncher and injected into SCRIT. The achievable luminosity exceeds 10^27/cm2/s.

In the 137Cs experiment, a luminosity of 10^26/cm2/s was obtained by injecting 2×10^7 target ions per pulse into SCRIT every 4 s, and the angular distribution of the 150-MeV elastic scattered electrons was measured in the range 30-60 degrees. This was the first on-line experiment, although the statistics were still unsatisfactory due to insufficient driver power to generate unstable nuclei. The driver power will be upgraded by a factor of 100 within the next two years. In this presentation, we will briefly describe the SCRIT facility and present the 137Cs experiment and future perspectives.