Proton emission
Encyclopedia
Proton emission is a 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
.
For a proton to escape a nucleus, the proton separation energy must be negative - the proton is therefore unbound, and tunnels out of the nucleus in a finite time. Proton emission is not seen in naturally occurring isotopes; proton emitters can be produced via nuclear reaction
s, usually utilising some kind of particle accelerator
.
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. 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 wonderfully 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, near Caen
). In 2005 it was experimentally determined (at the same facility) that Zinc
-54 can also undergo double proton decay.
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....
is ejected from a nucleus
Atomic nucleus
The 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...
. Proton emission can occur from high-lying excited states in a nucleus following a beta decay
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...
, in which case the process is known as beta-delayed proton emission, or can occur from the ground state (or a low-lying isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
) of very proton-rich nuclei, in which case the process is very similar to alpha decay
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...
.
For a proton to escape a nucleus, the proton separation energy must be negative - the proton is therefore unbound, and tunnels out of the nucleus in a finite time. Proton emission is not seen in naturally occurring isotopes; proton emitters can be produced via 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...
s, usually utilising some kind of particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
.
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
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
in West Germany. 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 wonderfully pure example of quantum tunneling.
In 2002, the simultaneous emission of two protons was observed from the nucleus Iron-45 in experiments at GSI
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
and GANIL
GANIL
The Grand Accélérateur National d’Ions Lourds , or Large Heavy Ion National Accelerator, is a French national nuclear physics research center in Caen. The facility consists primarily of two serialised synchrocyclotrons.- See also :Similar facilities:...
(Grand Accélérateur National d'Ions Lourds, near Caen
Caen
Caen is a commune in northwestern France. It is the prefecture of the Calvados department and the capital of the Basse-Normandie region. It is located inland from the English Channel....
). In 2005 it was experimentally determined (at the same facility) that Zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
-54 can also undergo double proton decay.
See also
- Proton drip line
- DiprotonDiprotonA diproton is a hypothetical isotope of helium nucleus consisting of two protons and no neutrons, and is predicted to be less stable than 5He...
(a particle possibly involved in double proton decay) - Free neutron
External links
- Nuclear Structure and Decay Data - IAEA with query on Proton Separation Energy