HOME

TheInfoList



OR:

A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed
electron The electron ( or ) is a subatomic particle with a negative one elementary charge, elementary electric charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are generally thought t ...

electron
or
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 ''elementary charge, e'', a spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest ...

positron
emitted by the
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive Decay chain, disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nucl ...

radioactive decay
of an
atomic nucleus The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden experiments, Geiger–Marsden gold foil experiment. After th ...
during the process of
beta decay
beta decay
. There are two forms of beta decay, β decay and β+ decay, which produce electrons and positrons respectively. Beta particles with an energy of 0.5 MeV have a range of about one metre in air; the distance is dependent on the particle energy. Beta particles are a type of
ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionization, ionize atoms or molecules by detaching electrons from them. Some particles ...
and for radiation protection purposes are regarded as being more ionising than
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...
s, but less ionising than
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than tha ...

alpha particle
s. The higher the ionising effect, the greater the damage to living tissue, but also the lower the penetrating power of the radiation.


Beta decay modes


β decay (electron emission)

An unstable atomic nucleus with an excess of
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...

neutron
s may undergo β decay, where a neutron is converted into a
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

proton
, an electron, and an electron antineutrino (the antiparticle of the
neutrino A neutrino ( ; denoted by the Greek letter Nu (letter), ) is a fermion (an elementary particle with spin-1/2, spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electric charge, electricall ...

neutrino
): : → + + This process is mediated by the
weak interaction In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, ...
. The neutron turns into a proton through the emission of a virtual W boson. At the
quark
quark
level, W emission turns a down quark into an up quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark). The virtual W boson then decays into an electron and an antineutrino. β− decay commonly occurs among the neutron-rich fission byproducts produced in
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

nuclear reactor
s. Free neutrons also decay via this process. Both of these processes contribute to the copious quantities of beta rays and electron antineutrinos produced by fission-reactor fuel rods.


β+ decay (positron emission)

Unstable atomic nuclei with an excess of protons may undergo β+ decay, also called positron decay, where a proton is converted into a neutron, a
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 ''elementary charge, e'', a spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest ...

positron
, and an electron neutrino: : → + + Beta-plus decay can only happen inside nuclei when the absolute value of the
binding energy
binding energy
of the daughter nucleus is greater than that of the parent nucleus, i.e., the daughter nucleus is a lower-energy state.


Beta decay schemes

The accompanying decay scheme diagram shows the beta decay of
caesium-137
caesium-137
. 137Cs is noted for a characteristic gamma peak at 661 KeV, but this is actually emitted by the daughter radionuclide 137mBa. The diagram shows the type and energy of the emitted radiation, its relative abundance, and the daughter nuclides after decay. Phosphorus-32 is a beta emitter widely used in medicine and has a short half-life of 14.29 days and decays into sulfur-32 by
beta decay
beta decay
as shown in this nuclear equation: : 1.709  MeV of energy is released during the decay. The kinetic energy of the
electron The electron ( or ) is a subatomic particle with a negative one elementary charge, elementary electric charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are generally thought t ...

electron
varies with an average of approximately 0.5 MeV and the remainder of the energy is carried by the nearly undetectable electron antineutrino. In comparison to other beta radiation-emitting nuclides, the electron is moderately energetic. It is blocked by around 1 m of air or 5 mm of acrylic glass.


Interaction with other matter

Of the three common types of radiation given off by radioactive materials,
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ', or ell, άλφα, álfa) is the first Letter (alphabet), letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician alphabet, P ...

alpha
, beta and gamma, beta has the medium penetrating power and the medium ionising power. Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substan ...

aluminium
. However, this does not mean that beta-emitting isotopes can be completely shielded by such thin shields: as they decelerate in matter, beta electrons emit secondary gamma rays, which are more penetrating than betas per se. Shielding composed of materials with lower atomic weight generates gammas with lower energy, making such shields somewhat more effective per unit mass than ones made of high-Z materials such as lead. Being composed of charged particles, beta radiation is more strongly ionizing than gamma radiation. When passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off
x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...

x-ray
s. In water, beta radiation from many
nuclear fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large atomic nucleus, nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutro ...
s typically exceeds the speed of light in that material (which is 75% that of light in vacuum), and thus generates blue Cherenkov radiation when it passes through water. The intense beta radiation from the fuel rods of swimming pool reactors can thus be visualized through the transparent water that covers and shields the reactor (see illustration at right).


Detection and measurement

The ionizing or excitation effects of beta particles on matter are the fundamental processes by which radiometric detection instruments detect and measure beta radiation. The ionization of gas is used in ion chambers and , and the excitation of scintillators is used in scintillation counters. The following table shows radiation quantities in SI and non-SI units: * The
gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be compose ...
(Gy), is the SI unit of absorbed dose, which is the amount of radiation energy deposited in the irradiated material. For beta radiation this is numerically equal to the equivalent dose measured by the sievert, which indicates the stochastic biological effect of low levels of radiation on human tissue. The radiation weighting conversion factor from absorbed dose to equivalent dose is 1 for beta, whereas alpha particles have a factor of 20, reflecting their greater ionising effect on tissue. * The rad is the deprecated unit for absorbed dose and the rem is the deprecated unit of equivalent dose, used mainly in the USA.


Applications

Beta particles can be used to treat health conditions such as eye and
bone cancer A bone tumor is an neoplastic, abnormal growth of tissue in bone, traditionally classified as benign, noncancerous (benign) or malignant, cancerous (malignant). Cancerous bone tumors usually originate from a cancer in another part of the body such ...
and are also used as tracers.
Strontium-90 Strontium-90 () is a radioactive Isotopes of strontium, isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes beta decay, β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 h ...

Strontium-90
is the material most commonly used to produce beta particles. Beta particles are also used in quality control to test the thickness of an item, such as
paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre e ...

paper
, coming through a system of rollers. Some of the beta radiation is absorbed while passing through the product. If the product is made too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the manufactured paper will then move the rollers to change the thickness of the final product. An illumination device called a '' betalight'' contains
tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleu ...

tritium
and a
phosphor A phosphor is a substance that exhibits the optical phenomenon, phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescence, fluorescent or phosphorescence, phosphorescent sub ...

phosphor
. As tritium , it emits beta particles; these strike the phosphor, causing the phosphor to give off
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are Massless particle, massless ...

photon
s, much like the
cathode-ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a Phosphorescence, phosphorescent screen. The images may represent electrical waveforms (osci ...
in a television. The illumination requires no external power, and will continue as long as the tritium exists (and the phosphors do not themselves chemically change); the amount of light produced will drop to half its original value in 12.32 years, the
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of tritium. Beta-plus (or
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 ''elementary charge, e'', a spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest ...

positron
) decay of a
radioactive tracer A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tr ...
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbe ...
is the source of the positrons used in
positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bl ...

positron emission tomography
(PET scan).


History

Henri Becquerel Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pier ...

Henri Becquerel
, while experimenting with
fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy ...

fluorescence
, accidentally found out that
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. ...

uranium
exposed a
photographic Photography is the visual art, art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It i ...

photographic
plate, wrapped with black paper, with some unknown
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visib ...

radiation
that could not be turned off like
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...

X-ray
s.
Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand physicist who came to be known as the father of nuclear physics. ''Encyclopædia Britannica'' considers him to be the greatest ...
continued these experiments and discovered two different kinds of radiation: *
alpha particles Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 atomic nucleus, nucleus. They are generally produced in the process of alpha decay, but may ...
that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper * beta particles which are 100 times more penetrating than alpha particles. He published his results in 1899. In 1900, Becquerel measured the
mass-to-charge ratio The mass-to-charge ratio (''m''/''Q'') is a physical quantity Ratio, relating the ''mass'' (quantity of matter) and the ''electric charge'' of a given particle, expressed in Physical unit, units of kilograms per coulomb (kg/C). It is most widely ...
() for beta particles by the method of
J. J. Thomson Sir Joseph John Thomson (18 December 1856 – 30 August 1940) was a British physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time sc ...
used to study cathode rays and identify the electron. He found that for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.


Health

Beta particles are moderately penetrating in living tissue, and can cause spontaneous
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...
in . Beta sources can be used in
radiation therapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Ra ...

radiation therapy
to kill cancer cells.


See also

* Common beta emitters *
Electron irradiation Electron-beam processing or electron irradiation Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing ra ...
*
Particle physics Particle physics or high energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standa ...
* n (neutron) rays * δ (delta) rays


References


Further reading


Radioactivity and alpha, beta, gamma and X­rays
!-- some company going out of business? -->

University of Virginia Lecture

at Idaho State University

at the Lawrence Berkeley National Laboratory {{Authority control Ionizing radiation Radioactivity