X-ray optics- applied industry optics, which studies the processes of propagation of X-rays in media, and also develops elements for X-ray devices. X-ray optics, unlike conventional optics, considers electromagnetic waves in the wavelength range x-ray 10−4 to 100 (from 10−14 to 10−8) and gamma radiation < 10 −4 Å.
General information
One of the reasons for the development of X-ray optics is the possibility of obtaining X-ray microscopes images of objects with incredibly small sizes due to increased resolution optical systems when using shorter wavelengths. X-ray optics is also used in X-ray lasers And X-ray telescopes.
Materials used in conventional optics are not applicable in X-ray optics due to their proximity to unity refractive index X-rays. In other words, X-rays pass through matter, practically without changing their trajectory. In addition, X-rays are strongly absorbed in matter due to photoelectric effect. So a layer of air 1 cm thick is almost completely opaque for soft x-ray radiation. Therefore, for the operation of X-ray optical systems, it is necessary vacuum, and X-ray telescopes are carried out into the atmosphere.
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Work principles
The main task of X-ray optics is focusing X-rays. That's why the most important characteristics optical systems is focal length and the width of the output beam. There are several types of optical systems depending on the operating principle.
Reflective X-ray optics
X-ray mirror
The reflection of electromagnetic waves from the interface between two media is described in optics Fresnel formulas. At normal When incident on a mirror, the reflection coefficient turns out to be too small, that is, X-rays are practically not reflected, but are only absorbed by the mirror or pass through it. Therefore, normal incidence mirrors are not used in X-ray optics. As the angle of incidence increases, the reflection coefficient increases, which makes it possible to use “oblique” incidence mirrors (the beam in them slides along the surface of the mirror), used in X-ray astronomy(cm. Voltaire telescope).
Cone capillary
This device is a hollow conical tube. Vacuum for X-rays is an optically denser medium, so if the beam falls on the smooth surface of a capillary at an angle less than the critical one, then it experiences total reflection This principle is implemented in Kumakhov optics.
Diffraction optics
Zone plates
A Fresnel zone plate can also be used to focus X-rays. The principle of its operation is based on dividing the wave front into zones in such a way that neighboring zones are in antiphase. For example, if you close (darken) all even zones, then the remaining open odd zones will all be in the same phase. As a result of interference, the signal will be amplified many times over. X-ray zone plates were first obtained in 1988 at Lawrence Livermore National Laboratory.
Bragg-Fresnel optics
Main article: Bragg-Fresnel optics
The width of the zones in a Fresnel plate depends on the wavelength of the radiation, so the larger it is monochromatic, the better the record performs. Therefore, the zone plate is sprayed onto single crystal and monochromatic radiation is ensured Bragg diffraction.
X-ray refractive optics
In the X-ray range, almost all materials have a refractive index close to unity. Therefore, a separate lens would have an extremely long focal length, which cannot be used in an x-ray experiment. This problem is solved by creating voids in a certain material. certain size and shapes that behave like a series of lenses; and also by creating separate parabolic refractive lenses, sets of which can focus X-rays at a small focal length. Such devices in English literature are called
) on the base Pan American Union, existing since 1889.
| Organization of American States (OAS) | |
|---|---|
| Organization of American states (OAS) | |
| Emblem |
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| Membership | 35 member states |
| Headquarters | Washington , USA |
| Type of organization | international organization |
| official languages | Spanish, English, French, Portuguese |
| Base | |
| Date of foundation | |
| oas.org (English) | |
| Organization of American States (OAS) at Wikimedia Commons | |
The headquarters is located in Washington. Working languages - Spanish , English , French And Portuguese.
Higher authorities- General Assembly, Permanent Council, Consultative Meeting of Foreign Ministers, General Secretariat.
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The Organization of American States is the oldest regional organization in the world, dating back to the First International Conference of American States, held in Washington from October 1889 to April 1890. At this meeting it was approved the creation International Union American republics, and the stage was set for the creation of a network of provisions and institutions that became known as the All-American System. The OAS came into being in 1948 with the signing of the OAS Charter in Bogota, Colombia, which came into force in December 1951.
Countries that gained independence after 1948 were generally admitted to the OAS upon gaining independence, with the exception of Canada, which only joined the OAS in 1990, and Guyana, adopted in 1991 (25 years after independence; like Canada, Guyana is a member Commonwealth of Nations). Guyana is currently the latest country to be admitted to the OAS.
In the 2000s, the Cuban leadership repeatedly came up with proposals to restore membership in the OAS. The decision to suspend Cuba's participation was reversed June 3 2009; Cuba welcomed the gesture, but refused to return to the OAS.
At the OAS General Assembly in April 1971 the Institute of Permanent Observers of the OAS was established; At the beginning of 2015, 70 states had this status, including Russia , Ukraine , Kazakhstan , Azerbaijan , Georgia And Armenia.
In the 21st century, the position of the OAS has been greatly shaken due to the emergence of new regional organizations, uniting purely Latin American states, without the participation of the United States - such as Community of Latin American and Caribbean Countries(CELAC) and Union of South American Nations(UNASUR).
At the end of April 2017 Secretary General The OAS received a letter from the President of Venezuela Nicolas Maduro that Venezuela immediately leaves this organization.
Goals and directions
The Organization was created for the purpose of achieving peace among its member states, as provided for in Article 1 of the Charter:
Maintain peace and justice, promote solidarity, strengthen cooperation and defend our sovereignty, our territorial integrity, and independence.
Today the OAS unites 34 states of Northern and South America(except Cuba) and is the main political, legal and social force in the hemisphere. [ ]
The organization uses four directions to effectively implement its main goal, based on its core principles: democracy, human rights, security and development.
General Assembly
Supreme governing body The OAS has a General Assembly. Every year, the OAS convenes a scheduled session of the assembly; in special cases, with the approval of two-thirds of the organization’s members, the Permanent Council can announce the convening of an extraordinary session.
Sessions meet in participating states, one by one. Countries are represented by elected delegates, usually foreign ministers or their deputies. Each member state has one vote in the Assembly. Solutions for individual important issues, determined by the rules of the assembly, are adopted by a two-thirds majority of the member states; In most cases, a simple majority vote is sufficient.
The powers of the General Assembly include determining general policy through resolutions and declarations, approving the budget, determining the amounts of contributions from member states, hearing reports and reports of special bodies of the OAS for the past year and electing members to these institutions.
Organization of American States, OAS (Spanish: Organización de los estados americanos, English: Organization of American states, French: Organization des États américains, port: Organização dos Estados Americanos) – international organization, created on April 30, 1948 at the 9th Inter-American Conference in Bogota (Colombia) on the basis of the Pan American Union, which had existed since 1889.
The Organization of American States was created for the purpose of achieving among its member states, as provided in Article 1 of the Charter, "to maintain peace and justice, promote solidarity, enhance cooperation and defend their sovereignty, their territorial integrity, and independence."
Today, the Organization of American States brings together 35 independent states Americas and is the main political, legal and social force in the hemisphere.
The Organization of American States uses four pillars to effectively implement its core purpose, based on its core principles: democracy, human rights, security and development.
Member States of the Organization of American States: Antigua and Barbuda, Argentina, Bahamas, Barbados, Belize, Bolivia, Brazil, Venezuela, Haiti, Guyana, Guatemala, Honduras, Grenada, Dominica, Dominican Republic, Canada, Colombia, Costa Rica, Cuba, Mexico, Nicaragua, Panama, Paraguay, Peru, El Salvador, Saint Vincent and the Grenadines, Saint Kitts and Nevis, Saint Lucia, USA, Suriname, Trinidad and Tobago, Uruguay, Chile , Ecuador, Jamaica.
The headquarters is located in Washington. Working languages are Spanish, English, French and Portuguese.
The highest bodies are the General Assembly, the Permanent Council, the Consultative Meeting of Foreign Ministers, the General Secretariat.
The Organization of American States is one of the oldest regional organizations in the world, dating back to the First International Conference of American States held in Washington. At this meeting, the creation of the International Union of American Republics was approved, and the stage was set for the creation of a network of regulations and institutions that became known as the All-American System. The Organization of American States was born in 1948 in connection with the signing of the OAS Charter in Bogota, Colombia, which came into force in December 1951.
Countries that gained independence after 1948 were generally admitted to the Organization of American States upon gaining independence, with the exception of Canada, which did not join the Organization of American States until 1990, and Guyana, which did not join the Organization of American States until 1991 (after 25 years after independence).
Until 1962, Cuba, as a member of the Organization of American States, took part in its work, but after Cuba transitioned to the socialist path of development, the leadership of the Organization of American States considered this incompatible with the system collective security America and suspended the Cuban government's membership in the organization. Cuba and the Soviet bloc countries considered this decision illegal. In the 2000s, the Cuban leadership repeatedly came up with proposals to restore membership in the Organization of American States. The decision to suspend Cuba's participation was reversed on June 3, 2009, but Cuba itself refused to return to the Organization of American States.
At the OAS General Assembly in April 1971, the institution of permanent observers of the OAS was established. At the end of the 2000s, the EU and 62 states, including Russia, had this status.
On July 4, 2009, the government of Honduras, which came as a result of a military coup, announced the denunciation of the OAS Charter and the immediate withdrawal of its country from this organization. Earlier, on July 2, 2009, the leadership of the Organization of American States demanded that power in the country be returned to President Manuel Zelaya within 72 hours, threatening otherwise to expel Honduras from the organization. On June 1, 2011, after ousted Honduran President Manuel Zelaye and current president Honduran Porfirio Lobo concluded an agreement on national reconciliation, Honduras' membership in the Organization of American States was restored.
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