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. Forty-one

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s have been characterized, with the most stable being ¹⁴⁵Pm with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

of 17.7 years, ¹⁴⁶Pm with a half-life of 5.53 years, and ¹⁴⁷Pm with a half-life of 2.6234 years. All of the remaining

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

isotopes have half-lives that are less than 365 days, and the majority of these have half-lives that are less than 30 seconds. This element also has 18

meta state A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ...

s with the most stable being ^148mPm (t_1/2 41.29 days), ^152m2Pm (t_1/2 13.8 minutes) and ^152mPm (t_1/2 7.52 minutes). The isotopes of promethium range in

mass number The mass number (symbol ''A'', from the German word ''Atomgewicht'' tomic weight, also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approxima ...

from 126 to 166. The primary decay mode for ¹⁴⁶Pm and lighter isotopes is

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...

, and the primary mode for heavier isotopes is

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

. The primary decay products before ¹⁴⁶Pm are

isotopes of neodymium Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes o ...

, and the primary products after are

isotopes of samarium Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.06 y) and 148Sm (7 y), with 152Sm being the most abundant (26. ...

List of isotopes

, - , ¹²⁶Pm , style="text-align:right" , 61 , style="text-align:right" , 65 , 125.95752(54)# , 0.5# s , , , , , - , ¹²⁷Pm , style="text-align:right" , 61 , style="text-align:right" , 66 , 126.95163(64)# , 1# s , , , 5/2+# , , - , rowspan=2, ¹²⁸Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 67 , rowspan=2, 127.94842(43)# , rowspan=2, 1.0(3) s , β⁺ , ¹²⁸Nd , rowspan=2, 6+# , rowspan=2, , - , p , ¹²⁷Nd , - , ¹²⁹Pm , style="text-align:right" , 61 , style="text-align:right" , 68 , 128.94316(43)# , 3# s 200 ns, β⁺ , ¹²⁹Nd , 5/2+# , , - , rowspan=2, ¹³⁰Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 69 , rowspan=2, 129.94045(32)# , rowspan=2, 2.6(2) s , β⁺ , ¹³⁰Nd , rowspan=2, (5+, 6+, 4+) , rowspan=2, , - , β⁺, p (rare) , ¹²⁹Pr , - , rowspan=2, ¹³¹Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 70 , rowspan=2, 130.93587(21)# , rowspan=2, 6.3(8) s , β⁺, p , ¹³⁰Pr , rowspan=2, 5/2+# , rowspan=2, , - , β⁺ , ¹³¹Nd , - , rowspan=2, ¹³²Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 71 , rowspan=2, 131.93375(21)# , rowspan=2, 6.2(6) s , β⁺ , ¹³²Nd , rowspan=2, (3+) , rowspan=2, , - , β⁺, p (5×10⁻⁵%) , ¹³¹Pr , - , ¹³³Pm , style="text-align:right" , 61 , style="text-align:right" , 72 , 132.92978(5) , 15(3) s , β⁺ , ¹³³Nd , (3/2+) , , - , rowspan=2 style="text-indent:1em" , ^133mPm , rowspan=2 colspan="3" style="text-indent:2em" , 130.4(10) keV , rowspan=2, 10# s , β⁺ , ¹³³Nd , rowspan=2, (11/2−) , rowspan=2, , - , IT , ¹³³Pm , - , ¹³⁴Pm , style="text-align:right" , 61 , style="text-align:right" , 73 , 133.92835(6) , 22(1) s , β⁺ , ¹³⁴Nd , (5+) , , - , style="text-indent:1em" , ^134mPm , colspan="3" style="text-indent:2em" , 0(100)# keV , ~5 s , IT , ¹³⁴Pm , (2+) , , - , ¹³⁵Pm , style="text-align:right" , 61 , style="text-align:right" , 74 , 134.92488(6) , 49(3) s , β⁺ , ¹³⁵Nd , (5/2+, 3/2+) , , - , style="text-indent:1em" , ^135mPm , colspan="3" style="text-indent:2em" , 50(100)# keV , 40(3) s , β⁺ , ¹³⁵Nd , (11/2−) , , - , ¹³⁶Pm , style="text-align:right" , 61 , style="text-align:right" , 75 , 135.92357(8) , 107(6) s , β⁺ , ¹³⁶Nd , (5−) , , - , style="text-indent:1em" , ^136mPm , colspan="3" style="text-indent:2em" , 130(120) keV , 47(2) s , β⁺ , ¹³⁶Nd , (2+) , , - , ¹³⁷Pm , style="text-align:right" , 61 , style="text-align:right" , 76 , 136.920479(14) , 2# min , β⁺ , ¹³⁷Nd , 5/2+# , , - , style="text-indent:1em" , ^137mPm , colspan="3" style="text-indent:2em" , 150(50) keV , 2.4(1) min , β⁺ , ¹³⁷Nd , 11/2− , , - , ¹³⁸Pm , style="text-align:right" , 61 , style="text-align:right" , 77 , 137.919548(30) , 10(2) s , β⁺ , ¹³⁸Nd , 1+# , , - , style="text-indent:1em" , ^138mPm , colspan="3" style="text-indent:2em" , 30(30) keV , 3.24(5) min , β⁺ , ¹³⁸Nd , 5−# , , - , ¹³⁹Pm , style="text-align:right" , 61 , style="text-align:right" , 78 , 138.916804(14) , 4.15(5) min , β⁺ , ¹³⁹Nd , (5/2)+ , , - , rowspan=2 style="text-indent:1em" , ^139mPm , rowspan=2 colspan="3" style="text-indent:2em" , 188.7(3) keV , rowspan=2, 180(20) ms , IT (99.83%) , ¹³⁹Pm , rowspan=2, (11/2)− , rowspan=2, , - , β⁺ (0.17%) , ¹³⁹Nd , - , ¹⁴⁰Pm , style="text-align:right" , 61 , style="text-align:right" , 79 , 139.91604(4) , 9.2(2) s , β⁺ , ¹⁴⁰Nd , 1+ , , - , style="text-indent:1em" , ^140mPm , colspan="3" style="text-indent:2em" , 420(40) keV , 5.95(5) min , β⁺ , ¹⁴⁰Nd , 8− , , - , ¹⁴¹Pm , style="text-align:right" , 61 , style="text-align:right" , 80 , 140.913555(15) , 20.90(5) min , β⁺ , ¹⁴¹Nd , 5/2+ , , - , style="text-indent:1em" , ^141m1Pm , colspan="3" style="text-indent:2em" , 628.40(10) keV , 630(20) ns , , , 11/2− , , - , style="text-indent:1em" , ^141m2Pm , colspan="3" style="text-indent:2em" , 2530.9(5) keV , >2 µs , , , , , - , ¹⁴²Pm , style="text-align:right" , 61 , style="text-align:right" , 81 , 141.912874(27) , 40.5(5) s , β⁺ , ¹⁴²Nd , 1+ , , - , style="text-indent:1em" , ^142mPm , colspan="3" style="text-indent:2em" , 883.17(16) keV , 2.0(2) ms , IT , ¹⁴²Pm , (8)− , , - , ¹⁴³Pm , style="text-align:right" , 61 , style="text-align:right" , 82 , 142.910933(4) , 265(7) d , β⁺ , ¹⁴³Nd , 5/2+ , , - , ¹⁴⁴Pm , style="text-align:right" , 61 , style="text-align:right" , 83 , 143.912591(3) , 363(14) d , β⁺ , ''¹⁴⁴Nd'' , 5− , , - , style="text-indent:1em" , ^144m1Pm , colspan="3" style="text-indent:2em" , 840.90(5) keV , 780(200) ns , , , (9)+ , , - , style="text-indent:1em" , ^144m2Pm , colspan="3" style="text-indent:2em" , 8595.8(22) keV , ~2.7 µs , , , (27+) , , - , rowspan=2, ¹⁴⁵Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 84 , rowspan=2, 144.912749(3) , rowspan=2, 17.7(4) y , EC , ¹⁴⁵Nd , rowspan=2, 5/2+ , rowspan=2, , - , α (2.8×10⁻⁷%) , ¹⁴¹Pr , - , rowspan=2, ¹⁴⁶Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 85 , rowspan=2, 145.914696(5) , rowspan=2, 5.53(5) y , EC (66%) , ¹⁴⁶Nd , rowspan=2, 3− , rowspan=2, , - , β⁻ (34%) , ¹⁴⁶Sm , - , ¹⁴⁷Pm Fission product , style="text-align:right" , 61 , style="text-align:right" , 86 , 146.9151385(26) , 2.6234(2) y , β⁻ , ''¹⁴⁷Sm'' , 7/2+ , Trace

Alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an at ...

daughter of primordial ¹⁵¹Eu , - , ¹⁴⁸Pm , style="text-align:right" , 61 , style="text-align:right" , 87 , 147.917475(7) , 5.368(2) d , β⁻ , ''¹⁴⁸Sm'' , 1− , , - , rowspan=2 style="text-indent:1em" , ^148mPm , rowspan=2 colspan="3" style="text-indent:2em" , 137.9(3) keV , rowspan=2, 41.29(11) d , β⁻ (95%) , ''¹⁴⁸Sm'' , rowspan=2, 5−, 6− , rowspan=2, , - , IT (5%) , ¹⁴⁸Pm , - , ¹⁴⁹Pm , style="text-align:right" , 61 , style="text-align:right" , 88 , 148.918334(4) , 53.08(5) h , β⁻ , ¹⁴⁹Sm , 7/2+ , , - , style="text-indent:1em" , ^149mPm , colspan="3" style="text-indent:2em" , 240.214(7) keV , 35(3) µs , , , 11/2− , , - , ¹⁵⁰Pm , style="text-align:right" , 61 , style="text-align:right" , 89 , 149.920984(22) , 2.68(2) h , β⁻ , ¹⁵⁰Sm , (1−) , , - , ¹⁵¹Pm , style="text-align:right" , 61 , style="text-align:right" , 90 , 150.921207(6) , 28.40(4) h , β⁻ , ¹⁵¹Sm , 5/2+ , , - , ¹⁵²Pm , style="text-align:right" , 61 , style="text-align:right" , 91 , 151.923497(28) , 4.12(8) min , β⁻ , ¹⁵²Sm , 1+ , , - , style="text-indent:1em" , ^152m1Pm , colspan="3" style="text-indent:2em" , 140(90) keV , 7.52(8) min , , , 4− , , - , style="text-indent:1em" , ^152m2Pm , colspan="3" style="text-indent:2em" , 250(150)# keV , 13.8(2) min , , , (8) , , - , ¹⁵³Pm , style="text-align:right" , 61 , style="text-align:right" , 92 , 152.924117(12) , 5.25(2) min , β⁻ , ¹⁵³Sm , 5/2− , , - , ¹⁵⁴Pm , style="text-align:right" , 61 , style="text-align:right" , 93 , 153.92646(5) , 1.73(10) min , β⁻ , ¹⁵⁴Sm , (0, 1) , - , style="text-indent:1em" , ^154mPm , colspan="3" style="text-indent:2em" , 120(120) keV , 2.68(7) min , β⁻ , ¹⁵⁴Sm , (3, 4) , , - , ¹⁵⁵Pm , style="text-align:right" , 61 , style="text-align:right" , 94 , 154.92810(3) , 41.5(2) s , β⁻ , ¹⁵⁵Sm , (5/2−) , , - , ¹⁵⁶Pm , style="text-align:right" , 61 , style="text-align:right" , 95 , 155.93106(4) , 26.70(10) s , β⁻ , ¹⁵⁶Sm , 4− , , - , ¹⁵⁷Pm , style="text-align:right" , 61 , style="text-align:right" , 96 , 156.93304(12) , 10.56(10) s , β⁻ , ¹⁵⁷Sm , (5/2−) , , - , ¹⁵⁸Pm , style="text-align:right" , 61 , style="text-align:right" , 97 , 157.93656(14) , 4.8(5) s , β⁻ , ¹⁵⁸Sm , , , - , ¹⁵⁹Pm , style="text-align:right" , 61 , style="text-align:right" , 98 , 158.93897(21)# , , β⁻ , ¹⁵⁹Sm , 5/2−# , , - , ¹⁶⁰Pm , style="text-align:right" , 61 , style="text-align:right" , 99 , 159.94299(32)# , , β⁻ , ¹⁶⁰Sm , , , - , rowspan=2, ¹⁶¹Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 100 , rowspan=2, 160.94586(54)# , rowspan=2, , β⁻ (98.91%) , ¹⁶¹Sm , rowspan=2, 5/2−# , rowspan=2, , - , β⁻, n (1.09%) , ¹⁶⁰Sm , - , rowspan=2, ¹⁶²Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 101 , rowspan=2, 161.95029(75)# , rowspan=2, , β⁻ (98.21%) , ¹⁶²Sm , rowspan=2, , rowspan=2, , - , β⁻, n (1.79%) , ¹⁶¹Sm , - , rowspan=2, ¹⁶³Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 102 , rowspan=2, 162.95368(86)# , rowspan=2, , β⁻ (95%) , ¹⁶³Sm , rowspan=2, 5/2−# , rowspan=2, , - , β⁻, n (1.79%) , ¹⁶²Sm , - , rowspan=2, ¹⁶⁴Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 103 , rowspan=2, , rowspan=2, , β⁻ (93.82%) , ¹⁶⁴Sm , rowspan=2, , rowspan=2, , - , β⁻, n (6.18%) , ¹⁶³Sm , - , rowspan=2, ¹⁶⁵Pm , rowspan=2 style="text-align:right" , 61 , rowspan=2 style="text-align:right" , 104 , rowspan=2, , rowspan=2, , β⁻ (86.74%) , ¹⁶⁵Sm , rowspan=2, , rowspan=2, , - , β⁻, n (13.26%) , ¹⁶⁴Sm , - , 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 , ¹⁶⁵Sm

Stability of promethium isotopes

Promethium is one of the two elements of the first 82 elements that have no stable isotopes; the other is

technetium Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous ...

(''Z'' = 43). This is a rarely occurring effect of the

liquid drop model In nuclear physics, the semi-empirical mass formula (SEMF) (sometimes also called the Weizsäcker formula, Bethe–Weizsäcker formula, or Bethe–Weizsäcker mass formula to distinguish it from the Bethe–Weizsäcker process) is used to approxi ...

Promethium-147

Promethium-147 has a half-life of 2.62 years, and is a fission product produced in

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

s via beta decay from

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...

-147. The isotopes ¹⁴²Nd, ¹⁴³Nd, ¹⁴⁴Nd, ¹⁴⁵Nd, ¹⁴⁶Nd, ¹⁴⁸Nd, and ¹⁵⁰Nd are either stable or nearly so, so the isotopes of promethium with those masses cannot be produced by beta decay and therefore are not fission products in significant quantities. ¹⁴⁹Pm and ¹⁵¹Pm have half-lives of only 53.08 and 28.40 hours, so are not found in

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

that has been cooled for months or years. It is found naturally mostly from the spontaneous fission of uranium-238 and less often from the

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an at ...

of europium-151. Promethium-147 is used as a beta particle source and a

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...

(RTG) fuel; its power density is about 2 watts per gram. Mixed with a phosphor, it was used to illuminate Apollo Lunar Module electrical switch tips and painted on control panels of the Lunar Roving Vehicle.

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Promethium Promethium