Cluster decay
Encyclopedia
Cluster decay is a type of nuclear decay in which a parent atomic nucleus with A nucleons and Z protons emits a cluster of Ne neutron
s and Ze proton
s heavier than an alpha particle
but lighter than a typical binary fission fragment
(although ternary fission
into three fragments produces products which overlap cluster decay). A chemical transformation of the parent nucleus leads to a different element, the daughter, with a mass number Ad = A - Ae and atomic number Zd = Z - Ze where Ae = Ne + Ze.
For example:
This type of rare decay mode was observed in radioisotopes that decay predominantly by alpha emission, and it occurs only in a small percentage of the decays for all such isotopes.
The branching ratio with respect to alpha decay
is rather small (see the Table below). Ta and Tc are the half-lives of the parent nucleus relative to alpha decay and cluster radioactivity, respectively.
Cluster decay, like alpha decay, is fundamentally a quantum tunneling process: in order to be emitted the cluster must penetrate a potential barrier. This is a different process than that which precedes light fragment emission in ternary fission
, which results from previous nuclear deformation and energy input, as a result of a nuclear reaction
(most often from a neutron
). By contrast, cluster emission is a type of spontaneous radioactive decay
.
Theoretically any nucleus with Z > 40 for which the released energy (Q value) is a positive quantity, can be a cluster-emitter. In practice, observations are severely restricted to limitations imposed by currently available experimental techniques which require a sufficiently short half-life, Tc < 1032 s, and a sufficiently large branching ratio B > 10 −17.
In the absence of any energy loss for fragment deformation and excitation, as in cold fission phenomena or in alpha decay, the total kinetic energy is equal to the Q-value and is divided between the particles in inverse proportion with their masses, as required by conservation of linear momentum
where Ad is the mass number of the daughter, Ad = A – Ae.
Cluster decay exists in an intermediate position between alpha decay (in which a nucleus spits out a He4 nucleus), and spontaneous fission
, in which a heavy nucleus splits into two (or more) large fragments and an assorted number of neutrons. Spontaneous fission ends up with a probabilistic distribution of daughter products, which sets it apart from cluster decay. In cluster decay for a given radioisotope, the emitted particle is a light nucleus and the decay method always emits this same particle. Nevertheless, for heavier emitted clusters there is practically no qualitative difference between cluster decay and spontaneous cold fission.
, beta
and gamma
) were known. They illustrate three of the fundamental interactions in nature: strong; weak, and electromagnetic. Spontaneous fission
became popular soon after its discovery in 1940 by K. Petrzhak and G. Flerov owing to both military and peaceful applications of neutron-induced fission discovered in 1939 by Otto Hahn
, Lise Meitner
and Fritz Strassmann
, employing the large amount of energy released during the process.
There are many other kinds of radioactivity, e.g. cluster decay, proton decay
, various beta-delayed decay modes (p, 2p, 3p, n, 2n, 3n, 4n, d, t, alpha, f), fission isomers, particle accompanied (ternary) fission, etc. The height of the potential barrier, mainly of Coulomb nature, for emission of the charged particles is much higher than the observed kinetic energy of the emitted particles. The spontaneous decay can only be explained by quantum tunneling in a similar way to the first application of the Quantum Mechanics to Nuclei given by G. Gamow for alpha decay.
“In 1980 A. Sandulescu, D.N. Poenaru, and W. Greiner described calculations indicating the possibility of a new type of decay of heavy nuclei intermediate between alpha decay and spontaneous fission. The first observation of heavy-ion radioactivity was that of a 30-MeV, carbon-14 emission from radium-223 by H.J. Rose and G.A. Jones in 1984“.
Usually the theory explains an already experimentally observed phenomenon. Cluster decay is one of the rare examples of phenomena predicted before experimental discovery. Theoretical predictions were made in 1980,
four years before experimental discovery.
Four theoretical approaches were used: fragmentation theory by solving a Schroedinger equation with mass assymetry as a variable to obtain the mass distributions of fragments; penetrability calculations similar to those used in traditional theory of alpha decay, and superasymmetric fission models, numerical (NuSAF) and analytical (ASAF). Superasymmetric fission models are based on the
macroscopic-microscopic approach
using the asymmetrical two-center shell model
level energies as input data for the shell and pairing corrections. Either the liquid drop model
or the Yukawa-plus-exponential model
extended to different charge-to-mass ratios
have been used to calculate the macroscopic deformation energy.
Penetrability theory predicted eight decay modes: 14C, 24Ne, 28Mg, 32,34Si, 46Ar and 48,50Ca from the following parent nuclei: 222,224Ra, 230,232Th, 236,238U, 244,246Pu, 248,250Cm, 250,252Cf, 252,254Fm and 252,254No.
The first experimental report was published in 1984, when physicists at Oxford University discovered that Ra223 emits one C14 nucleus out of every billion (109) alpha decays.
theory.
Both fission-like and alpha-like approaches are able to express the decay constant
= ln 2 / Tc, as a product of three model-dependent quantities
where
is the frequency of assaults on the barrier per second, S is the preformation probability of the cluster at the nuclear surface, and Ps is the penetrability of the external barrier. In alpha-like theories S is an overlap integral of the wave function of the three partners (parent, daughter and emitted cluster). In a fission theory the preformation probability is the penetrability of the internal part of the barrier from the initial turning point Ri to the touching point Rt.
Very frequently it is calculated by using the Wentzel-Kramers-Brillouin (WKB) approximation.
A very large number, of the order 105, of parent-emitted cluster combinations were considered in a systematic search for new decay modes. The large amount of computations could be performed in a reasonable time by using the ASAF model. The model was the first to be used to predict measurable quantities in cluster decay. More than 150 cluster decay modes have been predicted before any other kind of half-lives calculations have been reported. Comprehensive tables of half-lives, branching ratio
s, and kinetic energies have been published, e.g.
.
Potential barrier shapes similar to that considered within the ASAF model have been calculated by using the macroscopic-microscopic method.
Previously
it was shown that even alpha decay may be considered a particular case of cold fission
. The ASAF model may be used to describe in a unified manner cold alpha decay, cluster decay and cold fission (see figure 6.7, p. 287 of the Ref. [2]).
One can obtain with good approximation one universal curve (UNIV) for any kind of cluster decay mode with a mass number Ae, including alpha decay
In a logarithmic scale the equation log T = f(log Ps) represents a single straight line which can be conveniently used to estimate the half-life. A single universal curve for alpha decay and cluster decay modes results by expressing log T + log S = f(log Ps).
The experimental data on cluster decay in three groups of even-even, even-odd, and odd-even parent nuclei are reproduced with comparable accuracy by both types of universal curves, fission-like UNIV and UDL
derived using alpha-like R-matrix theory.
In order to find the released energy
one can use the compilation of measured masses
M, Md, and Me of the parent, daughter and emitted nuclei, c is the light velocity. The mass excess is transformed into energy according to the Einstein's formula E = mc2.
Detection of radiations is based on their interactions with matter, leading mainly to ionizations. Using a semiconductor telescope and conventional electronics to identify the 14C ions, the Rose and Jones's experiment was running for about six months in order to get 11 useful events.
With modern magnetic spectrometers (SOLENO and Enge-split pole), at Orsay and Argonne National Laboratory (see ch. 7 in Ref. [2] pp. 188–204), a very strong source could be used, so that results were obtained in a run of few hours.
Solid state nuclear track detector
s (SSNTD) insensitive to alpha particles and magnetic spectrometers in which alpha particles are deflected by a strong magnetic field have been used to overcome this difficulty. SSNTD are cheap and handy but they need chemical etching and microscope scanning.
A key role in experiments on cluster decay modes performed in Berkeley, Orsay, Dubna and Milano played P. Buford Price, Eid Hourany, Michel Hussonnois, Svetlana Tretyakova, A. A. Ogloblin, Roberto Bonetti and their coworkers.
The main region of 20 emitters experimentally observed until 2010 is above Z=86: 221Fr, 221-224,226Ra, 223,225Ac, 228,230Th, 231Pa, 230,232-236U, 236,238Pu, and 242Cm. Only upper limits could be detected in the following cases: 12C decay of 114Ba, 15N decay of 223Ac, 18O decay of 226Th, 24,26Ne decays of 232Th and of 236U, 28Mg decays of 232,233,235U, 30Mg decay of 237Np, and 34Si decay of 240Pu and of 241Am.
Some of the cluster emitters are members of the three natural radioactive families. Others should be produced by nuclear reactions. Up to now no odd-odd emitter has been observed.
From many decay modes with half-lives and branching ratios relative to alpha decay predicted with the analytical superasymmetric fission (ASAF) model, the following 11 have been experimentally confirmed: 14C, 20O, 23F, 22,24-26Ne, 28,30Mg, 32,34Si. The experimental data are in good agreement with predicted values. A strong shell effect can be seen: as a rule the shortest value of the half-life is obtained when the daughter nucleus has a magic number of neutrons (Nd = 126) and/or protons (Zd = 82).
The known cluster emissions as of 2010 are as follows:
first time by M. Greiner and W. Scheid in 1986.
The superconducting spectrometer SOLENO of IPN Orsay has been used since 1984 to identify 14C clusters emitted from 222-224,226Ra nuclei. Moreover it was used to discover
the fine structure observing transitions to excited states of the daughter. A transition with an excited state of 14C predicted in Ref. [24] was not yet observed.
Surprisingly, the experimentalists had seen a transition to the first excited state of the daughter stronger than that to the ground state. The transition is favoured if the uncoupled nucleon is left in the same state in both parent and daughter nuclei. Otherwise the difference in nuclear structure leads to a large hindrance.
The interpretation
was confirmed: the main spherical component of the deformed parent wave function has an i11/2 character, i.e. the main component is spherical.
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...
s and Ze proton
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....
s heavier than an alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
but lighter than a typical binary fission fragment
Fragment
Fragment may refer to:* A small part/portion broken off something; debris* Fragment , all the data necessary to generate a pixel in the frame buffer* Sentence fragment, a sentence not containing a subject or a predicate...
(although ternary fission
Ternary fission
Ternary fission is a comparatively rare type of nuclear fission in which three charged products are produced rather than two...
into three fragments produces products which overlap cluster decay). A chemical transformation of the parent nucleus leads to a different element, the daughter, with a mass number Ad = A - Ae and atomic number Zd = Z - Ze where Ae = Ne + Ze.
For example:
- 223Ra88 → 14C6 + 209Pb82
This type of rare decay mode was observed in radioisotopes that decay predominantly by alpha emission, and it occurs only in a small percentage of the decays for all such isotopes.
The branching ratio with respect to alpha decay
is rather small (see the Table below). Ta and Tc are the half-lives of the parent nucleus relative to alpha decay and cluster radioactivity, respectively.
Cluster decay, like alpha decay, is fundamentally a quantum tunneling process: in order to be emitted the cluster must penetrate a potential barrier. This is a different process than that which precedes light fragment emission in ternary fission
Ternary fission
Ternary fission is a comparatively rare type of nuclear fission in which three charged products are produced rather than two...
, which results from previous nuclear deformation and energy input, as a result of a nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
(most often from a neutron
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...
). By contrast, cluster emission is a type of spontaneous radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
.
Theoretically any nucleus with Z > 40 for which the released energy (Q value) is a positive quantity, can be a cluster-emitter. In practice, observations are severely restricted to limitations imposed by currently available experimental techniques which require a sufficiently short half-life, Tc < 1032 s, and a sufficiently large branching ratio B > 10 −17.
In the absence of any energy loss for fragment deformation and excitation, as in cold fission phenomena or in alpha decay, the total kinetic energy is equal to the Q-value and is divided between the particles in inverse proportion with their masses, as required by conservation of linear momentum
where Ad is the mass number of the daughter, Ad = A – Ae.
Cluster decay exists in an intermediate position between alpha decay (in which a nucleus spits out a He4 nucleus), and 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...
, in which a heavy nucleus splits into two (or more) large fragments and an assorted number of neutrons. Spontaneous fission ends up with a probabilistic distribution of daughter products, which sets it apart from cluster decay. In cluster decay for a given radioisotope, the emitted particle is a light nucleus and the decay method always emits this same particle. Nevertheless, for heavier emitted clusters there is practically no qualitative difference between cluster decay and spontaneous cold fission.
History
The first information about the atomic nucleus was obtained at the beginning of the 20th century by studying radioactivity. For a long period of time only three kinds of nuclear decay modes (alphaAlpha 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...
, beta
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...
and gamma
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
) were known. They illustrate three of the fundamental interactions in nature: strong; weak, and electromagnetic. 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...
became popular soon after its discovery in 1940 by K. Petrzhak and G. Flerov owing to both military and peaceful applications of neutron-induced fission discovered in 1939 by Otto Hahn
Otto Hahn
Otto Hahn FRS was a German chemist and Nobel laureate, a pioneer in the fields of radioactivity and radiochemistry. He is regarded as "the father of nuclear chemistry". Hahn was a courageous opposer of Jewish persecution by the Nazis and after World War II he became a passionate campaigner...
, Lise Meitner
Lise Meitner
Lise Meitner FRS was an Austrian-born, later Swedish, physicist who worked on radioactivity and nuclear physics. Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded the Nobel Prize...
and Fritz Strassmann
Fritz Strassmann
Friedrich Wilhelm "Fritz" Strassmann was a German chemist who, with Otto Hahn in 1938, identified barium in the residue after bombarding uranium with neutrons, which led to the interpretation of their results as being from nuclear fission...
, employing the large amount of energy released during the process.
There are many other kinds of radioactivity, e.g. cluster decay, proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
, various beta-delayed decay modes (p, 2p, 3p, n, 2n, 3n, 4n, d, t, alpha, f), fission isomers, particle accompanied (ternary) fission, etc. The height of the potential barrier, mainly of Coulomb nature, for emission of the charged particles is much higher than the observed kinetic energy of the emitted particles. The spontaneous decay can only be explained by quantum tunneling in a similar way to the first application of the Quantum Mechanics to Nuclei given by G. Gamow for alpha decay.
“In 1980 A. Sandulescu, D.N. Poenaru, and W. Greiner described calculations indicating the possibility of a new type of decay of heavy nuclei intermediate between alpha decay and spontaneous fission. The first observation of heavy-ion radioactivity was that of a 30-MeV, carbon-14 emission from radium-223 by H.J. Rose and G.A. Jones in 1984“.
Usually the theory explains an already experimentally observed phenomenon. Cluster decay is one of the rare examples of phenomena predicted before experimental discovery. Theoretical predictions were made in 1980,
four years before experimental discovery.
Four theoretical approaches were used: fragmentation theory by solving a Schroedinger equation with mass assymetry as a variable to obtain the mass distributions of fragments; penetrability calculations similar to those used in traditional theory of alpha decay, and superasymmetric fission models, numerical (NuSAF) and analytical (ASAF). Superasymmetric fission models are based on the
macroscopic-microscopic approach
using the asymmetrical two-center shell model
level energies as input data for the shell and pairing corrections. Either the liquid drop model
or the Yukawa-plus-exponential model
extended to different charge-to-mass ratios
have been used to calculate the macroscopic deformation energy.
Penetrability theory predicted eight decay modes: 14C, 24Ne, 28Mg, 32,34Si, 46Ar and 48,50Ca from the following parent nuclei: 222,224Ra, 230,232Th, 236,238U, 244,246Pu, 248,250Cm, 250,252Cf, 252,254Fm and 252,254No.
The first experimental report was published in 1984, when physicists at Oxford University discovered that Ra223 emits one C14 nucleus out of every billion (109) alpha decays.
Theory
The quantum tunneling may be calculated either by extending fission theory to a larger mass asymmetry or by heavier emitted particle from alpha decayAlpha 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...
theory.
Both fission-like and alpha-like approaches are able to express the decay constant
= ln 2 / Tc, as a product of three model-dependent quantities
where
is the frequency of assaults on the barrier per second, S is the preformation probability of the cluster at the nuclear surface, and Ps is the penetrability of the external barrier. In alpha-like theories S is an overlap integral of the wave function of the three partners (parent, daughter and emitted cluster). In a fission theory the preformation probability is the penetrability of the internal part of the barrier from the initial turning point Ri to the touching point Rt.Very frequently it is calculated by using the Wentzel-Kramers-Brillouin (WKB) approximation.
A very large number, of the order 105, of parent-emitted cluster combinations were considered in a systematic search for new decay modes. The large amount of computations could be performed in a reasonable time by using the ASAF model. The model was the first to be used to predict measurable quantities in cluster decay. More than 150 cluster decay modes have been predicted before any other kind of half-lives calculations have been reported. Comprehensive tables of half-lives, branching ratio
Branching ratio
In particle physics and nuclear physics, the branching fraction for a decay is the fraction of particles which decay by an individual decay mode with respect to the total number of particles which decay. It is equal to the ratio of the partial decay constant to the overall decay constant...
s, and kinetic energies have been published, e.g.
.
Potential barrier shapes similar to that considered within the ASAF model have been calculated by using the macroscopic-microscopic method.
Previously
it was shown that even alpha decay may be considered a particular case of cold fission
Cold fission
Cold fission or cold nuclear fission is defined as involving fission events for which fission fragments have such low excitation energy that no neutrons or gammas are emitted....
. The ASAF model may be used to describe in a unified manner cold alpha decay, cluster decay and cold fission (see figure 6.7, p. 287 of the Ref. [2]).
One can obtain with good approximation one universal curve (UNIV) for any kind of cluster decay mode with a mass number Ae, including alpha decay
In a logarithmic scale the equation log T = f(log Ps) represents a single straight line which can be conveniently used to estimate the half-life. A single universal curve for alpha decay and cluster decay modes results by expressing log T + log S = f(log Ps).
The experimental data on cluster decay in three groups of even-even, even-odd, and odd-even parent nuclei are reproduced with comparable accuracy by both types of universal curves, fission-like UNIV and UDL
derived using alpha-like R-matrix theory.
In order to find the released energy
one can use the compilation of measured masses
M, Md, and Me of the parent, daughter and emitted nuclei, c is the light velocity. The mass excess is transformed into energy according to the Einstein's formula E = mc2.
Experiments
The main experimental difficulty in observing cluster decay comes from the need to identify a few rare events among an enormous number of background alpha particle. The quantities experimentally determined are the partial halflife, Tc, and the kinetic energy of the emitted cluster Ek. There is also a need to identify the emitted particle.Detection of radiations is based on their interactions with matter, leading mainly to ionizations. Using a semiconductor telescope and conventional electronics to identify the 14C ions, the Rose and Jones's experiment was running for about six months in order to get 11 useful events.
With modern magnetic spectrometers (SOLENO and Enge-split pole), at Orsay and Argonne National Laboratory (see ch. 7 in Ref. [2] pp. 188–204), a very strong source could be used, so that results were obtained in a run of few hours.
Solid state nuclear track detector
Solid state nuclear track detector
A solid-state nuclear track detector or SSNTD is a section of a solid material uncovered to nuclear radiation , etched, and inspected microscopically...
s (SSNTD) insensitive to alpha particles and magnetic spectrometers in which alpha particles are deflected by a strong magnetic field have been used to overcome this difficulty. SSNTD are cheap and handy but they need chemical etching and microscope scanning.
A key role in experiments on cluster decay modes performed in Berkeley, Orsay, Dubna and Milano played P. Buford Price, Eid Hourany, Michel Hussonnois, Svetlana Tretyakova, A. A. Ogloblin, Roberto Bonetti and their coworkers.
The main region of 20 emitters experimentally observed until 2010 is above Z=86: 221Fr, 221-224,226Ra, 223,225Ac, 228,230Th, 231Pa, 230,232-236U, 236,238Pu, and 242Cm. Only upper limits could be detected in the following cases: 12C decay of 114Ba, 15N decay of 223Ac, 18O decay of 226Th, 24,26Ne decays of 232Th and of 236U, 28Mg decays of 232,233,235U, 30Mg decay of 237Np, and 34Si decay of 240Pu and of 241Am.
Some of the cluster emitters are members of the three natural radioactive families. Others should be produced by nuclear reactions. Up to now no odd-odd emitter has been observed.
From many decay modes with half-lives and branching ratios relative to alpha decay predicted with the analytical superasymmetric fission (ASAF) model, the following 11 have been experimentally confirmed: 14C, 20O, 23F, 22,24-26Ne, 28,30Mg, 32,34Si. The experimental data are in good agreement with predicted values. A strong shell effect can be seen: as a rule the shortest value of the half-life is obtained when the daughter nucleus has a magic number of neutrons (Nd = 126) and/or protons (Zd = 82).
The known cluster emissions as of 2010 are as follows:
| Isotope | Emitted particle | Branching ratio Branching ratio In particle physics and nuclear physics, the branching fraction for a decay is the fraction of particles which decay by an individual decay mode with respect to the total number of particles which decay. It is equal to the ratio of the partial decay constant to the overall decay constant... |
log T(s) | Q (MeV) |
|---|---|---|---|---|
| Ba114 | C12 Carbon-12 Carbon-12 is the more abundant of the two stable isotopes of the element carbon, accounting for 98.89% of carbon; it contains 6 protons, 6 neutrons, and 6 electrons.... |
< | > 4.10 | 18.985 |
| Fr221 | C14 Carbon-14 Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological... |
14.52 | 31.290 | |
| Ra221 | C14 | 13.39 | 32.394 | |
| Ra222 | C14 | 11.01 | 33.049 | |
| Ra223 | C14 | 15.04 | 31.829 | |
| Ra224 | C14 | 15.86 | 30.535 | |
| Ac223 | C14 | 12.96 | 33.064 | |
| Ac225 | C14 | 17.28 | 30.476 | |
| Ra226 | C14 | 21.19 | 28.196 | |
| Th228 | O20 | 20.72 | 44.723 | |
| Th230 | Ne24 | 24.61 | 57.758 | |
| Pa231 | F23 | 26.02 | 51.844 | |
| Ne24 | 22.88 | 60.408 | ||
| U232 | Ne24 | 20.40 | 62.309 | |
| Mg28 | < | > 22.26 | 74.318 | |
| U233 Uranium-233 Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years.... |
Ne24 | 24.84 | 60.484 | |
| Ne25 | 60.776 | |||
| Mg28 | < | > 27.59 | 74.224 | |
| U234 | Mg28 | 25.14 | 74.108 | |
| Ne24 | 25.88 | 58.825 | ||
| Ne26 | 59.465 | |||
| U235 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... |
Ne24 | 27.42 | 57.361 | |
| Ne25 | 57.756 | |||
| Mg28 | < | > 28.09 | 72.162 | |
| Mg29 | 72.535 | |||
| U236 Uranium-236 - See also :* Depleted uranium* Uranium market* Nuclear reprocessing* United States Enrichment Corporation* Nuclear fuel cycle* Nuclear power-External links:* *... |
Ne24 | < | > 25.90 | 55.944 |
| Ne26 | 56.753 | |||
| Mg28 | 27.58 | 70.560 | ||
| Mg30 | 72.299 | |||
| Pu236 | Mg28 | 21.52 | 79.668 | |
| Np237 | Mg30 | < | > 27.57 | 74.814 |
| Pu238 Plutonium-238 -External links:**... |
Si32 | 25.27 | 91.188 | |
| Mg28 | 25.70 | 75.910 | ||
| Mg30 | 76.822 | |||
| Pu240 Plutonium-240 Plutonium-240 is an isotope of the metal plutonium formed when plutonium-239 captures a neutron. About 62% to 73% of the time when Pu-239 captures a neutron it undergoes fission; the rest of the time it forms Pu-240. The longer a nuclear fuel element remains in a nuclear reactor the greater the... |
Si34 | < | > 25.52 | 91.026 |
| Am241 | Si34 | < | > 25.26 | 93.923 |
| Cm242 | Si34 | 23.15 | 96.508 |
Fine structure
The fine structure in 14-C radioactivity of 223-Ra was discussed for thefirst time by M. Greiner and W. Scheid in 1986.
The superconducting spectrometer SOLENO of IPN Orsay has been used since 1984 to identify 14C clusters emitted from 222-224,226Ra nuclei. Moreover it was used to discover
the fine structure observing transitions to excited states of the daughter. A transition with an excited state of 14C predicted in Ref. [24] was not yet observed.
Surprisingly, the experimentalists had seen a transition to the first excited state of the daughter stronger than that to the ground state. The transition is favoured if the uncoupled nucleon is left in the same state in both parent and daughter nuclei. Otherwise the difference in nuclear structure leads to a large hindrance.
The interpretation
was confirmed: the main spherical component of the deformed parent wave function has an i11/2 character, i.e. the main component is spherical.