Development and Trial Manufacture of Isotope Microscope.

我们为Cameca 3f二次离子质谱仪(SIMS)研制了一种用于观察抛光样品表面高分辨率二维同位素分布的二维CCD离子探测器系统的试验装置。该系统由以下单元组成。(1)ccd探测器单元、(2)ccd冷却杜瓦、(3)ccd驱动单元、(4)ccd控制单元、(5)ccd监视器单元、(6)控制计算机单元和(7)彩色监视器。CCD探测器单元由微通道板、荧光膜和电荷耦合器件(日本TI株式会社VID-272：6×9 mm：789×242像素)组成，二次离子被转换并放大为电子。研究发现，减小暗电流是获得高S/氮比的关键。为此，用液态镍将电荷耦合器件冷却到-60ﾟC，这种处理使弱离子图像测量和长期曝光成为可能。在对观测数据进行去噪处理后，进行了图像校正(亮度校正、对比度校正、累积时间校正、MCP灵敏度起伏校正、图像失真校正)。该系统已应用于艾伦德球粒陨石上氧同位素的二维分布观测，获得了前人从未报道过的氧同位素分布图。结果表明，一次照射一次初级离子束并测量极弱离子像(在~lt；18&gt；O的情况下为200个/秒)，就可以获得250×250微米的样品表面的二维信息。虽然该系统还存在一些问题需要进一步完善，但这一结果证明了该系统的高灵敏度。

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.