Isotopes of technetium

Technetium (abbreviation Tc, atomic number 43) is the first of the two elements in the first 82 that have no stable isotopes (all are radioactive); the other such element is promethium.[1] It is primarily artificial, only trace quantities existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc in 1936, the first artificial element to be produced. 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).[2]

Thirty-three other radioisotopes have been characterized with atomic masses ranging from 85Tc to 120Tc[3]. 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).[2]

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.[2]

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.[2][4]

Technetium-99 is the most common and most readily available isotope, as it is a major fission product from fission of actinides like uranium and plutonium with a fission product yield of 6% or more per fission, and in fact the most significant long-lived fission product. Lighter isotopes of technetium are almost never produced in fission because the initial fission products normally have a higher neutron/proton ratio than is stable for their mass range, and therefore undergo beta decay until reaching the ultimate product. Beta decay of fission products of mass 95-98 stops at the stable isotopes of molybdenum of those masses and does not reach technetium. For mass 100 and greater, the technetium isotopes of those masses are very short-lived and quickly beta decay to isotopes of ruthenium. Therefore the technetium in spent nuclear fuel is practically all 99Tc.

One gram of 99Tc produces 6.2×108 disintegrations a second (that is, 0.62 GBq/g).[5]

Technetium has no stable or nearly stable isotopes, and thus a standard atomic mass cannot be given.

Contents

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.[6]

Table

nuclide
symbol		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)[7][n 1]		 daughter
isotope(s)[n 2]		 nuclear
spin
excitation energy
85Tc 43 42 84.94883(43)# <110 ns β+ 85Mo 1/2-#
p 84Mo
β+, p 84Nb
86Tc 43 43 85.94288(32)# 55(6) ms β+ 86Mo (0+)
86mTc 1500(150) keV 1.11(21) µs (5+,5-)
87Tc 43 44 86.93653(32)# 2.18(16) s β+ 87Mo 1/2-#
87mTc 20(60)# keV 2# s 9/2+#
88Tc 43 45 87.93268(22)# 5.8(2) s β+ 88Mo (2,3)
88mTc 0(300)# keV 6.4(8) s β+ 88Mo (6,7,8)
89Tc 43 46 88.92717(22)# 12.8(9) s β+ 89Mo (9/2+)
89mTc 62.6(5) keV 12.9(8) s β+ 89Mo (1/2-)
90Tc 43 47 89.92356(26) 8.7(2) s β+ 90Mo 1+
90mTc 310(390) keV 49.2(4) s β+ 90Mo (8+)
91Tc 43 48 90.91843(22) 3.14(2) min β+ 91Mo (9/2)+
91mTc 139.3(3) keV 3.3(1) min β+ (99%) 91Mo (1/2)-
IT (1%) 91Tc
92Tc 43 49 91.915260(28) 4.25(15) min β+ 92Mo (8)+
92mTc 270.15(11) keV 1.03(7) µs (4+)
93Tc 43 50 92.910249(4) 2.75(5) h β+ 93Mo 9/2+
93m1Tc 391.84(8) keV 43.5(10) min IT (76.6%) 93Tc 1/2-
β+ (23.7%) 93Mo
93m2Tc 2185.16(15) keV 10.2(3) µs (17/2)-
94Tc 43 51 93.909657(5) 293(1) min β+ 94Mo 7+
94mTc 75.5(19) keV 52.0(10) min β+ (99.9%) 94Mo (2)+
IT (.1%) 94Tc
95Tc 43 52 94.907657(6) 20.0(1) h β+ 95Mo 9/2+
95mTc 38.89(5) keV 61(2) d β+ (96.12%) 95Mo 1/2-
IT (3.88%) 95Tc
96Tc 43 53 95.907871(6) 4.28(7) d β+ 96Mo 7+
96mTc 34.28(7) keV 51.5(10) min IT (98%) 96Tc 4+
β+ (2%) 96Mo
97Tc 43 54 96.906365(5) 2.6×106 a EC 97Mo 9/2+
97mTc 96.56(6) keV 91.4(8) d IT (99.66%) 97Tc 1/2-
EC (.34%) 97Mo
98Tc 43 55 97.907216(4) 4.2(3)×106 a β- 98Ru (6)+
98mTc 90.76(16) keV 14.7(3) µs (2)-
99Tc[n 3] 43 56 98.9062547(21) 2.111(12)×105 a β- 99Ru 9/2+
99mTc[n 4] 142.6832(11) keV 6.0058(12) h IT (99.99%) 99Tc 1/2-
β- (.0037%) 99Ru
100Tc 43 57 99.9076578(24) 15.8(1) s β- (99.99%) 100Ru 1+
EC (.0018%) 100Mo
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 β- 101Ru 9/2+
101mTc 207.53(4) keV 636(8) µs 1/2-
102Tc 43 59 101.909215(10) 5.28(15) s β- 102Ru 1+
102mTc 20(10) keV 4.35(7) min β- (98%) 102Ru (4,5)
IT (2%) 102Tc
103Tc 43 60 102.909181(11) 54.2(8) s β- 103Ru 5/2+
104Tc 43 61 103.91145(5) 18.3(3) min β- 104Ru (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 β- 105Ru (3/2-)
106Tc 43 63 105.914358(14) 35.6(6) s β- 106Ru (1,2)
107Tc 43 64 106.91508(16) 21.2(2) s β- 107Ru (3/2-)
107mTc 65.7(10) keV 184(3) ns (5/2-)
108Tc 43 65 107.91846(14) 5.17(7) s β- 108Ru (2)+
109Tc 43 66 108.91998(10) 860(40) ms β- (99.92%) 109Ru 3/2-#
β-, n (.08%) 108Ru
110Tc 43 67 109.92382(8) 0.92(3) s β- (99.96%) 110Ru (2+)
β-, n (.04%) 109Ru
111Tc 43 68 110.92569(12) 290(20) ms β- (99.15%) 111Ru 3/2-#
β-, n (.85%) 110Ru
112Tc 43 69 111.92915(13) 290(20) ms β- (97.4%) 112Ru 2+#
β-, n (2.6%) 111Ru
113Tc 43 70 112.93159(32)# 170(20) ms β- 113Ru 3/2-#
114Tc 43 71 113.93588(64)# 150(30) ms β- 114Ru 2+#
115Tc 43 72 114.93869(75)# 100# ms [>300 ns] β- 115Ru 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+#
  1. ^ Abbreviations:
    EC: Electron capture
    IT: Isomeric transition
  2. ^ Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
  3. ^ Long-lived fission product
  4. ^ Used in medicine

Notes

References

  1. ^ LANL Periodic Table, "Technetium" paragraph 2
  2. ^ a b c d EnvironmentalChemistry.com, "Technetium", Nuclides / Isotopes
  3. ^ Meet technetium-120and technetium-119, technetium's newest isotopes!
  4. ^ CRC Handbook, 85th edition, table of the isotopes
  5. ^ The Encyclopedia of the Chemical Elements, page 693, "Toxicology", paragraph 2
  6. ^ RADIOCHEMISTRY and NUCLEAR CHEMISTRY
  7. ^ http://www.nucleonica.net/unc.aspx
Isotopes of molybdenum Isotopes of technetium Isotopes of ruthenium
Index to isotope pages · Table of nuclides