Radiolysis
Encyclopedia
Radiolysis is the dissociation
of molecules by nuclear radiation
. It is the cleavage of one or several chemical bond
s resulting from exposure to high-energy flux. The radiation in this context is associated with radioactive decay
; radiolysis is therefore distinguished from, for example, photolysis
of the Cl2
molecule into two Cl-radicals
, where (ultraviolet
) or visible light
is used.
For example water dissociates under alpha radiation into a hydrogen radical
and a hydroxide
radical
, unlike ionisation of water which produces a hydrogen ion
and a hydroxide ion. The chemistry
of concentrated solutions under ionizing radiation
is extremely complex. Radiolysis can locally modify redox
conditions, and therefore the speciation
and the solubility
of the compounds.
, hydrogen radicals
and assorted oxygen compounds, such as ozone
, which when converted back into oxygen releases great amounts of energy. Some of these are explosive. This decomposition is produced mainly by the alpha particles, which can be entirely absorbed by very thin layers of water.
must be taken into account when designing nuclear power plants, in order to prevent coolant loss as a result of corrosion
.
is usually stored in water pools, awaiting permanent disposal or reprocessing
. The yield of hydrogen resulting from the irradiation of water with β and γ radiation is low (G-values = <1 molecule per 100 electronvolt
s of absorbed energy) but this is largely due to the rapid reassociation of the species arising during the initial radiolysis. If impurities are present or if physical conditions are created that prevent the establishment of a chemical equilibrium, the net production of hydrogen can be greatly enhanced.
Another approach uses radioactive waste as an energy source for regeneration of spent fuel by converting sodium borate to sodium borohydride
. By applying the proper combination of controls, stable borohydride compounds may be produced and used as hydrogen fuel storage medium.
. Molecular hydrogen and oxidants produced by the radiolysis of water may also provide a continuous source of energy to subsurface microbial
communities (Pedersen, 1999). Such speculation is supported by a discovery in the Mponeng
gold mine, South Africa
, where the researchers found a community dominated by a new phylotype of Desulfotomaculum
, feeding on primarily radiolytically produced H2
.
s, when simple mixing of reagent
s is too slow and other methods of initiating reactions have to be used.
The technique involves exposing a sample of material to a beam of highly accelerated electron
s, where the beam is generated by a LINAC. It has many applications. It was developed in the late 1950s and early 60s by John Keene in Manchester and Jack W. Boag in London.
is an alternative to pulse radiolysis that uses high power light pulses (e.g. from an excimer laser
) rather than beams of electrons to initiate chemical reactions. Typically ultraviolet light is used which requires less radiation shielding than required for the X-rays emitted in pulse radiolysis.
Pulse radiolysis
Dissociation (chemistry)
Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...
of molecules by nuclear radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
. It is the cleavage of one or several chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
s resulting from exposure to high-energy flux. The radiation in this context is associated with radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
; radiolysis is therefore distinguished from, for example, photolysis
Photodissociation
Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule....
of the Cl2
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
molecule into two Cl-radicals
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
, where (ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
) or visible light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
is used.
For example water dissociates under alpha radiation into a hydrogen radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
and a hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
, unlike ionisation of water which produces a hydrogen ion
Hydrogen ion
Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes.Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions....
and a hydroxide ion. The chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
of concentrated solutions under ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
is extremely complex. Radiolysis can locally modify redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
conditions, and therefore the speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
and the solubility
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
of the compounds.
Water decomposition
Of all the radiation-chemical reactions that have been studied, the most important is the decomposition of water. When exposed to radiation, water undergoes a breakdown sequence into hydrogen peroxideHydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
, hydrogen radicals
Free radical addition
Free radical addition is an addition reaction in organic chemistry involving free radicals. The addition may occur between a radical and a non-radical, or between two radicals....
and assorted oxygen compounds, such as ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, which when converted back into oxygen releases great amounts of energy. Some of these are explosive. This decomposition is produced mainly by the alpha particles, which can be entirely absorbed by very thin layers of water.
Corrosion Prediction & Prevention in Nuclear Power Plants
The possibility that enhanced concentration of hydroxyl present in irradiated water in the inner coolant loops of a light water reactorLight water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...
must be taken into account when designing nuclear power plants, in order to prevent coolant loss as a result of corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
.
Hydrogen production
The current interest in nontraditional methods for the generation of hydrogen has prompted a revisit of radiolytic splitting of water, where the interaction of various types of ionizing radiation (α, β, and γ) with water produces molecular hydrogen. This reevaluation was further prompted by the current availability of large amounts of radiation sources contained in the fuel discharged from nuclear reactors. This spent fuelNuclear fuel cycle
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
is usually stored in water pools, awaiting permanent disposal or reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
. The yield of hydrogen resulting from the irradiation of water with β and γ radiation is low (G-values = <1 molecule per 100 electronvolt
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
s of absorbed energy) but this is largely due to the rapid reassociation of the species arising during the initial radiolysis. If impurities are present or if physical conditions are created that prevent the establishment of a chemical equilibrium, the net production of hydrogen can be greatly enhanced.
Another approach uses radioactive waste as an energy source for regeneration of spent fuel by converting sodium borate to sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
. By applying the proper combination of controls, stable borohydride compounds may be produced and used as hydrogen fuel storage medium.
Spent nuclear fuel
Gas generation by radiolytic decomposition of hydrogen-containing materials, has been an area of concern for the transport and storage of radioactive materials and waste for a number of years. Potentially combustible and corrosive gases can be generated while at the same time, chemical reactions can remove hydrogen, and these reactions can be enhanced by the presence of radiation. The balance between these competing reactions is not well known at this time.Earth's History
A suggestion has been made that in the early stages of the Earth's development when its radioactivity was almost two orders of magnitude higher than at present, radiolysis could have been the principal source of atmospheric oxygen, which ensured the conditions for the origin and development of lifeLife
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...
. Molecular hydrogen and oxidants produced by the radiolysis of water may also provide a continuous source of energy to subsurface microbial
Microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...
communities (Pedersen, 1999). Such speculation is supported by a discovery in the Mponeng
Mponeng
Mponeng is a gold mine in South Africa's North West Province. It extends over two miles below the surface, and is considered to be one of the deepest and most substantial gold mines in the world. The trip from the surface to the bottom of the mine takes over an hour.6,000 tons of rock are...
gold mine, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, where the researchers found a community dominated by a new phylotype of Desulfotomaculum
Desulfotomaculum
Desulfotomaculum is a genus of Gram-positive, obligately anaerobic soil bacteria. A type of sulfate-reducing bacteria, Desulfotomaculum can cause food spoilage in poorly processed canned foods . Their presence can be identified by the release of hydrogen sulfide gas with its rotten egg smell when...
, feeding on primarily radiolytically produced H2
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
.
Pulse radiolysis
Pulse radiolysis is a recent method of initiating fast reactions to study reactions occurring on a timescale faster than approximately one hundred microsecondMicrosecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
s, when simple mixing of reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
s is too slow and other methods of initiating reactions have to be used.
The technique involves exposing a sample of material to a beam of highly accelerated electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, where the beam is generated by a LINAC. It has many applications. It was developed in the late 1950s and early 60s by John Keene in Manchester and Jack W. Boag in London.
Flash photolysis
Flash photolysisFlash photolysis
Flash photolysis is a pump-probe laboratory technique, in which a sample is firstly excited by a strong pulse of light from a laser of nanosecond, picosecond, or femtosecond pulse width or by a short-pulse light source such as a flash lamp...
is an alternative to pulse radiolysis that uses high power light pulses (e.g. from an excimer laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....
) rather than beams of electrons to initiate chemical reactions. Typically ultraviolet light is used which requires less radiation shielding than required for the X-rays emitted in pulse radiolysis.
External links and references
- Precursor and Transient Species in Condensed Phase Radiolysis
- Radiolysis for Borate Regeneration
- Water Radiolysis, a Possible Source of Atmospheric Oxygen
- The Dissociation of Water by Radiant Energy
- Resolution of Gas Generation Issues in Packages Containing Radioactive Waste/Materials
Pulse radiolysis
- What is pulse Radiolysis
- http://www.frrf.dl.ac.uk/history.html