Evaluation of background in the (e, e' n) Experiment using stretcher-booster

An (e, e' n) coincident experiment using the stretcher booster ring (STB) finished at the Laboratory of Nuclear Science, Tohoku University in 1998 was begun. The (e, e' n) experiment consists of a double focusing type magnetic spectrometer (LDM) for testing of scattered electron and a neutron detector mounted around a scattering chamber. The detector is composed of a NE213 liquid scintillator and a photomultiplier tube R1250, and is suitable for detecting neutron. But because of simultaneous detecting also γ-ray as background, it is necessary to separate neutron from γ-ray. And, the detector is easy to largely suffer an effect of background because of rising its detection efficiency. In addition, because of presence of STB and LDM in a same experimental room with a shielding wall, a gigantic background is present, so it is important how the background affecting the detector makes lower in a (e, e' n) experiment. Then, it was tested how background around LDM affected a neutron detector for the first (e, e' n) experiment. As a result, by setting a concrete wall, improvement of a beam transport system, and so forth, almost all troubles thought to come from the system with problems in this experiment at first, could be resolved. And, it was fond that the background the others could be enough corresponded by some setting-ups in actual experiments. (G.K.)