In
nuclear physicsNuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
,
beta decay is a type of
radioactive decayRadioactive 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...
in which a
beta particleBeta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
(an
electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
or a
positronThe positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
) 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
positron emissionPositron emission or beta plus decay is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino....
as beta plus . In electron emission, an electron antineutrino is also emitted, while positron emission is accompanied by an
electron neutrinoThe electron neutrino is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino...
. Beta decay is mediated by the
weak forceWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
.
Emitted beta particles have a continuous
kinetic energyThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
spectrum, ranging from 0 to the maximal available energy (
Q), which depends on the parent and daughter nuclear states that participate in the decay. A typical
Q is around 1 MeV, but it can range from a few keV to a few tens of MeV. Since the
rest mass energyIn physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
of the electron is 511 keV, the most energetic beta particles are
ultrarelativisticIn physics, a particle is called ultrarelativistic when its speed is very close to the speed of light c.Max Planck showed that the relativistic expression for the energy of a particle whose rest mass is m and momentum is p is given by E^2 = m^2 c^4 + p^2 c^2...
, with speeds very close to the
speed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
Sometimes
electron captureElectron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
decay is included as a type of beta decay (and is referred to as "inverse beta decay"), because the basic process, mediated by the weak force is the same. However, no beta particle is emitted, but only an electron neutrino. Instead of beta-plus emission, an inner atomic electron is captured by a proton in the nucleus. This type of decay is therefore analogous to positron emission (and also happens, as an alternative decay route, in all positron-emitters). However, the route of electron capture is the
only type of decay that is allowed in proton-rich nuclides that
do not have sufficient energy to emit a positron (and neutrino). These may still reach a lower energy state, by the equivalent process of electron-capture and neutrino-emission.
decay
In decay, the weak interaction converts a neutron into a proton while emitting an electron and an electron antineutrino :
At the fundamental level (as depicted in the
Feynman diagramFeynman diagrams are a pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, first developed by the Nobel Prize-winning American physicist Richard Feynman, and first introduced in 1948...
below), this is caused by the conversion of the negatively charged
down quarkThe down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the up quark, forms the neutrons and protons of atomic nuclei...
to the positively charged
up quarkThe up quark or u quark is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons and protons of atomic nuclei...
by emission of a
{{Nuclear physics}}
In
nuclear physicsNuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
,
beta decay is a type of
radioactive decayRadioactive 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...
in which a
beta particleBeta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
(an
electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
or a
positronThe positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
) 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 ({{SubatomicParticle|Beta-}}), while in the case of a
positron emissionPositron emission or beta plus decay is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino....
as beta plus ({{SubatomicParticle|Beta+}}). In electron emission, an electron antineutrino is also emitted, while positron emission is accompanied by an
electron neutrinoThe electron neutrino is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino...
. Beta decay is mediated by the
weak forceWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
.
Emitted beta particles have a continuous
kinetic energyThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
spectrum, ranging from 0 to the maximal available energy (
Q), which depends on the parent and daughter nuclear states that participate in the decay. A typical
Q is around 1 MeV, but it can range from a few keV to a few tens of MeV. Since the
rest mass energyIn physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
of the electron is 511 keV, the most energetic beta particles are
ultrarelativisticIn physics, a particle is called ultrarelativistic when its speed is very close to the speed of light c.Max Planck showed that the relativistic expression for the energy of a particle whose rest mass is m and momentum is p is given by E^2 = m^2 c^4 + p^2 c^2...
, with speeds very close to the
speed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
Sometimes
electron captureElectron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
decay is included as a type of beta decay (and is referred to as "inverse beta decay"), because the basic process, mediated by the weak force is the same. However, no beta particle is emitted, but only an electron neutrino. Instead of beta-plus emission, an inner atomic electron is captured by a proton in the nucleus. This type of decay is therefore analogous to positron emission (and also happens, as an alternative decay route, in all positron-emitters). However, the route of electron capture is the
only type of decay that is allowed in proton-rich nuclides that
do not have sufficient energy to emit a positron (and neutrino). These may still reach a lower energy state, by the equivalent process of electron-capture and neutrino-emission.
{{SubatomicParticle|Beta-}} decay
In {{SubatomicParticle|Beta-}} decay, the weak interaction converts a neutron ({{SubatomicParticle|Neutron}}) into a proton ({{SubatomicParticle|Proton}}) while emitting an electron ({{SubatomicParticle|Electron|link=yes}}) and an electron antineutrino ({{SubatomicParticle|Electron antineutrino}}):
At the fundamental level (as depicted in the
Feynman diagramFeynman diagrams are a pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, first developed by the Nobel Prize-winning American physicist Richard Feynman, and first introduced in 1948...
below), this is caused by the conversion of the negatively charged
down quarkThe down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the up quark, forms the neutrons and protons of atomic nuclei...
to the positively charged
up quarkThe up quark or u quark is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons and protons of atomic nuclei...
by emission of a
{{Nuclear physics}}
In
nuclear physicsNuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
,
beta decay is a type of
radioactive decayRadioactive 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...
in which a
beta particleBeta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
(an
electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
or a
positronThe positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
) 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 ({{SubatomicParticle|Beta-}}), while in the case of a
positron emissionPositron emission or beta plus decay is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino....
as beta plus ({{SubatomicParticle|Beta+}}). In electron emission, an electron antineutrino is also emitted, while positron emission is accompanied by an
electron neutrinoThe electron neutrino is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino...
. Beta decay is mediated by the
weak forceWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
.
Emitted beta particles have a continuous
kinetic energyThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
spectrum, ranging from 0 to the maximal available energy (
Q), which depends on the parent and daughter nuclear states that participate in the decay. A typical
Q is around 1 MeV, but it can range from a few keV to a few tens of MeV. Since the
rest mass energyIn physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
of the electron is 511 keV, the most energetic beta particles are
ultrarelativisticIn physics, a particle is called ultrarelativistic when its speed is very close to the speed of light c.Max Planck showed that the relativistic expression for the energy of a particle whose rest mass is m and momentum is p is given by E^2 = m^2 c^4 + p^2 c^2...
, with speeds very close to the
speed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
Sometimes
electron captureElectron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
decay is included as a type of beta decay (and is referred to as "inverse beta decay"), because the basic process, mediated by the weak force is the same. However, no beta particle is emitted, but only an electron neutrino. Instead of beta-plus emission, an inner atomic electron is captured by a proton in the nucleus. This type of decay is therefore analogous to positron emission (and also happens, as an alternative decay route, in all positron-emitters). However, the route of electron capture is the
only type of decay that is allowed in proton-rich nuclides that
do not have sufficient energy to emit a positron (and neutrino). These may still reach a lower energy state, by the equivalent process of electron-capture and neutrino-emission.
{{SubatomicParticle|Beta-}} decay
In {{SubatomicParticle|Beta-}} decay, the weak interaction converts a neutron ({{SubatomicParticle|Neutron}}) into a proton ({{SubatomicParticle|Proton}}) while emitting an electron ({{SubatomicParticle|Electron|link=yes}}) and an electron antineutrino ({{SubatomicParticle|Electron antineutrino}}):
At the fundamental level (as depicted in the
Feynman diagramFeynman diagrams are a pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, first developed by the Nobel Prize-winning American physicist Richard Feynman, and first introduced in 1948...
below), this is caused by the conversion of the negatively charged
down quarkThe down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the up quark, forms the neutrons and protons of atomic nuclei...
to the positively charged
up quarkThe up quark or u quark is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons and protons of atomic nuclei...
by emission of a {{SubatomicParticle; the {{SubatomicParticle|W boson-}} boson subsequently decays into an electron and an electron antineutrino:
{{SubatomicParticle|Beta-}} decay generally occurs in neutron rich nuclei.
{{SubatomicParticle|Beta+}} decay
{{see also|Positron emission}}
In {{SubatomicParticle|Beta+}} decay, energy is used to convert a proton into a neutron, while emitting a positron ({{SubatomicParticle|Positron}}) and an electron neutrino ({{SubatomicParticle|Electron Neutrino}}):
So unlike {{SubatomicParticle|Beta-}}, {{SubatomicParticle|Beta+}} decay cannot occur in isolation because it requires energy, the
massMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the neutron being greater than the mass of the proton. {{SubatomicParticle|Beta+}} decay can only happen inside nuclei when the value of the
binding energyBinding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...
of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.
{{clr}}
Electron capture (K-capture)
In all the cases where {{SubatomicParticle|Beta+}} decay is allowed energetically (and the proton is a part of a nucleus with electron shells), it is accompanied by the
electron captureElectron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
process, when an atomic electron is captured by a nucleus with the emission of a neutrino:
- {| border="0"
|- style="height:2em;"
|energy ||+ ||{{SubatomicParticle|Proton}} ||+ ||{{SubatomicParticle|Electron}} ||→ ||{{SubatomicParticle|Neutron}} ||+ ||{{SubatomicParticle|Electron Neutrino}}
|}
However, in proton-rich nuclei where the energy difference between initial and final states is less than 2
mec2, then {{SubatomicParticle|Beta+}} decay is not energetically possible, and electron capture is the sole decay mode.
This decay is also called K-capture because the inner most electron of an atom belongs to the K-shell of the electronic configuration of the atom, and this has the highest probability to interact with the nucleus.
There is an analogous process possible in theory in antimatter: antiproton-rich antimatter radioisotopes might decay via an analogous process of positron capture, but in practice no such complex antimatter nuclides have either been discovered or artificially constructed.
Nuclear transmutation
If the proton and neutron are part of an
atomic nucleusThe nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, these decay processes
transmuteNuclear 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'...
one chemical element into another. For example:
- {| border="0"
|- style="height:2em;"
|{{Nuclide2|link=yes|caesium|137}} || || ||→ ||{{Nuclide2|link=yes|barium|137}} ||+ ||{{SubatomicParticle|link=yes|Electron}} ||+ ||{{SubatomicParticle|link=yes|Electron Antineutrino}} ||(beta minus decay)
|- style="height:2em;"
|{{Nuclide2|link=yes|sodium|22}} || || ||→ ||{{Nuclide2|link=yes|neon|22}} ||+ ||{{SubatomicParticle|link=yes|Positron}} ||+ ||{{SubatomicParticle|link=yes|Electron Neutrino}} ||(beta plus decay)
|- style="height:2em;"
|{{Nuclide|link=yes|sodium|22}} ||+ ||{{SubatomicParticle|link=yes|Electron}} ||→ ||{{Nuclide2|link=yes|neon|22}} ||+ ||{{SubatomicParticle|link=yes|Electron Neutrino}} || || ||(electron capture)
|}
Beta decay does not change the number of
nucleonIn physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...
s,
A, in the nucleus but changes only its
chargeElectric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
,
Z. Thus the set of all
nuclideA 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....
s with the same
A can be introduced; these
isobaric nuclidesIsobars are atoms of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number but not in mass number. An example of a series of isobars would be 40S, 40Cl, 40Ar, 40K, and 40Ca...
may turn into each other via beta decay. Among them, several nuclides (at least one) are beta stable, because they present local minima of the
mass excessThe mass excess of a nuclide is the difference between its actual mass and its mass number in atomic mass units. It is one of the predominant methods for tabulating nuclear mass. The mass of an atomic nucleus is well approximated by its mass number, which indicates that most of the mass of a...
: if such a nucleus has (
A,
Z) numbers, the neighbour nuclei (
A,
Z−1) and (
A,
Z+1) have higher mass excess and can beta decay into (
A,
Z), but not vice versa. For all odd mass numbers
A the global minimum is also the unique local minimum. For even
A, there are up to three different beta-stable isobars experimentally known; for example, {{Nuclide2|zirconium|96}}, {{Nuclide2|Molybdenum|96}}, and {{Nuclide2|Ruthenium|96}} are all beta-stable, though the first one can undergo a very rare double beta decay (see below). There are about 355 known
beta-decay stable nuclidesBeta-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...
total.
A beta-stable nucleus may undergo other kinds of radioactive decay (
alpha decayAlpha 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...
, for example). In nature, most isotopes are beta stable, but a few exceptions exist with
half-livesHalf-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...
so long that they have not had enough time to decay since the moment of their
nucleosynthesisNucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
. One example is {{Nuclide2|link=yes|Potassium|40}}, which undergoes all three types of beta decay ({{SubatomicParticle|Beta-}}, {{SubatomicParticle|Beta+}} and electron capture) with a half-life of {{val|1.277|e=9}} years.
Double beta decay
Some nuclei can undergo
double beta decayDouble beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
(ββ decay) where the charge of the nucleus changes by two units. Double beta decay is difficult to study in most practically interesting cases, because both β decay and ββ decay are possible, with probability favoring β decay; the rarer ββ decay process is masked by these events. Thus, ββ decay is usually studied only for beta stable nuclei. Like single beta decay, double beta decay does not change
A; thus, at least one of the nuclides with some given
A has to be stable with regard to both single and double beta decay.
Beta decay can be considered as a
perturbationIn quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one. The idea is to start with a simple system for which a mathematical solution is known, and add an...
as described in quantum mechanics, and thus follows
Fermi's Golden RuleIn quantum physics, Fermi's golden rule is a way to calculate the transition rate from one energy eigenstate of a quantum system into a continuum of energy eigenstates, due to a perturbation....
.
Bound-state β- decay
For fully ionized atoms (bare nuclei), it is possible for electrons to be emitted from the nucleus into low-lying atomic bound states (orbitals). This can not occur for neutral atoms whose low-lying bound states are already filled.
The phenomenon was first observed for
163Dy
66+ in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research group. Although neutral
163Dy is a stable isotope, the fully ionized
163Dy
66+ undergoes β decay into the K and L shells with a half-life of 47 days.
Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for
187Re by Bosch et al., also at Darmstadt. Neutral
187Re does undergo β decay with a half-life of 42 x 10
9 years, but for fully ionized
187Re
75+ this is shortened by a factor of 10
9 to only 32.9 years. For comparison the variation of decay rates of other nuclear processes due to chemical environment is less than 1%. (See Radioactive decay#Changing decay rates)
Kurie plot
{{Expand section|date=June 2008}}
A
Kurie plot (also known as a
Fermi-Kurie plot) is a graph used in studying beta decay developed by
Franz N. D. KurieFranz Newell Devereux Kurie was an American physicist who, while working at Yale in 1933, showed that the neutron was neither a dumb-bell-shaped combination of proton and electron, nor an onion-shaped combination of an electron embracing the proton...
, in which the square root of the number of beta particles whose momenta (or energy) lie within a certain narrow range, divided by a function worked out by Fermi, is plotted against beta-particle energy; it is a straight line for allowed transitions and some forbidden transitions, in accord with the Fermi beta-decay theory.
Linear regression of a Fermi-Kurie Plot can help determining the maximum energy imparted to the electron/positron by determining the energy-axis(x-axis) intercept. This graph helps us to know a better way of understanding of emission of beta particle.
Discovery and characterization of {{SubatomicParticle|Beta-}} decay
Radioactivity was discovered in 1896 by
Henri BecquerelAntoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...
in uranium, and subsequently observed by
MarieMarie Skłodowska-Curie was a physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry...
and
Pierre CuriePierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...
in thorium and in the new elements polonium and radium.
In 1899
Ernest RutherfordErnest Rutherford, 1st Baron Rutherford of Nelson OM, FRS was a New Zealand-born British chemist and physicist who became known as the father of nuclear physics...
separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminum, whereas beta rays could penetrate several millimetres of aluminum. (In 1900 Paul Villard identified
gamma rayGamma 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...
s as a third, still more penetrating type of radiation.)
In 1900 Becquerel measured the ratio of electric charge to mass (e/m) for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that e/m for a beta particle is the same as for Thomson’s electron, and therefore suggested that the beta particle is in fact an electron.
In 1901 Rutherford and
Frederick SoddyFrederick Soddy was an English radiochemist who explained, with Ernest Rutherford, that radioactivity is due to the transmutation of elements, now known to involve nuclear reactions. He also proved the existence of isotopes of certain radioactive elements...
showed that alpha and beta radioactivity involves the
transmutationNuclear 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'...
of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and
Kazimierz Fajans-External links:*...
independently proposed their
radioactive displacement lawThe law of radioactive displacements, also known as Fajans and Soddy law, in radiochemistry and nuclear physics, is a rule governing the transmutation of elements during radioactive decay...
, which states that beta (i.e. {{SubatomicParticle|Beta-}}) emission from one element produces another element one place to the right in the periodic table, while alpha emission produces an element two places to the left.
Neutrinos in beta decay
Historically, the study of beta decay provided the first physical evidence of the
neutrinoA neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
. In 1911
Lise MeitnerLise 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
Otto HahnOtto 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...
performed an experiment that showed that the energies of electrons emitted by beta decay had a continuous rather than discrete spectrum. This was in apparent contradiction to the law of conservation of energy, as it appeared that energy was lost in the beta decay process. A second problem was that the
spinIn 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,...
of the Nitrogen-14 atom was 1, in contradiction to the Rutherford prediction of ½.
In 1920-1927,
Charles Drummond EllisSir Charles Drummond Ellis was a physicist and scientific administrator. His work on the magnetic spectrum of the beta-rays helped to develop a better understanding of nuclear structure....
(along with
James ChadwickSir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
and colleagues) established clearly that the beta decay spectrum is really continuous, ending all controversies.
In a famous letter written in 1930
Wolfgang PauliWolfgang Ernst Pauli was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after being nominated by Albert Einstein, he received the Nobel Prize in Physics for his "decisive contribution through his discovery of a new law of Nature, the exclusion principle or...
suggested that in addition to electrons and protons atoms also contained an extremely light neutral particle which he called the neutron. He suggested that this "neutron" was also emitted during beta decay and had simply not yet been observed. In 1931
Enrico FermiEnrico Fermi was an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics...
renamed Pauli's "neutron" to neutrino, and in 1934 Fermi published a very successful
model of beta decayIn particle physics, Fermi's interaction also known as Fermi coupling, is an old explanation of the weak force, proposed by Enrico Fermi, in which four fermions directly interact with one another at one vertex...
in which neutrinos were produced.
Other types of beta decay
In 1934
FrédéricJean Frédéric Joliot-Curie , born Jean Frédéric Joliot, was a French physicist and Nobel laureate.-Early years:...
and
Irène Joliot-CurieIrène Joliot-Curie was a French scientist, the daughter of Marie Skłodowska-Curie and Pierre Curie and the wife of Frédéric Joliot-Curie. Jointly with her husband, Joliot-Curie was awarded the Nobel Prize for chemistry in 1935 for their discovery of artificial radioactivity. This made the Curies...
bombarded aluminum with alpha particles to effect the nuclear reaction
4He +
27Al →
30P + n, and observed that the product isotope
30P emits a positron identical to those found in cosmic rays by
Carl David AndersonCarl David Anderson was an American physicist. He is best known for his discovery of the positron in 1932, an achievement for which he received the 1936 Nobel Prize in Physics, and of the muon in 1936.-Biography:...
in 1932. This was the first example of {{SubatomicParticle|Beta+}} decay, which they termed artificial radioactivity since
30P is a short-lived nuclide which does not exist in nature.
The theory of electron capture was first discussed by
Gian-Carlo WickGian Carlo Wick was an Italian theoretical physicist who made important contributions to quantum field theory...
in a 1934 paper, and then developed by
Hideki Yukawané , was a Japanese theoretical physicist and the first Japanese Nobel laureate.-Biography:Yukawa was born in Tokyo and grew up in Kyoto. In 1929, after receiving his degree from Kyoto Imperial University, he stayed on as a lecturer for four years. After graduation, he was interested in...
and others. K-electron capture was first observed in 1937 by
Luis AlvarezLuis W. Alvarez was an American experimental physicist and inventor, who spent nearly all of his long professional career on the faculty of the University of California, Berkeley...
, in the nuclide
48V. Alvarez went on to study electron capture in
67Ga and other nuclides.
See also
- Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
- Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
- Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
- 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...
- Betavoltaics
Betavoltaics are generators of electrical current, in effect a form of battery, which use energy from a radioactive source emitting beta particles . A common source used is the hydrogen isotope, tritium...
- Particle radiation
Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam....
- Radioactive isotope
- Tritium illumination, a form of fluorescent lighting powered by beta decay
External links
{{Nuclear processes}}
{{DEFAULTSORT:Beta Decay}}