Isotopes of promethium

Promethium (Pm) has no stable isotopes, and does not exist in nature, except in trace quantities as a product of spontaneous fission and alpha decay of ¹⁵¹Eu. It is a synthetic element, first produced in 1945. 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 (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 atomic weight from 125.95752 u (¹²⁶Pm) to 162.95368 u (¹⁶³Pm). The primary decay mode before the longest-lived isotope, ¹⁴⁵Pm, is electron capture, and the primary mode after is beta decay. The primary decay products before ¹⁴⁵Pm are isotopes of neodymium and the primary products after are isotopes of samarium.

Since promethium does not exist in nature, a relative atomic mass cannot be given.

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 (No. 43). This is a rarely occurring effect of the liquid drop model.

Promethium-147

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.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin
	excitation energy
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+ (.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	61	86	146.9151385(26)	2.6234(2) y	β−	147Sm	7/2+
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	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	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−#

Notes

• Values marked # are not purely derived from experimental data, but at least partly estimated from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Isotopes of neodymium	Isotopes of promethium	Isotopes of samarium
Table of nuclides