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Sunday, August 17, 2014

Louis Pasteur

Louis Pasteur

From Wikipedia, the free encyclopedia
   
Louis Pasteur
Louis Pasteur, foto av Félix Nadar Crisco edit.jpg
Photograph by Nadar
Born(1822-12-27)December 27, 1822
Dole, France
DiedSeptember 28, 1895(1895-09-28) (aged 72)
Marnes-la-Coquette, France
NationalityFrench
FieldsChemistry
Microbiology
InstitutionsUniversity of Strasbourg
Lille University of Science and Technology
École Normale Supérieure
Pasteur Institute
Alma materÉcole Normale Supérieure
Notable studentsCharles Friedel[1]
Notable awardsRumford Medal (1856, 1892)
Copley Medal (1874)
Albert Medal (1882)
Leeuwenhoek Medal (1895)
Signature

Louis Pasteur (/ˈli pæˈstɜr/, French: [lwi pastœʁ]; December 27, 1822 – September 28, 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases, and his discoveries have saved countless lives ever since. He reduced mortality from puerperal fever, and created the first vaccines for rabies and anthrax. His medical discoveries provided direct support for the germ theory of disease and its application in clinical medicine. He is best known to the general public for his invention of the technique of treating milk and wine to stop bacterial contamination, a process now called pasteurization. He is regarded as one of the three main founders of bacteriology, together with Ferdinand Cohn and Robert Koch, and is popularly known as the "father of microbiology".[2][3][4]

Pasteur also made significant discoveries in chemistry, most notably on the molecular basis for the asymmetry of certain crystals and racemization. He was the Director of the Pasteur Institute, established in 1887, till his death, and his body lies beneath the institute in a vault covered in depictions of his accomplishments in Byzantine mosaics.[5]

Early life

The house in which Pasteur was born, Dole

Louis Pasteur was born on December 27, 1822, in Dole, Jura, France, to a Catholic family of a poor tanner. He was the third child of Jean-Joseph Pasteur and Jeanne-Etiennette Roqui. In 1827, the family moved to Arbois, where he entered primary school in 1831. He was an average student in his early years, and not particularly academic, as his interests were fishing and sketching. His pastels and portraits of his parents and friends, made when he was 15, were later kept in the museum of the Pasteur Institute in Paris. In 1838, he left for Paris to join the Institution Barbet, but became homesick and returned in November. In 1839, he entered the Collège Royal de Besançon and earned his baccalauréat (BA) degree in 1840. He was appointed teaching assistant at the Besançon college while continuing a degree science course with special mathematics. He failed his first examination in 1841. He managed to pass the baccalauréat scientifique (general science) degree in 1842 from Dijon but with a poor grade in chemistry. After one failed attempt for the entrance test for the École Normale Supérieure in Paris in 1842, he succeeded in 1844. In 1845 he received the licencié ès sciences (Bachelor of Science) degree. In 1846, he was appointed professor of physics at the Collège de Tournon at Ardèche, but Antoine Jérome Balard (one of the discoverers of the element bromine) wanted him back at the École Normale Supérieure as a graduate assistant (préparateur) for chemistry courses. He joined Balard and simultaneously started his research in crystallography and in 1847, he submitted his two theses, one in chemistry and the other in physics. After serving briefly as professor of physics at the Dijon Lycée in 1848, he became professor of chemistry at the University of Strasbourg, where he met and courted Marie Laurent, daughter of the university's rector in 1849.
They were married on May 29, 1849, and together had five children, only two of whom survived to adulthood; the other three died of typhoid. These personal tragedies were his motivations for curing infectious diseases.[2][6]

Professional career

Pasteur was appointed to the Chair of Chemistry in the faculty of sciences of the University of Strasbourg. In 1854, he was named dean of the new faculty of sciences at Lille University. It was on this occasion that Pasteur uttered his oft-quoted remark: "dans les champs de l'observation, le hasard ne favorise que les esprits préparés." (In the field of observation, chance favors only the prepared mind.[7]) In 1856, he moved to Paris as the director of scientific studies at the École Normale Supérieure where he took control from 1858 to 1867 and introduced a series of reforms. The examinations became more rigid, which led to better results, greater competition, and increased prestige. He raised the standard of scientific work, leading to two serious student revolts.[2] In 1862, he was appointed professor of geology, physics, and chemistry at the École nationale supérieure des Beaux-Arts, the position which held until his resignation in 1867. In Paris, he established the Pasteur Institute in 1887, in which he was its director for the rest of his life.[3][4][6]

Research contributions

Molecular asymmetry

Pasteur separated the left and right crystal shapes from each other to form two piles of crystals: in solution one form rotated light to the left, the other to the right, while an equal mixture of the two forms canceled each other's effect, and does not rotate the polarized light.

In Pasteur's early work as a chemist, he resolved a problem concerning the nature of tartaric acid (1848).[8][9][10][11][12] A solution of this compound derived from living things (specifically, wine lees) rotated the plane of polarization of light passing through it. The mystery was that tartaric acid derived by chemical synthesis had no such effect, even though its chemical reactions were identical and its elemental composition was the same.[13] This was the first time anyone had demonstrated chiral molecules.

Germ theory of fermentation

Pasteur demonstrated that fermentation is caused by the growth of micro-organisms, and the emergent growth of bacteria in nutrient broths is due not to spontaneous generation, but rather to biogenesis (Omne vivum ex vivo "all life from life").
Pasteur experimenting in his laboratory.
Bottle en col de cygne (swan neck duct) used by Pasteur

He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths unless the flasks were broken open, showing that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. This was one of the last and most important experiments disproving the theory of spontaneous generation.

While Pasteur was not the first to propose the germ theory (Girolamo Fracastoro, Agostino Bassi, Friedrich Henle and others had suggested it earlier), he developed it and conducted experiments that clearly indicated its correctness and managed to convince most of Europe that it was true. Today, he is often regarded as the father of germ theory.[14]

Pasteur's research also showed that the growth of micro-organisms was responsible for spoiling beverages, such as beer, wine and milk. With this established, he invented a process in which liquids such as milk were heated to kill most bacteria and moulds already present within them. Claude Bernard and he completed the first test on April 20, 1862. This process was soon afterwards known as pasteurization.[14]

Beverage contamination led Pasteur to the idea that micro-organisms infecting animals and humans cause disease. He proposed preventing the entry of micro-organisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.

In 1865, two parasitic diseases called pébrine and flacherie were killing great numbers of silkworms at Alais (now Alès). Pasteur worked several years proving that these diseases were caused by a microbe attacking silkworm eggs, and that eliminating the microbe in silkworm nurseries would eradicate the disease.[14]

Pasteur also discovered anaerobiosis, whereby some micro-organisms can develop and live without air or oxygen, called the Pasteur effect.

Immunology and vaccination

Pasteur's later work on diseases included work on chicken cholera. During this work, a culture of the responsible bacteria had spoiled and failed to induce the disease in some chickens he was infecting with the disease. Upon reusing these healthy chickens, Pasteur discovered he could not infect them, even with fresh bacteria; the weakened bacteria had caused the chickens to become immune to the disease, though they had caused only mild symptoms.[2][14]

His assistant, Charles Chamberland (of French origin), had been instructed to inoculate the chickens after Pasteur went on holiday. Chamberland failed to do this, but instead went on holiday himself. On his return, the month-old cultures made the chickens unwell, but instead of the infections being fatal, as they usually were, the chickens recovered completely. Chamberland assumed an error had been made, and wanted to discard the apparently faulty culture when Pasteur stopped him. Pasteur guessed the recovered animals now might be immune to the disease, as were the animals at Eure-et-Loir that had recovered from anthrax.[15]

In the 1870s, he applied this immunization method to anthrax, which affected cattle, and aroused interest in combating other diseases.
Louis Pasteur in his laboratory, painting by A. Edelfeldt in 1885

Pasteur publicly claimed he had made the anthrax vaccine by exposing the bacilli to oxygen. His laboratory notebooks, now in the Bibliothèque Nationale in Paris, in fact show that he used the method of rival Jean-Joseph-Henri Toussaint, a Toulouse veterinary surgeon, to create the anthrax vaccine.[13][16] This method used the oxidizing agent potassium dichromate. Pasteur's oxygen method did eventually produce a vaccine but only after he had been awarded a patent on the production of an anthrax vaccine.

The notion of a weak form of a disease causing immunity to the virulent version was not new; this had been known for a long time for smallpox. Inoculation with smallpox was known to result in far less scarring, and greatly reduced mortality, in comparison with the naturally acquired disease. Edward Jenner had also discovered vaccination using cowpox to give cross-immunity to smallpox in 1796, and by Pasteur's time this had generally replaced the use of actual smallpox material in inoculation. The difference between smallpox vaccination and anthrax or chicken cholera vaccination was that the weakened form of the latter two disease organisms had been "generated artificially", so a naturally weak form of the disease organism did not need to be found. This discovery revolutionized work in infectious diseases, and Pasteur gave these artificially weakened diseases the generic name of "vaccines", in honour of Jenner's discovery. Pasteur produced the first vaccine for rabies by growing the virus in rabbits, and then weakening it by drying the affected nerve tissue.

The rabies vaccine was initially created by Emile Roux, a French doctor and a colleague of Pasteur who had been working with a killed vaccine produced by desiccating the spinal cords of infected rabbits. The vaccine had been tested only on 11 dogs before its first human trial. This vaccine was first used on 9-year old Joseph Meister, on July 6, 1885, after the boy was badly mauled by a rabid dog.[13] This was done at some personal risk for Pasteur, since he was not a licensed physician and could have faced prosecution for treating the boy. After consulting with colleagues, he decided to go ahead with the treatment. Three months later he examined Meister and found that he was in good health.[17] Pasteur was hailed as a hero and the legal matter was not pursued. The treatment's success laid the foundations for the manufacture of many other vaccines. The first of the Pasteur Institutes was also built on the basis of this achievement.[13]

Legal risk was not the only kind Pasteur undertook. In The Story of San Michele, Axel Munthe writes of the rabies vaccine research:
Pasteur himself was absolutely fearless. Anxious to secure a sample of saliva straight from the jaws of a rabid dog, I once saw him with the glass tube held between his lips draw a few drops of the deadly saliva from the mouth of a rabid bull-dog, held on the table by two assistants, their hands protected by leather gloves.
Because of his study in germs, Pasteur encouraged doctors to sanitize their hands and equipment before surgery. Prior to this, few doctors or their assistants practiced these procedures.

Pasteur Institute

The Pasteur Institute was established by Pasteur to perpetuate his commitment to basic research and its practical applications. He brought together scientists with various specialties. The first five departments were directed by two normaliens (graduates of the École Normale Supérieure): Emile Duclaux (general microbiology research) and Charles Chamberland (microbe research applied to hygiene), as well as a biologist, Ilya Ilyich Mechnikov (morphological microbe research) and two physicians, Jacques-Joseph Grancher (rabies) and Emile Roux (technical microbe research). One year after the inauguration of the institute, Roux set up the first course of microbiology ever taught in the world, then entitled Cours de Microbie Technique (Course of microbe research techniques). Since 1891 the Pasteur Institute had been extended to different countries, and currently there are 32 institutes in 29 countries in various parts of the world.[18]

Faith and spirituality

His grandson, Louis Pasteur Vallery-Radot, wrote that Pasteur had only kept from his Catholic background a spiritualism without religious practice,[19] although Catholic observers often said Louis Pasteur remained throughout his whole life an ardent Christian, and his son-in-law, in perhaps the most complete biography of Louis Pasteur, writes:
Absolute faith in God and in Eternity, and a conviction that the power for good given to us in this world will be continued beyond it, were feelings which pervaded his whole life; the virtues of the gospel had ever been present to him. Full of respect for the form of religion which had been that of his forefathers, he came simply to it and naturally for spiritual help in these last weeks of his life.[20]
Maurice Vallery-Radot, grandson of the brother of the son-in-law of Pasteur and outspoken Catholic, also holds that Pasteur fundamentally remained Catholic.[21] According to both Pasteur Vallery-Radot and Maurice Vallery-Radot, the following well-known quotation attributed to Pasteur is apocryphal:[22] "The more I know, the more nearly is my faith that of the Breton peasant. Could I but know all I would have the faith of a Breton peasant's wife".[2] According to Maurice Vallery-Radot,[23] the false quotation appeared for the first time shortly after the death of Pasteur.[24] However, despite his belief in God, it has been said that his views were that of a freethinker rather than a Catholic, a spiritual more than a religious man.[25][26][27] He was also against mixing science with religion.[28][29]

Principal works

Pasteur's principal works are:[2]

French TitleYearEnglish Title
Etudes sur le Vin1866Studies on Wine
"Etudes sur le Vinaigre"1868Studies on Vinegar
"Etudes sur la Maladie des Vers à Soie" (2 volumes)1870Studies on Silk Worm Disease
 ; "Quelques Réflexions sur la Science en France"1871Some Reflections on Science in France
"Etudes sur la Bière"1876Studies on Beer
"Les Microbes organisés, leur rôle dans la Fermentation, la Putréfaction et la Contagion'"1878Microbes organized, their role in fermentation, putrefaction and the Contagion
"Discours de Réception de M.L. Pasteur à l'Académie française"1882Speech by Mr L. Pasteur on reception to the Académie française
"Traitement de la Rage"1886Treatment of Rabies


Honours and final days

Pasteur was frequently struck by strokes since 1868, and the one in 1894 severely impaired his health. Failing to fully recover from the shock, he died in 1895, near Paris.[13] He was given a state funeral and was buried in the Cathedral of Notre Dame, but his remains were reinterred in a crypt in the Pasteur Institute in Paris, where the crypt is engraved with his life-saving works.

He was awarded the prize of 1,500 francs in 1853 by the Pharmaceutical Society for the synthesis of racemic acid. In 1856 the Royal Society of London presented him the Rumford Medal for his discovery of the nature of racemic acid and its relations to polarized light, and the Copley medal in 1874 for his work on fermentation. The French Academy of Sciences awarded him the Montyon Prizes in 1859 for experimental physiology, and the Jecker Prize in 1861 and the Alhumbert Prize in 1862 for his experimental refutation of spontaneous generation. Though he lost election in 1857 for membership to the French Academy of Sciences, he won it in 1862 in mineralogy section, and was appointed to permanent secretary of the physical science section of the academy in 1887. In 1873 he was elected to the Académie Nationale de Médecine. He was elected to Littré's seat at the Académie française in 1881.

In 1873 he was made the commander in the Brazilian Order of the Rose.

Pasteur won the Leeuwenhoek medal, microbiology's highest Dutch honor in Arts and Sciences, in 1895. Both the Institute Pasteur and Université Louis Pasteur were named after him.

He was made a Chevalier or Knight of the Legion of Honour in 1853, promoted to Commander in 1868, to Grand Officer in 1878 and made a Grand Croix of the Legion of Honor – one of only 75 in all of France - in 1881.[6]

On June 8, 1886, the Ottoman Sultan Abdul Hamid II awarded Pasteur with the Order of the Medjidie (I Class) and 10000 Ottoman liras.[31]

Legacy

Pasteur's street in Odessa.
Vulitsya Pastera or Pasteur Street in Odessa, Ukraine

In many localities worldwide, streets are named in his honor. For example, in the USA: Palo Alto and Irvine, California, Boston and Polk, Florida, adjacent to the University of Texas Health Science Center at San Antonio; Jonquière, Québec; San Salvador de Jujuy and Buenos Aires (Argentina), Great Yarmouth in Norfolk, in the United Kingdom, Jericho and Wulguru in Queensland, (Australia); Phnom Penh in Cambodia; Ho Chi Minh City; Batna in Algeria; Bandung in Indonesia, Tehran in Iran, near the central campus of the Warsaw University in Warsaw, Poland; adjacent to the Odessa State Medical University in Odessa, Ukraine; Milan in Italy and Bucharest, Cluj-Napoca and Timișoara in Romania. The Avenue Pasteur in Saigon, Vietnam, is one of the few streets in that city to retain its French name.

Avenue Louis Pasteur in the Longwood Medical and Academic Area in Boston, Massachusetts was named in his honor in the French manner with "Avenue" preceding the name of the dedicatee.[32]
The Lycée Pasteur in Neuilly-sur-Seine, France, Lycée Louis Pasteur in Calgary, Canada and a large university hospital in Košice, Slovakia are also named after him.

His statue is erected at San Rafael High School in San Rafael, California.

A bronze bust of Pasteur resides on the French Campus of Kaiser Permanente's San Francisco Medical Center in San Francisco, California. The sculpture was designed by Harriet G. Moore and cast in 1984 by Artworks Foundry.[33]

Controversies

Anthrax vaccine

In 1995, the centennial of the death of Louis Pasteur, the New York Times ran an article titled "Pasteur's Deception". After having thoroughly read Pasteur's lab notes, the science historian Gerald L. Geison declared Pasteur had given a misleading account of the preparation of the anthrax vaccine used in the experiment at Pouilly-le-Fort.[34] Max Perutz published a vigorous defense of Pasteur in the New York Review of Books.[35] The fact is that Pasteur publicly claimed his success in developing anthrax vaccine in 1881.[17] However his admirer-turned-rival, a veterinarian Toussaint was the one who developed the first vaccine. Toussaint isolated the Gram-negative bacteria cholera des poules (later named – to add irony – Pasteurella in honour of Pasteur) in 1879 and gave samples to Pasteur who used for his own works. In 1880 with his publishing on July 12 at the French Academy of Sciences, Toussaint presented his successful result with an attenuated vaccine against anthrax in dogs and sheep.[36] Pasteur purely on grounds of jealousy contested the discovery by publicly displaying his vaccination method in Pouilly-le-Fort on 5 May 1881. The promotional experiment was a success and helped Pasteur sell his products, getting all the benefits and glory.[37][38][39]

Experimental ethics

Pasteur experiments are often cited as against medical ethics, especially on his vaccination of Meister. Firstly, he did not have any experience in medical practice, and more importantly, a medical license. This is often cited as a serious threat to his professional and personal reputation.[40][41] Even his closest partner Dr. Emile Roux refused to participate in the unjust clinical trial.[42] But Pasteur executed vaccination of the boy under the close watch of practising physician Jacques-Joseph Grancher, head of the paediatric clinic at Paris Children's Hospital. He was even not allowed to hold the syringe, although the inoculations were entirely under his supervision.[43] It was Grancher who was responsible for the injections, and defended Pasteur before the French National Academy of Medicine in the issue.[44] Still giving someone a clinical test without proper diagnosis was unjustifiable. (Meister had not shown symptoms of rabies at the time.) Secondly, he kept secrecy of his procedure and did not give proper pre-clinical trials. But these accussations were not entirely correct. He disclosed his methods to a small group of scientists. He also tested vaccination in 40 dogs before his use in human.[45][46][47]

Jane Austin

Jane G. Austin

From Wikipedia, the free encyclopedia
 
Jane Goodwin Austin
Jane Goodwin Austin.jpg
BornMary Jane Goodwin
(1831-02-25)February 25, 1831
Worcester, Massachusetts
DiedMarch 30, 1894(1894-03-30) (aged 63)
Boston, Massachusetts
OccupationAuthor
LanguageEnglish
NationalityAmerican
GenreHistorical fiction
Notable worksBetty Alden: the first-born daughter of the Pilgrims[1]
SpouseHenry Austin
ChildrenRose Standish Austin, Le Baron Loring Austin, Lilian Ivers De Silva

Jane Goodwin Austin (Feb. 25, 1831 - March 30, 1894), born Mary Jane Goodwin, was an American writer, notable for her popular stories of the time. During her lifetime, she was the author of 24 books and numerous short stories.[2] Her friends throughout her life were some of the most well-known American authors, including Ralph Waldo Emerson, Nathaniel Hawthorne, and Louisa May Alcott.[3]

Life

Austin was born on February 25, 1831, in Worcester, Massachusetts, to Isaac Goodwin and Elizabeth Hammatt.[4] Her parents were from Plymouth and could trace eight distinct family lines back to the Pilgrims.[5] Jane's father, a lawyer, antiquary and genealogist, died in 1833, when she was only two. Behind him, he left a large archive of historical and legal documents from the Pilgrims. Her works, mostly historical fiction regarding the lives of the Pilgrims and their descendants, were accurate and reasonable through the impact her father's love of history had had on her.[4] Her brother, John A. Goodwin, had also written a book on the Pilgrims, The Pilgrim Republic. Her mother was a poet and song writer, and told Jane many stories of her ancestors, especially of Francis Le Baron — the nameless nobleman — and his descendants.[5] As a child, she was educated at nine different private schools in Boston.[1]

In 1850, she married Loring H. Austin, a classmate of James Russell Lowell. She lived for several years in Cambridge, and afterward in Concord, but her later life was chiefly spent in Boston.[6]

Works

  • Fairy Dreams (Boston, 1859)
  • Dora Darling (Boston, 1864)
  • Outpost: A Novel (1886)
  • Cipher: A Romance (New York, 1869)
  • The Shadow of Moloch Mountain (1870)
  • Mrs. Beauchamp Brown (Boston, 1880)
  • A Nameless Nobleman (1881)
  • The Desmond Hundred (1882)
  • Standish of Standish (1889)
  • Dr. Le Baron and his Daughter (1891)
  • David Alden's Daughter, and other Stories (1892)
She wrote a great number of magazine stories and some poems.

Ionizing radiation

Ionizing radiation

From Wikipedia, the free encyclopedia
   
Ionizing (or ionising) radiation is radiation that carries enough energy to liberate electrons from atoms or molecules, thereby ionizing them. Ionizing radiation comprises subatomic particles, ions or atoms moving at relativistic speeds, and electromagnetic waves on the short wavelength end of the electromagnetic spectrum. Gamma rays, X-rays, and the upper vacuum ultraviolet part of the ultraviolet spectrum are ionizing, whereas the lower ultraviolet, visible light (including laser light), infrared, microwaves, and radio waves are considered non-ionizing radiation.

Typical particles include alpha particles, beta particles and neutrons, as well as mesons that constitute cosmic rays.[1][2]

Ionizing radiation arises from a variety of sources, such as bombardment of the Earth by cosmic rays, the decay of radioactive materials, matter at extremely high temperatures (e.g. plasma discharge or the corona of the Sun), or acceleration of charged particles by electromagnetic fields (e.g. lightning or supernova explosions). Ionizing radiation can also be generated by the production of high energy particles in X-ray tubes and particle accelerators.

Ionizing radiation is invisible and not directly detectable by human senses, so radiation detection instruments such as Geiger counters are required. However, in some cases ionising radiation may lead to secondary emission of visible light upon interaction with matter, such as in Cherenkov radiation and radioluminescence.

It is applied in a wide variety of fields such as medicine, research, manufacturing, construction, and many other areas, but presents a health hazard if proper measures against undesired exposure aren't followed. Exposure to ionizing radiation causes damage to living tissue, and can result in mutation, radiation sickness, cancer, and death.

Types of ionizing radiation

 
Alpha (α) radiation consists of a fast-moving helium-4 (4He) nucleus and is stopped by a sheet of paper. Beta (β) radiation, consisting of electrons, is halted by an aluminium plate. Gamma (γ) radiation, consisting of energetic photons, is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons that are blocked using light elements, like hydrogen, which slow and/or capture them. Not shown: galactic cosmic rays that consist of energetic charged nuclei like protons, helium nuclei, and high-charged nuclei called HZE ions.

Ionizing radiation is categorized by the nature of the particles or electromagnetic waves creating the ionising effect. These have different ionization mechanisms, and may be grouped as directly or indirectly ionizing.

Directly ionizing

Any charged massive particle can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. This includes atomic nuclei, electrons, muons, charged pions, protons, and energetic charged nuclei stripped of their electrons, all of which must be moving at relativistic speeds to reach the required kinetic energy. The first two to be recognized were given special names, which are used today: Helium nuclei at relativistic speeds are called alpha particles, and electrons at relativistic speeds are called beta particles. Natural cosmic rays are made up primarily of relativistic protons but also include heavier atomic nuclei like helium ions and HZE ions and muons. Charged pions are very short-lived and seen only in large amounts in particle accelerators.

Alpha particles

Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+ or 4
2
He2+
indicating a Helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) Helium atom 4
2
He
.

They are a highly ionizing form of particle radiation, and when resulting from radioactive alpha decay have low penetration depth. They can be stopped by a few centimetres of air, or by the skin. However, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. The helium nuclei that form 10-12% of cosmic rays are also usually of much higher energy than those produced by nuclear decay processes, and are thus capable of being highly penetrating and able to traverse the human body and dense shielding, depending on their energy.

Beta particles

Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei, such as potassium-40. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β and β+, which respectively give rise to the electron and the positron.[3]

High-energy beta particles may produce X-rays known as bremsstrahlung ("braking radiation") or secondary electrons (delta ray)as they pass through matter. Both of these can subsequently ionize as an indirect ionization effect.

Bremsstrahlung is of concern when shielding beta emitters, because interaction of beta particles with the shielding material produces Bremsstrahlung radiation. This effect is greater with material of high atomic numbers, so material with low atomic numbers is used for beta source shielding.

Positrons

The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons (see electron–positron annihilation).

Positrons may be generated by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon. Positrons are common artificial sources of ionizing radiation in medical PET scans.

As positrons are positively charged particles they can also directly ionize an atom through Coulomb interactions.

Indirectly ionizing

Radiation interaction - gamma rays are represented by wavy lines, charged particles and neutrons by straight lines. The small circles show where ionization occurs.

Indirect ionising radiation is electrically neutral and therefore does not interact strongly with matter. The bulk of the ionisation effects are due to secondary ionisations.

Photon radiation

 
Different types of electromagnetic radiation
The total absorption coefficient of lead (atomic number 82) for gamma rays, plotted versus gamma energy, and the contributions by the three effects. Here, the photoelectric effect dominates at low energy. Above 5 MeV, pair production starts to dominate.

Even though photons are electrically neutral, they can ionize atoms directly through the photoelectric effect and the Compton effect. Either of those interactions will eject an electron at relativistic speeds, turning it into a beta particle that will ionize many more atoms. Since most of the affected atoms are ionized indirectly by the secondary beta particles, photons are considered to be indirectly ionizing.[4]
Photon radiation is called gamma rays if produced by a nuclear reaction, subatomic particle decay, or radioactive decay within the nucleus. It is otherwise called x-rays if produced outside the nucleus. The generic term photon is therefore used to describe both.[5][6][7]

X-rays normally have a lower energy than gamma rays, and an older convention was to define the boundary as a wavelength of 10−11 m or a photon energy of 100 keV.[8] That threshold was driven by limitations of older X-ray tubes and low awareness of isomeric transitions. Modern technologies and discoveries have resulted in an overlap between X-ray and gamma energies. In many fields they are functionally identical, differing for terrestrial studies only in origin of the radiation. In astronomy, however, where radiation origin often cannot be reliably determined, the old energy division has been preserved, with X-rays defined as being between about 120 eV and 120 keV, and gamma rays as being of any energy above 100 to 120 keV, regardless of source. Most astronomical "gamma-ray astronomy" are known not to originate in nuclear radioactive processes but, rather, result from processes like those that produce astronomical X-rays, except driven by much more energetic electrons.

Photoelectric absorption is the dominant mechanism in organic materials for photon energies below 100 keV, typical of classical X-ray tube originated X-rays. At energies beyond 100 keV, photons ionize matter increasingly through the Compton effect, and then indirectly through pair production at energies beyond 5 MeV. The accompanying interaction diagram shows two Compton scatterings happening sequentially. In every scattering event, the gamma ray transfers energy to an electron, and it continues on its path in a different direction and with reduced energy.

Charged nuclei

Charged nuclei are characteristic of galactic cosmic rays and solar particle events and have no natural sources on the earth. In space, however, very high energy protons, helium nuclei, and HZE ions can be initially stopped by relatively thin layers of shielding, clothes, or skin. However, the resulting interaction will generate secondary radiation and cause cascading biological effects. If just one atom of tissue is displaced by an energetic proton, for example, the collision will cause further interactions in the body. This is called "linear energy transfer" (LET), which utilizes elastic scattering.

LET can be visualized as a billiard ball hitting another in the manner of the conservation of momentum, sending both away with the energy of the first ball divided between the two unequally. When a charged nucleus strikes a relatively slow-moving nucleus of an object in space, LET occurs and neutrons, alpha particles, low-energy protons, and other nuclei will be released by the collisions and contribute to the total absorbed dose of tissue.[9]

Neutrons

Neutrons have zero electrical charge and cannot directly cause ionization. However, fast neutrons will interact with the protons in hydrogen via LET, and this mechanism scatters the nuclei of the materials in the target area. When neutrons strike the hydrogen nuclei, proton radiation (fast protons) results. These protons are ionizing because they are of high energy, are charged, and interact with the electrons in matter.

Neutrons that strike other nuclei besides hydrogen will transfer less energy to the other particle if LET does occur. But, for many nuclei struck by neutrons, inelastic scattering occurs. Whether elastic or inelastic scatter occurs is dependent on the speed of the neutron, whether fast or thermal or somewhere in between. It is also dependent on the nuclei it strikes and its neutron cross section.
In inelastic scattering, neutrons are readily absorbed in a process called neutron capture and attributes to the neutron activation of the nucleus. Neutron interactions with most types of matter in this manner usually produce radioactive nuclei. The abundant oxygen-16 nucleus, for example, undergoes neutron activation, rapidly decays by a proton emission forming nitrogen-16, which decays to oxygen-16.
This process contributes enormously to the radiation generated by a water-cooled nuclear reactor while operating, because the short-lived nitrogen-16 decay emits a powerful gamma ray and a proton.
Another dramatic activation occurs when small amounts of cobalt-59 are activated to cobalt-60, one of the most significant, long-lasting radioactive isotopes of nuclear power generation due to the half-life of 60Co.

For the best shielding of neutrons, hydrocarbons that have an abundance of hydrogen are used.
In fissile materials, secondary neutrons may produce nuclear chain reactions, causing a larger amount of ionization from the daughter products of fission.

Outside the nucleus, free neutrons are unstable and have a mean lifetime of 14 minutes, 42 seconds. Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay:[10]

In the diagram to the right, a neutron collides with a proton of the target material, and then becomes a fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by a nucleus in an (n,γ)-reaction that leads to the emission of a neutron capture photon. Such photons always have enough energy to qualify as ionizing radiation.

Physical Effects

 
Ionized air glows blue around a beam of particulate ionizing radiation from a cyclotron

Nuclear effects

Neutron radiation, alpha radiation, and extremely energetic gamma (> ~20 MeV) can cause nuclear transmutation and induced radioactivity. The relevant mechanisms are neutron activation, alpha absorption, and photodisintegration. A large enough number of transmutations can change macroscopic properties and cause targets to become radioactive themselves, even after the original source is removed.

Chemical effects

Ionization of molecules can lead to radiolysis (breaking chemical bonds), and formation of highly reactive free radicals. These free radicals may then react chemically with neighbouring materials even after the original radiation has stopped. (e.g., ozone cracking of polymers by ozone formed by ionization of air). Ionizing radiation can disrupt crystal lattices in metals, causing them to become amorphous, with consequent swelling, material creep, and embrittlement. Ionizing radiation can also accelerate existing chemical reactions such as polymerization and corrosion, by contributing to the activation energy required for the reaction. Optical materials darken under the effect of ionizing radiation.

High-intensity ionizing radiation in air can produce a visible ionized air glow of telltale bluish-purplish color. The glow can be observed, e.g., during criticality accidents, around mushroom clouds shortly after a nuclear explosion, or inside of a damaged nuclear reactor like during the Chernobyl disaster.

Monatomic fluids, e.g. molten sodium, have no chemical bonds to break and no crystal lattice to disturb, so they are immune to the chemical effects of ionizing radiation. Simple diatomic compounds with very negative enthalpy of formation, such as hydrogen fluoride will reform rapidly and spontaneously after ionization.

Electrical effects

Ionization of materials temporarily increases their conductivity, potentially permitting damaging current levels. This is a particular hazard in semiconductor microelectronics employed in electronic equipment, with subsequent currents introducing operation errors or even permanently damaging the devices. Devices intended for high radiation environments such as the nuclear industry and extra atmospheric (space) applications may be made radiation hard to resist such effects through design, material selection, and fabrication methods.

Proton radiation found in space can also cause single-event upsets in digital circuits.

The electrical effects of ionizing radiation are exploited in gas-filled radiation detectors, e.g. the Geiger-Muller counter or the ion chamber.

Health effects

In general, ionizing radiation is harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis.

Most adverse health effects of radiation exposure may be grouped in two general categories:
  • deterministic effects (harmful tissue reactions) due in large part to the killing/ malfunction of cells following high doses; and
  • stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.[11]
Its most common impact is the stochastic induction of cancer with a latent period of years or decades after exposure. The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. The most widely accepted model posits that the incidence of cancers due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5% per sievert.[12] If this linear model is correct, then natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second. Other stochastic effects of ionizing radiation are teratogenesis, cognitive decline, and heart disease.

High radiation dose gives rise to Deterministic effects which reliably occur above a threshold, and their severity increases with dose. Deterministic effects are not necessarily more or less serious than stochastic effects; either can ultimately lead to a temporary nuisance or a fatality. Examples are: radiation burns, and/or rapid fatality through acute radiation syndrome, chronic radiation syndrome, and radiation-induced thyroiditis.

Beneficially, controlled doses are used for medical imaging and radiotherapy, and some scientists suspect that low doses may have a mild hormetic effect that can improve health,[13] but the US National Academy of Sciences Biological Effects of Ionizing Radiation Committee "has concluded that there is no compelling evidence to indicate a dose threshold below which the risk of tumor induction is zero"[14]

When alpha particle emitting isotopes are ingested, they are far more dangerous than their half-life or decay rate would suggest. This is due to the high relative biological effectiveness of alpha radiation to cause biological damage after alpha-emitting radioisotopes enter living cells. Ingested alpha emitter radioisotopes such as transuranics or actinides are an average of about 20 times more dangerous, and in some experiments up to 1000 times more dangerous than an equivalent activity of beta emitting or gamma emitting radioisotopes.
External dose quantities used in radiation protection. See article on sievert on how these are calculated and used.

The human body cannot sense ionizing radiation except in very high doses, but the effects of ionization can be used to characterize the radiation. Parameters of interest include disintegration rate, particle flux, particle type, beam energy, kerma, dose rate, and radiation dose.

If the radiation type is not known then it can be determined by differential measurements in the presence of electrical fields, magnetic fields, or varying amounts of shielding.

The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake. Dose values may represent absorbed, equivalent, effective, or committed dose. The monitoring and calculation of doses to safeguard human health is called dosimetry and is undertaken within the science of health physics.
Key measurement tools are the use of dosimeters to give the external effective dose uptake and the use of bio-assay for ingested dose. The article on the sievert summarises the recommendations of the ICRU and ICRP on the use of dose quantities and includes a guide to the effects of ionizing radiation as measured in sieverts, and gives examples of approximate figures of dose uptake in certain situations.

The committed dose is a measure of the stochastic health risk due to an intake of radioactive material into the human body. The ICRP states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities. The radiation dose is determined from the intake using recommended dose coefficients".[15]

Measurement

The table below shows radiation and dose quantities in SI and non-SI units. The relationships of the ICRP dose quantities are shown in the accompanying diagram.
Graphic showing relationships between radioactivity and detected ionizing radiation
QuantityDetectorCGS unitsSI unitsOther units
Disintegration ratecuriebecquerel
Particle fluxgeiger counter, proportional counter, scintillatorcounts per minute, particles per cm2 per sec
Energy Fluencethermoluminescent dosimeter, Film badge dosimeterjoule/metre2
Beam energyproportional counterelectronvoltjoule
Linear energy transferderived quantityMeV/cmkeV/μm
Kermaionization chamber, semiconductor detector, quartz fiber dosimeter, Kearny Fallout Meteresu/cm3coulomb/kilogramroentgen
Absorbed dosecalorimeterradgrayrep
Equivalent dosederived quantityremsievert
Effective dosederived quantityremsievertBRET
Committed dosederived quantityremsievertbanana equivalent dose

Uses

Ionizing radiation has many industrial, military, and medical uses. Its usefulness must be balanced with its hazards, a compromise that has shifted over time. For example, at one time, assistants in shoe shops used X-rays to check a child's shoe size, but this practice was halted when the risks of ionizing radiation were better understood.[16]

Neutron radiation is essential to the working of nuclear reactors and nuclear weapons. The penetrating power of x-ray, gamma, beta, and positron radiation is used for medical imaging, nondestructive testing, and a variety of industrial gauges. Radioactive tracers are used in medical and industrial applications, as well as biological and radiation chemistry. Alpha radiation is used in static eliminators and smoke detectors. The sterilizing effects of ionizing radiation are useful for cleaning medical instruments, food irradiation, and the sterile insect technique. Measurements of Carbon-14, can be used to date the remains of long-dead organisms (such as wood that is thousands of years old).

Sources of radiation

Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields. Natural sources include the sun, lightning and supernova explosions. Artificial sources include nuclear reactors, particle accelerators, and x-ray tubes.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) itemized types of human exposures.

Type of radiation exposures
Public exposure
Natural SourcesNormal occurrencesCosmic radiation
Terrestrial radiation
Enhanced sourcesMetal mining and smelting
Phosphate industry
Coal mining and power production from coal
Oil and gas drilling
Rare earth and titanium dioxide industries
Zirconium and ceramics industries
Application of radium and thorium
Other exposure situations
Man-made sourcesPeaceful purposesNuclear power production
Transport of nuclear and radioactive material
Application other than nuclear power
Military purposesNuclear tests
Residues in the environment. Nuclear fallout
Historical situations
 
Exposure from accidents
 
Occupational radiation exposure
Natural SourcesCosmic ray exposures of aircrew and space crew
Exposures in extractive and processing industries
Gas and oil extraction industries
Radon exposure in workplaces other than mines
Man-made sourcesPeaceful purposesNuclear power industries
Medical uses of radiation
Industrial uses of radiation
Miscellaneous uses
Military purposesOther exposed workers
Source UNSCEAR 2008 Annex B retrieved 2011-7-4

The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake.

Background radiation

Background radiation comes from both natural and man-made sources.

The global average exposure of humans to ionizing radiation is about 3 mSv (0.3 rem) per year, 80% of which comes from nature. The remaining 20% results from exposure to man-made radiation sources, primarily from medical imaging. Average man-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine.

Natural background radiation comes from five primary sources: cosmic radiation, solar radiation, external terrestrial sources, radiation in the human body, and radon.

The background rate for natural radiation varies considerably with location, being as low as 1.5 mSv/a (1.5 mSv per year) in some areas and over 100 mSv/a in others. The highest level of purely natural radiation recorded on the Earth's surface is 90 µGy/h (0.8 Gy/a) on a Brazilian black beach composed of monazite.[17] The highest background radiation in an inhabited area is found in Ramsar, primarily due to naturally radioactive limestone used as a building material. Some 2000 of the most exposed residents receive an average radiation dose of 10 mGy per year, (1 rad/yr) ten times more than the ICRP recommended limit for exposure to the public from artificial sources.[18] Record levels were found in a house where the effective radiation dose due to external radiation was 135 mSv/a, (13.5 rem/yr) and the committed dose from radon was 640 mSv/a (64.0 rem/yr).[19] This unique case is over 200 times higher than the world average background radiation.

Cosmic radiation

The Earth, and all living things on it, are constantly bombarded by radiation from outside our solar system. This cosmic radiation consists of relativistic particles: positively-charged nuclei (ions) from 1 amu protons (about 85% of it) to 26 amu iron nuclei and even beyond. (The high-atomic number particles are called HZE ions.) The energy of this radiation can far exceed that which humans can create, even in the largest particle accelerators (see ultra-high-energy cosmic ray). This radiation interacts in the atmosphere to create secondary radiation that rains down, including x-rays, muons, protons, antiprotons, alpha particles, pions, electrons, positrons, and neutrons.

The dose from cosmic radiation is largely from muons, neutrons, and electrons, with a dose rate that varies in different parts of the world and based largely on the geomagnetic field, altitude, and solar cycle. The cosmic-radiation dose rate on airplanes is so high that, according to the United Nations UNSCEAR 2000 Report (see links at bottom), airline flight crew workers receive more dose on average than any other worker, including those in nuclear power plants. Airline crews receive more cosmic rays if they routinely work flight routes that take them close to the North or South pole at high altitudes, where this type of radiation is maximal.

Cosmic rays also include high-energy gamma rays, which are far beyond the energies produced by solar or human sources.

External terrestrial sources

Most materials on Earth contain some radioactive atoms, even if in small quantities. Most of the dose received from these sources is from gamma-ray emitters in building materials, or rocks and soil when outside. The major radionuclides of concern for terrestrial radiation are isotopes of potassium, uranium, and thorium. Each of these sources has been decreasing in activity since the formation of the Earth.

Internal radiation sources

All earthly materials that are the building-blocks of life contain a radioactive component. As humans, plants, and animals consume food, air, and water, an inventory of radioisotopes builds up within the organism (see banana equivalent dose). Some radionuclides, like potassium-40, emit a high-energy gamma ray that can be measured by sensitive electronic radiation measurement systems. These internal radiation sources contribute to an individual's total radiation dose from natural background radiation.

Radon

An important source of natural radiation is radon gas, which seeps continuously from bedrock but can, because of its high density, accumulate in poorly ventilated houses.

Radon-222 is a gas produced by the decay of radium-226. Both are a part of the natural uranium decay chain. Uranium is found in soil throughout the world in varying concentrations. Among non-smokers, radon is the largest cause of lung cancer and, overall, the second-leading cause.[20]

Radiation exposure

Various doses of radiation in sieverts, ranging from trivial to lethal.

There are three standard ways to limit exposure:
  1. Time: For people exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time will reduce the dose from the radiation source.
  2. Distance: Radiation intensity decreases sharply with distance, according to an inverse-square law (in an absolute vacuum).[21]
  3. Shielding: Air or skin can be sufficient to substantially attenuate low-energy alpha and beta radiation. Barriers of lead, concrete, or water give effective protection from more energetic particles such as gamma rays and neutrons. Some radioactive materials are stored or handled underwater or by remote control in rooms constructed of thick concrete or lined with lead.
  4. There are special plastic shields that stop beta particles, and air will stop most alpha particles. The effectiveness of a material in shielding radiation is determined by its half-value thicknesses, the thickness of material that reduces the radiation by half. This value is a function of the material itself and of the type and energy of ionizing radiation. Some generally accepted thicknesses of attenuating material are 5 mm of aluminum for most beta particles, and 3 inches of lead for gamma radiation.
These can all be applied to natural and man-made sources. For man-made sources the use of
Containment is a major tool in reducing dose uptake and is effectively a combination of shielding and isolation from the open environment. Radioactive materials are confined in the smallest possible space and kept out of the environment such as in a hot cell (for radiation) or glove box (for contamination). Radioactive isotopes for medical use, for example, are dispensed in closed handling facilities, usually gloveboxes, while nuclear reactors operate within closed systems with multiple barriers that keep the radioactive materials contained. Work rooms, hot cells and gloveboxes have slightly reduced air pressures to prevent escape of airborne material to the open environment.
In nuclear conflicts or civil nuclear releases civil defense measures can help reduce exposure of populations by reducing ingestion of isotopes and occupational exposure . One is the issue of potassium iodide (KI) tablets, which blocks the uptake of radioactive iodine (one of the major radioisotope products of nuclear fission) into the human thyroid gland.

Occupational exposure

Occupationally exposed individuals are controlled within the regulatory framework of the country they work in, and in accordance with any local nuclear licence constraints. These are usually based on the recommendations of the ICRP. The International Commission on Radiological Protection recommends limiting artificial irradiation. For occupational exposure, the limit is 50 mSv in a single year with a maximum of 100 mSv in a consecutive five-year period.[22]

The radiation exposure of these individuals is carefully monitored with the use of dosimeters and other radiological protection instruments which will measure radioactive particulate concentrations, area gamma dose readings and radioactive contamination. A legal record of dose is kept.

Examples of activities where occupational exposure is a concern include:
Some human-made radiation sources affect the body through direct radiation, known as effective dose (radiation) while others take the form of radioactive contamination and irradiate the body from within. This latter is known as committed dose

Public exposure

Medical procedures, such as diagnostic X-rays, nuclear medicine, and radiation therapy are by far the most significant source of human-made radiation exposure to the general public. Some of the major radionuclides used are I-131, Tc-99, Co-60, Ir-192, and Cs-137. The public also is exposed to radiation from consumer products, such as tobacco (polonium-210), combustible fuels (gas, coal, etc.), televisions, luminous watches and dials (tritium), airport X-ray systems, smoke detectors (americium), electron tubes, and gas lantern mantles (thorium).

Of lesser magnitude, members of the public are exposed to radiation from the nuclear fuel cycle, which includes the entire sequence from processing uranium to the disposal of the spent fuel. The effects of such exposure have not been reliably measured due to the extremely low doses involved. Opponents use a cancer per dose model to assert that such activities cause several hundred cases of cancer per year, an application of the widely accepted Linear no-threshold model (LNT).

The International Commission on Radiological Protection recommends limiting artificial irradiation to the public to an average of 1 mSv (0.001 Sv) of effective dose per year, not including medical and occupational exposures.[25]

In a nuclear war, gamma rays from both the initial weapon explosion and fallout would be the sources of radiation exposure.

Spaceflight

Massive particles are a concern for astronauts outside the earth's magnetic field who would receive solar particles from solar proton events (SPE) and galactic cosmic rays from cosmic sources. These high-energy charged nuclei are blocked by Earth's magnetic field but pose a major health concern for astronauts traveling to the moon and to any distant location beyond the earth orbit. Highly charged HZE ions in particular are known to be extremely damaging, although protons make up the vast majority of galactic cosmic rays. Evidence indicates past SPE radiation levels that would have been lethal for unprotected astronauts.[26]

Air travel

Air travel exposes people on aircraft to increased radiation from space as compared to sea level, including cosmic rays and from solar flare events.[27] Software programs such as Epcard, CARI, SIEVERT, PCAIRE are attempts to simulate exposure by aircrews and passengers.[27] An example of a measured dose (not simulated dose) is 6 μSv per hour from London Heathrow to Tokyo Narita on a high-latitude polar route.[27] However, dosages can vary, such as during periods of high solar activity.[27] The United States FAA requires airlines to provide flight crew with information about cosmic radiation, and an International Commission on Radiological Protection recommendation for the general public is no more than 1 mSv per year.[27] In addition, many airlines do not allow pregnant flightcrew members, to comply with a European Directive.[27] The FAA has a recommended limit of 1 mSv total for a pregnancy, and no more than 0.5 mSv per month.[27] Information originally based on Fundamentals of Aerospace Medicine published in 2008.[27]

Radiation hazard warning signs

Ionizing radiation hazard symbol
2007 ISO radioactivity danger symbol intended for IAEA Category 1, 2 and 3 sources defined as dangerous sources capable of death or serious injury.[28]

Hazardous levels of ionising radiation are signified by the trefoil sign on a yellow background. These are usually posted at the boundary of a radiation controlled area or in any place where radiation levels are significantly above background due to human intervention.

The red ionizing radiation warning symbol (ISO 21482) was launched in 2007, and is intended for IAEA Category 1, 2 and 3 sources defined as dangerous sources capable of death or serious injury, including food irradiators, teletherapy machines for cancer treatment and industrial radiography units.
The symbol is to be placed on the device housing the source, as a warning not to dismantle the device or to get any closer. It will not be visible under normal use, only if someone attempts to disassemble the device. The symbol will not be located on building access doors, transportation packages or containers.[29]

Introduction to entropy

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