Radioactivity definition

Radioactivity defined as the spontaneous emission of particles (alpha, beta, neutron) or radiation (gamma, K capture), or both at the same time, from the decay of certain nuclides that these particles are, due to an adjustment of their internal structure.

Radioactivity can be natural or artificial. In natural radioactivity, the substance already has radioactivity in the natural state. In artificial radioactivity, the radioactivity has been induced by irradiation.

A radionuclide is all the radioactive cores of the same kind. All radioactive cores forming a radionuclide have a well-defined radioactivity, which is common to all of them and that identifies them; the same way that a type of chemical reaction identifies the elements involved.

Quantitatively, radioactivity is a statistical phenomenon. Therefore, it should be observed to rate the behaviour of a set of nuclei of the same species. By the law of large numbers, we define a constant λ as the probability of radioactive decay of a nucleus per unit time. With this definition, the number N of radioactive nuclei of the same species found in a substance in a time t is given by N = No · e-λt, where No is the number of radioactive nuclei that existed before time t. In fact, hardly a radioactive substance is formed by a single radionuclide, although each of its components disintegrate becomes a different kernel, which as well, can also be radioactive.

The initial radionuclide is called parent and the derivative, child. This situation may continue throughout multiple affiliations and the set of all of them is called radioactive series or family. In this case, the relationship that gives the number of current radioactive nuclei is more complex because, in addition to considering the number of each one in the initial moment, we should consider that, by disintegration of some ones, other are formed.

The problem is simplified when you want to achieve radioactive equilibrium (also called secular equilibrium in the natural radioactive series), when a sufficiently long time has passed since the process of affiliation has started. Then, the rate of the decays is imposed by the radionuclide, which has the smallest radioactive constant.

Natural radioactive nuclides

In nature there are about 300 different nuclides, from which 25 are radioactive with a sufficiently long period so that they exist even today; other 35 have a much shorter period. Continuously they are created and they decay into radioactive series.

Artificial radioactive nuclides

Over 1000 artificial radionuclides have been created and identified. The radioactive series are called with the name of the parent nuclide of longer periods. There are four. Three of these are natural radioactive series: thorium´s series, uranium´s series and actinium´s series, ending in their own stable isotopes of lead. These isotopes have respectively the mass numbers of 208, 206 and 207. Regarding the neptunium series, as radionuclides that compose it have a short period compared to the length of the geological eras, this series is not from the nature and has been obtained artificially. The last nuclide of this series is the isotope 209 of bismuth.

Origin of radioactivity

In 1896, Antoine-Henri Becquerel discovered radioactivity. He observed that, in studies on the phosphorescence of substances, a mineral of uranium was able to gloss photographic plates, which were kept at his side.

Nuclear fuel definition

The nuclear fuel is the material that has been adapted for use in nuclear power generation.

When it comes to nuclear fuel we can be talking about the same item or set that is made ready it can be used for containing the material itself, but also other elements.

The most widely used process involving the nuclear fission fuel.

There are different types of nuclear fuel, but the most common fuel is consisting of fissile elements such as uranium, generating chain reactions in nuclear reactors. The most common isotope in the fission is uranium-235.

Production processes nuclear fuel forms the set called the nuclear fuel cycle.

Another nuclear process is much less used nuclear fusion. In nuclear fusion nuclear fuel used are lightisotopes such as tritium or deuterium.

There are other elements such as plutonium-238, among others, that are used to produce small amounts of nuclear energy by radioactive processes to radioisotope thermoelectric generators atomic piles or other disintegration.

Nuclear reactor

A nuclear reactor is an installation capable of initiating, controlling and maintaining nuclear reactions (fission usually) chain occurring in the core of the facility.

The composition of the nuclear reactor is formed by the fuel, coolant, control elements, structural materials and, in the event that it is a thermal nuclear reactor, the moderator.

Nuclear reactors can be classified as rapid thermal reactors and reactors.

Thermal reactors are those which function by delaying (moderating) the faster neutrons or increasing the proportion of fissile atoms. To slow the neutrons, called slow neutrons, a moderator is required which can be light water, heavy water or graphite.

Fast reactors are not required to moderate the speed of electrons and using fast neutrons.

To build a nuclear reactor is necessary to have enough fuel, we call critical mass. Having enough critical mass means having enough fissile material in good condition to maintain a chain reaction.

The provision of neutron absorbers and control rods to control the chain reaction and stopping and starting of the nuclear reactor.

In the reactor core occurs and manteiene the nuclear chain reaction in order to heat the water to be used for driving the turbine of the plant.

Components nuclear reactor core

A nuclear reactor consists of the following components:

Nuclear Fuel

Nuclear fuel is a material capable of fission enough to reach critical mass, that is, to maintain a nuclear chain reaction. Is positioned so that it can quickly remove the heat produced by this nuclear reaction chains.

In nuclear power plants using solid fuel. The nuclear fuels vary depending on the type of reactor used but generally uranium derivatives.

In general, a fuel element is constituted by a quadrangular arrangement of fuel rods, as seen in the image. While Russian nuclear reactor VVER pressurized water is constituted by a hexagonal arrangement.

The guide tubes are attached to the fuel support grids in this way is able to maintain the centers of the fuel rods and tubes guíaa the same distance.

The mechanical design of the different fuel elements is identical. Some contain bundles and control rods containing burnable poisons or other neutron sources.

To ensure the quality of the fuel elements, there are numerous inspections and testing of both raw materials and the final product.

Control rods

The control rods beams provide a rapid means for controlling the nuclear reaction. Allow rapid changes reactor power and eventually stop in case of emergency. They are made of neutron absorbing material (boron carbide or alloys of silver, indium and cadmium, etc.) and typically have the same dimensions as the fuel elements. The reactivity of the core increases or decreases by raising or lowering control rod, that is, modifying the presence of neutron absorbing material contained in them in the nucleus.

For a reactor operated for a period of time must have an excess of reactivity which is maximal with fresh fuel and decreases over the life of the same until it is canceled, when the refill is made of fuel.

In normal operation, a nuclear reactor is the control rods fully or partially extracted from the nucleus, but the nuclear plant design is such that any fault in a security system or reactor control, always acts in the sense of security of introducing reactor completely all the control rods in the reactor core and carrying a safe stop in a few seconds.

Moderator

The resulting neutron fission reaction have high kinetic energy (high speed gain). The higher your speed is less likely to fisionen other atoms so that this speed should be reduced to encourage new chain reactions. This is achieved by elastic collisions of the neutrons with nuclei makes moderator element.

Among the most commonly used moderators are light water, heavy water and graphite.

Coolant

In order to use the heat energy given off by nuclear fission reactions using a refrigerant. The function of this heat refrigerant and transport aboserver. Coolant must be corrosion, with a large heat capacity and should not absorb neutrons.

The most common refrigerants are gases, such as carbon dioxide and helium, and liquid as the light water and heavy water. There are even some liquid organic compounds and metals such as sodium, also using for this function.

Reflector

In a nuclear chain reaction, a certain number of neutron tends to escape from the region in which it occurs. This neutron leakage can be minimized with the existence of a reflecting means to redirect them into the reaction region. In this manner serves to increase the efficiency of the reactor. The medium reflector surrounding the core must have a low capture cross section for not reducing the number of neutrons and to reflect as many of them.

The choice of material depends on the type of reactor. If we have a thermal reactor, the reflector can be the moderator, but if we have a fast reactor reflector material must have a large atomic mass to reflect neutrons in the nucleus with its original speed (inelastic scattering).

Shield

When the reactor is in operation, it generates large amounts of radiation. Protection is needed to isolate the installation workers caused by radiation from fission products.

Therefore, biological shielding is placed around the reactor to intercept these emissions.

The materials used to build this shield are concrete, water and lead.

Uranium - nuclear fuel

Uranium is the most widely used nuclear fuel in nuclear fission reactions.

 For the particular makes the uranium so different from the other substances we must first consider some basic nuclear physics.

 Atom electrons comprises surrounding a core; in turn, a core consists of protons and neutrons. A proton has a positive charge; a neutron has no electric charge and is neutral. The positive charges of protons outward violently push attempt. But within the compact volume of a new class of core strength makes an appearance: an attractive force short range, immensely powerful, equally acts between protons and neutrons (which from this point of view, are all nucleons). The short-range nuclear force holds them together, opposing the repulsive effect of the positive charges of the protons. Thus, the neutrons act as "nuclear cement".

 However, in a core which contains 92 protons (which is a uranium core) repulsive force between protons is expiring nuclear force. While there are 146 neutrons, the nucleus can hardly remain intact. This form of uranium containing 238 nucleons in total, called uranium-238. The next most likely arrangement is a uranium nucleus containing three fewer neutrons, uranium-235. These atoms with lighter nuclei comprise about 0.7% of uranium that occurs naturally (if the cores have the same number of protons, these nuclei thereof chemical element. well, all 92 proton core is the nucleus of an atom of uranium atoms whose nuclei have the same number of protons but different numbers of neutrons are called isotopes of the element eg. uranium-238 and uranium-235 are isotopes of Uranium nucleus of uranium-235 has a unique property among more than two hundred types. nuclei found in nature in significant quantities The core of uranium-235 and is under a voltage close to the internal break,. a stray neutron approaching you can break it completely.

Indian scriptures mention gravity 1500 years before Isaac Newton: Former ISRO chief G Madhavan Nair

One of the country's leading scientists and former ISRO chairman G Madhavan Nair on Saturday propounded the theory that some shlokas in the Vedas mentioned about presence of water on the moon and astronomy experts like Aryabhatta knew about gravitational force much before Issac Newton.

The 71-year-old Padma Vibhushan awardee said the Indian vedas and ancient scriptures also had information on metallurgy, algebra, astronomy, maths, architecture and astrology way before the western world knew about them.

Speaking at an international conference on Vedas, he however, added that the information in vedas was in a "condensed format" which made it difficult for the modern science to accept it.

"Some sholkas in one of the Vedas say that there is water on the moon but no one believed it. Through our Chandrayaan mission, we could establish that and we were the first ones to find that out," Nair said, adding that everything in Vedas could not be understood as they were in chaste Sanskrit.

He also talked very highly about fifth century astronomer- mathematician Aryabhatta saying, "We are really proud that Aryabhatta and Bhaskara have done extensive work on planetary work and exploration of outer planets. It was one of the challenging fields.

"Even for Chandrayaan, the equation of Aryabhatta was used. Even the (knowledge of) gravitational field... Newton found it some 1500 years later... the knowledge existing (in our scriptures)," he said.

Nair, who was ISRO chairman from 2003-09, also claimed geometry was used to make calculations for building cities during the Harappan civilisation and the Pythagorean theorem also existed since the vedic period.

The comments by Nair came in the backdrop of many BJP leaders talking about ancient Indian scriptures having scientific information including on plastic surgery as well as aero-dynamics.

Popular Press Announces: The Big Bang Didn’t Happen!

Timeline of the Universe. Image credit: NASA

Did the big bang really happen? Yes, despite recent claims to the contrary.  A new paper in Physical Letters B has the popular press wondering if there was no big bang, but the actual paper claims no such thing.

The big bang is often presented as some kind of explosion from an initial point, but actually the big bang model simply posits that the universe was extremely hot and dense when the universe was young. The model makes certain predictions, such as the existence of a thermal cosmic background, that the universe is expanding, the abundance of elements, etc. All of these have matched observation with great precision. The big bang is a robust scientific theory that isn’t going away, and this new paper does nothing to question its legitimacy.

That doesn’t mean there aren’t unanswered questions about the big bang. For example, simple big bang models show that if you go back in time far enough, there is time when the entire universe was an infinitely dense singularity. This singularity would mark time zero for the cosmos. As many of you know,singularities are problematic, and they tend to stir up lots of debate. That’s where this paper comes in.

The paper presents a big bang model without an initial singularity. It does this by looking at a result derived from general relativity known as the Raychaudhuri equation. Basically his equation describes how a volume of matter changes over time, so its a great way of finding where physical singularities exist in your model. But rather than using the classical Raychaudhuri equation, the authors use a variation with a few quantum tweaks. This approach is often called semi-classical, because it uses some aspects of quantum theory, but isn’t a complete quantum gravity model (which we don’t have).

What the authors show is that their modified Raychaudhuri model eliminates the initial singularity of the big bang. It also predicts a cosmological constant, which is a proposed mechanism for dark energy. Their model is really basic, but this first result shows that this type of approach could work. The catch is that by eliminating the singularity, the model predicts that the universe had no beginning. It existed forever as a kind of quantum potential before “collapsing” into the hot dense state we call the big bang. Unfortunately many articles confuse “no singularity” with “no big bang.”

While this is an interesting model, it should be noted that it’s very basic. More of a proof of concept than anything else. It should also be noted that replacing the big bang singularity with an eternal history isn’t a new idea. Many inflation models, for example, make similar predictions. But none of these ideas eliminate the big bang, which is an established scientific fact.

The Armstrong Purse: Flown Apollo 11 Lunar Artifacts

At the National Air and Space Museum, as elsewhere around the world, we were enormously saddened when we learned that Neil Alden Armstrong, the first man to set foot on the Moon, had died of complications associated with heart surgery in August 2012. Not long afterwards his family contacted the Museum about artifacts he left in his home office in Ohio. In November, Museum curators Margaret Weitekamp (social and cultural history of space exploration), Alex Spencer (personal aeronautical equipment), and I (as Apollo curator) traveled to Cincinnati and were warmly greeted by his widow, Carol. We reviewed the items with the intention of listing those we felt appropriate for possible donation to the National Collection. The Armstrong family had already decided to donate Neil’s correspondence and paper files to his alma mater, Purdue University. The remaining collection of personal items and memorabilia was also extremely rich. Margaret and Alex may have the opportunity to write about these items in the near future.

This post is about something else however. A few weeks after we returned to Washington, D.C., I received an email from Carol Armstrong that she had located in one of Neil’s closets a white cloth bag filled with assorted small items that looked like they may have come from a spacecraft. She wanted to know if they were also of interest to the Museum. She provided the following photograph of the bag and the items spread out on her carpet.

Photograph provided by Carol Armstrong showing the objects found within the white cloth bag.

Needless to say, for a curator of a collection of space artifacts, it is hard to imagine anything more exciting. Realizing how important it would be to determine whether any or all of these items were actually flown in the Lunar Module Eagle during the historic Apollo 11 mission, I decided to enlist the expertise of Eric Jones, Ken Glover, and the team of experts who have put together the incredible Apollo Lunar Surface Journal (ALSJ) website, an indispensable site of detailed information about all aspects of the Apollo program.

The bag itself was immediately recognizable in that the ALSJ long has had a page devoted to what the astronauts referred to as a McDivitt Purse. The purse was a special container (officially called a Temporary Stowage Bag or TSB) stowed in the Lunar Module during launch but specially fitted with pins that fit into sockets in front of the Commander’s station to the left of the Lunar Module hatch. The TSB looks like a clutch purse in the way it opens and closes.

Apollo 11 Temporary Stowage Bag

The astronauts referred to it as a McDivitt purse, apparently because the need for a bag to temporarily stow items when there wasn’t time to return them to fixed stowage locations was first suggested by Apollo 9 Commander James McDivitt.

After a close examination of detailed photographs taken when the objects were in the Armstrong family’s possession and after they were shipped for cataloging and research to the National Air and Space Museum, the ALSJ experts were able to determine with almost complete certainty that all of the items were indeed from the Eagle, and that — although they were formally scheduled to be left behind — they were assembled in the Temporary Stowage Bag and saved from the fate that awaited Eagle’s ascent stage and all of its contents: crashing into the lunar surface.

Evidence that the items were intentionally preserved is found in the mission transcripts themselves. (The transcripts of voice communications are the documents around which the entire ALSJ is organized.) The rescued items are referenced by the Apollo 11 crew soon after Neil and Buzz Aldrin rejoined Michael Collins in lunar orbit. While still in the Lunar Module and after lunar orbit rendezvous with the Command Module, Neil and Buzz spent considerable time passing over to Mike the rock boxes and the contingency samples they had collected from the Moon. Less than an hour before they were ready to jettison Eagle, mission transcripts record Armstrong saying to Collins (Mission Elapsed Time (MET): 129:14:53): “You know, that — that one’s just a bunch of trash that we want to take back — LM parts, odds and ends, and it won’t stay closed by itself. We’ll have to figure something out for it.”

Later (MET 181:38:04) they would describe to mission control the container with the “odds and ends” as, “10 pounds of LM miscellaneous equipment.” It was important they account for the amount and distribution of any added weight so that the return trajectory and entry parameters could be calculated with precision.

As far as we know, Neil has never discussed the existence of these items and no one else has seen them in the 45 years since he returned from the Moon. (I asked James Hansen, Neil’s authorized biographer if he had mentioned the items, and he had not.) Each and every item has its own story and significance, and they are described with photographs in extraordinary detail in an addendum to the Apollo Lunar Surface Journal. But two of the items are especially timely. Both have been placed on display as part of the recently opened temporary exhibition Outside the Spacecraft: 50 Years of Extra-Vehicular Activity.

The first is the 16mm Data Acquisition Camera that was mounted in the window of the lunar module Eagle to record the historic landing and “one small step” made by Armstrong as humankind first set foot on another world.

Apollo 11 16mm Data Acquisition Camera. Below are a handful of images captured by this camera.

Neil Armstrong about to step on the Lunar surface as recorded by the 16mm Data Acquisition Camera.

Camera view of Neil and Buzz setting the American Flag.

The second is one of two waist tethers provided in the lunar module explicitly for securing astronauts should they have to spacewalk from the Lunar Module back to the Command Module had there been a problem reconnecting the two spacecraft in orbit around the Moon. We have determined that this tether was the one Neil Armstrong jerry-rigged to support his feet during the single rest period on the Moon, a story well told and documented in the new Journal entry.

Apollo 11 Waist Tether used by Neil Armstrong to suspend his legs as he attempted to get comfortable during the rest period inside the Lunar Module.

In the future, we hope to complete documenting and cataloging the entire collection of items and, as appropriate, to place them on public display. Seeing such things with one’s own eyes helps us to appreciate that these accomplishments are not just in history books or movies, but involved real people and real things, and that they involved an extraordinary amount of detailed engineering and planning.

Ancient Indian Planes Could Travel From One Planet to Another

Aeroplanes existed in India 7,000 years ago and they travelled from one country to another and from one planet to another, the Indian Science Congress was told today in a controversial lecture that examined ancient aviation technology in the Vedas.

The hosting of the lecture, presented by Captain Anand J Bodas, a retired principal of a pilot training facility, had recently attracted criticism from some scientists who said it undermined the primacy of empirical evidence on which the 102-year-old Congress was founded.

The lecture was presented on the second day of the Congress under the aegis of Mumbai University as part of a symposium on 'Ancient Sciences through Sanskrit'.

Drawing upon the ancient Vedic texts to support the claim that there was flying technology in ancient India, Bodas said, "There is a reference of ancient aviation in the Rigveda."

He said Maharishi Bharadwaj spoke 7,000 years ago of "the existence of aeroplanes which travel from one country to another, from one continent to another and from one planet to another. He mentioned 97 reference books for aviation."

"History merely notes that the Wright brothers first flew in 1904," he said.

Bharadwaj, who authored the book Vimana Samhita, had written about various types of metal alloys used to build an aeroplane, Bodas said, adding, "Now we have to import aeroplane alloys. The young generation should study the alloys mentioned in his book and make them here,"

He also spoke of the "huge" aeroplanes which flew in ancient India. "The basic structure was of 60 by 60 feet and in some cases, over 200 feet. They were jumbo planes," he said.

"The ancient planes had 40 small engines. Today's aviation does not know even of flexible exhaust system," he said.

The ancient Indian radar system was called 'rooparkanrahasya'. "In this system, the shape of the aeroplane was presented to the observer, instead of the mere blimp that is seen on modern radar systems," he said.

Bharadwaj's book mentioned a diet of pilots. It contained of milk of buffalo, cow and sheep for specific periods, Bodas said.

The pilot's dress cloth came from vegetation grown underwater, he said.

An online petition by a scientist at the NASA research centre had demanded that the scheduled lecture be cancelled as it mixes mythology with science.

The comments by Bodas came a day after Union Minister for Science and Technology Harsh Vardhan told the Congress that Algebra and the Pythagoras' theorem both originated in India but the credit for these has gone to people from other countries.

Indian Science Congress Association (ISCA), which hosts the annual event, is a premier scientific organisation of India with a membership strength of more than 30,000 scientists. It was founded in 1914 with the objective to "advance and promote the cause of science in India."