Stability of X-band EPR signals from fingernails under vacuum storage.
Stability of X-band EPR signals from fingernails under vacuum storage.
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DOI：
10.1016/j.radphyschem.2017.06.009
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发表时间：
2017-12
期刊：
影响因子：
--
通讯作者：
McKeever S
中科院分区：
文献类型：
--
作者：
Sholom S;McKeever S
用X波段EPR技术对不同储存条件下的指甲样品进行了不同来源的EPR信号测试。三种不同的信号，即在g=2.005的单峰，在g=2.004的双峰与分裂常数A=1.8 mT，和各向异性信号在g1=2.057，g2=2.029和g3=2.003（局部极值的位置）。所有的EPR光谱从指甲，无论是照射或机械应力，可以被描述为这三个信号的叠加。单线态负责背景信号（BG），是低剂量（100戈伊或更低）辐射诱导信号（RIS）的主要成分，也有助于机械诱导信号（MIS）。该信号在真空储存下相当稳定，但可以通过浸泡在水中而几乎降至零。该信号在环境条件下的行为取决于许多因素，例如吸收剂量、空气湿度和储存地点的环境照明强度。在指甲暴露于高剂量（几百戈伊或更高）或样品受到机械应力后出现双重峰。取决于如何获得该信号，它可能具有具有完全不同的稳定性特性的体或表面位置。位于表面的双峰（在切割或修剪过程中在指甲边缘产生）非常不稳定，对于在环境条件下储存的样品，在约两小时内衰减，对于浸入水中的样品，在几秒钟内衰减。体积分布的双重峰在水中几分钟内衰减，在环境条件下几小时，在真空中几天。各向异性信号也可以由电离辐射和机械应力两者产生;该信号在真空中相当稳定，并且在环境条件下在几天内或在水中几十分钟内衰减。获得了上述三个EPR信号的参考线，并开发了光谱去卷积程序，并对暴露于电离辐射和机械应力的样品进行了测试。
EPR signals of different origin have been tested in human finger- and toe-nails with an X-band EPR technique for different conditions of nail storage. Three different signals were identified, namely a singlet at g=2.005, a doublet at g=2.004 with a splitting constant A=1.8 mT, and an anisotropic signal at g1=2.057, g2=2.029 and g3=2.003 (positions of local extrema). All EPR spectra from nails, whether irradiated or mechanically stressed, can be described as a superposition of these three signals. The singlet is responsible for the background signal (BG), is the main component of radiation-induced signals (RIS) for low doses (100 Gy or lower) and also contributes to mechanically-induced signals (MIS). This signal is quite stable under vacuum storage, but can be reduced almost to zero by soaking in water. The behavior of this signal under ambient conditions depends on many factors, such as absorbed dose, air humidity, and ambient illumination intensity at the place of storage. The doublet arises after exposure of nails to high (few hundreds Gy and higher) doses or after mechanical stress of samples. Depending on how this signal was obtained, it may have bulk or surface locations with quite different stability properties. The surface-located doublet (generated on the nail edges during cutting or clipping) is quite unstable and decays over about two hours for samples stored at ambient conditions and within several seconds for samples immersed in water. The volume-distributed doublet decays within a few minutes in water, several hours at ambient conditions and several days in vacuum. The anisotropic signal may also be generated by both ionizing radiation and mechanical stress; this signal is quite stable in vacuum and decays over several days at ambient conditions or a few tens of minutes in water. The reference lines for the above-described three EPR signals were obtained and a procedure of spectra deconvolution was developed and tested on samples exposed to both ionizing radiation and mechanical stress.
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