# Isotopes of radium

Radium ($_{88}$Ra) 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 $^{226}$Ra with a half-life of 1600 years. $^{226}$Ra occurs in the decay chain of $^{238}$U (often referred to as the radium series). Radium has 34 known isotopes from $^{201}$Ra to $^{234}$Ra.
In the early history of the study of radioactivity, the different natural isotopes of radium were given different names, as it was not until Frederick Soddy's scientific career in the early 1900s that the concept of isotopes was realized. In this scheme, $^{223}$Ra was named actinium X (AcX), $^{224}$Ra thorium X (ThX), $^{226}$Ra radium (Ra), and $^{228}$Ra mesothorium 1 (MsTh$_1$). When it was realized that all of these are isotopes of the same element, many of these names fell out of use, and "radium" came to refer to all isotopes, not just $^{226}$Ra, though mesothorium 1 in particular was still used for some time, with a footnote explaining that it referred to $^{228}$Ra. Some of radium-226's decay products received historical names including "radium", ranging from radium A to radium G, with the letter indicating approximately how far they were down the chain from their parent $^{226}$Ra.
In 2013 it was discovered that the nucleus of radium-224 is pear-shaped. This was the first discovery of an asymmetrical nucleus.

## List of isotopes

| Nuclide | Historic name | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Isotopic abundance |
| Isotopic abundance |||
| $^{201}$Ra | | 88 | 113 | 201.012815(22) | 20(30) ms | α | $^{197}$Rn | (3/2−) | |
| $^{201m}$Ra | | 263(26) keV | 263(26) keV | 263(26) keV | 6(5) ms | α | $^{197}$Rn | 13/2+ | |
| $^{202}$Ra | | 88 | 114 | 202.009742(16) | 4.1(11) ms | α | $^{198}$Rn | 0+ | |
| $^{203}$Ra | | 88 | 115 | 203.009234(10) | 36(13) ms | α | $^{199}$Rn | 3/2− | |
| $^{203m}$Ra | | 246(14) keV | 246(14) keV | 246(14) keV | 25(5) ms | α | $^{199}$Rn | 13/2+ | |
| $^{204}$Ra | | 88 | 116 | 204.0065069(96) | 60(9) ms | α (99.7%) | $^{200}$Rn | 0+ | |
| $^{205}$Ra | | 88 | 117 | 205.006231(24) | 220(50) ms | α | $^{201}$Rn | 3/2− | |
| $^{205m}$Ra | | 263(25) keV | 263(25) keV | 263(25) keV | 180(50) ms | α | $^{201}$Rn | 13/2+ | |
| $^{206}$Ra | | 88 | 118 | 206.003828(19) | 0.24(2) s | α | $^{202}$Rn | 0+ | |
| $^{207}$Ra | | 88 | 119 | 207.003772(63) | 1.38(18) s | α (86%) | $^{203}$Rn | 5/2−# | |
| $^{207}$Ra | | 88 | 119 | 207.003772(63) | 1.38(18) s | β$^+$ (14%) | $^{207}$Fr | 5/2−# | |
| $^{207m}$Ra | | 560(60) keV | 560(60) keV | 560(60) keV | 57(8) ms | IT (85#%) | $^{207}$Ra | 13/2+ | |
| $^{207m}$Ra | | 560(60) keV | 560(60) keV | 560(60) keV | 57(8) ms | α (?%) | $^{203}$Rn | 13/2+ | |
| $^{208}$Ra | | 88 | 120 | 208.0018550(97) | 1.110(45) s | α (87%) | $^{204}$Rn | 0+ | |
| $^{208}$Ra | | 88 | 120 | 208.0018550(97) | 1.110(45) s | β$^+$ (13%) | $^{208}$Fr | 0+ | |
| $^{208m}$Ra | | 2147.4(4) keV | 2147.4(4) keV | 2147.4(4) keV | 263(17) ns | IT | $^{208}$Ra | (8+) | |
| $^{209}$Ra | | 88 | 121 | 209.0019949(62) | 4.71(8) s | α (90%) | $^{205}$Rn | 5/2− | |
| $^{209m}$Ra | | 882.4(7) keV | 882.4(7) keV | 882.4(7) keV | 117(5) μs | α (90%) | $^{205}$Rn | 13/2+ | |
| $^{209m}$Ra | | 882.4(7) keV | 882.4(7) keV | 882.4(7) keV | 117(5) μs | β$^+$ (10%) | $^{209}$Fr | 13/2+ | |
| $^{210}$Ra | | 88 | 122 | 210.0004754(99) | 4.0(1) s | α | $^{206}$Rn | 0+ | |
| $^{210m}$Ra | | 2050.9(7) keV | 2050.9(7) keV | 2050.9(7) keV | 2.29(3) μs | IT | $^{210}$Ra | 8+ | |
| $^{211}$Ra | | 88 | 123 | 211.0008930(53) | 12.6(12) s | α | $^{207}$Rn | 5/2− | |
| $^{211m}$Ra | | 1198.1(8) keV | 1198.1(8) keV | 1198.1(8) keV | 9.5(3) μs | IT | $^{211}$Ra | 13/2+ | |
| $^{212}$Ra | | 88 | 124 | 211.999787(11) | 13.0(2) s | α (?%) | $^{208}$Rn | 0+ | |
| $^{212}$Ra | | 88 | 124 | 211.999787(11) | 13.0(2) s | β$^+$ (?%) | $^{212}$Fr | 0+ | |
| $^{212m1}$Ra | | 1958.4(20) keV | 1958.4(20) keV | 1958.4(20) keV | 9.3(9) μs | IT | $^{212}$Ra | 8+ | |
| $^{212m2}$Ra | | 2613.3(20) keV | 2613.3(20) keV | 2613.3(20) keV | 0.85(13) μs | IT | $^{212}$Ra | 11− | |
| $^{213}$Ra | | 88 | 125 | 213.000371(11) | 2.73(5) min | α (87%) | $^{209}$Rn | 1/2− | |
| $^{213}$Ra | | 88 | 125 | 213.000371(11) | 2.73(5) min | β$^+$ (13%) | $^{213}$Fr | 1/2− | |
| $^{213m}$Ra | | 1768(4) keV | 1768(4) keV | 1768(4) keV | 2.20(5) ms | IT (99.4%) | $^{213}$Ra | (17/2−) | |
| $^{213m}$Ra | | 1768(4) keV | 1768(4) keV | 1768(4) keV | 2.20(5) ms | α (0.6%) | $^{209}$Rn | (17/2−) | |
| $^{214}$Ra | | 88 | 126 | 214.0000996(56) | 2.437(16) s | α (99.94%) | $^{210}$Rn | 0+ | |
| $^{214}$Ra | | 88 | 126 | 214.0000996(56) | 2.437(16) s | β$^+$ (0.059%) | $^{214}$Fr | 0+ | |
| $^{214m1}$Ra | | 1819.7(18) keV | 1819.7(18) keV | 1819.7(18) keV | 118(7) ns | IT | $^{214}$Ra | 6+ | |
| $^{214m2}$Ra | | 1865.2(18) keV | 1865.2(18) keV | 1865.2(18) keV | 67.3(15) μs | IT (99.91%) | $^{214}$Ra | 8+ | |
| $^{214m2}$Ra | | 1865.2(18) keV | 1865.2(18) keV | 1865.2(18) keV | 67.3(15) μs | α (0.09%) | $^{210}$Rn | 8+ | |
| $^{214m3}$Ra | | 2683.2(18) keV | 2683.2(18) keV | 2683.2(18) keV | 295(7) ns | IT | $^{214}$Ra | 11− | |
| $^{214m4}$Ra | | 3478.4(18) keV | 3478.4(18) keV | 3478.4(18) keV | 279(4) ns | IT | $^{214}$Ra | 14+ | |
| $^{214m5}$Ra | | 4146.8(18) keV | 4146.8(18) keV | 4146.8(18) keV | 225(4) ns | IT | $^{214}$Ra | 17− | |
| $^{214m6}$Ra | | 6577.0(18) keV | 6577.0(18) keV | 6577.0(18) keV | 128(4) ns | IT | $^{214}$Ra | (25−) | |
| $^{215}$Ra | | 88 | 127 | 215.0027182(77) | 1.669(9) ms | α | $^{211}$Rn | 9/2+# | |
| $^{215m1}$Ra | | 1877.8(3) keV | 1877.8(3) keV | 1877.8(3) keV | 7.31(13) μs | IT | $^{215}$Ra | (25/2+) | |
| $^{215m2}$Ra | | 2246.9(4) keV | 2246.9(4) keV | 2246.9(4) keV | 1.39(7) μs | IT | $^{215}$Ra | (29/2−) | |
| $^{215m3}$Ra | | 3807(50)# keV | 3807(50)# keV | 3807(50)# keV | 555(10) ns | IT | $^{215}$Ra | (43/2−) | |
| $^{216}$Ra | | 88 | 128 | 216.0035335(86) | 172(7) ns | α | $^{212}$Rn | 0+ | |
| $^{216}$Ra | | 88 | 128 | 216.0035335(86) | 172(7) ns | EC (<1×10$^{−8}$%) | $^{216}$Fr | 0+ | |
| $^{217}$Ra | | 88 | 129 | 217.0063227(76) | 1.95(12) μs | α | $^{213}$Rn | (9/2+) | |
| $^{218}$Ra | | 88 | 130 | 218.007134(11) | 25.91(14) μs | α | $^{214}$Rn | 0+ | |
| $^{219}$Ra | | 88 | 131 | 219.0100847(73) | 9(2) ms | α | $^{215}$Rn | (7/2)+ | |
| $^{219m}$Ra | | 16.7(8) keV | 16.7(8) keV | 16.7(8) keV | 10(3) ns | α | $^{215}$Rn | (11/2)+ | |
| $^{220}$Ra | | 88 | 132 | 220.0110275(82) | 18.1(12) ms | α | $^{216}$Rn | 0+ | |
| $^{221}$Ra | | 88 | 133 | 221.0139173(05) | 25(4) s | α | $^{217}$Rn | 5/2+ | Trace |
| $^{221}$Ra | | 88 | 133 | 221.0139173(05) | 25(4) s | CD (1.2×10$^{−10}$%) | $^{207}$Pb $^{14}$C | 5/2+ | Trace |
| $^{222}$Ra | | 88 | 134 | 222.0153734(48) | 33.6(4) s | α | $^{218}$Rn | 0+ | |
| $^{222}$Ra | | 88 | 134 | 222.0153734(48) | 33.6(4) s | CD (3.0×10$^{−8}$%) | $^{208}$Pb $^{14}$C | 0+ | |
| $^{223}$Ra | Actinium X | 88 | 135 | 223.0185006(22) | 11.4352(10) d | α | $^{219}$Rn | 3/2+ | Trace |
| $^{223}$Ra | Actinium X | 88 | 135 | 223.0185006(22) | 11.4352(10) d | CD (8.9×10$^{−8}$%) | $^{209}$Pb $^{14}$C | 3/2+ | Trace |
| $^{224}$Ra | Thorium X | 88 | 136 | 224.0202104(19) | 3.6316(14) d | α | $^{220}$Rn | 0+ | Trace |
| $^{224}$Ra | Thorium X | 88 | 136 | 224.0202104(19) | 3.6316(14) d | CD (4.0×10$^{−9}$%) | $^{210}$Pb $^{14}$C | 0+ | Trace |
| $^{225}$Ra | | 88 | 137 | 225.0236105(28) | 14.82(19) d | β$^−$ | $^{225}$Ac | 1/2+ | Trace |
| $^{225}$Ra | | 88 | 137 | 225.0236105(28) | 14.82(19) d | α (2.6×10$^{−3}$%) | $^{221}$Rn | 1/2+ | Trace |
| $^{226}$Ra | Radium | 88 | 138 | 226.0254082(21) | 1600(7) y | α | $^{222}$Rn | 0+ | Trace |
| $^{226}$Ra | Radium | 88 | 138 | 226.0254082(21) | 1600(7) y | CD (2.6×10$^{−9}$%) | $^{212}$Pb $^{14}$C | 0+ | Trace |
| $^{227}$Ra | | 88 | 139 | 227.0291762(21) | 42.2(5) min | β$^−$ | $^{227}$Ac | 3/2+ | |
| $^{228}$Ra | Mesothorium 1 | 88 | 140 | 228.0310686(21) | 5.75(3) y | β$^−$ | $^{228}$Ac | 0+ | Trace |
| $^{229}$Ra | | 88 | 141 | 229.034957(17) | 4.0(2) min | β$^−$ | $^{229}$Ac | 5/2+ | |
| $^{230}$Ra | | 88 | 142 | 230.037055(11) | 93(2) min | β$^−$ | $^{230}$Ac | 0+ | |
| $^{231}$Ra | | 88 | 143 | 231.041027(12) | 104(1) s | β$^−$ | $^{231}$Ac | (5/2+) | |
| $^{231m}$Ra | | 66.21(9) keV | 66.21(9) keV | 66.21(9) keV | ~53 μs | IT | $^{231}$Ra | (1/2+) | |
| $^{232}$Ra | | 88 | 144 | 232.0434753(98) | 4.0(3) min | β$^−$ | $^{232}$Ac | 0+ | |
| $^{233}$Ra | | 88 | 145 | 233.0475946(92) | 30(5) s | β$^−$ | $^{233}$Ac | 1/2+# | |
| $^{234}$Ra | | 88 | 146 | 234.0503821(90) | 30(10) s | β$^−$ | $^{234}$Ac | 0+ | |
| This table header & footer: view ||||||||||
* ↑ $^m$Ra – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* ↑ Modes of decay: EC:Electron capture CD:Cluster decay IT:Isomeric transition
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Intermediate decay product of $^{237}$Np
* ↑ Lightest known nuclide to undergo cluster decay
* ↑ Used for treating bone cancer
* ↑ Intermediate decay product of $^{235}$U
* 1 2 Intermediate decay product of $^{232}$Th
* ↑ Intermediate decay product of $^{237}$Np
* ↑ Source of element's name
* ↑ Theoretically capable of β$^−$β$^−$ decay to $^{226}$Th
* ↑ Intermediate decay product of $^{238}$U

## Actinides vs fission products

Actinides and fission products by half-life vte :
| Actinides by decay chain | Actinides by decay chain | Actinides by decay chain | Actinides by decay chain | Half-life range (a) | Fission products of $^{235}$U by yield | Fission products of $^{235}$U by yield | Fission products of $^{235}$U by yield |
| 4n | 4n + 1 | 4n + 2 | 4n + 3 | Half-life range (a) | 4.5–7% | 0.04–1.25% | <0.001% |
| Ra$^№$ | | | | 4–6 a | | Eu$^þ$ | |
| Bk | | | | > 9 a | | | |
| Cm$^ƒ$ | Pu$^ƒ$ | Cf | Ac$^№$ | 10–29 a | Sr | Kr | Cd$^þ$ |
| U$^ƒ$ | | Pu$^ƒ$ | Cm$^ƒ$ | 29–97 a | Cs | Sm$^þ$ | Sn |
| | Cf$^ƒ$ | Am$^ƒ$ | | 141–351 a | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| | Am$^ƒ$ | | Cf$^ƒ$ | 430–900 a | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| | | Ra$^№$ | Bk | 1.3–1.6 ka | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| Pu | Th | Cm$^ƒ$ | Am$^ƒ$ | 4.7–7.4 ka | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| | Cm$^ƒ$ | Cm | | 8.3–8.5 ka | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| | | | Pu$^ƒ$ | 24.1 ka | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| | | Th$^№$ | Pa$^№$ | 32–76 ka | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... | No fission products have a half-life in the range of 100 a–210 ka ... |
| Np$^ƒ$ | U$^ƒ$ | U$^№$ | | 150–250 ka | Tc$^₡$ | Sn |
| Cm | | Pu | | 327–375 ka | | Se$^₡$ |
| | | | | 1.33 Ma | Cs$^₡$ |
| | Np$^ƒ$ | | | 1.61–6.5 Ma | Zr | Pd |
| U | | | Cm$^ƒ$ | 15–24 Ma | | I$^₡$ |
| Pu | | | | 80 Ma | ... nor beyond 15.7 Ma | ... nor beyond 15.7 Ma | ... nor beyond 15.7 Ma |
| Th$^№$ | | U$^№$ | U$^{ƒ№}$ | 0.7–14.1 Ga | ... nor beyond 15.7 Ma | ... nor beyond 15.7 Ma | ... nor beyond 15.7 Ma |
| ₡, has thermal neutron capture cross section in the range of 8–50 barnsƒ, fissile№, primarily a naturally occurring radioactive material (NORM)þ, neutron poison (thermal neutron capture cross section greater than 3k barns) |||||||||