鐳沒有穩定或長壽命的同位素，故無法給出它的標準原子量。鐳有從 202Ra 到 234Ra 共 33 種同位素，其中最穩定也最常見的同位素是半衰期 1600 年的 226Ra。 2013 年發現鐳 224 的原子核呈梨形，首次發現不對稱原子核。 圖表 202Ra styletextalignright 88 styletextalignright 114 20200989 7 26 21 ms 07 333 ms 0 rowspan2203Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 115 rowspan220300927 9 rowspan24 3 ms 199Rn rowspan232 rowspan2 （不常見） 203Fr rowspan2 styletextindent1em 203mRa rowspan2 rowspan2 colspan3 styletextindent2em 220 90 keV rowspan241 17 ms 199Rn rowspan2132 rowspan2 （不常見） 203Fr rowspan2204Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 116 rowspan2204006500 17 rowspan260 11 ms 59 129 ms 997 200Rn rowspan20 rowspan2 3 204Fr rowspan2205Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 117 rowspan220500627 9 rowspan2220 40 ms 210 6040 ms 201Rn rowspan232 rowspan2 （不常見） 205Fr rowspan2 styletextindent1em 205mRa rowspan2 rowspan2 colspan3 styletextindent2em 310 110 keV rowspan2180 50 ms 170 6040 ms 201Rn rowspan2132 rowspan2 IT （不常見） 205Ra 206Ra styletextalignright 88 styletextalignright 118 206003827 19 024 2 s 202Rn 0 rowspan2207Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 119 rowspan220700380 6 rowspan213 2 s 90 203Rn rowspan25232 rowspan2 10 207Fr rowspan3 styletextindent1em 207mRa rowspan3 rowspan3 colspan3 styletextindent2em 560 50 keV rowspan357 8 ms IT 85 207Ra rowspan3132 rowspan3 15 203Rn 55 207Fr rowspan2208Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 120 rowspan2208001840 17 rowspan213 2 s 95 204Rn rowspan20 rowspan2 5 208Fr styletextindent1em 208mRa colspan3 styletextindent2em 1800 200 keV 270 ns 8 rowspan2209Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 121 rowspan220900199 5 rowspan246 2 s 90 205Rn rowspan252 rowspan2 10 209Fr rowspan2210Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 122 rowspan2210000495 16 rowspan237 2 s 96 206Rn rowspan20 rowspan2 4 210Fr styletextindent1em 210mRa colspan3 styletextindent2em 1800 200 keV 224 µs 8 rowspan2211Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 123 rowspan2211000898 28 rowspan213 2 s 97 207Rn rowspan252 rowspan2 3 211Fr rowspan2212Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 124 rowspan2211999794 12 rowspan2130 2 s 85 208Rn rowspan20 rowspan2 15 212Fr styletextindent1em 212m1Ra colspan3 styletextindent2em 19584 5 keV 109 4 µs 8 styletextindent1em 212m2Ra colspan3 styletextindent2em 26134 5 keV 085 13 µs 11 rowspan2213Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 125 rowspan2213000384 22 rowspan2274 6 min 80 209Rn rowspan212 rowspan2 20 213Fr rowspan2 styletextindent1em 213mRa rowspan2 rowspan2 colspan3 styletextindent2em 1769 6 keV rowspan221 1 ms IT 99 213Ra rowspan2172 rowspan2 1 209Rn rowspan2214Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 126 rowspan2214000108 10 rowspan2246 3 s 9994 210Rn rowspan20 rowspan2 06 214Fr 215Ra styletextalignright 88 styletextalignright 127 215002720 8 155 7 ms 211Rn 92 styletextindent1em 215m1Ra colspan3 styletextindent2em 18778 5 keV 71 2 µs 252 styletextindent1em 215m2Ra colspan3 styletextindent2em 22469 5 keV 139 7 µs 292 styletextindent1em 215m3Ra colspan3 styletextindent2em 37566 6X keV 0555 10 µs 432 rowspan2216Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 128 rowspan2216003533 9 rowspan2182 10 ns 212Rn rowspan20 rowspan2 1108 216Fr 217Ra styletextalignright 88 styletextalignright 129 217006320 9 163 17 µs 213Rn 92 218Ra styletextalignright 88 styletextalignright 130 218007140 12 252 3 µs 214Rn 0 219Ra styletextalignright 88 styletextalignright 131 219010085 9 10 3 ms 215Rn 72 220Ra styletextalignright 88 styletextalignright 132 220011028 10 179 14 ms 216Rn 0 rowspan2221Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 133 rowspan2221013917 5 rowspan228 2 s 217Rn rowspan252 rowspan2 121010 rowspan2222Ra rowspan2 rowspan2 styletextalignright 88 rowspan2 styletextalignright 134 rowspan2222015375 5 rowspan2380 5 s 218Rn rowspan20 rowspan2 痕量 3108 rowspan2223Ra 用於治療骨癌 rowspan2Actinium X rowspan2 styletextalignright 88 rowspan2 styletextalignright 135 rowspan22230185022 27 rowspan21143 5 d 219Rn rowspan232 rowspan2 痕量 235U 的衰變產物 64108 rowspan2224Ra rowspan2Thorium X rowspan2 styletextalignright 88 rowspan2 styletextalignright 136 rowspan22240202118 24 rowspan236319 23 d 220Rn rowspan20 rowspan2 痕量 232Th 的衰變產物 43109 225Ra styletextalignright 88 styletextalignright 137 225023612 3 149 2 d 225Ac 12 rowspan2226Ra rowspan2Radium 這個元素的名稱來源 rowspan2 styletextalignright 88 rowspan2 styletextalignright 138 rowspan22260254098 25 rowspan21600 7 y 222Rn rowspan20 rowspan2 痕量 238U 的衰變產物 26109 227Ra styletextalignright 88 styletextalignright 139 2270291778 25 422 5 min 227Ac 32 228Ra Mesothorium 1 styletextalignright 88 styletextalignright 140 2280310703 26 575 3 y 228Ac 0 痕量 229Ra styletextalignright 88 styletextalignright 141 229034958 20 40 2 min 229Ac 52 230Ra styletextalignright 88 styletextalignright 142 230037056 13 93 2 min 230Ac 0 231Ra styletextalignright 88 styletextalignright 143 23104122 32 103 3 s 231Ac 52 styletextindent1em 231mRa colspan3 styletextindent2em 6621 9 keV 53 µs 12 232Ra styletextalignright 88 styletextalignright 144 23204364 30 250 50 s 232Ac 0 233Ra styletextalignright 88 styletextalignright 145 23304806 50 30 5 s 233Ac 12 234Ra styletextalignright 88 styletextalignright 146 23405070 53 30 10 s 234Ac 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 Ra Category 鐳