How can alpha particles be represented

See also: Transuranium elements. For example, carbon is a negatron beta-particle emitter, with a half-period of about years, which can be produced in the laboratory as the product of a variety of different nuclear transmutation experiments. Nuclear bombardment of 11 B nuclei by alpha particles helium nuclei can produce excited compound nuclei of 15 N which promptly emit a proton hydrogen nucleus , leaving 14 C as the end product of the transmutation.

The same end-product 14 C can be produced by bombarding 14 N with neutrons, resulting in nuclear reaction This reaction is easily carried out by using neutrons from nuclear accelerators or a nuclear reactor. This particular transmutation reaction is one which occurs in nature also, because the nitrogen in the Earth's atmosphere is continually bombarded by neutrons which are produced by cosmic rays, thus producing radioactive 14 C.

Mixing of 14 C with stable carbon provides the basis for radiocarbon dating of systems that absorb carbon for times up to about 50, years ago 10 half-lives. See also: Cosmic ray ; Nuclear reaction ; Nuclear reactor ; Particle accelerator ; Radiocarbon dating. Also, 3 H is produced in the Sun, and the Earth's water as well as satellites show an additional concentration of 3 H from the Sun.

Over two dozen radioactive products, ranging in half-life from a few days to millions of years, have been identified in meteorites that have fallen to Earth. The carbon and hydrogen burning cycles that produce energy for stars produce radioactive 13 N, 15 O, 3 H. In addition to the production of radioactive as well as stable isotopes prior to the formation of the solar system, nucleosynthesis continues to go on in stars with the production of many short-lived radioactive atoms by different processes.

See also: Carbon-nitrogen-oxygen cycles astrophysics ; Nucleosynthesis ; Proton-proton chain. The yield of any radioactivity produced in the laboratory is the initial rate of the activity under the particular conditions of nuclear bombardment. The yield Y depends on the number of atoms A present in the target, the intensity of the beam of bombarding particles, and the cross section, or probability of the reaction per bombarding particle under the conditions of bombardment.

As noted in Eqs. Accordingly, many long chains or series of radioactive transformations are known. The three naturally occurring transformation series are headed by Th, U, and U Fig. Several of the isotopes in these chains, such as ,, U, Ra, and others are predicted to have such very weak, heavy cluster decay branches see Table 1. Each of the naturally occurring radioactive isotopes in these transformation series has two synonymous names.

For example, the commercially important radioisotope whose classical name is mesothorium-1 is known to be an isotope of radium with mass number of and is designated as radium Ra. Table 3 summarizes the names, symbols, and some radioactive properties of these three transformation series. However, these chains are not the only ones.

Their uniqueness or importance as chains is an accident of the very long half-lives of Th, U, and U. For example, element of mass has a succession of seven alpha decays and one electron capture and positron decay to Th. The special importance of the chains in Table 3 is related to the fact that they were essentially the only early sources of radioactive materials, and they also play a role in nuclear power.

See also: Nuclear power. Transformation series are now known for every element in the periodic table except hydrogen. Chains of neutron-rich isotopes have been produced and studied among the products of nuclear fission. Heavy-ion-induced reactions and high-flux reactors have been used to extend knowledge of the elements beyond uranium. The elements from number 93 neptunium to oganesson , which have so far not been found on Earth, were made in the laboratory.

Both proton- and heavy-ion-induced reactions have extended knowledge of chains and neutron-deficient isotopes of the stable elements. Alpha-particle decay refers to when a parent nucleus expels an alpha particle a helium nucleus , which contains two protons and two neutrons. Thus, the atomic number, or nuclear charge Z , of the decay product is 2 units less than that of the parent, and the nuclear mass A of the product is 4 atomic mass units less than that of the parent, because the emitted alpha particle carries away this amount of nuclear charge and mass.

The decrease of 2 units of atomic number or nuclear charge between parent and product means that the decay product will be a different chemical element, displaced by 2 units to the left in the periodic table of the elements.

For example, radium has atomic number 88 and is found in column 2 of the periodic table. Its decay product after the emission of an alpha particle is a different chemical element, radon, whose atomic number is 86 and whose position is in the last column of the periodic table as a noble gas. In the simplest case of alpha decay, every alpha particle would be emitted with exactly the same velocity and hence the same kinetic energy.

However, in most cases there are two or more discrete energy groups called lines Fig. When the 4. When a 4. This nucleus promptly transforms to its ground level by the emission of a 0. Thus, in all alpha-particle spectra, the alpha particles are emitted in one or more discrete and homogeneous energy groups, and alpha-particle spectra are accompanied by gamma-ray and conversion electron spectra whenever there are two or more alpha-particle groups in the spectrum.

There is a systematic relationship between the kinetic energy of the emitted alpha particles and the half-period of the alpha emitter. The highest-energy alpha particles are emitted by short-lived nuclides, and the lowest-energy alpha particles are emitted by the very long lived alpha-particle emitters.

The Geiger-Nuttall rule is inexplicable by classical physics but emerges clearly from quantum, or wave, mechanics. In , the hypothesis of transmission through nuclear potential barriers, as introduced by Russian-born U. See also: Quantum mechanics.

At very close distances, this electrostatic repulsion is opposed and overcome by short-range, nuclear, attractive forces. The net potential energy U as a function of the separation r between the alpha particle and its residual nucleus is the nuclear potential barrier.

At this distance, called the top of the nuclear barrier, the potential energy is about 25—30 MeV for typical cases of heavy, alpha-emitting nuclei Fig. Inside the nucleus, the alpha particle is represented as a de Broglie matter wave.

According to wave mechanics, this wave has a very small but finite probability of being transmitted through the nuclear potential energy barrier and thus of emerging as an alpha particle emitted from the nucleus.

The transmission of a particle through such an energy barrier is completely forbidden in classical electrodynamics but is possible according to wave mechanics. This transmission of a matter wave through an energy barrier is analogous to the familiar case of the transmission of ordinary visible light through an opaque metal such as gold: if the gold is thin enough, some light does get through, as in the case of the thin gold leaf which is sometimes used for lettering signs on store windows.

The wave-mechanical probability of the transmission of an alpha particle through the nuclear potential barrier is very strongly dependent upon the energy of the emitted alpha particle.

To a good approximation, Eq. The first term on the right side of Eq. See also: Planck's constant. Inspection of Eq. When the experimentally known values of alpha-decay energy are substituted into Eq. This range of about 10 20 is just what is needed to relate the alpha-decay energy to the broad domain of known alpha-decay half-periods. Equation 21 thus explains the Geiger-Nuttall rule very successfully Fig.

From Fig. If that had been the case, then radioactivity and the nucleus of the atom might never have been discovered. Knowledge of alpha-emitting isotopes was greatly enlarged through the identification of many isotopes' far off stability in the region just above tin and in the broad region from neodymium all the way to uranium.

For example, fusion reactions between MeV 58 Ni ions and 58 Ni and 63 Cu targets have been used to produce and study very neutron deficient radioactive isotopes, including 12 alpha emitters between tin and cesium. These results provide important data on the atomic masses of nuclei far from the stable ones in nature. These data test understanding of nuclear mass formulas and their validity in new regions of the periodic table. Beta-particle decay is a type of radioactivity in which the parent nucleus emits a beta particle.

In beta decay, the atomic number shifts by one unit of charge, while the mass number remains unchanged Table 1. In contrast to alpha decay, when beta decay takes place between two nuclei which have a definite energy difference, the beta particles from a large number of atoms will have a continuous distribution of energy Fig. See also: Positron. For each beta-particle emitter, there is a definite maximum or upper limit to the energy spectrum of beta particles.

This maximum energy, E max , corresponds to the change in nuclear energy in the beta decay. For positron decay to occur, the total decay energy must exceed 1. As in the case of alpha decay, most beta-particle spectra are not this simple, but include additional continuous spectra which have less maximum energy and which leave the product nucleus in an excited level from which gamma rays are then emitted. For nuclei very far from stability, the energies of these excited states populated in beta decay are so large that the excited states may decay by proton, two-proton, neutron, two-neutron, three-neutron or alpha emission, or spontaneous fission.

In some cases, the energies are so great that the number of excited states to which beta decay can occur is so large that only the gross strength of the beta decays to many states can be studied.

The continuous spectrum of beta-particle energies Fig. This particle is the neutrino. The sum of the kinetic energy of the neutrino and the beta particle equals E max for the particular transition involved except in the rare cases where internal bremsstrahlung or shake-off electrons are emitted along with the beta particle and neutrino.

See also: Neutrino. Two forms of neutrinos are distinguished in beta decay. In positron beta decay, a proton p in the nucleus transforms into a neutron n in the nucleus, thus reducing the nuclear charge by 1 unit.

Thus positron beta decay is represented by decay See also: Antimatter. There are, in fact, three classes of neutrinos. The neutrinos emitted in the two types of beta decay the decays in equations 22 and 23 are called electron neutrinos.

The number of leptons in a decay or reaction is considered to be conserved; this rule is called lepton number conservation. There must be the same net number of each type of lepton on each side of a decay or reaction. For example, because there are no leptons on the left sides of the decays in equations 22 and 23, there must be no net leptons on the right sides. The decays in equations 22 and 23 also conserve nucleon number. See also: Lepton. Because the neutron rest mass is greater than the proton rest mass, free neutrons can undergo beta decay in decay in equation 23 , but protons must use part of the nuclear binding energy available inside a nucleus to make up the rest mass difference in the decay in equation The interaction of neutrinos with matter is exceedingly feeble.

A neutrino can pass all the way through the Sun with little chance of collision. See also: Light-year. Charged particles, such as beta particles or alpha particles, are easily absorbed in matter, and their kinetic energy is thereby converted into heat.

In beta decay, the average energy E av of the beta particles is far less than the maximum energy E max of the particular beta-particle spectrum. The remaining decay energy is emitted as kinetic energy of neutrinos and is not recoverable in finite absorbers. There are other processes that carry off part of the energy of beta decay, including internal bremsstrahlung gamma rays and shake-off electrons atomic electrons.

In internal bremsstrahlung, through an interaction of the beta particle and the emitting nucleus, part of the decay energy is emitted as a gamma ray. In the shake-off process, part of the beta-decay energy is given to one of the atomic electrons.

The gamma rays are not absorbed in matter as easily as the beta particles. In addition, if one tries to absorb the beta particles in matter, the beta particles can interact with the atoms and give off external bremsstrahlung gamma rays.

The number of these gamma rays again is a strongly decreasing function of energy, but their emission extends up to the maximum energies of the beta particles. See also: Bremsstrahlung. By postulating the simultaneous emission of a beta particle and a neutrino, as in reaction 22 , Italian-born U. The energy distribution of beta particles in allowed transitions is then given by Eq.

The statistical spectrum is corrected by the Fermi function, F Z , W , and the new distribution agrees with experiments Fig. Equation 24 essentially matches the energy spectra of allowed beta-particle transitions and therefore furnishes one type of experimental verification of the properties of neutrinos.

Its counterpart in terms of the beta-particle momentum spectrum is often used for the analysis of spectra, and is given by Eq. The momentum distribution is much more nearly symmetric than its corresponding energy spectrum. After the work of Fermi which explained allowed decay, Polish-born U.

Allowed decays occur between nuclear states which differ in spin by 0 or 1 unit and which have the same parity. Konopinski and Uhlenbeck developed a theory to describe beta decays where energy is available for decay but the allowed selection rules on spin or parity or both are violated. It may occur to you that we have a logically difficult situation here. Nuclei do not contain electrons and yet during beta decay, an electron is emitted from a nucleus. At the same time that the electron is being ejected from the nucleus, a neutron is becoming a proton.

It is tempting to picture this as a neutron breaking into two pieces with the pieces being a proton and an electron.

That would be convenient for simplicity, but unfortunately that is not what happens more on this subject will be explained at the end of this section.

For convenience, we will treat beta decay as a neutron splitting into a proton and an electron. The proton stays in the nucleus, increasing the atomic number of the atom by one. The electron is ejected from the nucleus and is the particle of radiation called beta.

To insert an electron into a nuclear equation and have the numbers add up properly, an atomic number and a mass number had to be assigned to an electron. The mass number assigned to an electron is zero 0 , which is reasonable since the mass number is the number of protons plus neutrons, and an electron contains no protons and no neutrons.

The atomic number assigned to an electron is negative one -1 , because that allows a nuclear equation containing an electron to balance atomic numbers. Therefore, the nuclear symbol representing an electron beta particle is.

Thorium is a nucleus that undergoes beta decay. Here is the nuclear equation for this beta decay:. Frequently, gamma ray production accompanies nuclear reactions of all types. Virtually all of the nuclear reactions in this chapter also emit gamma rays, but for simplicity the gamma rays are generally not shown. Nuclear reactions produce a great deal more energy than chemical reactions. Nuclear reactions release some of the binding energy and may convert tiny amounts of matter into energy.

That means that nuclear changes involve almost one million times more energy per atom than chemical changes! Figure Confirm that this equation is correctly balanced by adding up the reactants' and products' atomic and mass numbers. The mass numbers of the original nucleus and the new nucleus are the same because a neutron has been lost, but a proton has been gained, and so the sum of protons plus neutrons remains the same. The atomic number in the process has been increased by one since the new nucleus has one more proton than the original nucleus.

In this beta decay, a thorium nucleus has one more proton than the original nucleus. In this beta decay, a thorium nucleus has become a protactinium nucleus. Protactinium is also a beta emitter and produces uranium Once again, the atomic number increases by one and the mass number remains the same; this confirms that the equation is correctly balanced.

When studying nuclear reactions in general, there is typically little information or concern about the chemical state of the radioactive isotopes, because the electrons from the electron cloud are not directly involved in the nuclear reaction in contrast to chemical reactions.

So it is acceptable to ignore charge in balancing nuclear reactions, and concentrate on balancing mass and atomic numbers only. This reaction is an alpha decay. Alpha Pegasi. Accessed 12 Nov. More Definitions for alpha particle. Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Log in Sign Up. Save Word. Definition of alpha particle. Examples of alpha particle in a Sentence Recent Examples on the Web The fourth decay can occur by two different routes, with each path releasing one alpha particle and one beta particle before reaching lead Gamma rays are a type of electromagnetic radiation.

There is no change in mass or charge for this type of decay. Alpha decay Alpha particles consist of two protons and two neutrons.

When a nucleus emits an alpha particle, these changes happen: the mass number decreases by 4 the atomic number decreases by 2 the nuclear charge decreases by 2 Example Radon decays into polonium by emitting an alpha particle. Beta decay A beta particle forms when a neutron changes into a proton and a high-energy electron.