Development and Trial Manufacture of Isotope Microscope.

研制了CAMECA 3f二次离子质谱仪（SIMS）的二维CCD离子探测器系统试验装置，用于观察抛光样品表面的高分辨率二维同位素分布。该系统由以下单元组成。(1) CCD探测单元，(2)CCD冷却杜瓦，(3)CCD驱动单元，(4)CCD控制单元，(5)CCD监控单元，(6)控制计算机单元，(7)彩色显示器。CCD探测器单元由微通道板、荧光膜和CCD（日本TI公司，型号VID-272: 6 × 9 mm: 789 × 242像素）组成，将二次离子转化放大为电子。结果表明，获得高信噪比的关键是减小暗电流。为此，使用液态Ni将CCD冷藏至60ºC，这种处理可以实现弱离子图像测量和长时间暴露。在消除观测数据中的噪声后，进行图像校正（亮度校正、对比度校正、积累时间校正、MCP灵敏度波动校正、图像畸变校正）。将该系统应用于对Allende球粒陨石上^<16>O和^<18>O氧同位素二维分布的观测，成功获得了前人从未报道过的^<18>O分布图。结果表明，通过一次主离子束照射和测量极弱离子图像（在^<18>O的情况下200次/秒），可以获得250 × 250 mum面积样品表面的二维信息。虽然该系统在未来的改进中还存在一些问题需要解决，但实验结果证明了CCD检测系统的高灵敏度。

We have developed and manufactured a trial device of 2-dimensional CCD ion-detector system for the CAMECA 3f Secondary Ion Mass Spectrometer (SIMS) for observing high-resolution 2-dimensional isotope distribution on a polishd specimen surface. The system is composed of following units. (1) CCD detector unit, (2) CCD cooling dewar, (3) CCD drive unit, (4) CCD control unit, (5) CCD monitor unit, (6) control computer unit and (7) color monitor. The CCD detector unit is constructed by a Micro Channel Plate, a fluorescence film and a CCD (Japan TI Co. Ltd, type VID-272 : 6 x 9 mm : 789 x 242 pixels) , and the secondary ion is transformed and amplified to electron. It was found that the most important point for obtaining high S/N ratio is the reduction of dark current. For this purpose, the CCD is refrigerated to-60 ﾟC using liquid Ni, and this treatment makes possible weak ion image measurement and long term exposure. After the elimination of noise from the observed data, several steps of image correction (brightness correction, contrast correction, accumulation time correction, MCP sensitivity fluctuation correction, image distortion correction) were made.This system have been applied on the observation of 2-dimensional distribution of ^<16>O and ^<18>O oxygen isotope on a Allende chondrite meteorite, and succeeded to obtain ^<18>O distribution mapping which has never been reported previously. As the results, it becomes possible to obtain the 2-dimensional information of 250 x 250 mum area specimen surface from one irradiation of primary ion beam and measuring very weak ion image (200 count/sec in the case of ^<18>O). Although there are several problems to solve for improving this system in future, this result proves the high sensitivity of the CCD detector system.