Basic Study of a New Approach to Super Heavy Elements by Incomplete Fusion Reactions

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1. Development of experimental apparatus and method(a) A new type solid-state detector striped on both sides has been made to improve position resolution even for alpha decays having low energy deposition. (b) The usual gas-filled separator (GARIS) utilizing a thin foil to separate the vacuum and gas-filled regions cannot stand high-intensity beam due to breakdown of the foil. We have adopted a differential pumping method to overcome this difficulty. (c) Careful calibration on pulse-height defects of the SSD for very heavy nuclei has been made to enable their mass analysis using their time-of-flight and energy measurements.2. Use of pre-equilibrium alpha emission for production of very heavy nucleiWe have performed a measurement on the ^<238>U(^<40>Ar, alpha2n)^<272>108 reaction using the GARIS to collect reaction products recoiling out of a thin target. Their velocities and energies were measured by a time-of-flight system and a position-sensitive detector (PSD) placed upstream and at the focal plane of the GARIS, respectivery. Subsequent alpha decays and spontaneous fissions were also measured in the same PSD.Based on the analysis of the time- and position-correlations, we have succeeded in identifying new alpha-decay events, which are considered to take place from the nucleus ^<272>108. The cross section of the above reacton is roughly 1nb, which is much larger than that obtained in the usual (HI,xn) type reaction.