1960年以åï¼CIPMï¼å½é
计é大ä¼ï¼ä»¥
å°çèªè½¬ä¸ºåºç¡ï¼å®ä¹ä»¥å¹³å太é³æ¥ä¹86400åä¹ä¸ä½ä¸ºç§å®ä¹ãå³1 Second = 1/86400 Mean Solar dayå
¶ç¨³å®åº¦å¨10-8å·¦å³ã
1960~1967å¹´CIPMæ¹ä»¥
å°çå
¬è½¬ä¸ºåºç¡ï¼å®ä¹è¥¿å
1900年为平å太é³å¹´ãç§å®ä¹æ´æ¹ä¸º:ä¸ç§ä¸ºå¹³å太é³å¹´ä¹31556925.9747åä¹ä¸ã1 Sec = 1/31556925.9747 Solar Year at 1900稳å®åº¦çº¦ä¸º10-9ã
äºåä¸ä¸çºªä¸å¶ï¼ç±äº
éååå¦çåå±ï¼åå±äºè¯¸å¦å
è°±è¶
ç²¾ç»ç»æãéå°åé·å°ãå
ç£å
±æ¯ï¼Optical Pumpingï¼ãååæç£å
±æ¯ãå离éè¡åºçå®éªåç 究ï¼ä½¿éåé¢çæ åå代以
天ä½è¿å¨ä¸ºæ åä¹å¤©ä½æ¶èæ为计æ¶æ åã1967å¹´ï¼CIPMå®ä¹ç§æ¯é¯133ååï¼Cs133ï¼
åºæç两个è¶
ç²¾ç»è½çº§ä¹é´è·è¿æ对åºçè¾å°ç9,192,631,770个å¨æææç»çæ¶é´ãæ¤ç§å®ä¹ä¸ç´ç»´æè³ä»ã