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Banana Equivalent Dose
Banana equivalent dose (BED) is an informal unit of measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas contain naturally occurring radioactive isotopes, particularly potassium-40 (40K), one of several naturally occurring isotopes of potassium. One BED is often correlated to 10 sievert (0.1 μSv); however, in practice, this dose is not cumulative, as the potassium in foods is excreted in urine to maintain homeostasis. The BED is only meant as an educational exercise and is not a formally adopted dose measurement. History The origins of the concept are uncertain, but one early mention can be found on the RadSafe nuclear safety mailing list in 1995, where Gary Mansfield of the Lawrence Livermore National Laboratory mentions that he has found the "banana equivalent dose" to be "very useful in attempting to explain infinitesimal doses (and c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, that is easily removed to create an ion with a positive charge – a cation, that combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac- colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and occurs in many minerals such as orthoclase, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta Ray
A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β− decay and β+ decay, which produce electrons and positrons respectively. Beta particles with an energy of 0.5 MeV have a range of about one metre in air; the distance is dependent on the particle energy. Beta particles are a type of ionizing radiation and for radiation protection purposes are regarded as being more ionising than gamma rays, but less ionising than alpha particles. The higher the ionising effect, the greater the damage to living tissue, but also the lower the penetrating power of the radiation. Beta decay modes β− decay (electron emission) An unstable atomic nucleus with an excess of neutrons may undergo β− decay, where a neutron is converted into a proton, an electron, and an electron antineutrino (the antip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon-14
Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples. Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California. Its existence had been suggested by Franz N. D. Kurie, Franz Kurie in 1934. There are three naturally occurring isotopes of carbon on Earth: carbon-12 (), which makes up 99% of all carbon on Earth; carbon-13 (), which makes up 1%; and carbon-14 (), which occurs in trace amounts, making up about 1 or 1.5 atoms per 1012 atoms of carbon in the atmosphere. Carbon-12 and carbon-13 are both stable, while carbon-14 is unstable and has a half-life of 5,730 ± 40 years. Carbon-14 decays into nitrogen-14 () through bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Logarithm
The natural logarithm of a number is its logarithm to the base of the mathematical constant , which is an irrational and transcendental number approximately equal to . The natural logarithm of is generally written as , , or sometimes, if the base is implicit, simply . Parentheses are sometimes added for clarity, giving , , or . This is done particularly when the argument to the logarithm is not a single symbol, so as to prevent ambiguity. The natural logarithm of is the power to which would have to be raised to equal . For example, is , because . The natural logarithm of itself, , is , because , while the natural logarithm of is , since . The natural logarithm can be defined for any positive real number as the area under the curve from to (with the area being negative when ). The simplicity of this definition, which is matched in many other formulas involving the natural logarithm, leads to the term "natural". The definition of the natural logarithm can then b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exponential Decay
A quantity is subject to exponential decay if it decreases at a rate proportional to its current value. Symbolically, this process can be expressed by the following differential equation, where is the quantity and (lambda) is a positive rate called the exponential decay constant, disintegration constant, rate constant, or transformation constant: :\frac = -\lambda N. The solution to this equation (see derivation below) is: :N(t) = N_0 e^, where is the quantity at time , is the initial quantity, that is, the quantity at time . Measuring rates of decay Mean lifetime If the decaying quantity, ''N''(''t''), is the number of discrete elements in a certain set, it is possible to compute the average length of time that an element remains in the set. This is called the mean lifetime (or simply the lifetime), where the exponential time constant, \tau, relates to the decay rate constant, λ, in the following way: :\tau = \frac. The mean lifetime can be looked at as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relative Atomic Mass
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant. The atomic mass constant (symbol: ''m'') is defined as being of the mass of a carbon-12 atom. Since both quantities in the ratio are masses, the resulting value is dimensionless; hence the value is said to be ''relative''. For a single given sample, the relative atomic mass of a given element is the weighted arithmetic mean of the masses of the individual atoms (including their isotopes) that are present in the sample. This quantity can vary substantially between samples because the sample's origin (and therefore its radioactive history or diffusion history) may have produced unique combinations of isotopic abundances. For example, due to a different mixture of stable carbon-12 and carbon-13 isoto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mole (unit)
The mole, symbol mol, is the unit of amount of substance in the International System of Units (SI). The quantity amount of substance is a measure of how many elementary entities of a given substance are in an object or sample. The mole is defined as containing exactly elementary entities. Depending on what the substance is, an elementary entity may be an atom, a molecule, an ion, an ion pair, or a subatomic particle such as an electron. For example, 10 moles of water (a chemical compound) and 10 moles of mercury (a chemical element), contain equal amounts of substance and the mercury contains exactly one atom for each molecule of the water, despite the two having different volumes and different masses. The number of elementary entities in one mole is known as the Avogadro number, which is the approximate number of nucleons (protons or neutrons) in one gram of ordinary matter. The previous definition of a mole was simply the number of elementary entities equal to that of 12 gram ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Avogadro's Number
The Avogadro constant, commonly denoted or , is the proportionality factor that relates the number of constituent particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample. It is an SI defining constant with an exact value of . It is named after the Italian scientist Amedeo Avogadro by Stanislao Cannizzaro, who explained this number four years after Avogadro's death while at the Karlsruhe Congress in 1860. The numeric value of the Avogadro constant expressed in reciprocal moles, a dimensionless number, is called the Avogadro number. In older literature, the Avogadro number is denoted or , which is the number of particles that are contained in one mole, exactly . The Avogadro number is the approximate number of nucleons (protons or neutrons) in one gram of ordinary matter. The value of the Avogadro constant was chosen so that the mass of one mole of a chemical compound, in grams, is approximately the number of nucleons in one cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mole Fraction
In chemistry, the mole fraction or molar fraction (''xi'' or ) is defined as unit of the amount of a constituent (expressed in moles), ''ni'', divided by the total amount of all constituents in a mixture (also expressed in moles), ''n''tot. This expression is given below: :x_i = \frac The sum of all the mole fractions is equal to 1: :\sum_^ n_i = n_\mathrm ; \ \sum_^ x_i = 1. The same concept expressed with a denominator of 100 is the mole percent, molar percentage or molar proportion (mol%). The mole fraction is also called the amount fraction. It is identical to the number fraction, which is defined as the number of molecules of a constituent ''Ni'' divided by the total number of all molecules ''N''tot. The mole fraction is sometimes denoted by the lowercase Greek letter (chi) instead of a Roman ''x''. For mixtures of gases, IUPAC recommends the letter ''y''. The National Institute of Standards and Technology of the United States prefers the term amount-of-substance fraction o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics, as if they were tennis balls for example, is not possible due to quantum effects. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions. The electrons of an atom are a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Becquerel
The becquerel (; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. For applications relating to human health this is a small quantity, and SI multiples of the unit are commonly used. The becquerel is named after Henri Becquerel, who shared a Nobel Prize in Physics with Pierre and Marie Skłodowska Curie in 1903 for their work in discovering radioactivity. Definition 1 Bq = 1 s−1 A special name was introduced for the reciprocal second (s−1) to represent radioactivity to avoid potentially dangerous mistakes with prefixes. For example, 1 µs−1 would mean 106 disintegrations per second: 1·(10−6 s)−1 = 106 s−1, whereas 1 µBq would mean 1 disintegration per 1 million seconds. Other names considered were hertz (Hz), a special name already in use for the reciprocal second, and Fourier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
