稀有事件搜索

Searching of Rare Events

简单介绍了远离核奇异性质研究的科学意义,报道了稀有事件的搜索方法,以高生成额、高分离效率和高探测效率的方法搜索稀有事件。通过放射化学分离方法从天然Th中提取出镭元素,准备薄的228Raβ→-228Ac源。由60MeV/u18O离子照射天然Th靶引起的232Th-2p反应产生230Ra,通过放射化学分离方法从被照射的靶中提取出镭元素并制成薄源,经230Raβ→-230Ac得到230Ac。利用35MeV的质子束轰击ThO2粉末靶,通过232Th(p,3n)反应产生230Pa核,经用放射化学分离方法分离出Pa,并制成230Paβ→-230U测量源。用固体径迹探测器和PHGe"射线探测器记录和测量来自源中的裂变碎片(重离子)和"谱,观测到它们的!延发裂变或重离子事件,得到228Ac和230Ac的!延发裂变概率分别为(5±2)×10-12和(1.19±0.85)×10-8,230U发射22Ne相当于α衰变的分支比B=$Ne/$#为(1.3±0.8)×10-14。

The significance of the study on exotic properties of nuclei far from β-stability is discussed. The searching methods for rare events are reviewed. The rare events may be searched with high production quantum, high separation efficiency and high detection efficiency. The radium is radiochemically separated from natural thorium, and thin Ra sources are prepared to obtain ^228Ac through ^226Ra→β^-^228Ac. The ^230Ra is produced via ^232Th-2p reaction induced by 60 MeV/u ^18O ion irradiation of natural thorium, The radium is then radiochemically separated from the mixture of thorium and reaction products and thin Ra sources are prepared to obtain ^230Ac through ^230Ra→β^-^230Ac The ^239Pa is produced from the reaction ^232Th （p, 3n） ^230Pa in the irradiation powder target of ThO2 with 35 MeV proton beams. The sources of ^230Ra→β^-^230U are prepared by radiochemical method. The sources of ^228Ac, ^230Ac and ^230U are exposed to the solid track detectors, and measured by an HPGe γ-ray detector. Theβ -delayed fission events for ^228Ac, ^230Ac and heavy ion ^22Ne from ^230U are observed. Theβ -delayed fission probability of ^228Ac and ^230Ac were found to be （5±2）×10^-12 and （1.19±0.40）×10^-8 respectively and the branching ratio to decay out of ^230U to be B=λNa/λa为（1.3±0.8）×10^-14.