Proton emission

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The decay of a proton rich nucleus A populates excited states of a daughter nucleus B by b+ emission or electron capture (EC). Those excited states that lie below the separation energy for protons (Sp) decay by g emission towards the ground state of daughter B. For the higher excited states a competitive decay channel of proton emission to the granddaughter C exists, called b-delayed proton emission. Zerfallsschema.svg
The decay of a proton rich nucleus A populates excited states of a daughter nucleus B by β+ emission or electron capture (EC). Those excited states that lie below the separation energy for protons (Sp) decay by γ emission towards the ground state of daughter B. For the higher excited states a competitive decay channel of proton emission to the granddaughter C exists, called β-delayed proton emission.

Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state (or a low-lying isomer) of very proton-rich nuclei, in which case the process is very similar to alpha decay.[ citation needed ] For a proton to escape a nucleus, the proton separation energy must be negative (Sp < 0)—the proton is therefore unbound, and tunnels out of the nucleus in a finite time. The rate of proton emission is governed by the nuclear, Coulomb, and centrifugal potentials of the nucleus, where centrifugal potential affects a large part of the rate of proton emission. The half-life of a nucleus with respect to proton emission is affected by the proton energy and its orbital angular momentum. [1] Proton emission is not seen in naturally occurring isotopes; proton emitters can be produced via nuclear reactions, usually using linear particle accelerators.

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Although prompt (i.e. not beta-delayed) proton emission was observed from an isomer in cobalt-53 as early as 1969, no other proton-emitting states were found until 1981, when the proton radioactive ground states of lutetium-151 and thulium-147 were observed at experiments at the GSI in West Germany. [2] Research in the field flourished after this breakthrough, and to date more than 25 isotopes have been found to exhibit proton emission. The study of proton emission has aided the understanding of nuclear deformation, masses, and structure, and it is a pure example of quantum tunneling.

In 2002, the simultaneous emission of two protons was observed from the nucleus iron-45 in experiments at GSI and GANIL (Grand Accélérateur National d'Ions Lourds at Caen). [3] In 2005 it was experimentally determined (at the same facility) that zinc-54 can also undergo double proton decay. [4]

See also

Related Research Articles

<span class="mw-page-title-main">Atom</span> Smallest unit of a chemical element

Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper. Atoms with the same number of protons but a different number of neutrons are called isotopes of the same element.

<span class="mw-page-title-main">Alpha decay</span> Type of radioactive decay

Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of +2 e and a mass of 4 Da. For example, uranium-238 decays to form thorium-234.

<span class="mw-page-title-main">Beta decay</span> Type of radioactive decay

In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle, transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release or Q value must be positive.

<span class="mw-page-title-main">Nuclear physics</span> Field of physics that studies atomic nuclei

Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.

<span class="mw-page-title-main">Beta particle</span> Ionizing radiation

A beta particle, also called beta ray or beta radiation, is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β decay and β+ decay, which produce electrons and positrons respectively.

<span class="mw-page-title-main">Electron capture</span> Process in which a proton-rich nuclide absorbs an inner atomic electron

Electron capture is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino.

<span class="mw-page-title-main">Nuclear isomer</span> Metastable excited state of a nuclide

A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels. "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). The term "metastable" is usually restricted to isomers with half-lives of 10−9 seconds or longer. Some references recommend 5 × 10−9 seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life. Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the 180m
73
Ta
nuclear isomer survives so long (at least 1015 years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by 180m
73
Ta
as well as 186m
75
Re
, 192m2
77
Ir
, 210m
83
Bi
, 212m
84
Po
, 242m
95
Am
and multiple holmium isomers.

<span class="mw-page-title-main">Radioactive decay</span> Emissions from unstable atomic nuclei

Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.

<span class="mw-page-title-main">Positron emission</span> Type of radioactive decay

Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino. Positron emission is mediated by the weak force. The positron is a type of beta particle (β+), the other beta particle being the electron (β) emitted from the β decay of a nucleus.

<span class="mw-page-title-main">Neutron emission</span> Type of radioactive decay

Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and beta-delayed neutron emission. As only a neutron is lost by this process the number of protons remains unchanged, and an atom does not become an atom of a different element, but a different isotope of the same element.

<span class="mw-page-title-main">Spontaneous fission</span> Form of radioactive decay

Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic process.

<span class="mw-page-title-main">Mass number</span> Number of heavy particles in the atomic nucleus

The mass number (symbol A, from the German word: Atomgewicht, "atomic weight"), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approximately equal to the atomic (also known as isotopic) mass of the atom expressed in atomic mass units. Since protons and neutrons are both baryons, the mass number A is identical with the baryon number B of the nucleus (and also of the whole atom or ion). The mass number is different for each isotope of a given chemical element, and the difference between the mass number and the atomic number Z gives the number of neutrons (N) in the nucleus: N = AZ.

<span class="mw-page-title-main">Neutron capture</span> Atomic nuclear process

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

<span class="mw-page-title-main">Cluster decay</span> Nuclear decay in which an atomic nucleus emits a small cluster of neutrons and protons

Cluster decay, also named heavy particle radioactivity, heavy ion radioactivity or heavy cluster decay, is a rare type of nuclear decay in which an atomic nucleus emits a small "cluster" of neutrons and protons, more than in an alpha particle, but less than a typical binary fission fragment. Ternary fission into three fragments also produces products in the cluster size. The loss of protons from the parent nucleus changes it to the nucleus of a different element, the daughter, with a mass number Ad = AAe and atomic number Zd = ZZe, where Ae = Ne + Ze. For example:

<span class="mw-page-title-main">Double electron capture</span> Mode of radioactive decay

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Yrast is a technical term in nuclear physics that refers to a state of a nucleus with a minimum of energy for a given angular momentum. Yr is a Swedish adjective sharing the same root as the English whirl. Yrast is the superlative of yr and can be translated whirlingest, although it literally means "dizziest" or "most bewildered". The yrast levels are vital to understanding reactions, such as off-center heavy ion collisions, that result in high-spin states.

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<span class="mw-page-title-main">Isobar (nuclide)</span> Atoms of different elements with the same number of nucleons

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number but have the same mass number. An example of a series of isobars is 40S, 40Cl, 40Ar, 40K, and 40Ca. While the nuclei of these nuclides all contain 40 nucleons, they contain varying numbers of protons and neutrons.

<span class="mw-page-title-main">Nuclear drip line</span> Atomic nuclei decay delimiter

The nuclear drip line is the boundary beyond which atomic nuclei are unbound with respect to the emission of a proton or neutron.

<span class="mw-page-title-main">Even and odd atomic nuclei</span> Nuclear physics classification method

In nuclear physics, properties of a nucleus depend on evenness or oddness of its atomic number Z, neutron number N and, consequently, of their sum, the mass number A. Most importantly, oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei generally less stable. This effect is not only experimentally observed, but is included in the semi-empirical mass formula and explained by some other nuclear models, such as the nuclear shell model. This difference of nuclear binding energy between neighbouring nuclei, especially of odd-A isobars, has important consequences for beta decay.

References

  1. Poenaru, Dorin N.; Rebel, Heinigerd; Wentz, Jürgen, eds. (2001). Nuclei Far from Stability and Astrophysics. Dordrecht: Springer Netherlands. pp. 79–81. doi:10.1007/978-94-010-0708-5. ISBN   978-0-7923-6937-0.
  2. S. Hofmann (1996). "Chapter 3: Proton radioactivity". In Dorin N. Poseru (ed.). Nuclear Decay Modes. Bristol: Institute of Physics Publishing. pp. 143–203. ISBN   0-7503-0338-7.
  3. Armand, Dominique (June 6, 2002). "A new mode of radioactive decay". CNRS. Archived from the original on 4 February 2005. Retrieved 2022-01-07.
  4. Blank, Bertram; Ploszajczak, Marek (December 17, 2013). "Two-proton radioactivity". Reports on Progress in Physics. 71 (4): 046301. arXiv: 0709.3797 . doi:10.1088/0034-4885/71/4/046301. S2CID   119276805.