1.
Wafer (electronics)
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Finally the individual microcircuits are separated and packaged. By 1960, silicon wafers were being manufactured in the U. S. by companies such as MEMC/SunEdison. In 1965, American engineers Eric O. Ernst, Donald J. Hurd, Wafers are formed of highly pure, nearly defect-free single crystalline material. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, an ingot of high purity mono crystalline semiconductor, such as silicon or germanium. The boule is then sliced with a saw and polished to form wafers. The size of wafers for photovoltaics is 100–200 mm square and the thickness is 200–300 μm, in the future,160 μm will be the standard. Electronics use wafer sizes from 100–450 mm diameter, Wafers are cleaned with weak acids to remove unwanted particles, or repair damage caused during the sawing process. When used for cells, the wafers are textured to create a rough surface to increase their efficiency. The generated PSG is removed from the edge of the wafer in the etching, silicon wafers are available in a variety of diameters from 25.4 mm to 300 mm. Semiconductor fabrication plants are defined by the diameter of wafers that they are tooled to produce, Wafers grown using materials other than silicon will have different thicknesses than a silicon wafer of the same diameter. Wafer thickness is determined by the strength of the material used. This was the cost basis for increasing wafer size, conversion to 300 mm wafers from 200 mm wafers began in earnest in 2000, and reduced the price per die about 30-40%. However, this was not without significant problems for the industry, there is considerable resistance to the 450 mm transition despite the possible productivity improvement, because of concern about insufficient return on investment. Higher cost semiconductor fabrication equipment for larger wafers increases the cost of 450 mm fabs, converting to larger 450 mm wafers would reduce price per die only for process operations such as etch where cost is related to wafer count, not wafer area. Cost for processes such as lithography is proportional to wafer area, nikon plans to deliver 450-mm lithography equipment in 2015, with volume production in 2017. In November 2013 ASML paused development of 450-mm lithography equipment, citing uncertain timing of chipmaker demand, the time-line for 450 mm has not been fixed. Mark Durcan, CEO of Micron Technology, said in February 2014 that he expects 450 mm adoption to be delayed indefinitely or discontinued, “I am not convinced that 450mm will ever happen but, to the extent that it does, it’s a long way out in the future
2.
Heat sink
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In computers, heat sinks are used to cool central processing units or graphics processors. A heat sink is designed to maximize its surface area in contact with the medium surrounding it. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink, heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sinks performance by filling air gaps between the sink and the heat spreader on the device. A heat sink is made out of copper and/or aluminium. Copper is used because it has many desirable properties for thermally efficient, first and foremost, copper is an excellent conductor of heat. This means that high thermal conductivity allows heat to pass through it quickly. Aluminum is used in applications where weight is a big concern, a heat sink transfers thermal energy from a higher temperature device to a lower temperature fluid medium. The fluid medium is air, but can also be water. If the fluid medium is water, the sink is frequently called a cold plate. In thermodynamics a heat sink is a reservoir that can absorb an arbitrary amount of heat without significantly changing temperature. Practical heat sinks for electronic devices must have a higher than the surroundings to transfer heat by convection, radiation. The power supplies of electronics are not 100% efficient, so heat is produced that may be detrimental to the function of the device. As such, a sink is included in the design to disperse heat to improve efficient energy use. To understand the principle of a sink, consider Fouriers law of heat conduction. The rate at which heat is transferred by conduction, q k, is proportional to the product of the temperature gradient, Q k = − k A d T d x Consider a heat sink in a duct, where air flows through the duct. It is assumed that the heat sink base is higher in temperature than the air, when compact heat exchangers are calculated, the logarithmic mean air temperature is used. M ˙ is the air flow rate in kg/s
3.
Laser engraving
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Laser engraving, which is a subset of laser marking, is the practice of using lasers to engrave an object. The impact of laser marking has been more pronounced for specially designed laserable materials and these include laser-sensitive polymers and novel metal alloys. The term laser marking is used as a generic term covering a broad spectrum of surfacing techniques including printing, hot-branding. The machines for laser engraving and laser marking are the same, a laser engraving machine can be thought of as three main parts, a laser, a controller, and a surface. The laser is like a pencil - the beam emitted from it allows the controller to trace patterns onto the surface, the controller controls the direction, intensity, speed of movement, and spread of the laser beam aimed at the surface. The surface is picked to match what the laser can act on, sometimes the laser is stationary and the workpiece moves. Sometimes the workpiece moves in the Y axis and the laser in the X axis, a second genre is for cylindrical workpieces where the laser effectively traverses a fine helix and on/off laser pulsing produces the desired image on a raster basis. In the third method, both the laser and workpiece are stationary and galvo mirrors move the beam over the workpiece surface. Laser engravers using this technology can work in either raster or vector mode, the point where the laser touches the surface should be on the focal plane of the lasers optical system, and is usually synonymous with its focal point. This point is small, perhaps less than a fraction of a millimeter. Only the area inside this focal point is significantly affected when the beam passes over the surface. The energy delivered by the changes the surface of the material under the focal point. It may heat up the surface and subsequently vaporize the material, or perhaps the material may fracture, cutting through the paint of a metal part is generally how material is laser engraved. A laser can remove material very efficiently because the beam can be designed to deliver energy to the surface in a manner which converts a high percentage of the light energy into heat. The beam is focused and collimated - in most non-reflective materials like wood, plastics and enamel surfaces. However, because of this efficiency, the equipment used in laser engraving may heat up rather quickly, elaborate cooling systems are required for the laser. Alternatively, the beam may be pulsed to decrease the amount of excessive heating. Different patterns can be engraved by programming the controller to traverse a path for the laser beam over time
4.
Integrated circuit
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An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material, normally silicon. The ICs mass production capability, reliability and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of using discrete transistors. ICs are now used in all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other home appliances are now inextricable parts of the structure of modern societies, made possible by the small size. These advances, roughly following Moores law, allow a computer chip of 2016 to have millions of times the capacity, ICs have two main advantages over discrete circuits, cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography rather than being constructed one transistor at a time, furthermore, packaged ICs use much less material than discrete circuits. Performance is high because the ICs components switch quickly and consume little power because of their small size, the main disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This high initial cost means ICs are only practical when high production volumes are anticipated, Circuits meeting this definition can be constructed using many different technologies, including thin-film transistor, thick film technology, or hybrid integrated circuit. However, in general usage integrated circuit has come to refer to the single-piece circuit construction originally known as a integrated circuit. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent, an immediate commercial use of his patent has not been reported. The idea of the circuit was conceived by Geoffrey Dummer. Dummer presented the idea to the public at the Symposium on Progress in Quality Electronic Components in Washington and he gave many symposia publicly to propagate his ideas, and unsuccessfully attempted to build such a circuit in 1956. A precursor idea to the IC was to create small ceramic squares, Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which seemed very promising in 1957, was proposed to the US Army by Jack Kilby, however, as the project was gaining momentum, Kilby came up with a new, revolutionary design, the IC. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material … wherein all the components of the circuit are completely integrated. The first customer for the new invention was the US Air Force, Kilby won the 2000 Nobel Prize in Physics for his part in the invention of the integrated circuit. His work was named an IEEE Milestone in 2009, half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilbys had not. Noyces design was made of silicon, whereas Kilbys chip was made of germanium, Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation, a key concept behind the IC
5.
Wire bonding
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Wire bonding is the method of making interconnections between an integrated circuit or other semiconductor device and its packaging during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one printed circuit board to another, Wire bonding is generally considered the most cost-effective and flexible interconnect technology, and is used to assemble the vast majority of semiconductor packages. If properly designed, wire bonding can be used at frequencies above 100 GHz, bondwires usually consist of one of the following materials, Aluminum Copper Silver Gold Wire diameters start at 15 µm and can be up to several hundred micrometres for high-powered applications. The wire bonding industry is transitioning from gold to copper and this change has been instigated by the rising cost of gold and the comparatively stable, and much lower, cost of copper. While possessing higher thermal and electrical conductivity than gold, copper had previously seen as less reliable due to its hardness. By 2015, it is expected that more than a third of all wire bonding machines in use will be set up for copper, Copper wire has become one of the preferred materials for wire bonding interconnects in many semiconductor and microelectronic applications. Copper is used for fine wire ball bonding in sizes up to 0.003 inch, Copper wire has the ability of being used at smaller diameters providing the same performance as gold without the high material cost. Copper wire up to 0.020 inch can be successfully wedge bonded with the proper set-up parameters, large diameter copper wire can and does replace aluminum wire where high current carrying capacity is needed or where there are problems with complex geometry. Annealing and process used by manufacturers enhance the ability to use large diameter copper wire to wedge bond to silicon without damage occurring to the die. Copper wire does pose some challenges in that it is harder than gold and aluminum, so bonding parameters must be kept under tight control. The formation of oxides is inherent with this material, so storage, special packaging is required in order to protect copper wire and achieve a longer shelf life. During the fabrication of wire bonds, copper wire, as well as its plated varieties, a method for coping with coppers relative hardness is the use of high purity varieties. Pure gold wire doped with controlled amounts of beryllium and other elements is used for ball bonding. This process brings together the two materials that are to be bonded using heat, pressure and ultrasonic energy referred to as thermosonic bonding, the most common approach in thermosonic bonding is to ball-bond to the chip, then stitch-bond to the substrate. Very tight controls during processing enhance looping characteristics and eliminate sagging, junction size, bond strength and conductivity requirements typically determine the most suitable wire size for a specific wire bonding application. Typical manufacturers make gold wire in diameters from 0.0005 inch, production tolerance on gold wire diameter is +/-3%. Alloyed aluminum wires are generally preferred to pure aluminum wire except in high-current devices because of greater drawing ease to fine sizes, pure aluminum and 0. 5% magnesium-aluminum are most commonly used in sizes larger than 0.004 inch. All-aluminum systems in semiconductor fabrication eliminate the purple plague sometimes associated with pure gold bonding wire, Aluminum is particularly suitable for thermosonic bonding
6.
Printed circuit board
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Components are generally soldered on the PCB. Advanced PCBs may contain components embedded in the substrate, PCBs can be single sided, double sided or multi-layer. Conductors on different layers are connected with vias, multi-layer PCBs allow for much higher component density. FR-4 glass epoxy is the primary insulating substrate, a basic building block of the PCB is an FR-4 panel with a thin layer of copper foil laminated to one or both sides. In multi-layer boards multiple layers of material are laminated together, printed circuit boards are used in all but the simplest electronic products. Alternatives to PCBs include wire wrap and point-to-point construction, PCBs require the additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Manufacturing circuits with PCBs is cheaper and faster than other wiring methods as components are mounted and wired with one single part. A minimal PCB with a component used for easier prototyping is called a breakout board. When the board has no embedded components it is correctly called a printed wiring board or etched wiring board. However, the printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly, the IPC preferred term for assembled boards is circuit card assembly, and for assembled backplanes it is backplane assemblies. The term PCB is used both for bare and assembled boards. The world market for bare PCBs exceeded $60.2 billion in 2014, initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the diagram the component pin pads were laid out on the mylar. Rub-on dry transfers of common component footprints increased efficiency, traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout, to fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards. Modern PCBs are designed with dedicated software, generally in the following steps. Card dimensions and template are decided based on required circuitry and case of the PCB, the positions of the components and heat sinks are determined
7.
Surface-mount technology
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Surface-mount technology is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards. An electronic device so made is called a surface-mount device, in the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. By employing SMT, the production process speeds up, but the risk of defects also increase due to the components miniaturization, in those conditions, the failures detection have become critical for any SMT manufacturing process. An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all and it may have short pins or leads of various styles, flat contacts, a matrix of solder balls, or terminations on the body of the component. Surface mounting was originally called planar mounting, surface-mount technology was developed in the 1960s and became widely used in the late 1980s. Much of the work in this technology was by IBM. Components were mechanically redesigned to have metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities. Adhesive is sometimes used to hold SMT components on the side of a board if a wave soldering process is used to solder both SMT and through-hole components simultaneously. Surface mounting lends itself well to a degree of automation, reducing labor cost. SMDs can be one-quarter to one-tenth the size and weight, solder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printing process. It can also be applied by a mechanism, similar to an inkjet printer. After pasting, the boards then proceed to the pick-and-place machines, the components to be placed on the boards are usually delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuits are delivered in static-free trays, numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB. The boards are then conveyed into the reflow soldering oven and they first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised. The boards then enter a zone where the temperature is high enough to melt the solder particles in the solder paste, there are a number of techniques for reflowing solder. One is to use infrared lamps, this is called infrared reflow, another is to use a hot gas convection. Another technology which is becoming popular again is special fluorocarbon liquids with high boiling points which use a method called vapor phase reflow, due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering
8.
Vacuum tube
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In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
9.
Solder
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Solder is a fusible metal alloy used to create a permanent bond between metal workpieces. The word solder comes from the Middle English word soudur, via Old French solduree and soulder, from the Latin solidare, meaning to make solid. In fact, solder must be melted in order to adhere to and connect the pieces together, whenever possible, the solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder that is intended for use in making connections between electronic components also usually has favorable electrical characteristics. Soft solder typically has a melting point range of 90 to 450 °C, and is used in electronics, plumbing. Manual soldering uses an iron or soldering gun. Alloys that melt between 180 and 190 °C are the most commonly used, soldering performed using alloys with a melting point above 450 °C is called hard soldering, silver soldering, or brazing. In specific proportions, some alloys can become eutectic — that is, non-eutectic alloys have markedly different solidus and liquidus temperatures, and within that range they exist as a paste of solid particles in a melt of the lower-melting phase. In electrical work, if the joint is disturbed in the pasty state before it has solidified totally, for electrical and electronics work, solder wire is available in a range of thicknesses for hand-soldering, and with cores containing flux. It is also available as a paste or as a preformed foil shaped to match the workpiece, alloys of lead and tin were commonly used in the past, and are still available, they are particularly convenient for hand-soldering. Lead-free solders have been increasing in use due to regulatory requirements plus the health and they are almost exclusively used today in consumer electronics. Plumbers often use bars of solder, much thicker than the used for electrical applications. Jewelers often use solder in thin sheets, which cut into snippets. In the US, manufacturers may receive tax benefits by reducing the use of lead-based solder, lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 5 to 20 °C higher and it may be desirable to use minor modification of the solder pots used in wave-soldering, to reduce maintenance cost due to increased tin-scavenging of high-tin solder. Lead-free solder may be desirable for critical applications, such as aerospace and medical projects. Tin-Silver-Copper solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, tin-based solders readily dissolve gold, forming brittle intermetallics, for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders are more suitable for soldering thicker gold layer as the rate of gold in indium is much slower
10.
Zero insertion force
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Zero insertion force is a type of IC socket or electrical connector that requires very little force for insertion. The lever is moved back, allowing the contacts to close. ZIF sockets are more expensive than standard IC sockets and also tend to take up a larger board area due to the space taken up by the lever mechanism. Therefore they are used when there is a good reason to do so. A normal integrated circuit socket requires the IC to be pushed into sprung contacts which then grip by friction, for an IC with hundreds of pins, the total insertion force can be very large, leading to a danger of damage to the device or the circuit board. Low insertion force sockets reduce the issues of insertion and extraction, large ZIF sockets are only commonly found mounted on PC motherboards, being used from about the mid 1990s forward. These CPU sockets are designed to support a range of CPUs, allowing computer retailers and consumers to assemble motherboard/CPU combinations based on individual budget. The rest of the industry has largely abandoned sockets and instead moved to the use of surface mount components soldered directly to the board. Smaller ZIF sockets are used in chip-testing and programming equipment, e. g. programming and testing on EEPROMs, Microcontrollers. Standard DIP packages come in a number of widths, with 0.3 in and 0.6 in being the most common, to allow design of programmers and similar devices that support a range of devices universal test sockets are produced. These have wide slots into which the pins drop allowing devices of differing widths to be inserted, ZIF sockets can be used for ball grid array chips, particularly during development. These sockets tend to be unreliable, failing to grab all the solder balls, another type of BGA socket, also free of insertion force but not a ZIF socket in the traditional sense, does a better job by using spring pins to push up underneath the balls. ZIF wire-to-board connectors are used for attaching wires to printed circuit boards inside electronic equipment, an example would be the cable between the LCD screen and motherboard in laptops. The wires, often formed into a cable, are pre-stripped. The two sliding parts of the connector are then pushed together, causing it to grip the wires, the most important advantage of this system is that it does not require a mating half to be fitted to the wire ends, therefore saving space and cost inside miniaturised equipment. ZIF tape connections are used for connecting Parallel ATA and Serial ATA disk drives, PATA hard drives with ZIF-style connectors were used primarily in the design of ultra-portable notebooks. They have since been phased out, as SATA has a relatively small-form-factor connector by default, mini-SATA can be used where even smaller form factors are required. Internally, nearly all hard drives use ZIF tape to connect their circuit board to their platter motor
11.
Epoxy
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Epoxy is either any of the basic components or the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups, Epoxy resins may be reacted either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids, phenols, alcohols and thiols. These co-reactants are often referred to as hardeners or curatives, reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with high mechanical properties, temperature and chemical resistance. Epoxy resins are low molecular weight pre-polymers or higher molecular weight polymers which contain at least two epoxide groups. The epoxide group is sometimes referred to as a glycidyl or oxirane group. A wide range of epoxy resins are produced industrially, the raw materials for epoxy resin production are today largely petroleum derived, although some plant derived sources are now becoming commercially available. Epoxy resins are polymeric or semi-polymeric materials, and as such rarely exist as pure substances, high purity grades can be produced for certain applications, e. g. using a distillation purification process. One downside of high purity liquid grades is their tendency to form crystalline solids due to their highly regular structure, an important criterion for epoxy resins is the epoxide content. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of curative to achieve maximum physical properties, use of blending, additives and fillers is often referred to as formulating. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers, as the molecular weight of the resin increases, the epoxide content reduces and the material behaves more and more like a thermoplastic. Very high molecular weight polycondensates form a class known as phenoxy resins and these resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e. g. with aminoplasts, phenoplasts and isocyanates. Bisphenol F may also undergo epoxidation in a fashion to bisphenol A. Compared to DGEBA, bisphenol F epoxy resins have lower viscosity and a higher mean epoxy content per gramme, reaction of phenols with formaldehyde and subsequent glycidylation with epichlorohydrin produces epoxidised novolacs, such as epoxy phenol novolacs and epoxy cresol novolacs. These are highly viscous to solid resins with typical mean epoxide functionality of around 2 to 6, the high epoxide functionality of these resins forms a highly crosslinked polymer network displaying high temperature and chemical resistance, but low flexibility. Aliphatic epoxy resins are typically formed by glycidylation of aliphatic alcohols or polyols, the resulting resins may be monofunctional, difunctional, or higher functionality. These resins typically display low viscosity at room temperature and are referred to as reactive diluents. They are rarely used alone, but are employed to modify the viscosity of other epoxy resins. This has led to the term ‘modified epoxy resin’ to denote those containing viscosity-lowering reactive diluents, a related class is cycloaliphatic epoxy resin, which contains one or more cycloaliphatic rings in the molecule
12.
Alpha particle
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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 decay. Alpha particles are named after the first letter in the Greek alphabet, the symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are sometimes written as He2+ or 4 2He2+ indicating a helium ion with a +2 charge. If the ion gains electrons from its environment, the particle can be written as a normal helium atom 4 2He. Some science authors may use doubly ionized helium nuclei and alpha particles as interchangeable terms, the nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors to be alpha particles. As with beta and gamma rays/particles, the used for the particle carries some mild connotations about its production process and energy. Thus, alpha particles may be used as a term when referring to stellar helium nuclei reactions. A higher energy version of alphas than produced in alpha decay is a product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators are less likely to be referred to as alpha particles, alpha particles, like helium nuclei, have a net spin of zero. Due to the mechanism of their production in standard alpha radioactive decay, alpha particles generally have an energy of about 5 MeV. They are a highly ionizing form of radiation, and have low penetration depth. They are able to be stopped by a few centimeters of air, however, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. To a lesser extent, this is true of very high-energy helium nuclei produced by particle accelerators. The best-known source of particles is alpha decay of heavier atoms. When an atom emits an alpha particle in alpha decay, the mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atomic number of the atom goes down by two, as a result of the loss of two protons – the atom becomes a new element. Examples of this sort of nuclear transmutation are when uranium becomes thorium, or radium becomes radon gas, alpha particles are commonly emitted by all of the larger radioactive nuclei such as uranium, thorium, actinium, and radium, as well as the transuranic elements
