Effect of positron source irradiation on positronium annihilation in fine powdered alumina
Effect of positron source irradiation on positronium annihilation in fine powdered alumina
复制标题
正电子源辐照对细粉氧化铝中正电子湮灭的影响
DOI：
10.1016/j.apsusc.2016.04.135
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发表时间：
2016-09
影响因子：
6.7
通讯作者：
Chen Z. Q.
中科院分区：
文献类型：
--
作者：
Liu Z. W.;Chen Z. Q.
为了研究22 Na正电子源对细粉氧化铝的辐照效应，测量了正电子湮没辐射的正电子寿命和多普勒展宽随时间的变化。将γ-Al 2 O3样品置于10 - 6 Torr的真空室中，用闭合循环氦气制冷机冷却至10 K。γ-Al_2O_3样品冷却后立即用正电子源辐照，辐照时间约为两天。之后，使样品经历从10 K到300 K的升温过程，其中步长为10 K。在这些过程中，同时测量了正电子寿命和多普勒展宽谱。观察到两个长寿命组分对应于正电子偶素湮没。在辐照过程中观察到这些长寿命组分的显著缩短和S参数的大幅增加。正电子源辐照在γ-Al_2O_3颗粒表面产生大量的顺磁中心，导致正电子素的自旋转换猝灭。辐照诱导的顺磁中心在70 K以上不稳定，当温度升高到190 K时几乎退火消失。样品升温至室温后，正电子寿命谱与辐照前相同。还发现，照射后，出现约5 ns的中长寿命分量，其强度随照射时间的增加而增加。这可能是由于表面电子-Ps态的形成。这种表面-Ps状态在升高的温度下也被抑制。我们的研究结果表明，正电子素是一个非常敏感的探针在多孔材料的表面缺陷。
Positron lifetime and Doppler broadening of positron annihilation radiation were measured as a function of time to study the irradiation effect by22Na positron source in fine powdered alumina. Theγ-Al2O3samples were put in a vacuum chamber with a pressure of about 10−6Torr and were cooled down to 10 K by a closed-cycle helium gas refrigerator. The irradiation ofγ-Al2O3samples by positron source was taken for a duration of about two days immediately after the sample was cooled down. After that, the sample was subjected to a warm up process from 10 K to 300 K with a step of 10 K. Positron lifetime and Doppler broadening spectra were measured simultaneously during these processes. Two long lifetime components corresponding to ortho-positronium annihilation were observed. A significant shortening of these long lifetime components and a large increase in S parameter is observed during irradiation. It is supposed that positron source irradiation creates a large number of paramagnetic centers on the surface of theγ-Al2O3grains, which induce spin conversion quenching of positronium. The irradiation induced paramagnetic centers are unstable above 70 K and are nearly annealed out when the temperature rises to 190 K. After warming up of the sample to room temperature, the positron lifetime spectrum is identical to that before irradiation. It was also found that after irradiation, a medium long lifetime component of about 5 ns appears, of which the intensity increases with increasing irradiation time. This may be originated from the formation of the surfaceo-Ps state. This surfaceo-Ps state is also inhibited at elevated temperatures. Our results indicate that positronium is a very sensitive probe for the surface defects in porous materials.
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影响因子：
6.7
作者：
Z. Liu;Heng Zhang;Zongyun Chen
通讯作者：
Z. Liu;Heng Zhang;Zongyun Chen
影响因子：
62.1
作者：
J. K. Thomas
通讯作者：
J. K. Thomas
DOI：
10.1039/df9613100203
发表时间：
1961
期刊：
Discussions of The Faraday Society
影响因子：
--
作者：
V. Kazansky;G. B. Pariisky;V. V. Voevodsky-V.
通讯作者：
V. Kazansky;G. B. Pariisky;V. V. Voevodsky-V.
影响因子：
2.9
作者：
N. Djourelov;Takenori Suzuki;V. Shantarovich;K. Kondo
通讯作者：
N. Djourelov;Takenori Suzuki;V. Shantarovich;K. Kondo
影响因子：
44.1
作者：
Tuomisto, Filip;Makkonen, Ilja
通讯作者：
Makkonen, Ilja