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 ...

(₄₃Tc) is one of the two elements with that have no stable

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

s; the other such element is

promethium Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...

. – Elements marked with a * have no stable isotope: 43, 61, and 83 and up. It is primarily artificial, with only trace quantities existing in nature produced by

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdo ...

(there are an estimated grams of ⁹⁹Tc per gram of

pitchblende Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes t ...

) or

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

. The first isotopes to be synthesized were ⁹⁷Tc and ⁹⁹Tc in 1936, the first artificial element to be produced. The most stable

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 are ⁹⁷Tc (

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 ato ...

of 4.21 million years), ⁹⁸Tc (half-life: 4.2 million years), and ⁹⁹Tc (half-life: 211,100 years). Thirty-three other radioisotopes have been characterized with

atomic mass The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nbs ...

es ranging from ⁸⁵Tc to ¹²⁰Tc. 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 91.0 days (0.097 MeV). This is followed by ^95mTc (half-life: 61 days, 0.038 MeV) and ^99mTc (half-life: 6.04 hours, 0.143 MeV). ^99mTc only emits

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

s, subsequently decaying to ⁹⁹Tc. For isotopes lighter than ⁹⁸Tc, the primary decay mode 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 ...

isotopes of molybdenum Molybdenum (42Mo) has 33 known isotopes, ranging in atomic mass from 83 to 115, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. All unstable isotopes of molybdenu ...

. For the heavier isotopes, the primary mode is

beta emission 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 exam ...

isotopes of ruthenium Naturally occurring ruthenium (44Ru) is composed of seven stable isotopes. Additionally, 27 radioactive isotopes have been discovered. Of these radioisotopes, the most stable are 106Ru, with a half-life of 373.59 days; 103Ru, with a half-life of 3 ...

, with the exception that ¹⁰⁰Tc can decay both by beta emission and electron capture.

Technetium-99m Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical ra ...

is the hallmark technetium isotope employed in the

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emitting ...

industry. Its low-energy

isomeric transition 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 ha ...

, which yields a gamma-ray at ~140.5 keV, is ideal for imaging using Single Photon Emission Computed Tomography (SPECT). Several technetium isotopes, such as ^94mTc, ^95gTc, and ^96gTc, which are produced via (p,n) reactions using a

cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Janu ...

targets, have also been identified as potential Positron Emission Tomography (PET) agents. Technetium-101 has been produced using a

D-D fusion Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices de ...

-based

neutron generator Neutron generators are neutron source devices which contain compact linear particle accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deu ...

from the ¹⁰⁰Mo(n,γ)¹⁰¹Mo reaction on natural molybdenum and subsequent beta-minus decay of ¹⁰¹Mo to ¹⁰¹Tc. Despite its shorter-half life (i.e., 14.22 min), ¹⁰¹Tc exhibits unique decay characteristics suitable for radioisotope diagnostic or

therapeutic A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis. As a rule, each therapy has indications and contraindications. There are many different ...

procedures, where it has been proposed that its implementation, as a supplement for dual-isotopic imaging or replacement for ^99mTc, could be performed by on-site production and dispensing at the point of patient care.

Technetium-99 Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting beta particles, but no gamma rays. It is the most significant long-lived fission product of uranium fission, produc ...

is the most common and most readily available isotope, as it is a major

fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...

from fission of

actinide The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...

s like

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

and

plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...

with a

fission product yield Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission. Yield can be broken down by: # Individual ...

of 6% or more, and in fact the most significant

long-lived fission product Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity it is necessary to isolate them from man ...

. 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 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 ...

until reaching the ultimate product. Beta decay of fission products of mass 95–98 stops at the stable

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

. Therefore, the technetium 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 an ...

is practically all ⁹⁹Tc. In the presence of

fast neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

s a small amount of will be produced by (n,2n) "knockout" reactions. If

nuclear transmutation Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed. A transmutatio ...

of fission-derived Technetium or Technetium waste from medical applications is desired, fast neutrons are therefore not desirable as the long lived increases rather than reducing the longevity of the radioactivity in the material. One gram of ⁹⁹Tc produces disintegrations a second (that is, 0.62 G Bq/g). Technetium has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given.

List of isotopes

, - , rowspan=3, ⁸⁵Tc , rowspan=3 style="text-align:right" , 43 , rowspan=3 style="text-align:right" , 42 , rowspan=3, 84.94883(43)# , rowspan=3, <110 ns , β⁺ , ⁸⁵Mo , rowspan=3, 1/2−# , rowspan=3 , , - , p , ⁸⁴Mo , - , β⁺, p , ⁸⁴Nb , - , ⁸⁶Tc , style="text-align:right" , 43 , style="text-align:right" , 43 , 85.94288(32)# , 55(6) ms , β⁺ , ⁸⁶Mo , (0+) , , - , style="text-indent:1em" , ^86mTc , colspan="3" style="text-indent:2em" , 1500(150) keV , 1.11(21) µs , , , (5+, 5−) , , - , ⁸⁷Tc , style="text-align:right" , 43 , style="text-align:right" , 44 , 86.93653(32)# , 2.18(16) s , β⁺ , ⁸⁷Mo , 1/2−# , , - , style="text-indent:1em" , ^87mTc , colspan="3" style="text-indent:2em" , 20(60)# keV , 2# s , , , 9/2+# , , - , ⁸⁸Tc , style="text-align:right" , 43 , style="text-align:right" , 45 , 87.93268(22)# , 5.8(2) s , β⁺ , ⁸⁸Mo , (2, 3) , , - , style="text-indent:1em" , ^88mTc , colspan="3" style="text-indent:2em" , 0(300)# keV , 6.4(8) s , β⁺ , ⁸⁸Mo , (6, 7, 8) , , - , ⁸⁹Tc , style="text-align:right" , 43 , style="text-align:right" , 46 , 88.92717(22)# , 12.8(9) s , β⁺ , ⁸⁹Mo , (9/2+) , , - , style="text-indent:1em" , ^89mTc , colspan="3" style="text-indent:2em" , 62.6(5) keV , 12.9(8) s , β⁺ , ⁸⁹Mo , (1/2−) , , - , ⁹⁰Tc , style="text-align:right" , 43 , style="text-align:right" , 47 , 89.92356(26) , 8.7(2) s , β⁺ , ⁹⁰Mo , 1+ , , - , style="text-indent:1em" , ^90mTc , colspan="3" style="text-indent:2em" , 310(390) keV , 49.2(4) s , β⁺ , ⁹⁰Mo , (8+) , , - , ⁹¹Tc , style="text-align:right" , 43 , style="text-align:right" , 48 , 90.91843(22) , 3.14(2) min , β⁺ , ⁹¹Mo , (9/2)+ , , - , rowspan=2 style="text-indent:1em" , ^91mTc , rowspan=2 colspan="3" style="text-indent:2em" , 139.3(3) keV , rowspan=2, 3.3(1) min , β⁺ (99%) , ⁹¹Mo , rowspan=2, (1/2)− , rowspan=2, , - , IT (1%) , ⁹¹Tc , - , ⁹²Tc , style="text-align:right" , 43 , style="text-align:right" , 49 , 91.915260(28) , 4.25(15) min , β⁺ , ⁹²Mo , (8)+ , , - , style="text-indent:1em" , ^92mTc , colspan="3" style="text-indent:2em" , 270.15(11) keV , 1.03(7) µs , , , (4+) , , - , ⁹³Tc , style="text-align:right" , 43 , style="text-align:right" , 50 , 92.910249(4) , 2.75(5) h , β⁺ , ⁹³Mo , 9/2+ , , - , rowspan=2 style="text-indent:1em" , ^93m1Tc , rowspan=2 colspan="3" style="text-indent:2em" , 391.84(8) keV , rowspan=2, 43.5(10) min , IT (76.6%) , ⁹³Tc , rowspan=2, 1/2− , rowspan=2, , - , β⁺ (23.4%) , ⁹³Mo , - , style="text-indent:1em" , ^93m2Tc , colspan="3" style="text-indent:2em" , 2185.16(15) keV , 10.2(3) µs , , , (17/2)− , , - , ⁹⁴Tc , style="text-align:right" , 43 , style="text-align:right" , 51 , 93.909657(5) , 293(1) min , β⁺ , ⁹⁴Mo , 7+ , , - , rowspan=2 style="text-indent:1em" , ^94mTc , rowspan=2 colspan="3" style="text-indent:2em" , 75.5(19) keV , rowspan=2, 52.0(10) min , β⁺ (99.9%) , ⁹⁴Mo , rowspan=2, (2)+ , rowspan=2, , - , IT (.1%) , ⁹⁴Tc , - , ⁹⁵Tc , style="text-align:right" , 43 , style="text-align:right" , 52 , 94.907657(6) , 20.0(1) h , β⁺ , ⁹⁵Mo , 9/2+ , , - , rowspan=2 style="text-indent:1em" , ^95mTc , rowspan=2 colspan="3" style="text-indent:2em" , 38.89(5) keV , rowspan=2, 61(2) d , β⁺ (96.12%) , ⁹⁵Mo , rowspan=2, 1/2− , rowspan=2, , - , IT (3.88%) , ⁹⁵Tc , - , ⁹⁶Tc , style="text-align:right" , 43 , style="text-align:right" , 53 , 95.907871(6) , 4.28(7) d , β⁺ , ⁹⁶Mo , 7+ , , - , rowspan=2 style="text-indent:1em" , ^96mTc , rowspan=2 colspan="3" style="text-indent:2em" , 34.28(7) keV , rowspan=2, 51.5(10) min , IT (98%) , ⁹⁶Tc , rowspan=2, 4+ , rowspan=2, , - , β⁺ (2%) , ⁹⁶Mo , - , ⁹⁷Tc , style="text-align:right" , 43 , style="text-align:right" , 54 , 96.906365(5) , 4.21×10⁶ y , EC , ⁹⁷Mo , 9/2+ , , - , rowspan=2 style="text-indent:1em" , ^97mTc , rowspan=2 colspan="3" style="text-indent:2em" , 96.56(6) keV , rowspan=2, 91.0(6) d , IT (99.66%) , ⁹⁷Tc , rowspan=2, 1/2− , rowspan=2, , - , EC (.34%) , ⁹⁷Mo , - , ⁹⁸Tc , style="text-align:right" , 43 , style="text-align:right" , 55 , 97.907216(4) , 4.2×10⁶ y , β⁻ , ⁹⁸Ru , (6)+ , , - , style="text-indent:1em" , ^98mTc , colspan="3" style="text-indent:2em" , 90.76(16) keV , 14.7(3) µs , , , (2)− , , - , ⁹⁹Tc

Long-lived fission product Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity it is necessary to isolate them from man ...

, style="text-align:right" , 43 , style="text-align:right" , 56 , 98.9062547(21) , 2.111(12)×10⁵ y , β⁻ , ⁹⁹Ru , 9/2+ , trace , - , rowspan=2 style="text-indent:1em" , ^99mTcUsed in medicine , rowspan=2 colspan="3" style="text-indent:2em" , 142.6832(11) keV , rowspan=2, 6.0067(5) h , IT (99.99%) , ⁹⁹Tc , rowspan=2, 1/2− , rowspan=2, , - , β⁻ (.0037%) , ⁹⁹Ru , - , rowspan=2, ¹⁰⁰Tc , rowspan=2 style="text-align:right" , 43 , rowspan=2 style="text-align:right" , 57 , rowspan=2, 99.9076578(24) , rowspan=2, 15.8(1) s , β⁻ (99.99%) , ¹⁰⁰Ru , rowspan=2, 1+ , rowspan=2, , - , EC (.0018%) , ''¹⁰⁰Mo'' , - , style="text-indent:1em" , ^100m1Tc , colspan="3" style="text-indent:2em" , 200.67(4) keV , 8.32(14) µs , , , (4)+ , , - , style="text-indent:1em" , ^100m2Tc , colspan="3" style="text-indent:2em" , 243.96(4) keV , 3.2(2) µs , , , (6)+ , , - , ¹⁰¹Tc , style="text-align:right" , 43 , style="text-align:right" , 58 , 100.907315(26) , 14.22(1) min , β⁻ , ¹⁰¹Ru , 9/2+ , , - , style="text-indent:1em" , ^101mTc , colspan="3" style="text-indent:2em" , 207.53(4) keV , 636(8) µs , , , 1/2− , , - , ¹⁰²Tc , style="text-align:right" , 43 , style="text-align:right" , 59 , 101.909215(10) , 5.28(15) s , β⁻ , ¹⁰²Ru , 1+ , , - , rowspan=2 style="text-indent:1em" , ^102mTc , rowspan=2 colspan="3" style="text-indent:2em" , 20(10) keV , rowspan=2, 4.35(7) min , β⁻ (98%) , ¹⁰²Ru , rowspan=2, (4, 5) , rowspan=2, , - , IT (2%) , ¹⁰²Tc , - , ¹⁰³Tc , style="text-align:right" , 43 , style="text-align:right" , 60 , 102.909181(11) , 54.2(8) s , β⁻ , ¹⁰³Ru , 5/2+ , , - , ¹⁰⁴Tc , style="text-align:right" , 43 , style="text-align:right" , 61 , 103.91145(5) , 18.3(3) min , β⁻ , ¹⁰⁴Ru , (3+)# , , - , style="text-indent:1em" , ^104m1Tc , colspan="3" style="text-indent:2em" , 69.7(2) keV , 3.5(3) µs , , , 2(+) , , - , style="text-indent:1em" , ^104m2Tc , colspan="3" style="text-indent:2em" , 106.1(3) keV , 0.40(2) µs , , , (+) , , - , ¹⁰⁵Tc , style="text-align:right" , 43 , style="text-align:right" , 62 , 104.91166(6) , 7.6(1) min , β⁻ , ¹⁰⁵Ru , (3/2−) , , - , ¹⁰⁶Tc , style="text-align:right" , 43 , style="text-align:right" , 63 , 105.914358(14) , 35.6(6) s , β⁻ , ¹⁰⁶Ru , (1, 2) , , - , ¹⁰⁷Tc , style="text-align:right" , 43 , style="text-align:right" , 64 , 106.91508(16) , 21.2(2) s , β⁻ , ¹⁰⁷Ru , (3/2−) , , - , style="text-indent:1em" , ^107mTc , colspan="3" style="text-indent:2em" , 65.7(10) keV , 184(3) ns , , , (5/2−) , , - , ¹⁰⁸Tc , style="text-align:right" , 43 , style="text-align:right" , 65 , 107.91846(14) , 5.17(7) s , β⁻ , ¹⁰⁸Ru , (2)+ , , - , rowspan=2, ¹⁰⁹Tc , rowspan=2 style="text-align:right" , 43 , rowspan=2 style="text-align:right" , 66 , rowspan=2, 108.91998(10) , rowspan=2, 860(40) ms , β⁻ (99.92%) , ¹⁰⁹Ru , rowspan=2, 3/2−# , rowspan=2, , - , β⁻, n (.08%) , ¹⁰⁸Ru , - , rowspan=2, ¹¹⁰Tc , rowspan=2 style="text-align:right" , 43 , rowspan=2 style="text-align:right" , 67 , rowspan=2, 109.92382(8) , rowspan=2, 0.92(3) s , β⁻ (99.96%) , ¹¹⁰Ru , rowspan=2, (2+) , rowspan=2, , - , β⁻, n (.04%) , ¹⁰⁹Ru , - , rowspan=2, ¹¹¹Tc , rowspan=2 style="text-align:right" , 43 , rowspan=2 style="text-align:right" , 68 , rowspan=2, 110.92569(12) , rowspan=2, 290(20) ms , β⁻ (99.15%) , ¹¹¹Ru , rowspan=2, 3/2−# , rowspan=2, , - , β⁻, n (.85%) , ¹¹⁰Ru , - , rowspan=2, ¹¹²Tc , rowspan=2 style="text-align:right" , 43 , rowspan=2 style="text-align:right" , 69 , rowspan=2, 111.92915(13) , rowspan=2, 290(20) ms , β⁻ (97.4%) , ¹¹²Ru , rowspan=2, 2+# , rowspan=2, , - , β⁻, n (2.6%) , ¹¹¹Ru , - , ¹¹³Tc , style="text-align:right" , 43 , style="text-align:right" , 70 , 112.93159(32)# , 170(20) ms , β⁻ , ¹¹³Ru , 3/2−# , , - , ¹¹⁴Tc , style="text-align:right" , 43 , style="text-align:right" , 71 , 113.93588(64)# , 150(30) ms , β⁻ , ¹¹⁴Ru , 2+# , , - , ¹¹⁵Tc , style="text-align:right" , 43 , style="text-align:right" , 72 , 114.93869(75)# , 100# ms 300 ns, β⁻ , ¹¹⁵Ru , 3/2−# , , - , ¹¹⁶Tc , style="text-align:right" , 43 , style="text-align:right" , 73 , 115.94337(75)# , 90# ms 300 ns, , , 2+# , , - , ¹¹⁷Tc , style="text-align:right" , 43 , style="text-align:right" , 74 , 116.94648(75)# , 40# ms 300 ns, , , 3/2−# , , - , ¹¹⁸Tc , style="text-align:right" , 43 , style="text-align:right" , 75 , 117.95148(97)# , 30# ms 300 ns, , , 2+# ,

Stability of technetium isotopes

Technetium and

are unusual light elements in that they have no stable isotopes. Using 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 approxim ...

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

nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state. The word ''nuclide'' was coined by Truman ...

s 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 The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...

, or capturing an electron). For a fixed number of nucleons ''A'', the binding energies lie on one or more

parabola In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One descript ...

s, 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: ²H, ⁶Li, ¹⁰B, and ¹⁴N). However, if this happens, there can be no stable isotope with an even number of neutrons and an even number of protons. (see

Beta-decay stable isobars Beta-decay stable isobars are the set of nuclides which cannot undergo beta decay, that is, the transformation of a neutron to a proton or a proton to a neutron within the nucleus. A subset of these nuclides are also stable with regards to dou ...

) For technetium (''Z'' = 43), the valley of beta stability is centered at around 98 nucleons. However, for every number of nucleons from 94 to 102, there is already at least one stable nuclide of either

(''Z'' = 42) or

ruthenium Ruthenium is a chemical element with the Symbol (chemistry), symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to ...

(''Z'' = 44), and the Mattauch isobar rule states that two adjacent isobars cannot both be stable. 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.''Radiochemistry and Nuclear Chemistry''

References

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