鎂共有 22 個已知同位素，質量數介於 1940 之間，其中有 3 個是穩定的，其他都具有放射性。天然存在的鎂同位素有 3 個，分別是 24Mg、25Mg、26Mg，皆為穩定同位素。其他放射性同位素都不出現在自然界中，只有在實驗室製造出來過，且半衰期都很短，非常不穩定，其中最長壽的是 28Mg，半衰期為 20915 小時。 圖表 18Mg styletextalignright 12 styletextalignright 6 2p 16Ne 0 19Mg styletextalignright 12 styletextalignright 7 1903417 5 5 3 ps 2p 17Ne 12 rowspan220Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 8 rowspan220018863 29 rowspan2908 24 ms 97 20Na rowspan20 rowspan2 rowspan2 β p 3 19Ne rowspan321Mg rowspan3 styletextalignright 12 rowspan3 styletextalignright 9 rowspan321011713 18 rowspan3122 2 ms β 669 21Na rowspan35232 rowspan3 rowspan3 β p 326 20Ne β α 05 17F 22Mg styletextalignright 12 styletextalignright 10 219995738 14 38755 12 s β 22Na 0 23Mg styletextalignright 12 styletextalignright 11 229941237 14 11317 11 s β 23Na 32 styletextalignright 12 styletextalignright 12 23985041700 14 colspan3 aligncenter 0 078965 49 07888 07905 25Mg styletextalignright 12 styletextalignright 13 2498583692 3 colspan3 aligncenter 穩定 52 010011 13 009988 010034 26Mg 用於測定太陽系早期歷史事件的放射性定年法中 styletextalignright 12 styletextalignright 14 25982592929 30 colspan3 aligncenter 穩定 0 011025 38 01096 01109 27Mg styletextalignright 12 styletextalignright 15 2698434059 5 9458 12 min β 27Al 12 28Mg styletextalignright 12 styletextalignright 16 279838768 22 20915 9 h β 28Al 0 29Mg styletextalignright 12 styletextalignright 17 28988600 15 130 12 s β 29Al 32 rowspan230Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 18 rowspan229990434 9 rowspan2335 17 ms β 9994 30Al rowspan20 rowspan2 rowspan2 β n 06 29Al rowspan231Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 19 rowspan230996546 13 rowspan2230 20 ms β 983 31Al rowspan232 rowspan2 rowspan2 β n 17 30Al rowspan232Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 20 rowspan231998975 19 rowspan286 5 ms β 976 32Al rowspan20 rowspan2 rowspan2 β n 24 31Al rowspan233Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 21 rowspan233005254 21 rowspan2905 16 ms β 83 33Al rowspan272 rowspan2 rowspan2 β n 17 32Al rowspan234Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 22 rowspan23400946 25 rowspan220 10 ms β 999 34Al rowspan20 rowspan2 rowspan2 β n 1 33Al rowspan235Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 23 rowspan23501734 43 rowspan270 40 ms β n 52 34Al rowspan272 rowspan2 rowspan2 β 48 35Al 36Mg styletextalignright 12 styletextalignright 24 3602300 54 39 13 ms β 36Al 0 rowspan237Mg rowspan2 styletextalignright 12 rowspan2 styletextalignright 25 rowspan23703140 97 rowspan240 ms 260 ns β 37Al rowspan272 rowspan2 rowspan2 β n 36Al 38Mg styletextalignright 12 styletextalignright 26 3803757 54 1 ms 260 ns 0 39Mg styletextalignright 12 styletextalignright 27 3904677 55 260 ns 72 40Mg styletextalignright 12 styletextalignright 28 4005393 97 1 ms 0 參考文獻 Isotope masses from Ame2003 Atomic Mass Evaluation by G Audi AH Wapstra C Thibault J Blachot and O Bersillon in Nuclear Physics A729 2003 Halflife spin and isomer data selected from these sources Editing notes on this articles talk page Audi Bersillon Blachot Wapstra The Nubase2003 evaluation of nuclear and decay properties Nuc Phys A 729 pp 3128 2003 National Nuclear Data Center Brookhaven National Laboratory Information extracted from the NuDat 21 database retrieved Sept 2005 David R Lide ed Norman E Holden in CRC Handbook of Chemistry and Physics 85th Edition online version CRC Press Boca Raton Florida 2005 Section 11 Table of the Isotopes Mg Category 鎂