Precise Measurement of NEET Probability on Au-197 by Using Synchrotron Radiation

在2004财年，我们开发了一种新的硅雪崩光电二极管（Si-AD）阵列，用于检测l -内部转换电子。该阵列在单片尖端上有三个像素（^H6×^V1 mm，30□m厚）。我们使用77.35 kev x射线（PAC编号：2004G031）对安装在光子工厂BL-14A光束线上的两个阵列的探测器进行了测试。在获得更好的阵列运行参数后，在SPring-8 （PAC号：2004B0783-ND3b-np）的BL09XU波束线上对Au-197进行了NEET实验。我们发现其中一个阵列通过靶的光电子照射输出噪声脉冲。这可能是由于SiO_2的表层带电引起的。我们现在正在考虑将Si-AD器件表面的SiO_2替换为Si_3N_4。在SPring-8的NEET实验中也测量了荧光x射线光谱。通过改变入射x射线在金K边缘周围的能量，我们观察到从金靶发射的荧光K x射线。通过比较核激发和原子跃迁的结果，我们发现NEET的起始能量比K边缘高40 eV， NEET边缘的宽度约为K边缘的三分之一。在2005财年，我们对上述实验结果进行了讨论，并将报告提交给Phys.Rev.Lett。研究了NEET模型来解释实验结果；理论分析正在进行中。

In FY2004,we developed a new silicon avalanche-photodiode (Si-AD) array for detecting L-internal conversion electrons. The array had three pixels (^H6×^V1 mm,30 □m thick) on a monolithic tip. We tested the detector mounting the two arrays at beamline BL-14A of the Photon Factory using 77.35-keV x-rays (PAC number : 2004G031). After obtaining the parameters for a better operation of the arrays, the NEET experiments on Au-197 were carried out in beamline BL09XU of SPring-8 (PAC number : 2004B0783-ND3b-np). We found that one of the arrays outputted noise pulses by irradiation of photo-electrons from the target. This was probably caused by the charge-up in the surface layer of SiO_2. We are now thinking of replacing SiO_2 to Si_3N_4 in the surface of the Si-AD device. The fluorescence x-ray spectra were also measured in the NEET experiments at SPring-8. By varying the energy of the incident x-rays around the gold K-edge, we observed the fluorescence K x-rays emitted from the gold target. With comparing the results of nuclear excitation and those of the atomic transition, we found that the NEET started from an energy 40 eV higher than the K edge and the width of the NEET edge was about one third of that of the K edge.In FY2005,we discussed the experimental results above and the report was submitted to Phys.Rev.Lett. The NEET model was also studied to explain the experimental results ; the theoretical analysis is now in progress.