Isotopes of technetium

Technetium (Tc) is one of the two elements in the first 82 that have no stable isotopes (in fact, it is the lowest-numbered element that is exclusively radioactive); the other such element is promethium. The most stable radioisotopes are ⁹⁸Tc (half-life of 4.2 Ma), ⁹⁷Tc (half-life: 2.6 Ma) and ⁹⁹Tc (half-life: 211.1 ka).

Twenty-two other radioisotopes have been characterized with atomic masses ranging from 87.933 u (⁸⁸Tc) to 112.931 u (¹¹³Tc). Most of these have half-lives that are less than an hour; the exceptions are ⁹³Tc (half-life: 2.75 hours), ⁹⁴Tc (half-life: 4.883 hours), ⁹⁵Tc (half-life: 20 hours), and ⁹⁶Tc (half-life: 4.28 days).

Technetium also has numerous meta states. ^97mTc is the most stable, with a half-life of 90.1 days (0.097 MeV). This is followed by ^95mTc (half life: 61 days, 0.038 MeV), and ^99mTc (half-life: 6.01 hours, 0.143 MeV). ^99mTc only emits gamma rays, subsequently decaying to ⁹⁹Tc.

For isotopes lighter than the most stable isotope, ⁹⁸Tc, the primary decay mode is electron capture, giving molybdenum. For the heavier isotopes, the primary mode is beta emission, giving ruthenium, with the exception that ¹⁰⁰Tc can decay both by beta emission and electron capture.

Technetium-99 is the most common and most readily available isotope, as it is a major product of the fission of uranium-235. One gram of ⁹⁹Tc produces 6.2×10⁸ disintegrations a second (that is, 0.62 GBq/g).

Stability of technetium isotopes

Technetium and promethium are unusual light elements in that they have no stable isotopes. The reason for this is somewhat complicated.

Using the liquid drop model for atomic nuclei, one can derive a semiempirical formula for the binding energy of a nucleus. This formula predicts a "valley of beta stability" along which nuclides do not undergo beta decay. Nuclides that lie "up the walls" of the valley tend to decay by beta decay towards the center (by emitting an electron, emitting a positron, or capturing an electron). For a fixed number of nucleons A, the binding energies lie on one or more parabolas, with the most stable nuclide at the bottom. One can have more than one parabola because isotopes with an even number of protons and an even number of neutrons are more stable than isotopes with an odd number of neutrons and an odd number of protons. A single beta decay then transforms one into the other. When there is only one parabola, there can be only one stable isotope lying on that parabola. When there are two parabolas, that is, when the number of nucleons is even, it can happen (rarely) that there is a stable nucleus with an odd number of neutrons and an odd number of protons (although this happens only in four instances). However, if this happens, there can be no stable isotope with an even number of neutrons and an even number of protons.

For technetium (Z=43), the valley of beta stability is centered at around 98 nucleons. However, for every number of nucleons from 95 to 102, there is already at least one stable nuclide of either molybdenum (Z=42) or ruthenium (Z=44). For the isotopes with odd numbers of nucleons, this immediately rules out a stable isotope of technetium, since there can be only one stable nuclide with a fixed odd number of nucleons. For the isotopes with an even number of nucleons, since technetium has an odd number of protons, any isotope must also have an odd number of neutrons. In such a case, the presence of a stable nuclide having the same number of nucleons and an even number of protons rules out the possibility of a stable nucleus.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
85Tc	43	42	84.94883(43)#	<110 ns	1/2-#
86Tc	43	43	85.94288(32)#	55(6) ms	(0+)
86mTc	1500(150) keV			1.11(21) µs	(5+,5-)
87Tc	43	44	86.93653(32)#	2.18(16) s	1/2-#
87mTc	20(60)# keV			2# s	9/2+#
88Tc	43	45	87.93268(22)#	5.8(2) s	(2,3)
88mTc	0(300)# keV			6.4(8) s	(6,7,8)
89Tc	43	46	88.92717(22)#	12.8(9) s	(9/2+)
89mTc	62.6(5) keV			12.9(8) s	(1/2-)
90Tc	43	47	89.92356(26)	8.7(2) s	1+
90mTc	310(390) keV			49.2(4) s	(8+)
91Tc	43	48	90.91843(22)	3.14(2) min	(9/2)+
91mTc	139.3(3) keV			3.3(1) min	(1/2)-
92Tc	43	49	91.915260(28)	4.25(15) min	(8)+
92mTc	270.15(11) keV			1.03(7) µs	(4+)
93Tc	43	50	92.910249(4)	2.75(5) h	9/2+
93m1Tc	391.84(8) keV			43.5(10) min	1/2-
93m2Tc	2185.16(15) keV			10.2(3) µs	(17/2)-
94Tc	43	51	93.909657(5)	293(1) min	7+
94mTc	75.5(19) keV			52.0(10) min	(2)+
95Tc	43	52	94.907657(6)	20.0(1) h	9/2+
95mTc	38.89(5) keV			61(2) d	1/2-
96Tc	43	53	95.907871(6)	4.28(7) d	7+
96mTc	34.28(7) keV			51.5(10) min	4+
97Tc	43	54	96.906365(5)	2.6E+6 a	9/2+
97mTc	96.56(6) keV			91.4(8) d	1/2-
98Tc	43	55	97.907216(4)	4.2(3)E+6 a	(6)+
98mTc	90.76(16) keV			14.7(3) µs	(2)-
99Tc	43	56	98.9062547(21)	2.111(12)E+5 a	9/2+
99mTc	142.6832(11) keV			6.0058(12) h	1/2-
100Tc	43	57	99.9076578(24)	15.8(1) s	1+
100m1Tc	200.67(4) keV			8.32(14) µs	(4)+
100m2Tc	243.96(4) keV			3.2(2) µs	(6)+
101Tc	43	58	100.907315(26)	14.22(1) min	9/2+
101mTc	207.53(4) keV			636(8) µs	1/2-
102Tc	43	59	101.909215(10)	5.28(15) s	1+
102mTc	20(10) keV			4.35(7) min	(4,5)
103Tc	43	60	102.909181(11)	54.2(8) s	5/2+
104Tc	43	61	103.91145(5)	18.3(3) min	(3+)#
104m1Tc	69.7(2) keV			3.5(3) µs	2(+)
104m2Tc	106.1(3) keV			0.40(2) µs	(+)
105Tc	43	62	104.91166(6)	7.6(1) min	(3/2-)
106Tc	43	63	105.914358(14)	35.6(6) s	(1,2)
107Tc	43	64	106.91508(16)	21.2(2) s	(3/2-)
107mTc	65.7(10) keV			184(3) ns	(5/2-)
108Tc	43	65	107.91846(14)	5.17(7) s	(2)+
109Tc	43	66	108.91998(10)	860(40) ms	3/2-#
110Tc	43	67	109.92382(8)	0.92(3) s	(2+)
111Tc	43	68	110.92569(12)	290(20) ms	3/2-#
112Tc	43	69	111.92915(13)	290(20) ms	2+#
113Tc	43	70	112.93159(32)#	170(20) ms	3/2-#
114Tc	43	71	113.93588(64)#	150(30) ms	2+#
115Tc	43	72	114.93869(75)#	100# ms [>300 ns]	3/2-#
116Tc	43	73	115.94337(75)#	90# ms [>300 ns]	2+#
117Tc	43	74	116.94648(75)#	40# ms [>300 ns]	3/2-#
118Tc	43	75	117.95148(97)#	30# ms [>300 ns]	2+#

Notes

• Values marked # are not purely derived from experimental data, but at least partly 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 Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
• Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
• Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
  • Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
  • National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
  • David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.

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