terça-feira, 24 de setembro de 2013

O desacelerador de anti-protões


A Fábrica de anti-matéria

A fábrica de anti-matéria

O Des-acelarador Anti-protão , máquina única de seu tipo, produz anti-protões de baixa energia para estudar a antimatéria e, em especial criar anti-átomos. No passado, no CERN e em outros lugares ", plantas anti-partículas " consistia de uma cadeia des-acelaradores , cada um executando uma das fases da criação de anti-partículas . Actualmente, o Decelerator realizado sozinho todas as tarefas associadas com a "produção" de antimatéria da produção de antiprótons para enviá-los a diferentes experiências.

Tudo começa com um feixe de prótons do PS ( Proton Synchrotron ) lançado contra um alvo metálico . A energia liberada é suficiente para obter uma vez em um milhão de colisões de um par próton- antipróton . Estes antiprotons que se deslocam a uma velocidade próxima da luz , são demasiado enérgicas para ser utilizado directamente na produção de anti- átomos. Eles também têm diferentes energias e movimentar de forma irregular. É graças aos rebeldes desacelerador de partículas são domados e transformado em vigas de baixa energia , usados ​​mais tarde na produção de antimatéria.





No primeiro, um anel ímã flexão e mantém foco antiprótons na mesma trajetória, como os fortes campos elétricos lentos. Em seguida, a dispersão de energias e desvios são reduzidos através da técnica de "cooling". Depois diminuiu para cerca de um décimo da velocidade da luz, pode ser ejectado antiprotons. Assim termina, depois de cerca de um minuto, um "ciclo de desaceleração."

Em 2002, a antimatéria acelerador foi o local de um grande primeiro científica: a ATHENA e colaborações ATRAP com o Decelerator foram capazes de produzir grandes quantidades de anti-átomos. Actualmente, a AD é usado em três experimentos que estudam a antimatéria: ALPHA e ATRAP ASACUSA. Os antipr'otons são também objecto do experimento ACE é avaliar o seu potencial para o tratamento de cancro.

Antimatter

In particle physics, antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but have opposite charge and other particle properties such as lepton and baryon number. Encounters between particles and antiparticles lead to the annihilation of both, giving rise to varying proportions of high-energy photons (gamma rays), neutrinos, and lower-mass particle–antiparticle pairs. 

Setting aside the mass of any product neutrinos, which represent released energy which generally continues to be unavailable, the end result of annihilation is a release of energy available to do work, proportional to the total matter and antimatter mass, in accord with the mass-energy equivalence equation, E=mc2.

Antiparticles bind with each other to form antimatter just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton can form an an tihydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements. To date, however, anti-atoms more complex than antihelium have neither been artificially produced nor observed in nature. Studies of cosmic rays have identified both positrons and antiprotons, presumably produced by high-energy collisions between particles of ordinary matter.

There is considerable speculation as to why the observable universe is apparently composed almost entirely of ordinary matter, as opposed to a more symmetric combination of matter and antimatter. This asymmetry of matter and antimatter in the visible universe is one of the greatest unsolved problems in physics.[2] The process by which this asymmetry between particles and antiparticles developed is called baryogenesis.

Antimatter in the form of anti-atoms is one of the most difficult materials to produce. Antimatter in the form of individual anti-particles, however, is commonly produced by particle accelerators and in some types of radioactive decay.

In 1995, CERN announced that it had successfully brought into existence nine antihydrogen atoms by implementing the SLAC/Fermilab concept during the PS210 experiment. The experiment was performed using the Low Energy Antiproton Ring (LEAR), and was led by Walter Oelert and Mario Macri. Fermilab soon confirmed the CERN findings by producing approximately 100 antihydrogen atoms at their facilities. 

The antihydrogen atoms created during PS210 and subsequent experiments (at both CERN and Fermilab) were extremely energetic ("hot") and were not well suited to study. To resolve this hurdle, and to gain a better understanding of antihydrogen, two collaborations were formed in the late 1990s, namely, ATHENA and ATRAP. In 2005, ATHENA disbanded and some of the former members (along with others) formed the ALPHA Collaboration, which is also based at CERN. The primary goal of these collaborations is the creation of less energetic ("cold") antihydrogen, better suited to study

In 1999, CERN activated the Antiproton Decelerator, a device capable of decelerating antiprotons from 3.5 GeV to 5.3 MeV — still too "hot" to produce study-effective antihydrogen, but a huge leap forward. In late 2002 the ATHENA project announced that they had created the world's first "cold" antihydrogen.[27] The ATRAP project released similar results very shortly thereafter. 

The antiprotons used in these experiments were cooled by decelerating them with the Antiproton Decelerator, passing them through a thin sheet of foil, and finally capturing them in a Penning-Malmberg trap. The overall cooling process is workable, but highly inefficient; approximately 25 million antiprotons leave the Antiproton Decelerator and roughly 25,000 make it to the Penning-Malmberg trap, which is about 1⁄1000or 0.1% of the original amount.

The antiprotons are still hot when initially trapped. To cool them further, they are mixed into an electron plasma. The electrons in this plasma cool via cyclotron radiation, and then sympathetically cool the antiprotons via Coulomb collisions. Eventually, the electrons are removed by the application of short-duration electric fields, leaving the antiprotons with energies less than 100 meV.[30] While the antiprotons are being cooled in the first trap, a small cloud of positrons is captured from radioactive sodium in a Surko-style positron accumulator. This cloud is then recaptured in a second trap near the antiprotons. 

Manipulations of the trap electrodes then tip the antiprotons into the positron plasma, where some combine with antiprotons to form antihydrogen. This neutral antihydrogen is unaffected by the electric and magnetic fields used to trap the charged positrons and antiprotons, and within a few microseconds the antihydrogen hits the trap walls, where it annihilates. Some hundreds of millions of antihydrogen atoms have been made in this fashion.

Most of the sought-after high-precision tests of the properties of antihydrogen could only be performed if the antihydrogen were trapped, that is, held in place for a relatively long time. While antihydrogen atoms are electrically neutral, the spins of their component particles produce a magnetic moment. These magnetic moments can interact with an inhomogeneous magnetic field; some of the antihydrogen atoms can be attracted to a magnetic minimum. Such a minimum can be created by a combination of mirror and multipole fields.Antihydrogen can be trapped in such a magnetic minimum (minimum-B) trap; in November 2010, the ALPHA collaboration announced that they had so trapped 38 antihydrogen atoms for about a sixth of a second. This was the first time that neutral antimatter had been trapped.

On 26 April 2011, ALPHA announced that they had trapped 309 antihydrogen atoms, some for as long as 1,000 seconds (about 17 minutes). This was longer than neutral antimatter had ever been trapped before. ALPHA has used these trapped atoms to initiate research into the spectral properties of the antihydrogen.

The biggest limiting factor in the large-scale production of antimatter is the availability of antiprotons. Recent data released by CERN states that, when fully operational, their facilities are capable of producing ten million antiprotons per minute. Assuming a 100% conversion of antiprotons to antihydrogen, it would take 100 billion years to produce 1 gram or 1 mole of antihydrogen (approximately6.02×1023 atoms of antihydrogen).


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