Antimatter
Antimatter (My old educational article)
If there are Antiquarks for quarks
Antiparticles for particles
Antimatter for matter
Do we humans have our mirror images (Anti-humans) in the far opposite universe, that could annhilate with us to create just Energy?
1.1.???????What is antimatter
Man has for ages called everything that exists on earth as "matter." As his knowledge increased over the years, scientists discovered that matter is made of tiny particles called atoms. These atoms, in turn, were discovered to have a nucleus at the center, surrounded by a cloud of electrical charges called "electrons." Still, later, it was discovered that the nuclei contain still smaller particles named protons and neutrons. The latest research shows that even the tiny protons and neutrons consist of even smaller "fundamental particles" called quarks. Quarks are believed (so far!) to be indivisible.
This knowledge about "matter" is relatively common. What is less commonly known is the scientific discovery that all matter or particles have partners or "mirror image" having most properties similar to their corresponding matter but with an opposite charge (and other electromagnetic properties). For want of a better name, scientists called their new discovery "antimatter."?
Figure 1:?Illustration of electric charge as well as the general size of particles (left) and antiparticles (right). From top to bottom; electron/positron, proton/antiproton, neutron/antineutron.
Antimatter is a large subject which is covered through all the science fields. Antimatter or antiparticles is often called the "mirror image" of ordinary matter. For every type of ordinary matter particle, an antimatter particle can be created that is identical in characteristics except for an opposite electric charge and some other properties like the magnetic moment. While staying with the topic of astronomy, this paper will describe?the discovery of antimatter, the origins of antimatter, and antimatter as energy and its application mainly in medical science and biomedical engineering.
?To describe antimatter we must first look at the history of its discovery. The history of discovering antimatter begins in 1929 with the proposal of an English Physicist named Paul Dirac. In attempting to combine quantum mechanics with special relativity to describe the behavior of an electron, he found that the solutions of the equation showed that if the matter is created from energy then an equal amount of antimatter is also created. For example, the equation, X squared equals four can have two possible solutions (X equals two) or (X equals negative two.) Dirac's equation proves two possible solutions, one for an electron with positive energy, and one for an electron with negative energy. This showed that for every proton in the universe there should be an antiproton or a proton with a negative charge, for every electron there is an anti-electron or an electron identical in every way but with a positive charge, and for every neutron, there is an antiparticle called an antineutron.
The combined theory was called the Quantum field theory. From 1930, the hunt for the mysterious antiparticles began. A scientist named Victor Hess had discovered a natural source of high-energy particles called cosmic rays. Cosmic rays are very high-energy particles that come from outer space and as they hit the Earth's atmosphere they produce huge showers of lower-energy particles that have proved very useful to physicists. In 1932 Carl Anderson, a professor at the California Institute of Technology, was studying showers of cosmic particles in a cloud chamber and saw a track left by a positively charged particle with the same mass as an electron. He concluded that the tracks were actually anti-electrons each produced alongside an electron from the impact of cosmic rays in the cloud chamber. He called the anti-electron a "positron", for its positive charge. This proved the existence of antiparticles as predicted by Dirac.
Since an antiproton (or proton) is almost 2000 times heavier than an anti-electron (or electron), it takes a lot more energy to create them. Twenty-three years later technology advanced enough to create enough energy to produce an antiproton. In 1954, a particle accelerator called the Bevatron was built at Lawrence Berkeley Laboratory which possessed sufficient energy to create its own antimatter. The Bevatron could collide two protons together at the energy of 6.2 GeV. This was expected to be the optimum for producing antiprotons. Meanwhile a team of physicists designed and built a special detector to see the antiprotons. In October 1955 the big news hit the front page of the New York Times with the discovery of the antiproton. A year later the Bevatron created the antineutron. So if particles bound together in atoms are the basic units of matter, it is natural to think that antiparticles bound together in anti-atoms are the basic units of antimatter. In 1965 two teams of physicists observed the making of an anti-deuteron, a nucleus of antimatter made out of an antiproton plus an antineutron. In 1995 an anti-electron was combined with an anti-deuteron to create an anti-atom. And finally, the Anti-hydrogen atom was created. Acceleration and deceleration of particles are not the only way to study antimatter. Antimatter could exist somewhere in outer space. Dirac was the first to consider the existence of antimatter on an astronomical scale. But if there is antiparticle for particles, antimatter for matter, is there a possibility of existing anti-galaxy for our galaxy and anti-human for humans? If it is so, where did they go?
1.2. ????Where did all the antimatter go?
From a physicist’s point of view what is strange about antimatter is that we don’t see more of it. When high-energy particles collide in accelerators there energy is converted into equal amounts of matter and antimatter particles (E= MC2).
Since we see matter and antimatter created in equal amounts in particle experiments, we expect that shortly after the Big Bang, when the universe was extremely dense and hot, equal amounts of matter and antimatter were created from the available energy. The obvious question is, therefore, where did the antimatter go?
Based on numerous astronomical observations and the results of particle physics and nuclear physics experiments, it is deduced that all the matter in the universe today is only about a billionth of the amount of matter that existed during the very early universe. As the universe expanded and cooled, almost every matter particle collided with an antimatter particle, and the two turned into two photons - gamma ray particles - in a process called annihilation, the opposite of pair production. But roughly a billionth of the matter particles survived, and it is those particles that now make the galaxies, stars, planets, and all living things on Earth, including our own bodies.
The survival of a small fraction of the matter particles indicates that, unlike what we wrote above, matter and antimatter are not exactly identical. There is a small difference between the ways they interact. This difference between matter and antimatter was first observed in particle accelerators in 1964 in an experiment for which Cronin and Fitch were awarded the 1980 Nobel Prize, and its connection to the existence of matter in the universe was realized in 1967 by Sakharov. ?When matter and antimatter annihilate each other a small fraction of matter survived.
1.3.???????Anti particles
i.???????????Positrons
Most forms of antimatter are quite rare and difficult to come by and are usually only to be found at big accelerator facilities, or in deep outer space. However, the electron’s antiparticle, the positron, which has the same mass as the electron but has a positive, rather than a negative charge, is relatively speaking, reasonably abundant. Positrons can be produced either through using a particle accelerator or by using a radioactive isotope which, in the process of nuclear decay, emits positrons.
An example of this type of decay occurs in sodium-22 which decays into neon-22 with the emission of a positron.
ii.??????????????Antiprotons
It is the equivalent of a particle photon. It has the same mass as that of the proton but with an opposite charge (-).?Antiprotons can be produced on a large scale using portable antiproton traps which are under development at Penn State University. The first portable trap will be capable of transporting about 1010 antiprotons. This would allow commercial delivery of a full trap to a clinic anywhere in the world for radiography and radiotherapy.
iii.????????????Antineutron
The antineutron is the antiparticle of the neutron with the symbol ?. It differs from the neutron only in that some of its properties have equal magnitude but opposite signs. It has the same mass as the neutron, and no net electric charge, but has the opposite baryon number (+1 for neutron, ?1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. In particular, the antineutron consists of one up antiquark and two down antiquarks.
Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its annihilation with ordinary matter are observed. In theory, a free antineutron should decay into an antiproton, a positron, and a neutrino in a process analogous to the beta decay of free neutrons. There are theoretical proposals that neutron–antineutron oscillations exist, a process which would occur only if there is an undiscovered physical process that violates baryon number conservation.(14)
The antineutron was discovered in proton-proton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was discovered.
iv.????????????Positronium
While positrons and electrons readily annihilate with each other and give up their rest mass in the form of gamma rays, they also have the ability to form a remarkable, if transient, ‘atom’ known as positronium. Positronium forms quite readily when a positron collides with an atom or molecule and strips one of the atomic electrons off to form an electron-positron pair in which the two particles mutually orbit one another. Positronium can ‘live’ for a relatively long time but ultimately; it too annihilates to produce gamma rays. Positronium lies at the heart of the research in the Centre and is a key component of many of the technological and biomedical uses of antimatter.
In free space, two atoms of positronium cannot combine together, because they have such excess energy that they simply fly apart again.
2.???SOURCE AND PRODUCTION OF ANTIMATTER
Apart from high voltage particle accelerators, there are different hypotheses and actual findings for the capturing and production of antiparticles/antimatter.
2.1.???????Black Holes May Fuel Antimatter Cloud
Those gamma rays coming out of the galactic center, flagging the presence of an antimatter cloud of enormous extent, have spawned few explanations more exotic than the one we consider today: Black holes. Primordial black holes, in fact, were produced in their trillions at the time of the Big Bang and left evaporating through so-called ‘Hawking radiation’ ever since. (2)
Hawking radiation?offers a mechanism for small black holes to lose mass over time. But since the phenomenon has never been observed, the upcoming launch of the?GLAST (Gamma-ray Large Area Space Telescope) satellite again looms large insignificance. GLAST should be able to find evaporating black holes, assuming they are there, and there is even some possibility of detecting tiny black holes created when high-energy cosmic rays slam into the upper atmosphere. If so, we would have a window, into any evaporative effects associated with these enigmatic events.
?But assuming that black holes do evaporate, the trick is to figure out how fast, and that rate depends upon mass, with more massive black holes producing fewer evaporated particles. A mass of about 1016?grams, roughly that of a fairly common asteroid, will produce the right amount of antimatter to explain the detections. Theoretically, the signature radiation from black holes of this particular size should be observable given the right equipment.????
?We have considered evaporating primordial BHs [black holes], as a possible source of positrons to generate the observed photon 511 keV line from the Galactic Bulge. The analysis of the accompanying continuous photon background produced, in particular, by the same evaporating BHs, allows to ?x the mass of the evaporating BHs near 1016?g. It is interesting that the necessary amount of BHs could be of the same order of magnitude as the amount of dark matter in the Galactic Bulge. This opens the possibility that such primordial BHs may form all cosmological dark matter. The background MeV photons created by these primordial BHs can be registered in the near future, while the neutrino ?ux may be still beyond observation. The significance of this model would be difficult to overestimate because these BHs would present a unique link connecting the early universe and particle physics.(3)
2.2.???????The Hunt for Ancient Antimatter
There is evidence that antimatter is produced naturally, at least in trace amounts, in the relativistic jets produced by black holes and pulsars. Indeed, a?cloud of antimatter?10,000 light-years across has been described around our own galaxy’s center. And at least one scientist, James Bickford (Draper Laboratory), has worked out ways to?extract antimatter?produced here in the Solar System; a method that he believes would be five orders of magnitude more cost-effective than creating the stuff on Earth. But what about early antimatter, particles leftover from the earliest days of the universe? According to prevalent theory, the universe may have been awash with the stuff shortly after the Big Bang, but most of it is assumed to have annihilated with ordinary matter, leaving only the slightly more numerous remnants of matter behind. Could any antimatter have survived?
?If clumps of matter and antimatter existed next to each other before inflation, they may now be separated by more than the scale of the observable Universe, so we would never see them meet. But, they might be separated on smaller scales, such as those of superclusters or clusters, which is a much more interesting possibility.
Usefully, we might be able to observe evidence for such antimatter in collisions between two galactic clusters. That signature would be marked by X-rays from the hot gases involved in the collision and the gamma rays associated with antimatter annihilation.
?If antimatter is present, these results mean it amounts to less than three parts per million in this system. The search continues, hoping to learn whether other colliding galaxy clusters show a similar paucity of antimatter. It would be helpful if an antimatter signature could tell us about the mysterious period of inflation — how long, for example, did it last? This a long shot. The collision of matter and antimatter is the most efficient process for generating energy in the Universe, but it just may not happen on very large scales.
2.3.???????Antimatter Source Near the Earth
?Now that NASA’s Institute for Advanced Concepts (NIAC) studies the possibility of harvesting antimatter rather than producing it in huge particle accelerators. The idea resonates at a time when the worldwide output of antimatter is measured in nanograms per year, and the overall cost is pegged at something like $100 trillion per gram. Find natural antimatter sources in space and you can think about collecting the ten micrograms that might power a 100-ton payload for a one-year round trip mission to Jupiter. (2,3)
The bombardment of the upper atmosphere of the Earth by high-energy galactic cosmic rays should result in ‘pair production,’ creating an elementary particle and its antiparticle.
A planetary magnetic field can hold such particles in place, producing a localized source of antiprotons. The detection of antimatter in this configuration has now been confirmed by a team of researchers using data from the Pamela satellite (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics). In fact, Pamela picks up thousands of times more antiprotons in a region called the South Atlantic Anomaly than would be expected from normal particle decays.
Figure 2: A cross-sectional view of the Van Allen radiation belts, noting the point where the South Atlantic Anomaly occurs (2).
Antiprotons are created in pair production processes in reactions of energetic CRs [cosmic rays] with Earth’s exosphere. Some of the antiparticles produced in the innermost region of the magnetosphere are captured by the geomagnetic field allowing the formation of an antiproton radiation belt around the Earth. The particles accumulate until they are removed due to annihilation or ionization losses. The trapped particles are characterized by a narrow pitch angle distribution centered around 90 degrees and drift along geomagnetic field lines belonging to the same McIlwain L-shell where they were produced. Due to magnetospheric transport processes, the antiproton population is expected to be distributed over a wide range of radial distances.
?The antiprotons eventually encounter normal matter in the Earth’s atmosphere and are annihilated, but new antiparticles continue to be produced. The question is whether there may be enough antimatter. Antimatter trapped in Earth’s inner radiation belt offers us useful savings, ?space harvesting will prove five orders of magnitude more cost-effective than antimatter creation here on Earth. Obviously, exploiting antimatter trapped near the Earth and other Solar System worlds assumes a robust space-based infrastructure, but it may be one that will finally be able to bring antimatter propulsion into a new era of experimentation.
?Antiprotons are currently produced during high-energy collisions in large particle accelerators. Based on current capabilities, the electricity cost alone for the process is estimated to be $160 trillion per gram collected. In comparison, high-energy cosmic rays bombard the Earth’s upper atmosphere and produce the antiprotons naturally through pair production. A fraction of these is subsequently concentrated within the Van Allen radiation belts of the Earth similar to their standard matter counterparts. Satellite and high altitude balloon measurements have confirmed the fractional existences of antimatter in the normal background of ionizing radiation. As particles are lost through diffusion processes, new ones are generated to maintain a quasi-static supply trapped in the near dipole field of the Earth. Based on preliminary calculations, it is estimated that 10 micrograms of antiprotons and 10 milligrams of positrons are locally contained within the Earth’s magnetosphere at any given time. The Jovian planets with their strong magnetic fields are expected to contain significantly more within their radiation belts. Draper Laboratory and its collaborators propose to use a magnetic scoop to extract large quantities of these trapped antiparticles. The principles of a Bussard magnetic scoop, first proposed for relativistic propulsion, will be adapted for use on a satellite in a planetary orbit. Particles bouncing between mirror points near the planet’s poles will pass through and be concentrated by the superimposed magnetic field. Separation and cooling techniques from particle accelerators will be adapted for extracting and separating the desired particles from the radiation flux near satellites. (3)
3.????APPLICATIONS OF ANTIMATTER
Antiprotons currently can only be produced at large facilities.?The creation of antiprotons is accomplished by sending protons, near the speed of light, into a metal, usually tungsten.?When the photon hits the target, it is slowed or stopped by collisions with nuclei of the target.??Then, the mass increase due to traveling near the speed of light is converted into the matter in the form of various subatomic particles, some of which are antiprotons.?The antiprotons are then separated from the other subatomic particles electromagnetically.?The collection, storage, and handling of antimatter protons are very complicated because antiprotons annihilate when they come into contact with normal matter.?To prevent this, they must be contained within a vacuum by electromagnetic fields.
3.1.???????Aircraft Propulsion system
Antiprotons can be used in propulsion to produce direct thrust, energize a propellant, or heat a solid core.?There are many different concepts regarding antimatter propulsion.?The simplest concept uses antiprotons to heat a sold metal core, usually tungsten.?The tungsten absorbs the gamma rays and ions from the antimatter/matter annihilation and is heated.?Small holes are placed in the cylinder containing the core where hydrogen gas can enter.?As the hydrogen gas enters, the tungsten core is cooled while the hydrogen gas is heated.?The hydrogen propellant is then expanded through a nozzle to produce thrust.?The performance of an antiproton solid core-generated thrust rocket is about equal to that of a nuclear rocket. Another concept of propulsion is the use of a plasma core instead of a beamed core.?In a plasma core, antiprotons are injected to annihilate and heat the plasma.?Heat is rapidly transferred to the propellant and released out of the vehicle at a very high velocity.?The beam core concept strays away from the concept of heating a secondary fluid.?In a beam core vessel, the charged particles of the antiproton annihilation are directly released out of the vehicle along an axial magnetic field at a very high velocity near the speed of light.?
When the antiprotons and protons collide and annihilate, about 62% of the mass is converted into charged pions.?The pions are then deflected by the magnetic nozzle which causes a very high specific impulse.?The very high specific impulse allows a beam core system to travel near the speed of light.?Energy efficiency is very high in this system, but the thrust and flow rates remain very low.?The figure below shows a basic representation of a beamed core propulsion system.?In this figure, a ring-shaped magnet is used to generate the magnetic field for the nozzle.?A radiation shield is placed between the magnetic nozzle and the engine to protect the engine from the gamma rays produced by the antiproton-proton annihilation and the decay of neutral pions.?A shadow shield is placed between the magnetic nozzle and the rest of the vehicle to protect the vehicle from exposure to radiation.?
Figure 3.?Beam Core Propulsion System ?
Presently, there exist a few problems with the beam core concept.?The amount of antimatter required for this type of system is far beyond what is capable of being produced today.?A magnetic nozzle that can handle high temperatures still needs to be developed as well as a cooling system in order to use the beam core concept in propulsion activities.?A beam core spacecraft would also have to be very long because the annihilating particles travel near the speed of light.?The figure below shows an artist's representation of a beam core spacecraft.
Figure 4.?Artist representation of a beam core spacecraft?
There are many other systems that use antiprotons to initiate the fission of fusion processes.?All of the energy in these systems used for propulsion comes from fusion reactions.?There are two concepts that use this type of energy, which are being researched and developed at Pennsylvania State University.?First, there is Antimatter-Catalyzed Micro-Fission/Fusion (ACMF).?In this application, a pellet of Deuterium-Tritium (D-T) and Uranium-238 (U-238) is compressed with particle beams and irradiated with a low-intensity beam of antiprotons.?Antiprotons are absorbed by the U-238 and initiate a hyper-neutronic fission process that rapidly heats and ignites the D-T core, which then expands to produce a pulsed thrust.?(1)
Figure 5.?ICAN-II Spacecraft (ACMF System) [10].?
The second concept is called Antimatter-Initiated Microfusion (AIM).?Electric and magnetic fields continuously compress antiproton plasma while droplets containing D-T are injected into the plasma.?The antiprotons annihilate with a fissile seed, which together heat the plasma.?The resulting product is expelled out a magnetic nozzle to produce thrust
Antimatter requirements are minimized in ACMF and AIM systems for missions that require a smaller velocity (ΔV = 103 km/sec).?ACMF also shows the best performance for planetary and simple interplanetary missions.?ACMF systems were originally designed to accommodate a manned vehicle so ACMF vessels are restricted to missions requiring ΔV is less than 100 km/sec.?The relationship between the amounts of mass required for a spacecraft of a given payload with respect to its ΔV is given in Figure 6 below.
Figure?6.?Antimatter Requirements for Different Propulsion Concepts
Portable antiproton traps are being developed to capture antiprotons and then transfer them to research facilities.?Penn State University developed a Mark I portable antiproton Penning Trap in 1999 that was designed to hold 1010.?NASA Marshall Spaceflight Center is currently constructing an improved Mark II with a 100-fold greater capacity.?Figure 7 is a design of a portable Penning trap used to transfer antiprotons for propulsion activities.
Figure 7. (a)Portable Penning Trap. (b)Antiproton Penning Trap Developed by Penn State University.
3.2.???????Military application
An antimatter weapon is a hypothetical device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons do not currently exist due to the cost of production and the limited technology available to produce and contain antimatter in sufficient quantities for it to be a useful weapon. The United States Air Force, however, has been interested in military uses including destructive applications of antimatter since the Cold War, when it began funding antimatter-related physics research. The primary theoretical advantage of such a weapon is that antimatter and matter collisions, though significantly limited by neutrino losses, still convert a larger fraction of the weapon's mass into explosive energy than a fusion reaction in a hydrogen bomb, which is on the order of only 0.7% (12)
?There is considerable skepticism within the physics community about the viability of antimatter weapons. According to an article on the website of the CERN (European Council for Nuclear Research) laboratories, which regularly produces antimatter, "There is no possibility to make antimatter bombs for the same reason you cannot use it to store energy: we can't accumulate enough of it at high enough density. ?If we could assemble all the antimatter we've ever made at CERN and annihilate it with the matter, we would have enough energy to light a single electric light bulb for a few minutes.", but this would be a considerable feat because the accumulated antimatter would weigh less than one billionth of a gram. (13)
领英推荐
Antimatter catalyzed nuclear pulse propulsion proposes the use of antimatter as a "trigger" to initiate small nuclear explosions; the explosions provide thrust to a spacecraft. The same technology could theoretically be used to make very small and possibly "fission-free" (very low nuclear fallout) weapons. ?
Antimatter catalyzed weapons could be more discriminate and result in less long-term contamination than conventional nuclear weapons, and their use might therefore be more politically acceptable.
Igniting fusion fuel requires at least a few kilojoules of energy (for laser-induced fast ignition of fuel precompressed by a z-pinch), which corresponds to around 10?13 gram of antimatter, or 1011 anti-hydrogen atoms. Fuel compressed by high explosives could be ignited using around 1018 protons to produce a weapon with a one kiloton yield. ?These quantities are clearly more feasible than those required for "pure" antimatter weapons, but the technical barriers to producing and storing even small amounts of antimatter remain formidable.
3.3.????????Materials science
Positrons are becoming a key analytical tool in many areas of materials science and materials development. In particular, they are becoming a useful probe in the analysis of open and porous material structure. When positrons are injected into a material, they tend to drift towards any open volumes very small holes or pores. As the electron density in these pores is lower, the lifetime of the positron against annihilation is longer and indeed the lifetime can be used as a measure of the size of the pores. By measuring the lifetime of positrons in a material, we can get information about the size and distribution of pores or defects, at the nanometer level, and pores of this size can be related to important properties in some materials, such as porosity and conductivity. They can also be an early indicator of material degradation. ?Positron beamlines can be used for the study of materials for various applications, from new generation plastics to silicon wafers and novel porous materials for drug delivery and waste confinement.
?3.4.???????Medical application
PET has become one of the tools of choice for active imaging of metabolism in the body, including brain function and certain types of cancers. These scans involve attaching a positron-emitting radio-isotope to a carrier molecule (e.g. glucose) which provides specific site selectivity for the delivery of the isotope. The material is normally injected into the patient and a sophisticated detector array searches the body for the annihilation of gamma rays, which result from the continuous positron emission. Despite the fact that this is a very well-established diagnostic tool, there is little understanding at a fundamental level of what happens between the emission of the position and the detection of the annihilation of gamma rays. The positrons are emitted with very high energy and must slow down to very low energies before combining with an electron and producing the gamma rays. (4) The next section discusses some of the medical/biomedical engineering applications of antimatter.
???4.???Biomedical Applications of Antimatter
?Certain important and accepted medical applications could be made more available and/or effective using antiprotons delivered to clinics in portable traps. This presentation illustrates some of these applications and attempts to show how they can be carried out in a practical and cost-effective way. We conclude by describing the progress currently being made in the development of such a portable trap.
?Two most medical applications of a portable antiproton trap and positrons are outlined in this paper. These are a radioisotope generator for Positron Emission Tomography (PET), and radiography for detection and ultimate treatment (radiotherapy) of tumors. (4) In both instances, I have focused on applications where currently available numbers of antiprotons could make a serious impact, and where clinical results and/or availability could be significantly improved over techniques currently being used in these areas.
?4.1.???????Positron emission tomography (PET)
Positron emission tomography (PET) is a nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer analysis. In modern scanners, three-dimensional imaging is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine. (11)
If the biologically active molecule chosen for PET is FDG, an analog of glucose, the concentrations of tracer imaged then give tissue metabolic activity, in terms of regional glucose uptake. The use of this tracer to explore the possibility of cancer metastasis (i.e., spreading to other sites) results in the most common type of PET scan in standard medical care (90% of current scans). However, on a minority basis, many other radiotracers are used in PET to image the tissue concentration of many other types of molecules of interest.
The four most important PET isotopes are radioactive species of carbon, nitrogen, oxygen, and fluorine (see Table below). Their decay lifetimes range from several minutes to less than two?hours, making it essential that they are produced by an accelerator (current method), or portable antiproton trap (proposed method) located close to the PET scanner. The nuclear reactions are shown in Table below (current method) or antiproton annihilation is responsible for the production of the desired radioisotope. (5)
Table 1. Important PET isotopes, lifetimes, cyclotron production reactions, radiopharmaceutical applications, and diagnostic uses. (5)
Radiopharmaceuticals, which are the molecules labeled by these isotopes, are put to a variety of diagnostic uses, as illustrated in Table 1. They direct the radioisotope to sites in the human body based on chemical affinity. The radioisotope emits a positron, which annihilates into two 511 keV photons after migrating one mm or so from the decay site. After several thousand back-to-back photon pairs are detected, an image of the decay site can be constructed.
?The figure below shows a series of images of a normal brain, generated by the injection of 7 mCi of F18 DG into the patient on a rotating PET scanner [5]. This technique, where available, has become commonplace in the diagnosis of abnormalities of the brain, such as tumors, as well as other maladies such as epilepsy, Alzheimer's disease, and dyslexia. Whereas x-ray CT imaging provides accurate density profiles, PET provides profiles linked to chemical uptake and related organ function.
?The number of disorders and clinical treatments using PET is increasing rapidly. Far too few institutions in the US have cyclotrons to make PET isotopes to satisfy the growing demand. Further, these cyclotrons cost several $M each, which severely restricts the number and geographical distribution of PET centers. The solution to this problem is to develop a portable source, analogous to the Mo99 generator used as a source of Tc99 gamma-ray emitting isotopes. (5)
Figure 8. Imaging the utilization of glucose in the brain by the BGO-based PET scanner at Geneva University Hospital [5].
PET and PET/CT scans are performed to (6)
?4.2.?????????Antiproton radiotherapy and radiography
Proton radiotherapy and radiography are rapidly advancing fields. Antiprotons offer the primary advantage of protons, namely efficient deposition of energy at the end of their range. In addition, the annihilation mechanism which occurs when the antiproton stops provide unique and valuable assets in the task of treating (and imaging) tumors. These assets include more efficient and precise dose deposition, and the ability to monitor the process in real-time using annihilation information. (5)
?Because of the unique annihilation mechanism, the antiproton profile is much more concentrated at the end of its range, the so-called Bragg peak.
This feature would enhance the accurate placement of dose in radiotherapy procedures. It is estimated that 1010 antiprotons injected into a patient at 200 MeV and stopped in a 10-gram brain tumor would render a dose of approximately 25 GYE (Gray Equivalent).
?The second advantage of antiprotons is that the annihilation at the end of the range produces three (on average) highly penetrating charged pions, which can be readily detected external to the patient. Because the pions are emitted isotropically, the stopping point can be very accurately imaged in three dimensions and in real-time, allowing more accurate and rapid diagnosis of tumor development than available with proton radiography. Figure 9 shows simulated images of a phantom, indicating sub-mm resolution in depth achieved with less than one million antiprotons. (5)
?Presently, the accuracy with which stopping proton beams can be placed is typically a few mm of depth. New methods are being explored in terms of achieving greater accuracy in proton radiotherapy procedures.
Proton radiography is being studied as a means of confirming and reinforcing standard x-ray CT treatment methodology [6]. Also, proton dose monitoring using PET techniques is being investigated for the same purpose. Relative to standards offered by these technologies, in my opinion, antiproton radiotherapy and radiography appear to be very promising in terms of significantly improving the precision of dose deposition.
Figure 9.?Antiproton annihilation in human tissue, releasing charged pions (π±), gamma rays (g), and nuclear fragments.
4.3.???????Positherapy
Positherapy is a targeted breast cancer therapy technique with 18F-FDG; (15) Preclinical studies suggest that 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) kills breast cancer cells without significant marrow toxicity or parenchymal toxicity. Radiation dose calculations estimated from fluorodeoxyglucose positron emission tomography images in women with metastatic disease indicate that 18F-FDG should be a feasible and safe option in humans. Because the available radiotherapeutic agents, strontium 89 and samarium 153 provide palliation to a limited population of women with bony metastases, new radiopharmaceutical agents with broader applicability are needed. The development of 18F-FDG as the first positron-emitting radiotherapeutic has the potential to be an innovative treatment, not only in osteoblastic disease but also in osteolytic disease and in soft tissue metastases.
Tumor-bearing mice were treated with a dose of the radiotracer equivalent to the maximum tolerated dose for humans. The treatment resulted in significant prolongation of survival and a decrease in tumor growth rate in comparison with non-treated controls. Substantial differences in the distribution of glucose transporters (GLUT) 1, 4, and 8 in tumor masses were observed, with GLUT1 localizing mainly in necrotic areas and expressed mostly at the cell membrane, indicating that GLUT1 was probably the most responsible for cellular uptake. These results are important for the development of posttherapy with 18FFDG for refractory metastatic breast and other cancers. (16)
?5.??Negative Effects of Antimatter
The danger associated with anti-matter depends on how much of it. As practical matter anti-matter is usually generated in an evacuated chamber a few atomic particles at a time. They don't escape from the chamber and even if they did they could destroy only a few atoms of ordinary matter, making them not dangerous. If you get a large mass of anti-matter it would be extremely dangerous because you'd be entirely annihilated if you touched it, but it's hard to think of any circumstance under which that could happen.
If you collided a single electron and positron you would only get a pair of gamma photons, the odds of doing much damage with just 2 photons are pretty small.
If the safe dose of gamma is around 10mSv (that is absorbed 10mJ/kg of body weight) and you weigh 100kg (it's worth hitting the burgers to make the maths easier) then you can absorb about 1kJ of gamma rays - that is the energy output of small campfire (say 1kw) in 1 second.
While Phase World lists anti-matter as the primary source of power for Phase World starship, Anti-matter is unfortunately not the wonder power source that some people think it is. Many people who watch a lot of science fiction get their ideas about anti-matter from Star Trek, which the writers seem to not realize how dangerous anti-matter really is. An example of the way Star Trek treats anti-matter can be seen in an early episode of Star Trek Next Generation. This episode has Wesley Crusher carrying around enough anti-matter to propel a starship into warp within what appears to be a clear plastic globe. (8)
Anti-matter / Matter reactions are very efficient on a mass to power output ratio and are very tempting as a power source but the dangers of the system need to be known so that people can consider this.
The energy released by Matter/Anti-matter Reactions:?
Most Nuclear warheads are less than 5 Mega-Tons and most modern warheads are in the range of hundreds of kilotons. The most powerful nuclear device ever constructed was constructed by the old Soviet Union and has a blast of 50 megatons but was the size of a large van. Most Anti-matter reactions would probably involve far less anti-matter than this.
It is quite possible to build atmospheric vehicles using an antimatter drive. After all, a tenth of a gram of the stuff could power a family flivver to orbit and back. But no machine is perfect, and even that tiny smidgen of antimatter would devastate the countryside if anything went wrong. When antimatter drives first become practical, we can expect treaties banning its use for propulsion within Earth’s atmosphere. There are other potential uses for it on Earth; for example, as an ultimate compact source of energy to power an MHD [magneto hydrodynamic] electric plant. The exhaust product is a high-temperature plasma… MHD power does not have to be used to propel vehicles; it could also take care of those demand surges on a nation’s electrical power grid. Will the treaties ban this use, too? We will risk a guess: yes. We will have other sources of energy from space by that time, and they do not involve the potential destruction of even a milligram of antimatter gone astray. So far as we know, antimatter drives are the ultimate in propulsion efficiency. They may have to wait, however, for those orbital factories.
If we ever find so much as a single antimatter molecule of the heavier stuff that we did not make — anti-uranium, for an extreme example — it would prove the existence of an antistar in which antihydrogen was cooked into heavier nuclei. This in turn would prove the existence of an antigalaxy. We could communicate with its citizens from a mutually safe distance, but handshakes between us would be a mite hazardous to our health. (9)
5. AntiHumans?
If there are Antiquarks for quarks
Antiparticles for particles
Antimatter for matter
Do we humans have our mirror images (Anti-humans) in the far opposite universe, that could annhilate with us to create just Energy?
The energy generated by matter-antimatter collisions is enormous. A milligram of antimatter could produce more energy than 2 tons of rocket fuel. If a human were to meet his antihuman and they were both annihilated, the energy generated would be equivalent to1,000 one-megaton nuclear bombs. Each of these bombs could easily destroy an entire city.
6.???The Future of Antimatter
Ponder how far we have to go before we can start talking about practical antimatter propulsion. The challenge, of course, is in making the stuff. Yes, a tenth of a gram would devastate the nearby landscape if a craft carrying it were to crash. But today’s best antimatter producer, the huge CERN particle accelerator in Switzerland, can produce about enough in a year to power a 100-watt bulb for 15 minutes. At present, making antiprotons requires 10 billion times more energy than it produces. None of this should be construed as an argument against antimatter propulsion, but rather a reminder that the real breakthrough will come not from engine design but a host of new techniques in antimatter production, storage, and transport.
Scientists are studying what could arguably be the first application of an exotic substance known as antimatter in medical treatment.
Scientists at CERN, the European Organization for Nuclear Research, outside Geneva, are testing the effects of beams of antiprotons fired at live cells.?
?The work could portend a new form of radiation therapy, a cancer treatment in which beams of particles are aimed at tumor cells to destroy them.
Antiprotons have four times greater cell-killing power than protons, used in standard radiation therapy.?
Antiprotons can be produced in small amounts in laboratories. But antimatter is rare as a rule because when matter and antimatter particles meet, they annihilate each other. Since there is a preponderance of matter in the known universe, antimatter particles, once created, usually run into matter particles and vanish in short order.
This would be a useful property for antiprotons on therapy. An antiproton annihilates with protons in atoms of the target cell. The result is a sort of tiny explosion that spreads the damage to immediately neighboring cells. The researchers are planning further tests. If all goes well, the first clinical application would still be a decade or more away. Antimatter is currently harnessed in medicine for a few limited applications, but not normally in actual treatment.
A diagnostic technique called Positron Emission Tomography uses positrons, antiparticles of electrons, for scanning tissue. And an uncommon form of radiation therapy uses pions, a hybrid form of matter, and antimatter subatomic particles called quarks. In that sense, one could perhaps talk of antimatter having been applied in medical treatment, but it would be stretching it a bit. Other than that, the CERN experiments would be the first application of antimatter in medical treatment
?REFERENCES
?1.?????https://conferences.fnal.gov/lp2003/forthepublic/matter/ (Accessed on May 11/2012).
2.?????The discovery of geomagnetically trapped cosmic ray antiprotons,”?astrophysical journal letters?vol. 37, no. 2, l29.
3.?????Antiparticle content in the magnetosphere?advances in space research, volume 42, issue 9, p. 1550-1555 (2008).
4.?????Australian research council center of excellence for antimatter-matter studies annual report, 2010.
5.?????Antiproton portable traps and medical applications* r.a. lewis and g. a. smith, department of physics, Pennsylvania state university, 2006
6.?????Radiologyinfo.org, the radiology information resource for patients
7.?????Basic physics of nuclear medicine by kieran maher and other Wikibooks contributors. 2004-2006
8.?????Star trek movie
9.?????The future of flight, Dean Ing and leik myrabo,?(New York: Baen, 1985), pp. 158-159.
10.?L. Krauss, "The Physics of Star Trek," Basic Books, (Harper Collins Publishers, Inc., 1995) p.92.
11.?Wikipedia/ Positron emission tomography?(PET) (Accessed on May 14/2012)
12.?https://www.engr.psu.edu/antimatter/papers/nasa_anti.pdf?(Accessed on May 15/2012)
13.?www.wikipedia.com/Antimatter_weapon.htm (Accessed on May 15/2012)
14.?Neutron-Anti-Neutron Oscillation: Theory and Phenomenology. R. N. Mohapatra (2009). Journal of Physics pp-36.
15.?THE JOURNAL OF NUCLEAR MEDICINE ? Vol. 46 ? No. 4 ? April 2005.
16.?Positron emitting 18F-2-deoxy-2-fluoro-D-glucose:?potential hot new therapy, Joanne E Mortimer?and Marie E Taylor, Eastern Virginia Medical School, Department of Medicine, Division of Medical Oncology, Norfolk, Virginia, USA
AI Researcher & Full Stack Developer | Focus on Computer Vision, NLP, and Software development
3 年Very interesting study. Can't wait to meet anti-mizanu. Together we will make the world kaboom.
Biomedical Engineer, Innovator, Computed System Designer. looking for fully covered master program in biomedical engineering/Medical imaging/Medical physics
3 年Interesting topic and that's a good work.
Technical Leader at Afework international group |Biomedical_Engineering | sells | promotions| business strategies and consultant | Clinical | health| entrepreneurship
3 年Good work Teacher ??