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Magnetic quenching of positronium studied by positron annihilation lifetime and Doppler broadening measurements
Radiation Physics and Chemistry ( IF 2.9 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.radphyschem.2020.108712
J.D. Liu , J.Q. Guo , M. Luo , Z. Wang , H.J. Zhang , B.J. Ye , Z.Q. Chen

Abstract Annihilation of positronium (Ps) in static magnetic fields is investigated by positron annihilation lifetime (PAL) and Doppler broadening (DB) measurements of γ-Al2O3 nanopowder. The properties of four eigenstates of Ps atoms ( | 1,1 ⟩ , | 1 , − 1 ⟩ , | + ⟩ (long-lived eigenstate mixed from | 1,0 ⟩ and | 0,0 ⟩ due to Zeeman effect), and | − ⟩ (short-lived eigenstate mixed from | 1,0 ⟩ and | 0,0 ⟩ due to Zeeman effect)) were revealed from PAL and DB results. Thereafter, with magnetic field increasing from 0.105 to 0.760 T, clear and regular variation of Ps annihilation parameters are observed: (1) The mean lifetime of the three long-lived Ps states ( | 1,1 ⟩ , | 1 , − 1 ⟩ , and | + ⟩ ) shows clear quenching effect; (2) The formation probability of each Ps eigenstate ( | 1,1 ⟩ , | 1 , − 1 ⟩ , | + ⟩ , and | − ⟩ ) keeps unchanged; (3) The intensity of the narrow component (derived from multi-Gaussian fitting) of DB spectrum exhibits a gradual increase which is in good agreement with the theoretical calculation from PAL results (2γ decay of | + ⟩ and | − ⟩ states, and pick-off quenching of long-lived Ps states); (4) The intensity of the low energy region of DB spectrum is diminished by the decrease of 3γ decay of | + ⟩ state. The quantitative correlations between magnetic field and o-Ps annihilation parameters will be helpful for the further understanding of complex Ps quenching effects, such as the effect mixed from orhto-para spin conversion and magnetic quenching.

中文翻译:

通过正电子湮灭寿命和多普勒展宽测量研究正电子的磁猝灭

摘要 通过γ-Al2O3 纳米粉末的正电子湮灭寿命(PAL) 和多普勒展宽(DB) 测量研究了静磁场中正电子(Ps) 的湮灭。Ps 原子的四种本征态的性质( | 1,1 ⟩ , | 1 , − 1 ⟩ , | + ⟩(由于塞曼效应,由 | 1,0 ⟩ 和 | 0,0 ⟩ 混合而成的长寿命本征态),以及| − ⟩(由于塞曼效应由 | 1,0 ⟩ 和 | 0,0 ⟩ 混合而成的短寿命本征态))是从 PAL 和 DB 结果中揭示的。此后,随着磁场从 0.105 T 增加到 0.760 T,观察到 Ps 湮灭参数的清晰而有规律的变化:(1)三个长寿命 Ps 状态的平均寿命( | 1,1 ⟩ , | 1 , − 1 ⟩ , 和 | + ⟩ ) 显示出明显的淬灭效果;(2) 每个Ps本征态(| 1,1 ⟩ , | 1 , − 1 ⟩ , | + ⟩ , and | − ⟩ )的形成概率保持不变;(3) DB光谱的窄分量(由多高斯拟合得出)强度逐渐增加,这与PAL结果的理论计算非常吻合(| + ⟩和| − ⟩状态的2γ衰减,和长寿命 Ps 状态的触发淬灭);(4) DB光谱低能区的强度随着|的3γ衰变的减少而减弱。+ ⟩ 状态。磁场与o-Ps湮灭参数之间的定量相关性将有助于进一步理解复杂的Ps猝灭效应,例如正交对位自旋转换和磁猝灭的混合效应。
更新日期:2020-06-01
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