实验六X-RAY绕射实验.docVIP

實驗六 X-ray繞射實驗 原理：電磁波波長可用光柵測量，但X光波長極小，光柵不易製作。Sr L. Bragg認為晶體可作為X-光之光柵。如圖(1)，建設性干涉時，入射及反射線之夾角滿足Bragg條件： (Herht: Optics或Guenther: Modern Optics) 晶體中原子的間距d可由其分子量M及密度計算 如NaCl 典型的繞射分佈如圖(2)，圖中可以看出Cu之及之1,2,3級繞射，由及d可算出波長。 注意：晶體極易潮解，不可觸摸、不可對之呼氣。請戴手套、口罩 　　　並用鑷子夾取。 實驗結束時，請助教點收晶體。 A. EXPERIMENTAL TECHNIQUES Primary Beam: The X-ray emission from the tube is collimated at the lead glass dome to be a circular beam of 5mm diameter, see Fig.1; this primary beam diverges from the Basic Port to give a useful beam diameter at the Crystal Post of 15mm diameter, at Experimental Station (ES) 13 of 20mm diameter and at Experimental Station (ES) 30 of 38mm diameter. Where the primary beam impinges on the lead back-stop it has a diameter of 60mm and a penumbral width of approximately 20mm. With the unit operating at 30kV and 50μA the intensity of radiation in the useful beam at 20cm (ES.28) from the focus is about 2 rads per minute. Primary Collimators: The primary beam can be collimated to a fine circular beam using the 1mm diameter collimator TEL 582.002 and to a ribbon beam using the 1mm Slot collimator, TEL 582.001; each of these collimators is installed by inserting the “O” ring shank into the Basic Port and pushing it home; the “O” ring retains the collimator in position and allows exchange of the collimators even when they become warm. The collimators should be rotated when they are inserted to ensure that they are securely seated. The 1mm Slot Collimator can be rotated in position the provide a vertical ribbon of X-rays, a horizontal ribbon or any diametrical ribbon. Secondary Collimators: There are two secondary collimators, a 1mm Slot Collimator, TEL 562.015 and a 3mm Slot Collimator, TEL 562.016. Each of these collimators is slide mounted and can be positioned in any E.S. on the Spectrometer Arm. Always use a E.S. Spring Clip, see Fig.1, when positioning these collimators (and indeed any of the experimental slides) to ensure that all the slides are centered on the X-ray