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

2004财年，我们研制了一种用于探测L内转换电子的新型硅雪崩光电二极管(Si-AD)阵列。该阵列在单片顶端有三个像素(^H6×^V1 mm，30米厚)。我们用77.35keV的X射线(PAC编号：2004G031)对安装在光子工厂光束线BL-14A上的探测器进行了测试。在获得阵列更好运行的参数后，在SPRING-8(PAC编号：2004B0783-ND3b-NP)光束线BL09XU上对Au-197进行了NEET实验。我们发现，其中一个阵列通过照射来自目标的光电子而输出噪声脉冲。这可能是由于SiO_2表面层的荷电引起的。我们现在正在考虑将Si-AD器件表面的SiO_2替换为Si_3N_4。此外，还在Spring-8的NEET实验中测量了荧光x射线能谱。通过改变入射X射线在金K边周围的能量，我们观察到了从金靶发出的荧光Kx射线。通过比较核激发和原子跃迁的结果，我们发现NEET从比K边高40 eV的能量开始，NEET边的宽度大约是K边的三分之一。在2005财年，我们讨论了上述实验结果，并将报告提交给Phys.Rev.Lett。对NEET模型也进行了研究，以解释实验结果；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.