ＣＡＮＤＬＥＳによるＣａ４８の二重ベータ崩壊の研究

Candles研究Ca48的双β衰变

• 批准号: 14J00905
• 负责人: 王 偉
• 金额: $ 0.7万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for JSPS Fellows
• 财政年份: 2014
• 资助国家: 日本
• 起止时间: 2014 至 2015-03-31
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14J00905/
• 关键词: Ca48; lifetime; beta decay; Kamioka; Low background; underground laboratory

Experimental observation of neutrinoless double decay(0vββ)will provides evidence on the lepton number non-conservation to explain the matter-dominated universe. Clear understanding of the background is the most important part for our 0vββ experiment with 48Ca. Among them, 2vββ background estimation is extremely important because it can never be avoided. For the precisely estimation, the β decay study of 48Ca is necessary because it could be substantial background for 2vββ spectrum since we use large size CaF2 crystals. We propose to reach sensitivity of β decay half lifetime of 48Ca to the theoretic predictionT1/2(β)=(1.1±0.6)×1021 yr. This is the first time to use triple coincidence for β decay study in the world. In order to reach higher sensitivity of β decay of 48Ca, 48Sc (the β decay product) will be enriched from 1500L CaC12 solution with ion exchange method by special capture resin. (The expenses of experiment will mainly concentrate on the enrichment from huge mount of CaCl2 solutions). We will use 32 CsI sintillators for the triple coincidence measurement and the detection efficiency can improve to 5%. In second year we will setup the experiment in Kamioka Underground Labrotory which has extremly low background from cosmic rays. Expecting events from β decay is 22.1/year compare with 6.4/year for background events. Thus the expecting sensitivity of β decay is 2.4×1021 yr (95%C. L) with 1 year measurement. That sensitivity is over the upper limit of theoretical prediction. Then we will get better result with less statistical error for 2vββand 0vββ decay of 48Ca.

无中微子双衰变（0 v ββ）的实验观测将为解释物质主导宇宙提供轻子数不守恒的证据。对本底的清楚理解是我们用48 Ca进行0 v ββ实验的最重要部分。其中，2 v ββ背景估计是极其重要的，因为它永远无法避免。由于我们使用大尺寸的CaF_2晶体，~（48）Ca的β衰变可能成为2 v ββ谱的重要本底，因此，为了精确估算~（48）Ca的β衰变，有必要对其进行研究。我们提出~（48）Ca β衰变半衰期的灵敏度达到理论预言的T_（1/2）（β）=（1.1±0.6）× 10 ~（21）年。这是国际上首次使用三重符合进行β衰变研究。为了提高~（48）Ca β衰变的灵敏度，采用离子交换法，用特制的捕获树脂从1500 L氯化钙溶液中富集β衰变产物~（48）Sc。(The实验费用主要集中在大量CaCl 2溶液的富集上）。我们将使用32个CsI闪烁体进行三重符合测量，探测效率可提高到5%。在第二年，我们将在神冈地下实验室设置实验，那里的宇宙射线背景非常低。β衰变的预期事件为22.1/年，而背景事件为6.4/年。因此，β衰变的预期灵敏度为2.4× 10 ~（21）年（95%C.（1）1年测量。这种灵敏度超过了理论预测的上限。这样对48 Ca的2 v ββ和0 v ββ衰变都能得到统计误差较小的较好结果。