Atomic number: 85 Symbol: At
(this element does not have any stable isotopes)
Atomic weight of the most stable isotope: 209.987148(8) u
| Isotope | Atomic weight/u | Half-life |
| 194 | 193.99873(20) | ≈ 40 ms |
| 195 | 194.996268(10) | 147 ms 5 |
| 196 | 195.995790(60) | 0.388 s 7 |
| 197 | 196.993190(50) | 0.388 s 6 |
| 198 | 197.992840(50) | 4.2 s 3 |
| 199 | 198.990530(50) | 7.03 s 15 |
| 200 | 199.990351(26) | 43 s 1 |
| 201 | 200.988417(9) | 85.2 s 16 |
| 202 | 201.988630(30) | 182 s 2 |
| 203 | 202.986942(13) | 7.4 m 2 |
| 204 | 203.987251(26) | 9.2 m 2 |
| 205 | 204.986074(16) | 26.9 m 8 |
| 206 | 205.986667(22) | 30.6 m 8 |
| 207 | 206.985784(23) | 1.80 h 4 |
| 208 | 207.986590(28) | 1.63 h 3 |
| 209 | 208.986173(8) | 5.41 h 5 |
| 210 | 209.987148(8) | 8.1 h 4 |
| 211 | 210.9874963(30) | 7.214 h 7 |
| 212 | 211.990745(8) | 0.314 s 2 |
| 217 | 217.004719(5) | 32.3 ms 4 |
| 218 | 218.008694(12) | 1.5 s 3 |
| 219 | 219.011162(4) | 56 s 3 |
| 220 | 220.015410(60) | 3.71 m 4 |
| 221 | 221.01805(21) | 2.3 m 2 |
| 222 | 222.02233(32) | 54 s 10 |
| 223 | 223.02519(43) | 50 s 7 |
Units: y = year, d = day, h = hour, m = minute, s = second, ms = millisecond, µs = microsecond.
Numbers in italics are uncertainties with the same unit as the last digit of the half-life.
Atomic weights were obtained from NIST Database 144
Half-lifes of radioactive isotopes were extracted from the NuDat 2 database
(Atomic Line List 2.05b16, compiled on Jan 13, 2012)