arXiv 1201.01652012-01nucl-ex

HPGe探测器在无中子双β衰变实验中的α本底

Alpha Backgrounds for HPGe Detectors in Neutrinoless Double-Beta Decay Experiments

R. A. Johnson, T. H. Burritt, S. R. Elliott, V. M. Gehman, V. E. Guiseppe, J. F. Wilkerson

备注：: 10 pages, 11 figures, submitted to NIM A
DOI：: 10.1016/j.nima.2012.06.043

摘要：

马约拉纳实验将使用浓缩HPGe探测器阵列来寻找76 Ge的无中微子双β衰变。如果发现这种衰变，将表明轻子数违反并证实中微子的马约拉纳性质。对这种罕见事件的调查受到模糊背景的阻碍，必须尽可能地理解和减轻。对这个和其他双β衰变实验的一个潜在的重要背景贡献可能来自探测器表面或附近的232 Th和238 U衰变链中的α放射同位素的衰变。发射到HPGe晶体外部的α粒子可能在进入探测器的有源区之前损失能量，无论是在一些外部大块材料中还是在晶体的死区内。测得的事件能量只相当于α粒子总动能的一部分，可能会掩盖无中微子双β衰变的信号。建立了一个试验台，并进行了测量，以定量评估这一背景。我们提出了这些测量的结果，并将其与使用Geant 4的模拟进行比较。这些结果然后被用于测量阿尔法背景在地下探测器在原位。我们还估计了使用固态探测器的双β衰变实验的表面污染容限。

英文摘要：

The Majorana Experiment will use arrays of enriched HPGe detectors to search for the neutrinoless double-beta decay of 76Ge. Such a decay, if found, would show lepton-number violation and confirm the Majorana nature of the neutrino. Searches for such rare events are hindered by obscuring backgrounds which must be understood and mitigated as much as possible. A potentially important background contribution to this and other double-beta decay experiments could come from decays of alpha-emitting isotopes in the 232Th and 238U decay chains on or near the surfaces of the detectors. An alpha particle emitted external to an HPGe crystal can lose energy before entering the active region of the detector, either in some external-bulk material or within the dead region of the crystal. The measured energy of the event will only correspond to a partial amount of the total kinetic energy of the alpha and might obscure the signal from neutrinoless double-beta decay. A test stand was built and measurements were performed to quantitatively assess this background. We present results from these measurements and compare them to simulations using Geant4. These results are then used to measure the alpha backgrounds in an underground detector in situ. We also make estimates of surface contamination tolerances for double-beta decay experiments using solid-state detectors.

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