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

1. 实验装置和方法的发展(a)研制了一种新型的双面条纹固态探测器，即使对低能量沉积的α衰变也能提高位置分辨率。(b)通常的充气分离器（GARIS）利用薄箔来分离真空和充气区域，由于箔的击穿，不能承受高强度的光束。为了克服这一困难，我们采用了差动泵送方法。(c)对非常重的原子核的固态固体的脉冲高度缺陷进行了仔细的校准，以便能够利用它们的飞行时间和能量测量进行质量分析。我们利用GARIS对^<238>U(^<40 >ar, α 2n)^<272>108反应进行了测量，以收集从薄靶中反冲出来的反应产物。它们的速度和能量分别由放置在GARIS上游和焦平面的飞行时间系统和位置敏感探测器（PSD）测量。随后的α衰变和自发裂变也在同一PSD中进行了测量。基于对时间和位置相关性的分析，我们成功地确定了新的α衰变事件，这些事件被认为发生在原子核^<272>108。上述反应的截面约为1nb，比通常的（HI,xn）型反应的截面大得多。

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.