Photodisintegration
Encyclopedia
Photodisintegration is a physical process in which an extremely high energy gamma ray
interacts with an atomic nucleus
and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single proton
or neutron
is effectively knocked out of the nucleus by the incoming gamma ray. This process is essentially the reverse of nuclear fusion
, where lighter elements at high temperatures combine together forming heavier elements and releasing energy. Photodisintegration is endothermic
(energy absorbing) for atomic nuclei lighter than iron
and exothermic
(energy releasing) for atomic nuclei heavier than iron
. Photodisintegration is responsible for the nucleosynthesis
of at least some heavy, proton rich elements via p-process
which takes place in supernova
e.
was used by James Chadwick
and Maurice Goldhaber
to measure the proton-neutron mass difference. This experiment proves that a neutron is not a bound state of a proton and an electron, as had been proposed by Ernest Rutherford
.
), photodisintegration is a major factor in the supernova
event. As the star reaches the end of its life, it reaches temperatures and pressures where photodisintegration's energy-absorbing effects temporarily reduce pressure and temperature within the star's core. This causes the core to start to collapse as energy is taken away by photodisintegration, and the collapsing core leads to the formation of a black hole
.
is a similar but different process, in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission
(splits into two fragments of nearly equal mass). Very high energy gamma rays have been shown to induce fission in elements as light as tin
.
Gamma ray
Gamma 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...
interacts with an atomic 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...
and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single proton
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....
or neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
is effectively knocked out of the nucleus by the incoming gamma ray. This process is essentially the reverse of nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
, where lighter elements at high temperatures combine together forming heavier elements and releasing energy. Photodisintegration is endothermic
Endothermic
In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...
(energy absorbing) for atomic nuclei lighter than iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
(energy releasing) for atomic nuclei heavier than iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
. Photodisintegration is responsible for the nucleosynthesis
Nucleosynthesis
Nucleosynthesis 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...
of at least some heavy, proton rich elements via p-process
P-process
The term p-process is used in two ways in the scientific literature concerning the astrophysical origin of the elements . Originally it referred to a proton capture process which is the source of certain, naturally occurring, proton-rich isotopes of the elements from selenium to mercury...
which takes place in supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
e.
Photodisintegration of deuterium
A photodisintegration reaction| → |
was used by James Chadwick
James Chadwick
Sir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
and Maurice Goldhaber
Maurice Goldhaber
Maurice Goldhaber was an Austrian-born American physicist, who in 1957 established that neutrinos have negative helicity.-Early Life and Childhood:...
to measure the proton-neutron mass difference. This experiment proves that a neutron is not a bound state of a proton and an electron, as had been proposed by Ernest Rutherford
Ernest Rutherford
Ernest 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...
.
Hypernovae
In explosions of very large stars (250 or more times the mass of earth's SunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
), photodisintegration is a major factor in the supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
event. As the star reaches the end of its life, it reaches temperatures and pressures where photodisintegration's energy-absorbing effects temporarily reduce pressure and temperature within the star's core. This causes the core to start to collapse as energy is taken away by photodisintegration, and the collapsing core leads to the formation of a black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
.
Photofission
PhotofissionPhotofission
Photofission is a process in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission .Very high energy gamma rays have been shown to induce fission in elements as light as tin.-Photodisintegration:...
is a similar but different process, in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
(splits into two fragments of nearly equal mass). Very high energy gamma rays have been shown to induce fission in elements as light as tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
.