Isotopes of caesium
Encyclopedia
Caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

(Cs) has 40 known isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

s. The atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....

es of these isotopes range from 112 to 151. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 2.3 million years, 137Cs with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.

Beginning in 1945 with the commencement of nuclear testing
Nuclear testing
Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...

, caesium isotopes were released into the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 where it is absorbed readily into solution and is returned to the surface of the earth as a component of radioactive fallout. Once caesium enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport. As a result, the input function of these isotopes can be estimated as a function of time.

Standard atomic mass: 132.9054519(2) u

Caesium-133

Caesium-133 is the only naturally occurring and only stable isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of caesium. It is also produced by nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 in nuclear reactors. One specific quantum transition in the Caesium-133 atom is used to define the second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

, a unit of time.

Caesium-134

Caesium-134 has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of 2.0652 years. It is produced both directly (at a very small yield because 134Xe is stable) as a fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

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

 from nonradioactive Cs-133 (neutron capture cross section
Neutron cross-section
In nuclear and particle physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power...

 29 barns
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...

), which is a common fission product. Caesium 134 is not produced via beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...

 of other fission product nuclides of mass 134 since beta decay stops at stable 134Xe. It is also not produced by nuclear weapons because 133Cs is created by beta decay of original fission products only long after the nuclear explosion is over.

The combined yield of 133Cs and 134Cs is given as 6.7896%. The proportion between the two will change with continued neutron irradiation. 134Cs also captures neutrons with a cross section of 140 barns, becoming long-lived radioactive 135Cs.

Caesium-135

Caesium-135 is a mildly radioactive isotope of caesium, undergoing low-energy beta decay to barium-135 with a half-life of 2.3 million years. It is one of the 7 long-lived fission product
Long-lived fission product
Long-lived fission products are radioactive materials with a long half-life produced by nuclear fission.-Evolution of radioactivity in nuclear waste:...

s and the only alkaline one. In nuclear reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...

, it stays with Cs-137 and other medium-lived fission products rather than with other long-lived fission products. The low decay energy
Decay energy
The decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation...

, lack of gamma radiation, and long half-life of 135Cs make this isotope much less hazardous than 137Cs
Caesium-137
Caesium-137 is a radioactive isotope of caesium which is formed as a fission product by nuclear fission.It has a half-life of about 30.17 years, and decays by beta emission to a metastable nuclear isomer of barium-137: barium-137m . Caesium-137 is a radioactive isotope of caesium which is formed...

 or 134Cs.

Its precursor 135Xe
Xenon-135
Xenon-135 is an unstable isotope of xenon with a half-life of about 9.2 hours. 135Xe is a fission product of uranium and Xe-135 is the most powerful known neutron-absorbing nuclear poison , with a significant effect on nuclear reactor operation...

 has a high fission product yield
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 isotope...

 (e.g. 6.3333% for 235U
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

 and thermal neutrons) but also has the highest known thermal neutron neutron capture cross section of any nuclide. Because of this, much of the 135Xe produced in current thermal reactor
Thermal reactor
A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons...

s (as much as >90% at steady-state full power) will be converted to stable 136Xe before it can decay to 135Cs. Little or no 135Xe will be destroyed by neutron capture after a reactor shutdown, or in a molten salt reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

 that continuously removes xenon from its fuel, a fast neutron reactor
Fast neutron reactor
A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons...

, or a nuclear weapon.

A nuclear reactor will also produce much smaller amounts of 135Cs from the nonradioactive fission product Cs-133 by successive neutron capture to 134Cs and then 135Cs.

The thermal neutron capture cross section and resonance integral of 135Cs are and respectively. Disposal of Cs-135 by nuclear transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...

 is difficult, because of the low cross section as well as because neutron irradiation of mixed-isotope fission caesium produces more Cs-135 from stable Cs-133. In addition, the intense medium-term radioactivity of Cs-137 makes handling of nuclear waste difficult.

Caesium-137

137Cs with a half-life of 30.17 years is one of the two principal medium-lived fission products, along with 90Sr
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...

, which are responsible for most of the radioactivity of spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...

 after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the Chernobyl accident. 137Cs beta decays to barium-137m (a short-lived nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...

) then to nonradioactive barium-137, and is also a strong emitter of gamma radiation. 137Cs has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. 137Cs has been used as a tracer
Tracer
Tracer may refer to:* Histochemical tracer, a substance used for tracing purposes in histochemistry, the study of the composition of cells and tissues...

 in hydrologic studies, analogous to the use of 3H
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

.

Other isotopes of caesium

The other isotopes have half-lives from a few days to fractions of a second.
Almost all caesium produced from nuclear fission comes from beta decay of originally more neutron-rich fission products, passing through isotopes of iodine
Isotopes of iodine
There are 37 known isotopes of iodine and only one, 127I, is stable. Iodine is thus a monoisotopic element.Its longest-lived radioactive isotope, 129I, has a half-life of 15.7 million years, which is far too short for it to exist as a primordial nuclide...

 then isotopes of xenon
Isotopes of xenon
Naturally occurring xenon is made of nine stable isotopes. Xenon has the second highest number of stable isotopes. Only tin, with 10 stable isotopes, has more...

. Because these elements are volatile and can diffuse through nuclear fuel or air, caesium is often created far from the original site of fission.

Table

nuclide
Nuclide
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state....


symbol
Z(p
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

)
N(n
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

)
 
isotopic mass (u)
 
half-life decay
mode(s)Abbreviations:
EC: Electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...


IT: Isomeric transition
Isomeric transition
An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer....

daughter
isotope(s)Bold for stable isotopes, bold italics for near-stable isotopes (half-life longer than the age of the universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...

)
nuclear
spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...

representative
isotopic
composition
(mole fraction)
range of natural
variation
(mole fraction)
excitation
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....

 energy
112Cs 55 57 111.95030(33)# 500(100) µs p
Proton emission
Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very...

111Xe 1+#
α
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...

108I
113Cs 55 58 112.94449(11) 16.7(7) µs p (99.97%) 112Xe 5/2+#
β+
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...

 (.03%)
113Xe
114Cs 55 59 113.94145(33)# 0.57(2) s β+ (91.09%) 114Xe (1+)
β+, p (8.69%) 113I
β+, α (.19%) 110Te
α (.018%) 110I
115Cs 55 60 114.93591(32)# 1.4(8) s β+ (99.93%) 115Xe 9/2+#
β+, p (.07%) 114I
116Cs 55 61 115.93337(11)# 0.70(4) s β+ (99.67%) 116Xe (1+)
β+, p (.279%) 115I
β+, α (.049%) 112Te
116mCs 100(60)# keV 3.85(13) s β+ (99.48%) 116Xe 4+,5,6
β+, p (.51%) 115I
β+, α (.008%) 112Te
117Cs 55 62 116.92867(7) 8.4(6) s β+ 117Xe (9/2+)#
117mCs 150(80)# keV 6.5(4) s β+ 117Xe 3/2+#
118Cs 55 63 117.926559(14) 14(2) s β+ (99.95%) 118Xe 2
β+, p (.042%) 117I
β+, α (.0024%) 114Te
118mCs 100(60)# keV 17(3) s β+ (99.95%) 118Xe (7-)
β+, p (.042%) 117I
β+, α (.0024%) 114Te
119Cs 55 64 118.922377(15) 43.0(2) s β+ 119Xe 9/2+
β+, α (2×10−6%) 115Te
119mCs 50(30)# keV 30.4(1) s β+ 119Xe 3/2(+)
120Cs 55 65 119.920677(11) 61.2(18) s β+ 120Xe 2(-#)
β+, α (2×10−5%) 116Te
β+, p (7×10−6%) 118I
120mCs 100(60)# keV 57(6) s β+ 120Xe (7-)
β+, α (2×10−5%) 116Te
β+, p (7×10−6%) 118I
121Cs 55 66 120.917229(15) 155(4) s β+ 121Xe 3/2(+)
121mCs 68.5(3) keV 122(3) s β+ (83%) 121Xe 9/2(+)
IT
Isomeric transition
An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer....

 (17%)
121Cs
122Cs 55 67 121.91611(3) 21.18(19) s β+ 122Xe 1+
β+, α (2×10−7%) 118Te
122m1Cs 45.8 keV >1 µs (3)+
122m2Cs 140(30) keV 3.70(11) min β+ 122Xe 8-
122m3Cs 127.0(5) keV 360(20) ms (5)-
123Cs 55 68 122.912996(13) 5.88(3) min β+ 123Xe 1/2+
123m1Cs 156.27(5) keV 1.64(12) s IT 123Cs (11/2)-
123m2Cs 231.63+X keV 114(5) ns (9/2+)
124Cs 55 69 123.912258(9) 30.9(4) s β+ 124Xe 1+
124mCs 462.55(17) keV 6.3(2) s IT 124Cs (7)+
125Cs 55 70 124.909728(8) 46.7(1) min β+ 125Xe 1/2(+)
125mCs 266.6(11) keV 900(30) ms (11/2-)
126Cs 55 71 125.909452(13) 1.64(2) min β+ 126Xe 1+
126m1Cs 273.0(7) keV >1 µs
126m2Cs 596.1(11) keV 171(14) µs
127Cs 55 72 126.907418(6) 6.25(10) h β+ 127Xe 1/2+
127mCs 452.23(21) keV 55(3) µs (11/2)-
128Cs 55 73 127.907749(6) 3.640(14) min β+ 128Xe 1+
129Cs 55 74 128.906064(5) 32.06(6) h β+ 129Xe 1/2+
130Cs 55 75 129.906709(9) 29.21(4) min β+ (98.4%) 130Xe 1+
β- (1.6%) 130Ba
130mCs 163.25(11) keV 3.46(6) min IT (99.83%) 130Cs 5-
β+ (.16%) 130Xe
131Cs 55 76 130.905464(5) 9.689(16) d EC
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...

131Xe 5/2+
132Cs 55 77 131.9064343(20) 6.480(6) d β+ (98.13%) 132Xe 2+
β- (1.87%) 132Ba
133CsUsed to define the second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

Fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

55 78 132.905451933(24) Observationally StableBelieved to be capable of spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...

7/2+ 1.0000
134Cs 55 79 133.906718475(28) 2.0652(4) a β- 134Ba 4+
EC (3×10−4%) 134Xe
134mCs 138.7441(26) keV 2.912(2) h IT 134Cs 8-
135Cs 55 80 134.9059770(11) 2.3(3)×106 a β- 135Ba 7/2+
135mCs 1632.9(15) keV 53(2) min IT 135Cs 19/2-
136Cs 55 81 135.9073116(20) 13.16(3) d β- 136Ba 5+
136mCs 518(5) keV 19(2) s β- 136Ba 8-
IT 136Cs
137Cs
Caesium-137
Caesium-137 is a radioactive isotope of caesium which is formed as a fission product by nuclear fission.It has a half-life of about 30.17 years, and decays by beta emission to a metastable nuclear isomer of barium-137: barium-137m . Caesium-137 is a radioactive isotope of caesium which is formed...

55 82 136.9070895(5) 30.1671(13) a β- (95%) 137mBa 7/2+
β- (5%) 137Ba
138Cs 55 83 137.911017(10) 33.41(18) min β- 138Ba 3-
138mCs 79.9(3) keV 2.91(8) min IT (81%) 138Cs 6-
β- (19%) 138Ba
139Cs 55 84 138.913364(3) 9.27(5) min β- 139Ba 7/2+
140Cs 55 85 139.917282(9) 63.7(3) s β- 140Ba 1-
141Cs 55 86 140.920046(11) 24.84(16) s β- (99.96%) 141Ba 7/2+
β-, n
Neutron emission
Neutron emission is a type of radioactive decay of atoms containing excess neutrons, in which a neutron is simply ejected from the nucleus. Two examples of isotopes which emit neutrons are helium-5 and beryllium-13...

(.0349%)
140Ba
142Cs 55 87 141.924299(11) 1.689(11) s β- (99.9%) 142Ba 0-
β-, n (.091%) 141Ba
143Cs 55 88 142.927352(25) 1.791(7) s β- (98.38%) 143Ba 3/2+
β-, n (1.62%) 142Ba
144Cs 55 89 143.932077(28) 994(4) ms β- (96.8%) 144Ba 1(-#)
β-, n (3.2%) 143Ba
144mCs 300(200)# keV <1 s β- 144Ba (>3)
IT 144Cs
145Cs 55 90 144.935526(12) 582(6) ms β- (85.7%) 145Ba 3/2+
β-, n (14.3%) 144Ba
146Cs 55 91 145.94029(8) 0.321(2) s β- (85.8%) 146Ba 1-
β-, n (14.2%) 145Ba
147Cs 55 92 146.94416(6) 0.235(3) s β- (71.5%) 147Ba (3/2+)
β-, n (28.49%) 147Ba
148Cs 55 93 147.94922(62) 146(6) ms β- (74.9%) 148Ba
β-, n (25.1%) 147Ba
149Cs 55 94 148.95293(21)# 150# ms [>50 ms] β- 149Ba 3/2+#
β-, n 148Ba
150Cs 55 95 149.95817(32)# 100# ms [>50 ms] β- 150Ba
β-, n 149Ba
151Cs 55 96 150.96219(54)# 60# ms [>50 ms] β- 151Ba 3/2+#
β-, n 150Ba

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK