Radiation chemistry

Last updated

Radiation chemistry is a subdivision of nuclear chemistry which studies the chemical effects of ionizing radiation on matter. This is quite different from radiochemistry, as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into hydrogen gas and hydrogen peroxide.

Contents

Radiation interactions with matter

As ionizing radiation moves through matter its energy is deposited through interactions with the electrons of the absorber. [1] The result of an interaction between the radiation and the absorbing species is removal of an electron from an atom or molecular bond to form radicals and excited species. The radical species then proceed to react with each other or with other molecules in their vicinity. It is the reactions of the radical species that are responsible for the changes observed following irradiation of a chemical system. [2]

Charged radiation species (α and β particles) interact through Coulombic forces between the charges of the electrons in the absorbing medium and the charged radiation particle. These interactions occur continuously along the path of the incident particle until the kinetic energy of the particle is sufficiently depleted. Uncharged species (γ photons, x-rays) undergo a single event per photon, totally consuming the energy of the photon and leading to the ejection of an electron from a single atom. [3] Electrons with sufficient energy proceed to interact with the absorbing medium identically to β radiation.

An important factor that distinguishes different radiation types from one another is the linear energy transfer (LET), which is the rate at which the radiation loses energy with distance traveled through the absorber. Low LET species are usually low mass, either photons or electron mass species (β particles, positrons) and interact sparsely along their path through the absorber, leading to isolated regions of reactive radical species. High LET species are usually greater in mass than one electron, [4] for example α particles, and lose energy rapidly resulting in a cluster of ionization events in close proximity to one another. Consequently, the heavy particle travels a relatively short distance from its origin.

Areas containing a high concentration of reactive species following absorption of energy from radiation are referred to as spurs. In a medium irradiated with low LET radiation, the spurs are sparsely distributed across the track and are unable to interact. For high LET radiation, the spurs can overlap, allowing for inter-spur reactions, leading to different yields of products when compared to the same medium irradiated with the same energy of low LET radiation. [5]

Reduction of organics by solvated electrons

A recent area of work has been the destruction of toxic organic compounds by irradiation; [6] after irradiation, "dioxins" (polychlorodibenzo-p-dioxins) are dechlorinated in the same way as PCBs can be converted to biphenyl and inorganic chloride. This is because the solvated electrons react with the organic compound to form a radical anion, which decomposes by the loss of a chloride anion. If a deoxygenated mixture of PCBs in isopropanol or mineral oil is irradiated with gamma rays, then the PCBs will be dechlorinated to form inorganic chloride and biphenyl. The reaction works best in isopropanol if potassium hydroxide ( caustic potash ) is added. The base deprotonates the hydroxydimethylmethyl radical to be converted into acetone and a solvated electron, as the result the G value (yield for a given energy due to radiation deposited in the system) of chloride can be increased because the radiation now starts a chain reaction, each solvated electron formed by the action of the gamma rays can now convert more than one PCB molecule. [7] [8] If oxygen, acetone, nitrous oxide, sulfur hexafluoride or nitrobenzene [9] is present in the mixture, then the reaction rate is reduced. This work has been done recently in the US, often with used nuclear fuel as the radiation source. [10] [11]

In addition to the work on the destruction of aryl chlorides, it has been shown that aliphatic chlorine and bromine compounds such as perchloroethylene, [12] Freon (1,1,2-trichloro-1,2,2-trifluoroethane) and halon-2402 (1,2-dibromo-1,1,2,2-tetrafluoroethane) can be dehalogenated by the action of radiation on alkaline isopropanol solutions. Again a chain reaction has been reported. [13]

In addition to the work on the reduction of organic compounds by irradiation, some work on the radiation induced oxidation of organic compounds has been reported. For instance, the use of radiogenic hydrogen peroxide (formed by irradiation) to remove sulfur from coal has been reported. In this study it was found that the addition of manganese dioxide to the coal increased the rate of sulfur removal. [14] The degradation of nitrobenzene under both reducing and oxidizing conditions in water has been reported. [15]

Reduction of metal compounds

In addition to the reduction of organic compounds by the solvated electrons it has been reported that upon irradiation a pertechnetate solution at pH 4.1 is converted to a colloid of technetium dioxide. Irradiation of a solution at pH 1.8 soluble Tc(IV) complexes are formed. Irradiation of a solution at pH 2.7 forms a mixture of the colloid and the soluble Tc(IV) compounds. [16] Gamma irradiation has been used in the synthesis of nanoparticles of gold on iron oxide (Fe2O3). [17]

It has been shown that the irradiation of aqueous solutions of lead compounds leads to the formation of elemental lead. When an inorganic solid such as bentonite and sodium formate are present then the lead is removed from the aqueous solution. [18]

Polymer modification

Another key area uses radiation chemistry to modify polymers. Using radiation, it is possible to convert monomers to polymers, to crosslink polymers, and to break polymer chains. [19] [20] Both man-made and natural polymers (such as carbohydrates [21] ) can be processed in this way.

Water chemistry

Both the harmful effects of radiation upon biological systems (induction of cancer and acute radiation injuries) and the useful effects of radiotherapy involve the radiation chemistry of water. The vast majority of biological molecules are present in an aqueous medium; when water is exposed to radiation, the water absorbs energy, and as a result forms chemically reactive species that can interact with dissolved substances (solutes). Water is ionized to form a solvated electron and H2O+, the H2O+ cation can react with water to form a hydrated proton (H3O+) and a hydroxyl radical (HO.). Furthermore, the solvated electron can recombine with the H2O+ cation to form an excited state of the water. This excited state then decomposes to species such as hydroxyl radicals (HO.), hydrogen atoms (H.) and oxygen atoms (O.). Finally, the solvated electron can react with solutes such as solvated protons or oxygen molecules to form hydrogen atoms and dioxygen radical anions, respectively. The fact that oxygen changes the radiation chemistry might be one reason why oxygenated tissues are more sensitive to irradiation than the deoxygenated tissue at the center of a tumor. The free radicals, such as the hydroxyl radical, chemically modify biomolecules such as DNA, leading to damage such as breaks in the DNA strands. Some substances can protect against radiation-induced damage by reacting with the reactive species generated by the irradiation of the water.

It is important to note that the reactive species generated by the radiation can take part in following reactions; this is similar to the idea of the non-electrochemical reactions which follow the electrochemical event which is observed in cyclic voltammetry when a non-reversible event occurs. For example, the SF5 radical formed by the reaction of solvated electrons and SF6 undergo further reactions which lead to the formation of hydrogen fluoride and sulfuric acid. [22]

In water, the dimerization reaction of hydroxyl radicals can form hydrogen peroxide, while in saline systems the reaction of the hydroxyl radicals with chloride anions forms hypochlorite anions.

The action of radiation upon underground water is responsible for the formation of hydrogen which is converted by bacteria into methane. [23] [24]

Equipment

Radiation chemistry applied in industrial processing equipment

To process materials, either a gamma source or an electron beam can be used. The international type IV (wet storage) irradiator is a common design, of which the JS6300 and JS6500 gamma sterilizers (made by 'Nordion International', which used to trade as 'Atomic Energy of Canada Ltd') are typical examples. [25] In these irradiation plants, the source is stored in a deep well filled with water when not in use. When the source is required, it is moved by a steel wire to the irradiation room where the products which are to be treated are present; these objects are placed inside boxes which are moved through the room by an automatic mechanism. By moving the boxes from one point to another, the contents are given a uniform dose. After treatment, the product is moved by the automatic mechanism out of the room. The irradiation room has very thick concrete walls (about 3 m thick) to prevent gamma rays from escaping. The source consists of 60Co rods sealed within two layers of stainless steel. The rods are combined with inert dummy rods to form a rack with a total activity of about 12.6PBq (340kCi).

Research equipment

While it is possible to do some types of research using an irradiator much like that used for gamma sterilization, it is common in some areas of science to use a time resolved experiment where a material is subjected to a pulse of radiation (normally electrons from a LINAC). After the pulse of radiation, the concentration of different substances within the material are measured by emission spectroscopy or Absorption spectroscopy, hence the rates of reactions can be determined. This allows the relative abilities of substances to react with the reactive species generated by the action of radiation on the solvent (commonly water) to be measured. This experiment is known as pulse radiolysis [26] which is closely related to flash photolysis.

In the latter experiment the sample is excited by a pulse of light to examine the decay of the excited states by spectroscopy; [27] sometimes the formation of new compounds can be investigated. [28] Flash photolysis experiments have led to a better understanding of the effects of halogen-containing compounds upon the ozone layer. [29]

Chemosensor

The SAW chemosensor [30] is nonionic and nonspecific. It directly measures the total mass of each chemical compound as it exits the gas chromatography column and condenses on the crystal surface, thus causing a change in the fundamental acoustic frequency of the crystal. Odor concentration is directly measured with this integrating type of detector. Column flux is obtained from a microprocessor that continuously calculates the derivative of the SAW frequency.

See also

Related Research Articles

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Functional group</span> Set of atoms in a molecule which augment its chemical and/or physical properties

In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.

<span class="mw-page-title-main">Solvation</span> Association of molecules of a solvent with molecules or ions of a solute

Solvation describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration.

<span class="mw-page-title-main">Aqueous solution</span> Solution in which the solvent is water

An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be represented as Na+(aq) + Cl−(aq). The word aqueous means pertaining to, related to, similar to, or dissolved in, water. As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified.

<span class="mw-page-title-main">Radical anion</span> Free radical species

In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a non-carbon radical anion is the superoxide anion, formed by transfer of one electron to an oxygen molecule. Radical anions are typically indicated by .

<span class="mw-page-title-main">Hydrogen iodide</span> Chemical compound

Hydrogen iodide is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under standard conditions, whereas the other is an aqueous solution of the gas. They are interconvertible. HI is used in organic and inorganic synthesis as one of the primary sources of iodine and as a reducing agent.

<span class="mw-page-title-main">Diazonium compound</span> Group of organonitrogen compounds

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X− where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.

Radiolysis is the dissociation of molecules by ionizing radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux. The radiation in this context is associated with ionizing radiation; radiolysis is therefore distinguished from, for example, photolysis of the Cl2 molecule into two Cl-radicals, where (ultraviolet or visible spectrum) light is used.

An inorganic nonaqueous solvent is a solvent other than water, that is not an organic compound. These solvents are used in chemical research and industry for reactions that cannot occur in aqueous solutions or require a special environment. Inorganic nonaqueous solvents can be classified into two groups, protic solvents and aprotic solvents. Early studies on inorganic nonaqueous solvents evaluated ammonia, hydrogen fluoride, sulfuric acid, as well as more specialized solvents, hydrazine, and selenium oxychloride.

Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule.

<span class="mw-page-title-main">Photopolymer</span>

A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light. An example is shown below depicting a mixture of monomers, oligomers, and photoinitiators that conform into a hardened polymeric material through a process called curing.

A solvated electron is a free electron in a solution, and is the smallest possible anion. Solvated electrons occur widely. Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and other solvents – in fact, in any solvent that mediates outer-sphere electron transfer. The solvated electron is responsible for a great deal of radiation chemistry.

Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials.

<span class="mw-page-title-main">Photoinitiator</span>

A photoinitiator is a molecule that creates reactive species when exposed to radiation. Synthetic photoinitiators are key components in photopolymers.

This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it features an extensive vocabulary and a significant amount of jargon.

<span class="mw-page-title-main">Ion</span> Particle, atom or molecule with a net electrical charge

An ion is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons.

<span class="mw-page-title-main">Radical (chemistry)</span> Atom, molecule, or ion that has an unpaired valence electron; typically highly reactive

In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes.

In chemistry, the amino radical, ·NH2, also known as the aminyl radical or azanyl radical, is the neutral form of the amide ion. Aminyl radicals are highly reactive and consequently short-lived, like most radicals; however, they form an important part of nitrogen chemistry. In sufficiently high concentration, amino radicals dimerise to form hydrazine. While NH2 as a functional group is common in nature, forming a part of many compounds, the radical cannot be isolated in its free form.

<span class="mw-page-title-main">Nitroethylene</span> Chemical compound

Nitroethylene (also known as nitroethene) is a liquid organic compound with the formula C2H3NO2. It is the simplest nitroalkene, which are unsaturated carbon chains with at least one double bond and a NO2 functional group. Nitroethylene serves as a useful intermediate in the production of various other chemicals.

Free radical damage to DNA can occur as a result of exposure to ionizing radiation or to radiomimetic compounds. Damage to DNA as a result of free radical attack is called indirect DNA damage because the radicals formed can diffuse throughout the body and affect other organs. Malignant melanoma can be caused by indirect DNA damage because it is found in parts of the body not exposed to sunlight. DNA is vulnerable to radical attack because of the very labile hydrogens that can be abstracted and the prevalence of double bonds in the DNA bases that free radicals can easily add to.

References

  1. ↑ J. W. T. Spinks. R. J. Woods: An Introduction to Radiation Chemistry, Third Edition, John-Wiley and Sons, Inc., New York, Toronto 1990. ISBN   0-471-61403-3
  2. ↑ Turner, J.E. Atoms, Radiation, and Radiation Protection. United States: Pergamon Books Inc., Elmsford, NY, 1986. Print
  3. ↑ Bigelow, R. A. Radiation Interactions in Matter.
  4. ↑ Essentials of radiation, biology and protection, S. Forshier, Cengage Learning, Jul 22, 2008, p46
  5. ↑ Simon M. Pimblott, Jay A. LaVerne, J. Phys. Chem., 1994, 98 (24), pp 6136–6143, doi : 10.1021/j100075a016, Publication Date: June 1994
  6. ↑ Zhao C et al. (2007) Radiation Physics and Chemistry, 76:37-45
  7. ↑ Ajit Singh and Walter Kremers, Radiation Physics and Chemistry, 2002, 65(4-5), 467-472
  8. ↑ Bruce J. Mincher, Richard R. Brey, René G. Rodriguez, Scott Pristupa and Aaron Ruhter, Radiation Physics and Chemistry, 2002, 65(4-5), 461-465
  9. ↑ A. G. Bedekar, Z. Czerwik and J. Kroh, "Pulse radiolysis of ethylene glycol and 1,3-propanediol glasses—II. Kinetics of trapped electron decay", 1990, 36, 739-742
  10. ↑ Energy Citations Database (ECD) - - Document #10116942
  11. ↑ Process for the solvent extraction for the radiolysis and dehalogenation of halogenated organic compounds in soils, sludges, sediments and slurries - US Patent 6132561 Archived 2007-03-11 at the Wayback Machine
  12. ↑ V. Múka, *, R. Silber, M. Pospíil, V. Kliský and B. Bartoníek, Radiation Physics and Chemistry, 1999, 55(1), 93-97
  13. ↑ Seiko Nakagawa and Toshinari Shimokawa, Radiation Physics and Chemistry, 2002, 63(2), 151-156
  14. ↑ P. S. M. Tripathi, K. K. Mishra, R. R. P. Roy and D. N. Tewari, "γ-Radiolytic desulphurisation of some high-sulphur Indian coals catalytically accelerated by MnO2", Fuel Processing Technology, 2001, 70, 77-96
  15. ↑ Shao-Hong Feng, Shu-Juan Zhang, Han-Qing Yu, and Qian-Rong Li, "Radiation-induced Degradation of Nitrobenzene in Aqueous Solutions", Chemistry Letters, 2003, 32(8), 718
  16. ↑ T. Sekine, H. Narushima, T. Suzuki, T. Takayama, H. Kudo, M. Lin and Y. Katsumura, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004, 249(1-3), 105-109
  17. ↑ Satoshi Seino, Takuya Kinoshita, Yohei Otome, Kenji Okitsu, Takashi Nakagawa, and Takao A. Yamamoto, "Magnetic Composite Nanoparticle of Au/γ-Fe2O3 Synthesized by Gamma-Ray Irradiation", Chemistry Letters, 2003, 32(8), 690
  18. ↑ M. Pospίšil, V. Čuba, V. Múčka and B. Drtinová, "Radiation removal of lead from aqueous solutions- effects of various sorbants and nitrous oxide", Radiation Physics and Chemistry, 2006, 75, 403-407
  19. ↑ Energy Citations Database (ECD) - - Document #7313004
  20. ↑ IAEA report - Radiation Formation of Hydrogels for Biomedical Applications; the use of radiation technique - Mechanism of the radiation-induced crosslinking of polymers in aqueous solution Archived 2007-04-26 at the Wayback Machine
  21. ↑ IAEA-TECDOC-1422
  22. ↑ K.-D. Asmus and J.H. Fendler, "The reaction of sulfur hexafluoride with solvated electrons", The Journal of Physical Chemistry, 1968, 72, 4285-4289
  23. ↑ Chapelle, Francis H.; O'Neill, Kathleen; Bradley, Paul M.; Methé, Barbara A.; Ciufo, Stacy A.; Knobel, Leroy L.; Lovley, Derek R. (2002). "A hydrogen-based subsurface microbial community dominated by methanogens". Nature. 415 (6869): 312–315. Bibcode:2002Natur.415..312C. doi:10.1038/415312a. PMID   11797006. S2CID   4327881.
  24. ↑ Lin, Li-Hung; Slater, Greg F.; Sherwood Lollar, Barbara; Lacrampe-Couloume, Georges; Onstott, T.C. (2005). "The yield and isotopic composition of radiolytic H2, a potential energy source for the deep subsurface biosphere" (PDF). Geochimica et Cosmochimica Acta. 69 (4): 893–903. Bibcode:2005GeCoA..69..893L. doi:10.1016/j.gca.2004.07.032. hdl:1912/659. Archived from the original (PDF) on 2010-06-17.
  25. ↑ Features of the design are discussed in the International Atomic Energy Agency report on a human error accident in such an irradiation plant
  26. ↑ "Pulse Radiolysis". dur.ac.uk. 2007-03-28. Archived from the original on 2007-03-28.
  27. ↑ Hanley, Luke. "Flash Photolysis of Benzophenone" (PDF). Archived from the original (PDF) on 2011-07-20.
  28. ↑ Porter, George (11 December 1967). "Flash photolysis and some of its applications (Nobel lecture)" (PDF). Archived from the original (PDF) on 2014-10-08. Retrieved 2022-08-09.
  29. ↑ RE Huie; B Laszlo; MJ Kurylo; et al. (1995). Atmospheric Chemistry of Iodine Monoxide (PDF). Halon Options Technical Working Conference . Retrieved 2012-04-19.
  30. ↑ Abnormal Chemosensory Jump 6 Is a Positive Transcriptional Regulator of the Cholinergic Gene Locus in Drosophila Olfactory Neurons - Lee and Salvaterra 22 (13): 5291 - Journal of Neuroscience
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.