Francium (87Fr) has no stable isotopes. A standard atomic weight cannot be given. Its most stable isotope is 223Fr with a half-life of 22 minutes, occurring in trace quantities in nature as an intermediate decay product of 235U.
Of elements whose most stable isotopes have been identified with certainty, francium is the most unstable. All elements with atomic number of 106 (seaborgium) or greater have most-stable-known isotopes shorter than that of francium, but as those elements have only a relatively small number of isotopes discovered, the possibility remains that undiscovered isotopes of these elements may have longer half-lives.
List of isotopes
Nuclide [n 1] |
Historic name |
Z | N | Isotopic mass (Da) [n 2][n 3] |
Half-life [n 4] |
Decay mode [n 5] |
Daughter isotope |
Spin and parity [n 6][n 4] |
Isotopic abundance | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy[n 4] | |||||||||||||||||||
197Fr | 87 | 110 | 197.01101(6) | 2.3(19) ms | α | 193At | (7/2−) | ||||||||||||
198Fr | 87 | 111 | 198.01028(3) | 15(3) ms | α | 194At | 3+# | ||||||||||||
199Fr | 87 | 112 | 199.00726(4) | 16(7) ms | α | 195At | 1/2+# | ||||||||||||
200Fr | 87 | 113 | 200.00657(8) | 24(10) ms | α | 196At | 3+# | ||||||||||||
200mFr | 60(110) keV | 190(120) ms | α | 196At | 10−# | ||||||||||||||
201Fr | 87 | 114 | 201.00386(8) | 67(3) ms | α (99%) | 197At | (9/2−) | ||||||||||||
β+ (1%) | 201Rn | ||||||||||||||||||
202Fr | 87 | 115 | 202.00337(5) | 290(30) ms | α (97%) | 198At | (3+) | ||||||||||||
β+ (3%) | 202Rn | ||||||||||||||||||
202mFr | 330(90)# keV | 340(40) ms | α (97%) | 198At | (10−) | ||||||||||||||
β+ (3%) | 202Rn | ||||||||||||||||||
203Fr | 87 | 116 | 203.000925(17) | 0.55(2) s | α (95%) | 199At | (9/2−)# | ||||||||||||
β+ (5%) | 203Rn | ||||||||||||||||||
204Fr | 87 | 117 | 204.000653(26) | 1.7(3) s | α (96%) | 200At | (3+) | ||||||||||||
β+ (4%) | 204Rn | ||||||||||||||||||
204m1Fr | 50(4) keV | 2.6(3) s | α (90%) | 200At | (7+) | ||||||||||||||
β+ (10%) | 204Rn | ||||||||||||||||||
204m2Fr | 326(4) keV | 1.7(6) s | (10−) | ||||||||||||||||
205Fr | 87 | 118 | 204.998594(8) | 3.80(3) s | α (99%) | 201At | (9/2−) | ||||||||||||
β+ (1%) | 205Rn | ||||||||||||||||||
206Fr | 87 | 119 | 205.99867(3) | ~16 s | β+ (58%) | 206Rn | (2+, 3+) | ||||||||||||
α (42%) | 202At | ||||||||||||||||||
206m1Fr | 190(40) keV | 15.9(1) s | (7+) | ||||||||||||||||
206m2Fr | 730(40) keV | 700(100) ms | (10−) | ||||||||||||||||
207Fr | 87 | 120 | 206.99695(5) | 14.8(1) s | α (95%) | 203At | 9/2− | ||||||||||||
β+ (5%) | 207Rn | ||||||||||||||||||
208Fr | 87 | 121 | 207.99714(5) | 59.1(3) s | α (90%) | 204At | 7+ | ||||||||||||
β+ (10%) | 208Rn | ||||||||||||||||||
209Fr | 87 | 122 | 208.995954(16) | 50.0(3) s | α (89%) | 205At | 9/2− | ||||||||||||
β+ (11%) | 209Rn | ||||||||||||||||||
210Fr | 87 | 123 | 209.996408(24) | 3.18(6) min | α (60%) | 206At | 6+ | ||||||||||||
β+ (40%) | 210Rn | ||||||||||||||||||
211Fr | 87 | 124 | 210.995537(23) | 3.10(2) min | α (80%) | 207At | 9/2− | ||||||||||||
β+ (20%) | 211Rn | ||||||||||||||||||
212Fr | 87 | 125 | 211.996202(28) | 20.0(6) min | β+ (57%) | 212Rn | 5+ | ||||||||||||
α (43%) | 208At | ||||||||||||||||||
213Fr | 87 | 126 | 212.996189(8) | 34.14(6) s[2] | α (99.45%) | 209At | 9/2− | ||||||||||||
β+ (.55%) | 213Rn | ||||||||||||||||||
214Fr | 87 | 127 | 213.998971(9) | 5.0(2) ms | α | 210At | (1−) | ||||||||||||
214m1Fr | 123(6) keV | 3.35(5) ms | α | 210At | (8−) | ||||||||||||||
214m2Fr | 638(6) keV | 103(4) ns | (11+) | ||||||||||||||||
214m3Fr | 6477+Y keV | 108(7) ns | (33+) | ||||||||||||||||
215Fr | 87 | 128 | 215.000341(8) | 86(5) ns | α | 211At | 9/2− | ||||||||||||
216Fr | 87 | 129 | 216.003198(15) | 0.70(2) μs | α | 212At | (1−) | ||||||||||||
216mFr | 219(6) keV | 850(30) ns | α[n 7] | 212At | (9−) | ||||||||||||||
217Fr | 87 | 130 | 217.004632(7) | 16.8(19) μs | α | 213At | 9/2− | ||||||||||||
218Fr | 87 | 131 | 218.007578(5) | 1.0(6) ms | α | 214At | 1− | ||||||||||||
218m1Fr | 86(4) keV | 22.0(5) ms | α | 214At | (8−) | ||||||||||||||
218m2Fr | 200(150)# keV | high | |||||||||||||||||
219Fr | 87 | 132 | 219.009252(8) | 20(2) ms | α | 215At | 9/2− | ||||||||||||
220Fr | 87 | 133 | 220.012327(4) | 27.4(3) s | α (99.65%) | 216At | 1+ | ||||||||||||
β− (.35%) | 220Ra | ||||||||||||||||||
221Fr | 87 | 134 | 221.014255(5) | 4.9(2) min | α (99.9%) | 217At | 5/2− | Trace[n 8] | |||||||||||
β− (.1%) | 221Ra | ||||||||||||||||||
CD (8.79×10−11%)[n 9] | 207Tl 14C | ||||||||||||||||||
222Fr | 87 | 135 | 222.017552(23) | 14.2(3) min | β− | 222Ra | 2− | ||||||||||||
223Fr | Actinium K | 87 | 136 | 223.0197359(26) | 22.00(7) min | β− (99.99%) | 223Ra | 3/2(−) | Trace[n 10] | ||||||||||
α (.006%) | 219At | ||||||||||||||||||
224Fr | 87 | 137 | 224.02325(5) | 3.33(10) min | β− | 224Ra | 1− | ||||||||||||
225Fr | 87 | 138 | 225.02557(3) | 4.0(2) min | β− | 225Ra | 3/2− | ||||||||||||
226Fr | 87 | 139 | 226.02939(11) | 49(1) s | β− | 226Ra | 1− | ||||||||||||
227Fr | 87 | 140 | 227.03184(11) | 2.47(3) min | β− | 227Ra | 1/2+ | ||||||||||||
228Fr | 87 | 141 | 228.03573(22)# | 38(1) s | β− | 228Ra | 2− | ||||||||||||
229Fr | 87 | 142 | 229.03845(4) | 50.2(4) s | β− | 229Ra | (1/2+)# | ||||||||||||
230Fr | 87 | 143 | 230.04251(48)# | 19.1(5) s | β− | 230Ra | |||||||||||||
231Fr | 87 | 144 | 231.04544(50)# | 17.6(6) s | β− | 231Ra | (1/2+)# | ||||||||||||
232Fr | 87 | 145 | 232.04977(69)# | 5(1) s | β− | 232Ra | |||||||||||||
233Fr | 87 | 146 | 233.052518(21) | 900(100) ms | β− | 233Ra | 1/2+ # | ||||||||||||
This table header & footer: |
- mFr – 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).
- # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- Modes of decay:
CD: Cluster decay IT: Isomeric transition - ( ) spin value – Indicates spin with weak assignment arguments.
- The nuclide with the lowest atomic number known to undergo cluster decay
- Intermediate decay product of 235U