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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.

Main isotopes of promethium (61Pm)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
145Pm trace 17.7 y ε 145Nd
146Pm syn 5.53 y ε 146Nd
β 146Sm
147Pm trace 2.6234 y β 147Sm

Thirty-eight radioisotopes have been characterized, with the most stable being 145Pm with a half-life 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 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 states with the most stable being 148mPm (t1/2 41.29 days), 152m2Pm (t1/2 13.8 minutes) and 152mPm (t1/2 7.52 minutes).

The isotopes of promethium range in atomic weight from 125.95752 u (126Pm) to 162.95368 u (163Pm). The primary decay mode for 146Pm and lighter isotopes is electron capture, and the primary mode for heavier isotopes is beta decay. The primary decay products before 146Pm are isotopes of neodymium, and the primary products after are isotopes of samarium.

Contents

List of isotopesEdit

Nuclide
[n 1]
Z N Isotopic mass (u)
[n 2][n 3]
Half-life
[n 4]
Decay
mode

[n 5]
Daughter
isotope

[n 6][n 7]
Spin and
parity
[n 8][n 4]
Isotopic
abundance
Excitation energy[n 4]
126Pm 61 65 125.95752(54)# 0.5# s
127Pm 61 66 126.95163(64)# 1# s 5/2+#
128Pm 61 67 127.94842(43)# 1.0(3) s β+ 128Nd 6+#
p 127Nd
129Pm 61 68 128.94316(43)# 3# s [>200 ns] β+ 129Nd 5/2+#
130Pm 61 69 129.94045(32)# 2.6(2) s β+ 130Nd (5+, 6+, 4+)
β+, p (rare) 129Pr
131Pm 61 70 130.93587(21)# 6.3(8) s β+, p 130Pr 5/2+#
β+ 131Nd
132Pm 61 71 131.93375(21)# 6.2(6) s β+ 132Nd (3+)
β+, p (5×10−5%) 131Pr
133Pm 61 72 132.92978(5) 15(3) s β+ 133Nd (3/2+)
133mPm 130.4(10) keV 10# s β+ 133Nd (11/2−)
IT 133Pm
134Pm 61 73 133.92835(6) 22(1) s β+ 134Nd (5+)
134mPm 0(100)# keV ~5 s IT 134Pm (2+)
135Pm 61 74 134.92488(6) 49(3) s β+ 135Nd (5/2+, 3/2+)
135mPm 50(100)# keV 40(3) s β+ 135Nd (11/2−)
136Pm 61 75 135.92357(8) 107(6) s β+ 136Nd (5−)
136mPm 130(120) keV 47(2) s β+ 136Nd (2+)
137Pm 61 76 136.920479(14) 2# min β+ 137Nd 5/2+#
137mPm 150(50) keV 2.4(1) min β+ 137Nd 11/2−
138Pm 61 77 137.919548(30) 10(2) s β+ 138Nd 1+#
138mPm 30(30) keV 3.24(5) min β+ 138Nd 5−#
139Pm 61 78 138.916804(14) 4.15(5) min β+ 139Nd (5/2)+
139mPm 188.7(3) keV 180(20) ms IT (99.83%) 139Pm (11/2)−
β+ (0.17%) 139Nd
140Pm 61 79 139.91604(4) 9.2(2) s β+ 140Nd 1+
140mPm 420(40) keV 5.95(5) min β+ 140Nd 8−
141Pm 61 80 140.913555(15) 20.90(5) min β+ 141Nd 5/2+
141m1Pm 628.40(10) keV 630(20) ns 11/2−
141m2Pm 2530.9(5) keV >2 µs
142Pm 61 81 141.912874(27) 40.5(5) s β+ 142Nd 1+
142mPm 883.17(16) keV 2.0(2) ms IT 142Pm (8)−
143Pm 61 82 142.910933(4) 265(7) d β+ 143Nd 5/2+
144Pm 61 83 143.912591(3) 363(14) d β+ 144Nd 5−
144m1Pm 840.90(5) keV 780(200) ns (9)+
144m2Pm 8595.8(22) keV ~2.7 µs (27+)
145Pm 61 84 144.912749(3) 17.7(4) y EC 145Nd 5/2+
α (2.8×10−7%) 141Pr
146Pm 61 85 145.914696(5) 5.53(5) y EC (66%) 146Nd 3−
β (34%) 146Sm
147Pm[n 9] 61 86 146.9151385(26) 2.6234(2) y β 147Sm 7/2+ Trace[n 10]
148Pm 61 87 147.917475(7) 5.368(2) d β 148Sm 1−
148mPm 137.9(3) keV 41.29(11) d β (95%) 148Sm 5−, 6−
IT (5%) 148Pm
149Pm[n 9] 61 88 148.918334(4) 53.08(5) h β 149Sm 7/2+
149mPm 240.214(7) keV 35(3) µs 11/2−
150Pm 61 89 149.920984(22) 2.68(2) h β 150Sm (1−)
151Pm[n 9] 61 90 150.921207(6) 28.40(4) h β 151Sm 5/2+
152Pm 61 91 151.923497(28) 4.12(8) min β 152Sm 1+
152m1Pm 140(90) keV 7.52(8) min 4−
152m2Pm 250(150)# keV 13.8(2) min (8)
153Pm 61 92 152.924117(12) 5.25(2) min β 153Sm 5/2−
154Pm 61 93 153.92646(5) 1.73(10) min β 154Sm (0, 1)
154mPm 120(120) keV 2.68(7) min β 154Sm (3, 4)
155Pm 61 94 154.92810(3) 41.5(2) s β 155Sm (5/2−)
156Pm 61 95 155.93106(4) 26.70(10) s β 156Sm 4−
157Pm 61 96 156.93304(12) 10.56(10) s β 157Sm (5/2−)
158Pm 61 97 157.93656(14) 4.8(5) s β 158Sm
159Pm 61 98 158.93897(21)# 1.47(15) s β 159Sm 5/2−#
160Pm 61 99 159.94299(32)# 2# s β 160Sm
161Pm 61 100 160.94586(54)# 700# ms β 161Sm 5/2−#
162Pm 61 101 161.95029(75)# 500# ms β 162Sm
163Pm 61 102 162.95368(86)# 200# ms β 163Sm 5/2−#
  1. ^ mPm – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ a b c # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. ^ Modes of decay:
    EC: Electron capture
    IT: Isomeric transition


    p: Proton emission
  6. ^ Bold italics symbol as daughter – Daughter product is nearly stable.
  7. ^ Bold symbol as daughter – Daughter product is stable.
  8. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  9. ^ a b c Fission product
  10. ^ Alpha decay daughter of primordial 151Eu

Stability of promethium isotopesEdit

Promethium is one of the two elements of the first 82 elements that have no stable isotopes; the other is technetium (Z = 43). This is a rarely occurring effect of the liquid drop model.

Promethium-147Edit

Promethium-147 has a half-life of 2.62 years, and is a fission product produced in nuclear reactors via beta decay from neodymium-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 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 Apollo Lunar Module electrical switch tips and painted on control panels of the Lunar Roving Vehicle.[1]

ReferencesEdit

  1. ^ "Apollo Experience Report - Protection Against Radiation" (PDF). NASA. Retrieved 9 December 2011.