Paramagnetic relaxation of spin polarized 3He at bare glass surfaces
Paramagnetic relaxation of spin polarized 3He at bare glass surfaces
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DOI：
10.1140/epjd/e2006-00050-2
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发表时间：
2006-03
期刊：
影响因子：
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通讯作者：
Jörg Schmiedeskamp;Werner Heil;Ernst W. Otten;R. Kremer;A. Simón;J. Zimmer
中科院分区：
文献类型：
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作者：
Jörg Schmiedeskamp;Werner Heil;Ernst W. Otten;R. Kremer;A. Simón;J. Zimmer
在这第一次在一系列的三个文件的壁松弛自旋极化，气态3 He，我们调查的理论和实验表面诱导的自旋弛豫由于顺磁性网站在包含玻璃。我们目前的实验和理论证据表明，与传统的观点相反，远偶极耦合到玻璃中的顺磁性杂质，特别是铁离子，不能是占主导地位的松弛机制of 3 He-自旋，虽然铁占主导地位的体静态磁导率。相反，悬挂键型缺陷的玻璃基质中发现，通过各向同性费米接触相互作用的相互作用强得多。本文提出了一个考虑费米接触相互作用的顺磁位控~ 3 He弛豫模型。合理的半经验假设，我们的模型可以满意地描述测量的弛豫，无论是在溶解为主的制度的熔融石英或硼硅酸盐玻璃的Pyrex类型，以及在表面为主的情况下，铝硅酸盐玻璃只有一个低渗透性的He原子。在由各种铝硅酸盐玻璃制成的1.1升电池的大样品中，在污染物铁磁颗粒已经预先去磁的情况下达到150小时的平均弛豫时间。从250 h的最大观测值出发，在减去气相中的偶极弛豫后，我们得到室温下的顺磁表面弛豫率ρ<0.005 cm/h。
In this first in a series of three papers on wall relaxation of spin polarized, gaseous3He we investigate both by theory and by experiment surface-induced spin relaxation due to paramagnetic sites in the containing glass. We present experimental and theoretical evidence that — contrary to the traditional opinion — distant dipolar coupling to paramagnetic impurities in the glass, in particular iron ions, cannot be the dominant relaxation mechanism of3He-spins, although iron dominates the bulk static permeability. Instead dangling-bond type defects in the glass matrix are found to interact much stronger via the isotropic Fermi contact interaction. A model of paramagnetic site controlled3He relaxation including the Fermi contact interaction is presented. With reasonable semi-empirical assumptions our model allows to describe satisfactorily the measured relaxivities, both in the dissolution-dominated regime of fused silica or borosilicate glasses of the Pyrex type as well as in the surface dominated situation of aluminosilicate glasses which have only a low permeability for He atoms. In a large sample of 1.1 litre cells, built from various aluminosilicate glasses, an average relaxation time of 150 h is reached in case contaminant ferromagnetic particles have been demagnetized beforehand. From the maximum observed value of 250 h we derive after subtraction of dipolar relaxation in the gas phase a paramagnetic surface relaxivity of ρ<0.005 cm/h at room temperature.