Isotopes of actinium

List of isotopes

Actinium-218m1

|-id=Actinium-203 | 203Ac | | | | α | 199Fr | (1/2+) | |-id=Actinium-204 |204Ac | | | | α | 200Fr | | |-id=Actinium-205 |205Ac | | 205.01514(6) | | α | 201Fr | 9/2− | |-id=Actinium-206 | 206Ac | | 206.01448(7) | 25(7) ms | α | 202Fr | (3+) | |-id=Actinium-206m | | 41(16) ms | α | 202mFr | (10−) | |-id=Actinium-207 | 207Ac | | 207.01197(6) | 31(8) ms | α | 203Fr | 9/2−# | |-id=Actinium-208 | 208Ac | | 208.01155(7) | 97(15) ms | α | 204Fr | (3+) | |-id=Actinium-208m | α

| | 209.00950(6) | 94(10) ms | α | 205Fr | (9/2−) | |-id=Actinium-210 | 210Ac | | 210.00941(7) | 350(40) ms | α | 206Fr | 7+# | |-id=Actinium-211 | 211Ac | | 211.00767(6) | 213(25) ms | α | 207Fr | 9/2− | |-id=Actinium-212 | 212Ac | | 212.007836(23) | 895(28) ms | α | 208Fr | 7+ | |-id=Actinium-213 |213Ac | | 213.006593(13) | 738(16) ms | α | 209Fr | 9/2− | |-id=Actinium-214 | α (93%)

| | 185(30) ns | IT | 215Ac | (21/2−) | |-id=Actinium-215m2 | | 335(10) ns | IT | 215Ac | (29/2+) | |-id=Actinium-216 | 216Ac | | 216.008749(10) | 440(16) μs | α | 212Fr | (1−) | |-id=Actinium-216m1 | | 441(7) μs | α | 212Fr | (9−) | |-id=Actinium-216m2 | | ~300 ns | IT | 216Ac | | |-id=Actinium-217 | 217Ac | | 217.009342(12) | 69(4) ns | α | 213Fr | 9/2− | |-id=Actinium-217m | | 740(40) ns | | | 29/2+ | |-id=Actinium-218 | 218Ac | | 218.01165(6) | 1.00(4) μs | α | 214Fr | (1−) | |-id=Actinium-218m | | 103(11) ns | IT | 218Ac | (11+) | |-id=Actinium-219 | 219Ac | | 219.01242(6) | 9.4(10) μs | α | 215Fr | 9/2− | |-id=Actinium-220 | 220Ac | | 220.014755(7) | 26.36(19) ms | α | 216Fr | (3−) | |-id=Actinium-221 | 221Ac | | 221.01560(6) | 52(2) ms | α | 217Fr | 9/2−# | |-id=Actinium-222 | α

| | 229.032947(13) | 62.7(5) min | β− | 229Th | 3/2+ | |-id=Actinium-230 | 230Ac | | 230.036327(17) | 122(3) s | β− | 230Th | (1+) | |-id=Actinium-231 | 231Ac | | 231.038393(14) | 7.5(1) min | β− | 231Th | 1/2+ | |-id=Actinium-232 | 232Ac | | 232.042034(14) | 1.98(8) min | β− | 232Th | (1+) | |-id=Actinium-233 | 233Ac | | 233.044346(14) | 143(10) s | β− | 233Th | (1/2+) | |-id=Actinium-234 | 234Ac | | 234.048139(15) | 45(2) s | β− | 234Th | | |-id=Actinium-235 | 235Ac | | 235.050840(15) | 62(4) s | β− | 235Th | 1/2+# | |-id=Actinium-236 | 236Ac | | 236.05499(4) | | β− | 236Th | |

Actinides vs fission products

Notable isotopes

Actinium-225

Main article: Actinium-225

Actinium-225 is a highly radioactive isotope with 136 neutrons. It is an alpha emitter and has a half-life of 9.919 days. As of 2024, it is being researched as a possible alpha source in targeted alpha therapy. Actinium-225 undergoes a series of three alpha decays – via the short-lived francium-221 and astatine-217 – to 213Bi, which itself is used as an alpha source. Another benefit is that the decay chain of 225Ac ends in the nuclide 209Bi, which has a considerably shorter biological half-life than lead. However, a major factor limiting its usage is the difficulty in producing the short-lived isotope, as it is most commonly isolated from aging parent nuclides (such as 233U); it may also be produced in cyclotrons, linear accelerators, or fast breeder reactors.

Actinium-226

Actinium-226 is an isotope of actinium with a half-life of 29.37 hours. It mainly (83%) undergoes beta decay, sometimes (17%) undergo electron capture, and rarely (0.006%) undergo alpha decay. There are researches on 226Ac to use it in SPECT.

Actinium-227

Actinium-227 is the most stable isotope of actinium, with a half-life of 21.772 years. It mainly (98.62%) undergoes beta decay, but sometimes (1.38%) it will undergo alpha decay instead. 227Ac is a member of the actinium series. It is found only in traces in uranium ores – one tonne of uranium in ore contains about 0.2 milligrams of 227Ac. 227Ac is prepared, in milligram amounts, by the neutron irradiation of in a nuclear reactor. :^{226}{88}Ra + ^{1}{0}n - ^{227}{88}Ra -[\beta^-][42.2 \ \ce{min}] ^{227}{89}Ac

227Ac is highly radioactive and was therefore studied for use as an active element of radioisotope thermoelectric generators, for example in spacecraft. The oxide of 227Ac pressed with beryllium is also an efficient neutron source with the activity exceeding that of the standard americium-beryllium and radium-beryllium pairs. In these applications, 227Ac (a weak beta source emitting few alphas of its own) is essentially a progenitor which generates alpha-emitting isotopes upon its decay. Beryllium captures alpha particles and emits neutrons owing to its large cross-section for the (α,n) nuclear reaction:

: ^{9}{4}Be + ^{4}{2}He - ^{12}{6}C + ^{1}{0}n + \gamma

The 227AcBe neutron sources can be applied in a neutron probe – a standard device for measuring the quantity of water present in soil, as well as moisture/density for quality control in highway construction. Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations.

The medium half-life of 227Ac makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed 235U. Its decay product, 231Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. 231Pa decays to 227Ac; however, the concentration of the latter isotope does not follow the 231Pa depth profile, but instead increases toward the sea bottom. This occurs because of the mixing processes which raise some additional 227Ac from the sea bottom. Thus analysis of both 231Pa and 227Ac depth profiles allows researchers to model the mixing behavior.

Notes

References

References

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