Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of . 226Ra occurs in the decay chain of 238U (often referred to as the radium series). Radium has 34 known isotopes from 201Ra to 234Ra.
In 2013 it was discovered that the nucleus of radium-224 is pear-shaped.[1] This was the first discovery of an asymmetrical nucleus.
|-| 201Ra[2] || style="text-align:right" | 88| style="text-align:right" | 113| | | α| 197Rn| (3/2−)||-| style="text-indent:1em" | 201mRa[3] | | colspan="3" style="text-indent:2em" | 260(30) keV| | α| 197mRn| (13/2+)||-| 202Ra|| style="text-align:right" | 88| style="text-align:right" | 114| 202.00989(7)| [2] | α| 198Rn| 0+||-| rowspan=2|203Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 115| rowspan=2|203.00927(9)| rowspan=2|4(3) ms| α| 199Rn| rowspan=2|(3/2−)| rowspan=2||-| β+ (rare)| 203Fr|-| rowspan=2 style="text-indent:1em" | 203mRa| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 220(90) keV| rowspan=2|41(17) ms| α| 199Rn| rowspan=2|(13/2+)| rowspan=2||-| β+ (rare)| 203Fr|-| rowspan=2|204Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 116| rowspan=2|204.006500(17)| rowspan=2|60(11) ms
[59(+12−9) ms]| α (99.7%)| 200Rn| rowspan=2|0+| rowspan=2||-| β+ (.3%)| 204Fr|-| rowspan=2|205Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 117| rowspan=2|205.00627(9)| rowspan=2|220(40) ms
[210(+60−40) ms]| α| 201Rn| rowspan=2|(3/2−)| rowspan=2||-| β+ (rare)| 205Fr|-| rowspan=2 style="text-indent:1em" | 205mRa| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 310(110)# keV| rowspan=2|180(50) ms
[170(+60−40) ms]| α| 201Rn| rowspan=2|(13/2+)| rowspan=2||-| IT (rare)| 205Ra|-| 206Ra|| style="text-align:right" | 88| style="text-align:right" | 118| 206.003827(19)| 0.24(2) s| α| 202Rn| 0+||-| rowspan=2|207Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 119| rowspan=2|207.00380(6)| rowspan=2|1.3(2) s| α (90%)| 203Rn| rowspan=2|(5/2−, 3/2−)| rowspan=2||-| β+ (10%)| 207Fr|-| rowspan=3 style="text-indent:1em" | 207mRa| rowspan=3|| rowspan=3 colspan="3" style="text-indent:2em" | 560(50) keV| rowspan=3|57(8) ms| IT (85%)| 207Ra| rowspan=3|(13/2+)| rowspan=3||-| α (15%)| 203Rn|-| β+ (.55%)| 207Fr|-| rowspan=2|208Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 120| rowspan=2|208.001840(17)| rowspan=2|1.3(2) s| α (95%)| 204Rn| rowspan=2|0+| rowspan=2||-| β+ (5%)| 208Fr|-| style="text-indent:1em" | 208mRa|| colspan="3" style="text-indent:2em" | 1800(200) keV| 270 ns||| (8+)||-| rowspan=2|209Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 121| rowspan=2|209.00199(5)| rowspan=2|4.6(2) s| α (90%)| 205Rn| rowspan=2|5/2−| rowspan=2||-| β+ (10%)| 209Fr|-| rowspan=2|210Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 122| rowspan=2|210.000495(16)| rowspan=2|3.7(2) s| α (96%)| 206Rn| rowspan=2|0+| rowspan=2||-| β+ (4%)| 210Fr|-| style="text-indent:1em" | 210mRa|| colspan="3" style="text-indent:2em" | 1800(200) keV| 2.24 μs||| (8+)||-| rowspan=2|211Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 123| rowspan=2|211.000898(28)| rowspan=2|13(2) s| α (97%)| 207Rn| rowspan=2|5/2(−)| rowspan=2||-| β+ (3%)| 211Fr|-| rowspan=2|212Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 124| rowspan=2|211.999794(12)| rowspan=2|13.0(2) s| α (85%)| 208Rn| rowspan=2|0+| rowspan=2||-| β+ (15%)| 212Fr|-| style="text-indent:1em" | 212m1Ra|| colspan="3" style="text-indent:2em" | 1958.4(5) keV| 10.9(4) μs||| (8)+||-| style="text-indent:1em" | 212m2Ra|| colspan="3" style="text-indent:2em" | 2613.4(5) keV| 0.85(13) μs||| (11)−||-| rowspan=2|213Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 125| rowspan=2|213.000384(22)| rowspan=2|2.74(6) min| α (80%)| 209Rn| rowspan=2|1/2−| rowspan=2||-| β+ (20%)| 213Fr|-| rowspan=2 style="text-indent:1em" | 213mRa| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 1769(6) keV| rowspan=2|2.1(1) ms| IT (99%)| 213Ra| rowspan=2|17/2−#| rowspan=2||-| α (1%)| 209Rn|-| rowspan=2|214Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 126| rowspan=2|214.000108(10)| rowspan=2|2.46(3) s| α (99.94%)| 210Rn| rowspan=2|0+| rowspan=2||-| β+ (.06%)| 214Fr|-| 215Ra|| style="text-align:right" | 88| style="text-align:right" | 127| 215.002720(8)| 1.55(7) ms| α| 211Rn| (9/2+)#||-| style="text-indent:1em" | 215m1Ra|| colspan="3" style="text-indent:2em" | 1877.8(5) keV| 7.1(2) μs||| (25/2+)||-| style="text-indent:1em" | 215m2Ra|| colspan="3" style="text-indent:2em" | 2246.9(5) keV| 1.39(7) μs||| (29/2−)||-| style="text-indent:1em" | 215m3Ra|| colspan="3" style="text-indent:2em" | 3756.6(6)+X keV| 0.555(10) μs||| (43/2−)||-| rowspan=2|216Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 128| rowspan=2|216.003533(9)| rowspan=2|182(10) ns| α| 212Rn| rowspan=2|0+| rowspan=2||-| EC (<1×10−8%)| 216Fr|-| 217Ra|| style="text-align:right" | 88| style="text-align:right" | 129| 217.006320(9)| 1.63(17) μs| α| 213Rn| (9/2+)||-|218Ra|| style="text-align:right" | 88|style="text-align:right" | 130|218.007140(12)|25.2(3) μs| α| 214Rn|0+||-| 219Ra|| style="text-align:right" | 88| style="text-align:right" | 131| 219.010085(9)| 10(3) ms| α| 215Rn| (7/2)+||-| 220Ra|| style="text-align:right" | 88| style="text-align:right" | 132| 220.011028(10)| 17.9(14) ms| α| 216Rn| 0+||-| rowspan=2|221Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 133| rowspan=2|221.013917(5)| rowspan=2|28(2) s| α| 217Rn| rowspan=2|5/2+| rowspan=2|Trace[4] |-| CD (1.2×10−10%)[5] | 207Pb
14C|-| rowspan=2|222Ra| rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 134| rowspan=2|222.015375(5)| rowspan=2|38.0(5) s| α| 218Rn| rowspan=2|0+| rowspan=2||-| CD (3×10−8%)| 208Pb
14C|-| rowspan=2|223Ra[6] | rowspan=2|Actinium X| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 135| rowspan=2|223.0185022(27)| rowspan=2|11.43(5) d| α| 219Rn| rowspan=2|3/2+| rowspan=2|Trace[7] |-| CD (6.4×10−8%)| 209Pb
14C|-| rowspan=2|224Ra| rowspan=2|Thorium X| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 136| rowspan=2|224.0202118(24)| rowspan=2|3.6319(23) d| α| 220Rn| rowspan=2|0+| rowspan=2|Trace[8] |-| CD (4.3×10−9%)| 210Pb
14C|-|rowspan=2| 225Ra|rowspan=2|| rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 137| rowspan=2| 225.023612(3)| rowspan=2| 14.9(2) d|β−| 225Ac| rowspan=2| 1/2+| rowspan=2| Trace[9] |-|α (2.0%)[10] |221Rn|-| rowspan=2|226Ra| rowspan=2|Radium[11] | rowspan=2 style="text-align:right" | 88| rowspan=2 style="text-align:right" | 138| rowspan=2|226.0254098(25)| rowspan=2|1600(7) y| α| 222Rn| rowspan=2|0+| rowspan=2|Trace[12] |-| CD (2.6×10−9%)| 212Pb
14C|-| 227Ra|| style="text-align:right" | 88| style="text-align:right" | 139| 227.0291778(25)| 42.2(5) min| β−| 227Ac| 3/2+||-| 228Ra| Mesothorium 1| style="text-align:right" | 88| style="text-align:right" | 140| 228.0310703(26)| 5.75(3) y| β−| 228Ac| 0+| Trace|-| 229Ra|| style="text-align:right" | 88| style="text-align:right" | 141| 229.034958(20)| 4.0(2) min| β−| 229Ac| 5/2(+)||-| 230Ra|| style="text-align:right" | 88| style="text-align:right" | 142| 230.037056(13)| 93(2) min| β−| 230Ac| 0+||-| 231Ra|| style="text-align:right" | 88| style="text-align:right" | 143| 231.04122(32)#| 103(3) s| β−| 231Ac| (5/2+)||-| style="text-indent:1em" | 231mRa|| colspan="3" style="text-indent:2em" | 66.21(9) keV| ~53 μs||| (1/2+)||-| 232Ra|| style="text-align:right" | 88| style="text-align:right" | 144| 232.04364(30)#| 250(50) s| β−| 232Ac| 0+||-| 233Ra|| style="text-align:right" | 88| style="text-align:right" | 145| 233.04806(50)#| 30(5) s| β−| 233Ac| 1/2+#||-| 234Ra|| style="text-align:right" | 88| style="text-align:right" | 146| 234.05070(53)#| 30(10) s| β−| 234Ac| 0+|