Isotopes of promethium

Promethium (₆₁Pm) is an artificial element, except in trace quantities as a product of spontaneous fission of ²³⁸U and ²³⁵U and alpha decay of ¹⁵¹Eu, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was first synthesized in 1945.

The known isotopes run from ¹²⁸Pm to ¹⁶⁶Pm, 39 in all; the most stable are ¹⁴⁵Pm with a half-life of 17.7 years, ¹⁴⁶Pm with a half-life of 5.53 years, and ¹⁴⁷Pm (the common isotope) with a half-life of 2.6234 years. ¹⁴³Pm and ¹⁴⁴Pm also have lengthy if poorly-known lives on the order of a year, but all the others have half-lives that are less than six days, with the majority less than a few minutes. There are also 24 known meta states with the most stable being ^148mPm at a half-life of 41.29 days.

The primary decay mode for isotopes lighter than ¹⁴⁶Pm is electron capture resulting in isotopes of neodymium, and the primary decay mode heavier than ¹⁴⁶Pm is beta decay giving isotopes of samarium; promethium-146 itself decays both ways.

List of isotopes

|-id=Promethium-125 | ¹²⁵Pm | style="text-align:right" | 61 | style="text-align:right" | 64 | | >310&nbsp;ns | | | | |-id=Promethium-126 | ¹²⁶Pm | style="text-align:right" | 61 | style="text-align:right" | 65 | 125.95733(54)# | 500#&nbsp;ms<br>[>310&nbsp;ns] | | | | |-id=Promethium-127 | ¹²⁷Pm | style="text-align:right" | 61 | style="text-align:right" | 66 | 126.95136(43)# | 1#&nbsp;s<br>[>310&nbsp;ns] | | | 3/2+# | |-id=Promethium-128 | rowspan=2|¹²⁸Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 67 | rowspan=2|127.94823(32)# | rowspan=2|1.0(3)&nbsp;s | β⁺ (?%) | ¹²⁸Nd | rowspan=2|4+# | rowspan=2| |- | β⁺, p (?%) | ¹²⁷Pr |-id=Promethium-129 | ¹²⁹Pm | style="text-align:right" | 61 | style="text-align:right" | 68 | 128.94291(32)# | 2.4(9)&nbsp;s | β⁺ | ¹²⁹Nd | 5/2+# | |-id=Promethium-130 | rowspan=2|¹³⁰Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 69 | rowspan=2|129.94045(22)# | rowspan=2|2.6(2)&nbsp;s | β⁺ (?%) | ¹³⁰Nd | rowspan=2|(5+, 6+, 4+) | rowspan=2| |- | β⁺, p (?%) | ¹²⁹Pr |-id=Promethium-131 | ¹³¹Pm | style="text-align:right" | 61 | style="text-align:right" | 70 | 130.93583(22)# | 6.3(8)&nbsp;s | β⁺ | ¹³¹Nd | (11/2−) | |-id=Promethium-132 | rowspan=2|¹³²Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 71 | rowspan=2|131.93384(16)# | rowspan=2|6.2(6)&nbsp;s | β⁺ | ¹³²Nd | rowspan=2|(3+) | rowspan=2| |- | β⁺, p (5×10^{−5}%) | ¹³¹Pr |-id=Promethium-133 | ¹³³Pm | style="text-align:right" | 61 | style="text-align:right" | 72 | 132.929782(54) | 13.5(21)&nbsp;s | β⁺ | ¹³³Nd | (3/2+) | |-id=Promethium-133m | style="text-indent:1em" | ^133mPm | colspan="3" style="text-indent:2em" | 129.7(7)&nbsp;keV | 8#&nbsp;s | | | (11/2−) | |-id=Promethium-134 | ¹³⁴Pm | style="text-align:right" | 61 | style="text-align:right" | 73 | 133.928326(45) | 22(1)&nbsp;s | β⁺ | ¹³⁴Nd | (5+) | |-id=Promethium-134m1 | style="text-indent:1em" | ^134m1Pm | colspan="3" style="text-indent:2em" | 50(50)#&nbsp;keV | ~5&nbsp;s | β⁺ | ¹³⁴Nd | (2+) | |-id=Promethium-134m2 | style="text-indent:1em" | ^134m2Pm | colspan="3" style="text-indent:2em" | 120(50)#&nbsp;keV | 20(1)&nbsp;μs | IT | ¹³⁴Pm | (7−) | |-id=Promethium-135 | ¹³⁵Pm | style="text-align:right" | 61 | style="text-align:right" | 74 | 134.924785(89) | 49(3)&nbsp;s | β⁺ | ¹³⁵Nd | (3/2+, 5/2+) | |-id=Promethium-135m | style="text-indent:1em" | ^135mPm | colspan="3" style="text-indent:2em" | 240(100)#&nbsp;keV | 40(3)&nbsp;s | β⁺ | ¹³⁵Nd | (11/2−) | |-id=Promethium-136 | ¹³⁶Pm | style="text-align:right" | 61 | style="text-align:right" | 75 | 135.923596(74) | 107(6)&nbsp;s | β⁺ | ¹³⁶Nd | 7+# | |-id=Promethium-136m1 | style="text-indent:1em" | ^136m1Pm | colspan="3" style="text-indent:2em" | 100(120)&nbsp;keV | 90(35)&nbsp;s | β⁺ | ¹³⁶Nd | 2+# | |-id=Promethium-136m2 | style="text-indent:1em" | ^136m2Pm | colspan="3" style="text-indent:2em" | 42.7(2)&nbsp;keV | 1.5(1)&nbsp;μs | IT | ¹³⁶Pm | 7−# | |-id=Promethium-137 | ¹³⁷Pm | style="text-align:right" | 61 | style="text-align:right" | 76 | 136.920480(14) | 2#&nbsp;min | | | 5/2−# | |-id=Promethium-137m | style="text-indent:1em" | ^137mPm | colspan="3" style="text-indent:2em" | 160(50)&nbsp;keV | 2.4(1)&nbsp;min | β⁺ | ¹³⁷Nd | 11/2− | |-id=Promethium-138 | ¹³⁸Pm | style="text-align:right" | 61 | style="text-align:right" | 77 | 137.919576(12) | 3.24(5)&nbsp;min | β⁺ | ¹³⁸Nd | 3−# | |-id=Promethium-139 | ¹³⁹Pm | style="text-align:right" | 61 | style="text-align:right" | 78 | 138.916799(15) | 4.15(5)&nbsp;min | β⁺ | ¹³⁹Nd | (5/2)+ | |-id=Promethium-139m | style="text-indent:1em" | ^139mPm | colspan="3" style="text-indent:2em" | 188.7(3)&nbsp;keV | 180(20)&nbsp;ms | IT | ¹³⁹Pm | (11/2)− | |-id=Promethium-140 | ¹⁴⁰Pm | style="text-align:right" | 61 | style="text-align:right" | 79 | 139.916036(26) | 9.2(2)&nbsp;s | β⁺ | ¹⁴⁰Nd | 1+ | |-id=Promethium-140m | style="text-indent:1em" | ^140mPm | colspan="3" style="text-indent:2em" | 429(28)&nbsp;keV | 5.95(5)&nbsp;min | β⁺ | ¹⁴⁰Nd | 8− | |-id=Promethium-141 | ¹⁴¹Pm | style="text-align:right" | 61 | style="text-align:right" | 80 | 140.913555(15) | 20.90(5)&nbsp;min | β⁺ | ¹⁴¹Nd | 5/2+ | |-id=Promethium-141m1 | style="text-indent:1em" | ^141m1Pm | colspan="3" style="text-indent:2em" | 628.62(7)&nbsp;keV | 630(20)&nbsp;ns | IT | ¹⁴¹Pm | 11/2− | |-id=Promethium-141m2 | style="text-indent:1em" | ^141m2Pm | colspan="3" style="text-indent:2em" | 2530.75(17)&nbsp;keV | >2&nbsp;μs | IT | ¹⁴¹Pm | (23/2+) | |-id=Promethium-142 | rowspan=2|¹⁴²Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 81 | rowspan=2|141.912891(25) | rowspan=2|40.5(5)&nbsp;s | β⁺ (77.1%) | rowspan=2|¹⁴²Nd | rowspan=2|1+ | rowspan=2| |- | EC (22.9%) |-id=Promethium-142m1 | style="text-indent:1em" | ^142m1Pm | colspan="3" style="text-indent:2em" | 883.17(16)&nbsp;keV | 2.0(2)&nbsp;ms | IT | ¹⁴²Pm | (8)− | |-id=Promethium-142m2 | style="text-indent:1em" | ^142m2Pm | colspan="3" style="text-indent:2em" | 2828.7(6)&nbsp;keV | 67(5)&nbsp;μs | IT | ¹⁴²Pm | (13−) | |-id=Promethium-143 | rowspan=2|¹⁴³Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 82 | rowspan=2 | 142.9109381(32) | rowspan=2 | 265(7)&nbsp;d | EC | rowspan=2 | ¹⁴³Nd | rowspan=2 | 5/2+ | rowspan=2 | |- | β⁺ (<5.7×10^{−6}%) |-id=Promethium-144 | rowspan=2|¹⁴⁴Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 83 | rowspan=2 | 143.9125962(31) | rowspan=2 | 363(14)&nbsp;d | EC | rowspan=2 | ¹⁴⁴Nd | rowspan=2 | 5− | rowspan=2 | |- | β⁺ (<8×10^{−5}%) |-id=Promethium-144m1 | style="text-indent:1em" | ^144m1Pm | colspan="3" style="text-indent:2em" | 840.90(5)&nbsp;keV | 780(200)&nbsp;ns | IT | ¹⁴⁴Pm | (9)+ | |-id=Promethium-144m2 | style="text-indent:1em" | ^144m2Pm | colspan="3" style="text-indent:2em" | 8595.8(22)&nbsp;keV | ~2.7&nbsp;μs | IT | ¹⁴⁴Pm | (27+) | |-id=Promethium-145 | rowspan=2|¹⁴⁵Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 84 | rowspan=2|144.9127557(30) | rowspan=2|17.7(4)&nbsp;y | EC | ¹⁴⁵Nd | rowspan=2|5/2+ | rowspan=2| |- | α (2.8×10^{−7}%) | ¹⁴¹Pr |-id=Promethium-146 | rowspan=2|¹⁴⁶Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 85 | rowspan=2|145.9147022(46) | rowspan=2|5.53(5)&nbsp;y | EC (66.0%) | ¹⁴⁶Nd | rowspan=2|3− | rowspan=2| |- | β^− (34.0%) | ¹⁴⁶Sm |- | ¹⁴⁷Pm | style="text-align:right" | 61 | style="text-align:right" | 86 | 146.9151449(14) | 2.6234(2)&nbsp;y | β^− | ¹⁴⁷Sm | 7/2+ | Trace |-id=Promethium-148 | ¹⁴⁸Pm | style="text-align:right" | 61 | style="text-align:right" | 87 | 147.9174811(61) | 5.368(7)&nbsp;d | β^− | ¹⁴⁸Sm | 1− | |-id=Promethium-148m | rowspan=2 style="text-indent:1em" | ^148mPm | rowspan=2 colspan="3" style="text-indent:2em" | 137.9(3)&nbsp;keV | rowspan=2|41.29(11)&nbsp;d | β^− (95.8%) | ¹⁴⁸Sm | rowspan=2|5−, 6− | rowspan=2| |- | IT (4.2%) | ¹⁴⁸Pm |-id=Promethium-149 | ¹⁴⁹Pm | style="text-align:right" | 61 | style="text-align:right" | 88 | 148.9183415(23) | 53.08(5)&nbsp;h | β^− | ¹⁴⁹Sm | 7/2+ | |-id=Promethium-149m | style="text-indent:1em" | ^149mPm | colspan="3" style="text-indent:2em" | 240.214(7)&nbsp;keV | 35(3)&nbsp;μs | IT | ¹⁴⁹Pm | 11/2− | |-id=Promethium-150 | ¹⁵⁰Pm | style="text-align:right" | 61 | style="text-align:right" | 89 | 149.920990(22) | 2.698(15)&nbsp;h | β^− | ¹⁵⁰Sm | (1−) | |-id=Promethium-151 | ¹⁵¹Pm | style="text-align:right" | 61 | style="text-align:right" | 90 | 150.9212166(49) | 28.40(4)&nbsp;h | β^− | ¹⁵¹Sm | 5/2+ | |-id=Promethium-152 | ¹⁵²Pm | style="text-align:right" | 61 | style="text-align:right" | 91 | 151.923505(28) | 4.12(8)&nbsp;min | β^− | ¹⁵²Sm | 1+ | |-id=Promethium-152m | style="text-indent:1em" | ^152mPm | colspan="3" style="text-indent:2em" | 140(90)&nbsp;keV | 7.52(8)&nbsp;min | β^− | ¹⁵²Sm | 4(−) | |-id=Promethium-153 | ¹⁵³Pm | style="text-align:right" | 61 | style="text-align:right" | 92 | 152.9241563(97) | 5.25(2)&nbsp;min | β^− | ¹⁵³Sm | 5/2− | |-id=Promethium-154 | ¹⁵⁴Pm | style="text-align:right" | 61 | style="text-align:right" | 93 | 153.926713(27) | 2.68(7)&nbsp;min | β^− | ¹⁵⁴Sm | (4+) | |-id=Promethium-154m | style="text-indent:1em" | ^154mPm | colspan="3" style="text-indent:2em" | −230(50)&nbsp;keV | 1.73(10)&nbsp;min | β^− | ¹⁵⁴Sm | (1−) | |-id=Promethium-155 | ¹⁵⁵Pm | style="text-align:right" | 61 | style="text-align:right" | 94 | 154.9281370(51) | 41.5(2)&nbsp;s | β^− | ¹⁵⁵Sm | (5/2−) | |-id=Promethium-156 | ¹⁵⁶Pm | style="text-align:right" | 61 | style="text-align:right" | 95 | 155.9311141(13) | 27.4(5)&nbsp;s | β^− | ¹⁵⁶Sm | 4+ | |-id=Promethium-156m | rowspan=2 style="text-indent:1em" | ^156mPm | rowspan=2 colspan="3" style="text-indent:2em" | 150.30(10)&nbsp;keV | rowspan=2|2.3(20)&nbsp;s | IT (98%) | ¹⁵⁶Pm | rowspan=2|1+# | rowspan=2| |- | β^− (2%) | ¹⁵⁶Sm |-id=Promethium-157 | ¹⁵⁷Pm | style="text-align:right" | 61 | style="text-align:right" | 96 | 156.9331213(75) | 10.56(10)&nbsp;s | β^− | ¹⁵⁷Sm | (5/2−) | |-id=Promethium-158 | ¹⁵⁸Pm | style="text-align:right" | 61 | style="text-align:right" | 97 | 157.93654695(95) | 4.8(5)&nbsp;s | β^− | ¹⁵⁸Sm | (0+,1+)# | |-id=Promethium-158m | style="text-indent:1em" | ^158mPm | colspan="3" style="text-indent:2em" | 150(50)#&nbsp;keV | >16&nbsp;μs | IT | ¹⁵⁸Pm | 5+# | |-id=Promethium-159 | ¹⁵⁹Pm | style="text-align:right" | 61 | style="text-align:right" | 98 | 158.939286(11) | | β^− | ¹⁵⁹Sm | (5/2−) | |-id=Promethium-159m | rowspan=2 style="text-indent:1em" | ^159mPm | rowspan=2 colspan="3" style="text-indent:2em" | 1465.0(5)&nbsp;keV | rowspan=2|4.42(17)&nbsp;μs | IT | ¹⁵⁹Pm | rowspan=2|17/2+# | rowspan=2| |- | β^−, n (<0.6%) | ¹⁵⁸Sm |-id=Promethium-160 | rowspan=2|¹⁶⁰Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 99 | rowspan=2|159.9432153(22) | rowspan=2| | β^− | ¹⁶⁰Sm | rowspan=2|6−# | rowspan=2| |- | β^−, n (<0.1%) | ¹⁵⁹Sm |-id=Promethium-160m | style="text-indent:1em" | ^160mPm | colspan="3" style="text-indent:2em" | 191(11)&nbsp;keV | >700&nbsp;ms | | | 1−# | |-id=Promethium-161 | rowspan=2|¹⁶¹Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 100 | rowspan=2|160.9462298(97) | rowspan=2| | β^− (98.91%) | ¹⁶¹Sm | rowspan=2|(5/2−) | rowspan=2| |- | β^−, n (1.09%) | ¹⁶⁰Sm |-id=Promethium-161m | style="text-indent:1em" | ^161mPm | colspan="3" style="text-indent:2em" | 965.9(9)&nbsp;keV | 890(90)&nbsp;ns | IT | ¹⁶¹Pm | (13/2+) | |-id=Promethium-162 | rowspan=2|¹⁶²Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 101 | rowspan=2|161.95057(32)# | rowspan=2| | β^− (98.21%) | ¹⁶²Sm | rowspan=2| 2+# | rowspan=2| |- | β^−, n (1.79%) | ¹⁶¹Sm |-id=Promethium-163 | rowspan=2|¹⁶³Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 102 | rowspan=2|162.95388(43)# | rowspan=2| | β^− (95%) | ¹⁶³Sm | rowspan=2|5/2−# | rowspan=2| |- | β^−, n (5.00%) | ¹⁶²Sm |-id=Promethium-164 | rowspan=2|¹⁶⁴Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 103 | rowspan=2|163.95882(43)# | rowspan=2| | β^− (93.82%) | ¹⁶⁴Sm | rowspan=2|5−# | rowspan=2| |- | β^−, n (6.18%) | ¹⁶³Sm |-id=Promethium-165 | rowspan=2|¹⁶⁵Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 104 | rowspan=2|164.96278(54)# | rowspan=2| | β^− (86.74%) | ¹⁶⁵Sm | rowspan=2|5/2−# | rowspan=2| |- | β^−, n (13.26%) | ¹⁶⁴Sm |-id=Promethium-166 | rowspan=2|¹⁶⁶Pm | rowspan=2 style="text-align:right" | 61 | rowspan=2 style="text-align:right" | 105 | rowspan=2| | rowspan=2| | β^− | ¹⁶⁶Sm | rowspan=2| | rowspan=2| |- | β^−, n (<52%) | ¹⁶⁵Sm

Stability of promethium isotopes

Promethium is one of the two elements of the first 82 elements that has no stable isotopes. This is a rarely occurring effect of the liquid drop model. Namely, promethium does not have any beta-stable isotopes, as for any mass number, it is energetically favorable for a promethium isotope to undergo positron emission or beta decay, respectively forming a neodymium or samarium isotope which has a higher binding energy per nucleon. The other element for which this happens is technetium (Z&nbsp;=&nbsp;43).

Promethium-147

Promethium-147 beta decays to the long-lived primordial radioisotope samarium-147 with a half-life of 2.6234 years, emitting low-energy beta radiation without gamma emission. It is a common fission product, produced in nuclear reactors and in trace quantities in nature, where it is also produced by the alpha decay of europium-151.

In the reactor environment, it is almost exclusively produced through beta decay of neodymium-147 as usual for fission products. The isotopes ^142-146Nd, ¹⁴⁸Nd, and ¹⁵⁰Nd are all stable with respect to beta decay, so the isotopes of promethium with those masses are not produced by beta decay and are therefore not significant fission products (as they could only be produced directly, rather than through a beta-decay chain). ¹⁴⁹Pm and ¹⁵¹Pm are, but have half-lives of only 53.08 and 28.40 hours, so are not found in spent nuclear fuel that has been cooled for months or years.

Promethium-147 is used as a beta particle source and a radioisotope thermoelectric generator (RTG) fuel; its power density is about 2 watts per gram. Mixed with a phosphor, it was used to illuminate the Apollo Lunar Module electrical switch tips and the control panels of the Lunar Roving Vehicle. For luminescent applications, it has generally been replaced by tritium, which is even safer and has a longer half-life (12.32 years).

See also

Daughter products other than promethium

• Isotopes of samarium
• Isotopes of neodymium
• Isotopes of praseodymium

References