R＆D for high-resolution (p, 2p) proton knockout reactions using unstable nuclear beams

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Utilizing (p, 2p) proton-knockout reactions with RI beams and proton target in the inverse kinematics, information concerning the single-particle orbits such as the orbital angular momentum and the nucleon-separation energy can be deduced. Experimentally, unstable nuclear beams With about 100 A MeV incident energy are guided to the proton target, and the energy and the momenta of two protons are measured. Since NaI(T1) detectors were used as proton detectors, the separation-energy resolution was about 1.5 MeV (rms) in previous experiments.Since various final states can not be separated with such a resolution, we have performed various R＆D for imporoving the separation-energy resolution. The most important part was the development of the High-Purity Ge detectors as the proton detector. Although small Ge crystals have been used in various nuclear experiments, the detector we have developed contains planar HP Ge crystals with 70 mm in diameter and 30 mm in thickness. For the sake of convenience, the crystal was contained in the cryostats with a thin Be foil as the entrance window. This detector can measure proton energies unto 105 MeV.For real measurements, several other detectors were developed : Low-pressure MWPC for high-precision measurement of secondary-beam energy, position-sensitive gas detectors with high position resolution for measuring the momentum vector of protons, Si-strip detectors for measuring the energy loss for particle identification.After finishing all these detector elements, the whole detector systems were tested using proton and 12C beams in the accelerator facility. Although the data analysis are in progress, separation energy resolution of 0.5 MeV (rms) has been obtained. Since this value is about a factor of 3 worse than expected, we are planning to test the detector system again using the particle beams from the accelerator, after modifying part of the detector elements.