Selasa, 16 Juni 2009

mengenal lebih jauh antimateri (sorry dont have time for translating)

sumber :

Does CERN exist?

Well, yes, it does. You can see us to the left and slightly up from the centre of the city of Meyrin.
Is it located in Switzerland?
Part is in Switzerland, part in France across the border. CERN is not a Swiss institute, but an international organization. We are very close to Geneva's international airport.
What does the acronym CERN mean?
That is a long story, but the name CERN is derived from the French ‘Conseil EuropĂ©en pour la Recherche NuclĂ©aire’.

Does it consist of red brick buildings with white-frocked scientists running around carrying files?

No, that is rather far from reality; we have mostly white buildings made of concrete and the scientists wear everyday clothes and they mostly do not carry files.
Was the Web really invented at CERN as the book states?
Yes, indeed, the Web came from CERN, invented here by Tim Berners-Lee in 1989.

Does antimatter exist?

Yes, it does, and we produce it routinely at CERN. Antimatter was predicted by P.A.M. Dirac in 1928 and the first antiparticles were discovered soon after by Carl Anderson. CERN is not the only research institute to produce and study antimatter.

How is antimatter contained?

It is very difficult to contain antimatter, because any contact between a particle and its anti-particle leads to their immediate annihilation.
For electrically charged antimatter particles we know how to contain them by using ‘electromagnetic traps’. These traps make it possible to contain up to about 1012 (anti-) particles of the same charge. However, like charges repel each other. So it is not possible to store a much larger quantity of e.g. antiprotons because the repulsive forces between them would become too strong for the electromagnetic fields to hold them away from the walls.
For electrically neutral anti-particles or anti-atoms, the situation is even more difficult. It is impossible to use constant electric or magnetic fields to contain neutral antimatter, because these fields have no grip on the particles at all. Scientists work on ideas to use ‘magnetic bottles’ (with inhomogeneous magnetic fields acting on the magnetic moment), or ‘optical traps’ (using lasers) but this is still under development.

What is the future use of antimatter?

Anti-electrons (positrons) are already used in PET scanners in medicine (Positron-Emission Tomography = PET). One day it might be even possible to use antiprotons for tumour irradiation.
But antimatter at CERN is mainly used to study the laws of nature. We focus on the question of the symmetry between matter and antimatter. The LHCb experiment will compare precisely the decay of b-quarks and anti-b-quarks. Eventually we also hope to be able to use anti-hydrogen atoms as high-precision tools.

Do antimatter atoms exist?

The team of the PS210 experiment at the Low Energy Antiproton Ring (LEAR) at CERN made the first anti-hydrogen atoms in 1995. Then, in 2002 two experiments (ATHENA and ATRAP) managed to produce tens of thousands of antihydrogen atoms, later even millions. However, although "tens of thousands" may sound a lot, it's really a very, very small amount. You would need 10,000,000,000,000,000 times that amount to have enough anti-hydrogen gas to fill a toy balloon! If we could somehow store our daily production, it would take us several billion years to fill the balloon. But the universe has been around for only 13.7 billion years...So the Angels and Demons scenario is pure fiction.

Can we hope to use antimatter as a source of energy? Do you feel antimatter could power vehicles in the future, or would it just be used for major power sources?

There is no possibility to use antimatter as energy ‘source’. Unlike solar energy, coal or oil, antimatter does not occur in nature; we first have to make every single antiparticle, and we have to invest (much) more energy than we get back during annihilation.
You can imagine antimatter as a storage medium for energy, much like you store electricity in rechargeable batteries. The process of charging the battery is reversible with relatively small loss. Still, it takes more energy to charge the battery than you get back.
The inefficiency of antimatter production is enormous: you get only a tenth of a billion (10-10) of the invested energy back. If we could assemble all the antimatter we've ever made at CERN and annihilate it with matter, we would have enough energy to light a single electric light bulb for a few minutes.
I was hoping antimatter would be the future answer to our energy needs. It seems more research is needed for this to happen.
No, even more research will not change this situation fundamentally; antimatter is certainly not able to solve our energy problems. First of all, you need energy to make antimatter (E=mc2) and unfortunately you do not get the same amount of energy back out of it. (See above, the loss factors are enormous.)
Furthermore, the conversion from energy to matter and antimatter particles follows certain laws of nature, which also allow the production of many other, but very short-lived particles and antiparticles (e.g. muons, pions, neutrinos). These particles decay rapidly during the production process, and their energy is lost.
Antimatter could only become a source of energy if you happened to find a large amount of antimatter lying around somewhere (e.g. in a distant galaxy), in the same way we find oil and oxygen lying around on Earth. But as far as we can see (billions of light years), the universe is entirely made of normal matter, and antimatter has to be painstakingly created.
By the way, this shows that the symmetry between matter and antimatter as stated above does not seem to hold at very high energies, such as shortly after the Big Bang, as otherwise there should be as much matter as antimatter in the Universe. Future research might tell us is how this asymmetry came about.

Can we make antimatter bombs?

No. It would take billions of years to produce enough antimatter for a bomb having the same destructiveness as ‘typical’ hydrogen bombs, of which there exist more than ten thousand already.
Sociological note: scientists realized that the atom bomb was a real possibility many years before one was actually built and exploded, and then the public was totally surprised and amazed. On the other hand, the public somehow anticipates the antimatter bomb, but we have known for a long time that it cannot be realized in practice.

Why has antimatter received no media attention?

It has received a lot of media attention, but usually in the scientific press. Also, antimatter is not ‘new’. Antiparticles have been known and studied for 75 years. What is new is the possibility to produce anti-hydrogen atoms, but this is also mainly a matter of scientific interest.

Is antimatter truly 100% efficient?

It depends on what you mean by efficient. If you start from two equal quantities m/2 of matter and m/2 of antimatter, then the energy output is, of course, exactly E=mc2. Mass is converted into energy with 100% efficiency.
But that is not the point: how much effort do you have to put in to get m/2 grams of antimatter? Well, theoretically E=mc2 because half of the energy will become normal matter. So you gain nothing. But the process of creating antimatter is highly inefficient; when you dissipate energy into particles with mass, many different - also short-lived - particles and antiparticles are produced. A major part of the energy gets lost, and a lot of the stable antimatter-particles (e.g. positrons and antiprotons) go astray before you can catch them. Everything happens at nearly the speed of light, and the particles created zoom off in all directions. Somewhat like cooking food over a campfire: most of the heat is lost and does not go into the cooking of the food, it disappears as radiation into the dark night sky. Very inefficient.

Do you make antimatter as described in the book?

No. The production and storage of antimatter at CERN is not at all as described in the book: you cannot stand next to the Large Hadron Collider (LHC) and see it come out, especially since the LHC accelerator is not yet in operation.
To make antiprotons, we collide protons at nearly the speed of light (to be precise, with a kinetic energy of about 25 GeV) with a block of metal, e.g. copper or tungsten. These collisions produce a large number of particles, some of which are antiprotons. Only the antiprotons are useful, and only those that fly out in the right direction. So that's where your energy loss goes: it is like trying to water a pot of flowers but with a sprinkler that sprays over the whole garden. Of course, we constantly apply new tricks to become more efficient at collecting antiparticles, but at the level of elementary particles this is extremely difficult.

Why then do you build the LHC?

The reason for building the LHC accelerator is not to make antimatter but to produce an energy concentration high enough to study effects that will help us to understand some of the remaining questions in physics. We say concentrations, because we are not talking about huge amounts but an enormous concentration of energy. Each particle accelerated in the LHC carries an amount of energy equivalent to that of a flying mosquito. Not much at all in absolute terms, but it will be concentrated in a very minute volume, and there things will resemble the state of the universe very shortly (about a trillionth of a second) after the Big Bang.
You should compare the concentration effect to what you can learn about the quality of a wooden floor by walking over it. If a large man wearing normal shoes and a petite woman wearing sharp stiletto heels walk over the same floor, the man will not make dents, but the woman, despite her lower weight, may leave marks; the pressure created by the stiletto heels is far higher. So that is like the job of the LHC: concentrate a little energy into a very minute space to produce a huge energy concentration and learn something about the Big Bang.

Does CERN have a particle accelerator 27 kilometres long?

The LHC accelerator is a ring 27 kilometres in circumference. It is installed in a tunnel about 100 m underground. You can see the round outline of it marked on a map of the area.

In fact, why do you make antimatter at CERN?

The principal reason is to study the laws of nature. The current theories of physics predict a number of subtle effects concerning antimatter. If experiments do not observe these predictions, then the theory is not accurate and needs to be amended or reworked. This is how science progresses.
Another reason is to get extremely high energy densities in collisions of matter and antimatter particles, since they annihilate completely when they meet. From this annihilation energy other interesting particles may be created. This was mainly how the Large Electron Positron (LEP) collider functioned at CERN until 2000, or the Tevatron currently operates at Fermilab near Chicago.

How is energy extracted from antimatter?

When a normal matter particle hits an antimatter particle, they mutually annihilate into a very concentrated burst of pure energy, from which in turn new particles (and antiparticles) are created. The number and mass of the annihilation products depends on the available energy.
The annihilation of electrons and positrons at low energies produces only two (or three) highly energetic photons. But with annihilation at very high energy, hundreds of new particle-antiparticle pairs can be made. The decay of these particles produces, among others, many neutrinos, which do not interact with the environment at all. This is not very useful for energy extraction.

How safe is antimatter?

Perfectly safe, given the minute quantities we can make. It would be very dangerous if we could make a few grams of it, but this would take us billions of years.

If so, does CERN have protocols to keep the public safe?

There is no danger from antimatter. There are of course other dangers on the CERN site, as in any laboratory: high voltage in certain areas, deep pits to fall in, etc. but for these dangers the usual industrial safety measures are in place. There is no danger of radioactive leaks as you might find near nuclear power stations.

Does one gram of antimatter contain the energy of a 20 kilotonne nuclear bomb?

Twenty kilotonnes of TNT is the equivalent of the atom bomb that destroyed Hiroshima. The explosion of a kilotonne (=1000 tonnes) of TNT corresponds to a energy release of 4.2x1012 joules (1012 is a 1 followed by 12 zeros, i.e. a million million). For comparison, a 60 watt light bulb consumes 60 J per second.

You are probably asking for the explosive release of energy by the sudden annihilation of one gram of antimatter with one gram of matter. Let's calculate it.
To calculate the energy released in the annihilation of 1 g of antimatter with 1 g of matter (which makes 2 g = 0.002 kg), we have to use the formula E=mc2, where c is the speed of light (300,000,000 m/s):
E= 0.002 x (300,000,000)2 kg m2/s2 = 1.8 x 1014 J = 180 x 1012 J. Since 4.2x1012 J corresponds to a kilotonne of TNT, then 2 g of matter-antimatter annihilation correspond to 180/4.2 = 42.8 kilotonnes, about double the 20 kt of TNT.
This means that you ‘only’ need half a gram of antimatter to be equally destructive as the Hiroshima bomb, since the other half gram of (normal) matter is easy enough to find.
At CERN we make quantities of the order of 107 antiprotons per second and there are 6x1023 of them in a single gram of antihydrogen. You can easily calculate how long it would take to get one gram: we would need 6x1023/107=6x1016 seconds. There are only 365 (days) x 24 (h) x 60 (min) x 60 (sec) = around 3x107 seconds in a year, so it would take roughly 6x1016 / 3x107 = 2x109 = two billion years! It is quite unlikely that anyone wants to wait that long.

Did CERN scientists actually invent the Internet?

No. The Internet was originally based on work done by Louis Pouzin in France, taken up by Vint Cerf and Bob Kahn in the US in the 1970s. However, the Web was invented and developed entirely by Tim Berners-Lee and a small team at CERN during 1989-1994. The story of the Internet and the Web can be read in ‘How the Web was born’. Perhaps not as sexy as Angels and Demons, but everything in ‘How the Web was born’ was first-hand testimony and research.
Does CERN own an X-33 spaceplane?
Unfortunately not.

1 komentar:

LampuKu mengatakan...

Can we make antimatter bombs?

No. It would take billions of years to produce enough antimatter for a bomb having the same destructiveness as ‘typical’ hydrogen bombs, of which there exist more than ten thousand already.
Ternyata nggak bisa ya kang....Beda ama yang di pilem "Angel and Demon" yach???
Btw, salam kenal bang..keep blooging ae