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doc21838 | Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the new elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ... | Beta decay |
doc21839 | In 1900, Becquerel measured the mass-to-charge ratio (m/e) for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that m/e for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.[5] | Beta decay |
doc21840 | In 1901, Rutherford and Frederick Soddy showed that alpha and beta radioactivity involves the transmutation of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and Kazimierz Fajans independently proposed their radioactive displacement law, which state... | Beta decay |
doc21841 | The study of beta decay provided the first physical evidence for the existence of the neutrino. In both alpha and gamma decay, the resulting particle has a narrow energy distribution, since the particle carries the energy from the difference between the initial and final nuclear states. However, the kinetic energy dist... | Beta decay |
doc21842 | A second problem is related to the conservation of angular momentum. Molecular band spectra showed that the nuclear spin of nitrogen-14 is 1 (i.e. equal to the reduced Planck constant) and more generally that the spin is integral for nuclei of even mass number and half-integral for nuclei of odd mass number. This was l... | Beta decay |
doc21843 | From 1920–1927, Charles Drummond Ellis (along with Chadwick and colleagues) further established that the beta decay spectrum is continuous. In 1933, Ellis and Nevill Mott obtained strong evidence that the beta spectrum has an effective upper bound in energy. Niels Bohr had suggested that the beta spectrum could be ex... | Beta decay |
doc21844 | In a famous letter written in 1930, Wolfgang Pauli attempted to resolve the beta-particle energy conundrum by suggesting that, in addition to electrons and protons, atomic nuclei also contained an extremely light neutral particle, which he called the neutron. He suggested that this "neutron" was also emitted during bet... | Beta decay |
doc21845 | In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction 4
2He + 27
13Al → 30
15P + 1
0n, and observed that the product isotope 30
15P emits a positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example ... | Beta decay |
doc21846 | The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others. K-electron capture was first observed in 1937 by Luis Alvarez, in the nuclide 48V.[11][12][13] Alvarez went on to study electron capture in 67Ga and other nuclides.[11][14][15] | Beta decay |
doc21847 | In 1956, Tsung-Dao Lee and Chen Ning Yang noticed that there was no evidence that parity was conserved in weak interactions, and so they postulated that this symmetry may not be preserved by the weak force. They sketched the design for an experiment for testing conservation of parity in the laboratory.[16] Later that y... | Beta decay |
doc21848 | In β− decay, the weak interaction converts an atomic nucleus into a nucleus with atomic number increased by one, while emitting an electron (e−) and an electron antineutrino (ν
e). β− decay generally occurs in neutron-rich nuclei.[20] The generic equation is: | Beta decay |
doc21849 | where A and Z are the mass number and atomic number of the decaying nucleus, and X and X' are the initial and final elements, respectively. | Beta decay |
doc21850 | Another example is when the free neutron (1
0n) decays by β− decay into a proton (p): | Beta decay |
doc21851 | At the fundamental level (as depicted in the Feynman diagram on the right), this is caused by the conversion of the negatively charged (−1/3 e) down quark to the positively charged (+2/3 e) up quark by emission of a W− boson; the W− boson subsequently decays into an electron and an electron antineutrino: | Beta decay |
doc21852 | In β+ decay, or "positron emission", the weak interaction converts an atomic nucleus into a nucleus with atomic number decreased by one, while emitting a positron (e+) and an electron neutrino (ν
e). β+ decay generally occurs in proton-rich nuclei. The generic equation is: | Beta decay |
doc21853 | This may be considered as the decay of a proton inside the nucleus to a neutron | Beta decay |
doc21854 | However, β+ decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton. β+ decay can only happen inside nuclei when the daughter nucleus has a greater binding energy (and therefore a lower total energy) than the mother nucleus. The differ... | Beta decay |
doc21855 | In all cases where β+ decay (positron emission) of a nucleus is allowed energetically, so too is electron capture allowed. This is a process during which a nucleus captures one of its atomic electrons, resulting in the emission of a neutrino: | Beta decay |
doc21856 | An example of electron capture is one of the decay modes of krypton-81 into bromine-81: | Beta decay |
doc21857 | All emitted neutrinos are of the same energy. In proton-rich nuclei where the energy difference between the initial and final states is less than 2mec2, β+ decay is not energetically possible, and electron capture is the sole decay mode.[21] | Beta decay |
doc21858 | If the captured electron comes from the innermost shell of the atom, the K-shell, which has the highest probability to interact with the nucleus, the process is called K-capture.[22] If it comes from the L-shell, the process is called L-capture, etc. | Beta decay |
doc21859 | Electron capture is a competing (simultaneous) decay process for all nuclei that can undergo β+ decay. The converse, however, is not true: electron capture is the only type of decay that is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino.[21] | Beta decay |
doc21860 | If the proton and neutron are part of an atomic nucleus, the above described decay processes transmute one chemical element into another. For example: | Beta decay |
doc21861 | Beta decay does not change the number (A) of nucleons in the nucleus, but changes only its charge Z. Thus the set of all nuclides with the same A can be introduced; these isobaric nuclides may turn into each other via beta decay. For a given A there is one that is most stable. It is said to be beta stable, because it p... | Beta decay |
doc21862 | Usually, unstable nuclides are clearly either "neutron rich" or "proton rich", with the former undergoing beta decay and the latter undergoing electron capture (or more rarely, due to the higher energy requirements, positron decay). However, in a few cases of odd-proton, odd-neutron radionuclides, it may be energetical... | Beta decay |
doc21863 | Most naturally occurring nuclides on earth are beta stable. Those that are not have half-lives ranging from under a second to periods of time significantly greater than the age of the universe. One common example of a long-lived isotope is the odd-proton odd-neutron nuclide 40
19K, which undergoes all three types of be... | Beta decay |
doc21864 | Beta decay just changes neutron to proton or, in the case of positive beta decay (electron capture) proton to neutron so the number of individual quarks don't change. It is only the baryon flavor that changes, here labelled as the isospin. | Beta decay |
doc21865 | Up and down quarks have total isospin
I
=
1
2
{\displaystyle I={\frac {1}{2}}}
and isospin projections | Beta decay |
doc21866 | All other quarks have I = 0. | Beta decay |
doc21867 | so all leptons have assigned a value of +1, antileptons −1, and non-leptonic particles 0. | Beta decay |
doc21868 | For allowed decays, the net orbital angular momentum is zero, hence only spin quantum numbers are considered. | Beta decay |
doc21869 | The electron and antineutrino are fermions, spin-1/2 objects, therefore they may couple to total
S
=
1
{\displaystyle S=1}
(parallel) or
S
=
0
{\displaystyle S=0}
(anti-parallel). | Beta decay |
doc21870 | For forbidden decays, orbital angular momentum must also be taken into consideration. | Beta decay |
doc21871 | The Q value is defined as the total energy released in a given nuclear decay. In beta decay, Q is therefore also the sum of the kinetic energies of the emitted beta particle, neutrino, and recoiling nucleus. (Because of the large mass of the nucleus compared to that of the beta particle and neutrino, the kinetic energy... | Beta decay |
doc21872 | Since the rest mass of the electron is 511 keV, the most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light. | Beta decay |
doc21873 | Consider the generic equation for beta decay | Beta decay |
doc21874 | The Q value for this decay is | Beta decay |
doc21875 | where
m
N
(
X
Z
A
)
{\displaystyle m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)}
is the mass of the nucleus of the A
ZX atom,
m
e
{\displaystyle m_{e}}
is the mass of the electron, and
m
ν
¯
e
{\displaystyle m_{{\overline {\nu }}_{e}}}
is the mass of t... | Beta decay |
doc21876 | That is, the total atomic mass is the mass of the nucleus, plus the mass of the electrons, minus the sum of all electron binding energies Bi for the atom. This equation is rearranged to find
m
N
(
X
Z
A
)
{\displaystyle m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)}
, and
m
N
... | Beta decay |
doc21877 | This energy is carried away as kinetic energy by the electron and neutrino. | Beta decay |
doc21878 | Because the reaction will proceed only when the Q-value is positive, β− decay can occur when the mass of atom A
ZX is greater than the mass of atom A
Z+1X’.[26] | Beta decay |
doc21879 | The equations for β+ decay are similar, with the generic equation | Beta decay |
doc21880 | However, in this equation, the electron masses do not cancel, and we are left with | Beta decay |
doc21881 | Because the reaction will proceed only when the Q-value is positive, β+ decay can occur when the mass of atom A
ZX exceeds that of A
Z-1X’ by at least twice the mass of the electron.[26] | Beta decay |
doc21882 | The analogous calculation for electron capture must take into account the binding energy of the electrons. This is because the atom will be left in an excited state after capturing the electron, and the binding energy of the captured innermost electron is significant. Using the generic equation for electron capture | Beta decay |
doc21883 | which simplifies to | Beta decay |
doc21884 | where Bn is the binding energy of the captured electron. | Beta decay |
doc21885 | Because the binding energy of the electron is much less than the mass of the electron, nuclei that can undergo β+ decay can always also undergo electron capture, but the reverse is not true.[26] | Beta decay |
doc21886 | Beta decay can be considered as a perturbation as described in quantum mechanics, and thus Fermi's Golden Rule can be applied. This leads to an expression for the kinetic energy spectrum N(T) of emitted betas as follows:[27] | Beta decay |
doc21887 | where T is the kinetic energy, CL is a shape function that depends on the forbiddenness of the decay (it is constant for allowed decays), F(Z, T) is the Fermi Function (see below) with Z the charge of the final-state nucleus, E=T + mc2 is the total energy, p=√(E/c)2 − (mc)2 is the momentum, and Q is the Q value of the ... | Beta decay |
doc21888 | As an example, the beta decay spectrum of 210Bi (originally called RaE) is shown to the right. | Beta decay |
doc21889 | The Fermi function that appears in the beta spectrum formula accounts for the Coulomb attraction / repulsion between the emitted beta and the final state nucleus. Approximating the associated wavefunctions to be spherically symmetric, the Fermi function can be analytically calculated to be:[28] | Beta decay |
doc21890 | where S=√1 − α2 Z2 (α is the fine-structure constant), η=± αZE/pc (+ for electrons, − for positrons), ρ=rN/ℏ (rN is the radius of the final state nucleus), and Γ is the Gamma function. | Beta decay |
doc21891 | For non-relativistic betas (Q ≪ mec2), this expression can be approximated by:[29] | Beta decay |
doc21892 | Other approximations can be found in the literature.[30][31] | Beta decay |
doc21893 | A Kurie plot (also known as a Fermi–Kurie plot) is a graph used in studying beta decay developed by Franz N. D. Kurie, in which the square root of the number of beta particles whose momenta (or energy) lie within a certain narrow range, divided by the Fermi function, is plotted against beta-particle energy.[32][33] I... | Beta decay |
doc21894 | After the discovery of parity non-conservation (see History), it was found that, in beta decay, electrons are emitted mostly with negative helicity, i.e., they move, naively speaking, like left-handed screws driven into a material (they have negative longitudinal polarization).[35] Conversely, positrons have mostly pos... | Beta decay |
doc21895 | The higher the energy of the particles, the higher their polarization. | Beta decay |
doc21896 | Beta decays can be classified according to the angular momentum (L-value) and total spin (S-value) of the emitted radiation. Since total angular momentum must be conserved, including orbital and spin angular momentum, beta decay occurs by a variety of quantum state transitions to various nuclear angular momentum or spi... | Beta decay |
doc21897 | Other decay modes, which are rare, are known as bound state decay and double beta decay. | Beta decay |
doc21898 | A Fermi transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin
S
=
0
{\displaystyle S=0}
, leading to an angular momentum change
Δ
J
=
0
{\displaystyle \Delta J=0}
between the initial and final states of the nucleus (assuming an ... | Beta decay |
doc21899 | with
G
V
{\displaystyle G_{V}}
the weak vector coupling constant,
τ
±
{\displaystyle \tau _{\pm }}
the isospin raising and lowering operators, and
a
{\displaystyle a}
running over all protons and neutrons in the nucleus. | Beta decay |
doc21900 | A Gamow-Teller transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin
S
=
1
{\displaystyle S=1}
, leading to an angular momentum change
Δ
J
=
0
,
±
1
{\displaystyle \Delta J=0,\pm 1}
between the initial and final states of the nu... | Beta decay |
doc21901 | with
G
A
{\displaystyle G_{A}}
the weak axial-vector coupling constant, and
σ
{\displaystyle \sigma }
the spin Pauli matrices, which can produce a spin-flip in the decaying nucleon. | Beta decay |
doc21902 | When L > 0, the decay is referred to as "forbidden". Nuclear selection rules require high L-values to be accompanied by changes in nuclear spin (J) and parity (π). The selection rules for the Lth forbidden transitions are: | Beta decay |
doc21903 | where Δπ=1 or −1 corresponds to no parity change or parity change, respectively. The special case of a transition between isobaric analogue states, where the structure of the final state is very similar to the structure of the initial state, is referred to as "superallowed" for beta decay, and proceeds very quickly. Th... | Beta decay |
doc21904 | A very small minority of free neutron decays (about four per million) are so-called "two-body decays", in which the proton, electron and antineutrino are produced, but the electron fails to gain the 13.6 eV energy necessary to escape the proton, and therefore simply remains bound to it, as a neutral hydrogen atom.[37] ... | Beta decay |
doc21905 | For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons. | Beta decay |
doc21906 | The phenomenon in fully ionized atoms was first observed for 163Dy66+ in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research group. Although neutral 163Dy is a stable isotope, the fully ionized 163Dy66+ undergoes β decay into the K and L shells with a half-life of 47 days.[38] | Beta decay |
doc21907 | Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for 187Re by Bosch et al., also at Darmstadt. Neutral 187Re does undergo β decay with a half-life of 42 × 109 years, but for fully ionized 187Re75+ this is shortened by a factor of 109 to only 32.9 years.[39] For compari... | Beta decay |
doc21908 | Some nuclei can undergo double beta decay (ββ decay) where the charge of the nucleus changes by two units. Double beta decay is difficult to study, as the process has an extremely long half-life. In nuclei for which both β decay and ββ decay are possible, the rarer ββ decay process is effectively impossible to observe.... | Beta decay |
doc21909 | "Ordinary" double beta decay results in the emission of two electrons and two antineutrinos. If neutrinos are Majorana particles (i.e., they are their own antiparticles), then a decay known as neutrinoless double beta decay will occur. Most neutrino physicists believe that neutrinoless double beta decay has never been ... | Beta decay |
doc26026 | Malonyl-CoA is a coenzyme A derivative of malonic acid. | Malonyl-CoA |
doc26027 | It plays a key role in chain elongation in fatty acid biosynthesis and polyketide biosynthesis. | Malonyl-CoA |
doc26028 | In the former, it provides 2-carbon units to fatty acids and commits them to fatty acid chain synthesis. | Malonyl-CoA |
doc26029 | Malonyl-CoA is formed by carboxylating acetyl-CoA using the enzyme acetyl-CoA carboxylase. One molecule of acetyl-CoA joins with a molecule of bicarbonate,[1] requiring energy rendered from ATP. | Malonyl-CoA |
doc26030 | Malonyl-CoA is utilised in fatty acid biosynthesis by the enzyme malonyl coenzyme A:acyl carrier protein transacylase (MCAT). MCAT serves to transfer malonate from malonyl-CoA to the terminal thiol of holo-acyl carrier protein (ACP). | Malonyl-CoA |
doc26031 | MCAT is also involved in bacterial polyketide biosynthesis. The enzyme MCAT together with an acyl carrier protein (ACP), and a polyketide synthase (PKS) and chain-length factor heterodimer, constitutes the minimal PKS of type II polyketides. | Malonyl-CoA |
doc26032 | Malonyl-CoA is a highly regulated molecule in fatty acid synthesis; as such, it inhibits the rate-limiting step in beta-oxidation of fatty acids. Malonyl CoA inhibits fatty acids from associating with carnitine by regulating the enzyme carnitine acyltransferase, thereby preventing them from entering the mitochondria, w... | Malonyl-CoA |
doc29464 | Blood alcohol content (BAC), also called blood alcohol concentration, blood ethanol concentration, or blood alcohol level, is most commonly used as a metric of alcohol intoxication for legal or medical purposes. | Blood alcohol content |
doc29465 | Blood alcohol concentration is usually expressed as a percentage of ethanol in the blood in units of mass of alcohol per volume of blood or mass of alcohol per mass of blood, depending on the country. For instance, in North America a BAC of 0.1 (0.1% or one tenth of one percent) means that there are 0.10 g of alcohol f... | Blood alcohol content |
doc29466 | To calculate estimated peak blood alcohol concentration (EBAC), a variation, including drinking period in hours, of the Widmark formula was used. The formula is:[2] | Blood alcohol content |
doc29467 | Regarding metabolism (MR) in the formula; Females demonstrated a higher average rate of elimination (mean, 0.017; range, 0.014–0.021 g/210 L) than males (mean, 0.015; range, 0.013–0.017 g/210 L). Female subjects on average had a higher percentage of body fat (mean, 26.0; range, 16.7–36.8%) than males (mean, 18.0; range... | Blood alcohol content |
doc29468 | Note: This chart defines a drink as 14g of ethanol, while the formula defines a drink as 10g of ethanol. | Blood alcohol content |
doc29469 | Standard Drink Sizes (Australia) | Blood alcohol content |
doc29470 | The National Institute on Alcohol Abuse and Alcoholism (NIAAA) define the term "binge drinking" as a pattern of drinking that brings a person’s blood alcohol concentration (BAC) to 0.08 grams percent or above. This typically happens when men consume 5 or more drinks, and when women consume 4 or more drinks, in about ... | Blood alcohol content |
doc29471 | There are several different units in use around the world for defining blood alcohol concentration. Each is defined as either a mass of alcohol per volume of blood or a mass of alcohol per mass of blood (never a volume per volume). 1 milliliter of blood has a mass of approximately 1.06 grams. Because of this, units by ... | Blood alcohol content |
doc29472 | For purposes of law enforcement, blood alcohol content is used to define intoxication and provides a rough measure of impairment. Although the degree of impairment may vary among individuals with the same blood alcohol content, it can be measured objectively and is therefore legally useful and difficult to contest in c... | Blood alcohol content |
doc29473 | The alcohol level at which a person is considered legally impaired varies by country. The list below gives limits by country. These are typically blood alcohol content limits for the operation of a vehicle. | Blood alcohol content |
doc29474 | Zero effective tolerance | Blood alcohol content |
doc29475 | It is illegal to have any measurable alcohol in the blood while driving in these countries. Most jurisdictions have a tolerance slightly higher than zero to account for false positives and naturally occurring alcohol in the body. Some of the following jurisdictions have a general prohibition of alcohol. | Blood alcohol content |
doc29476 | In certain countries, alcohol limits are determined by the breath alcohol content (BrAC), not to be confused with blood alcohol content (BAC). | Blood alcohol content |
doc29477 | Blood alcohol tests assume the individual being tested is average in various ways. For example, on average the ratio of blood alcohol content to breath alcohol content (the partition ratio) is 2100 to 1. In other words, there are 2100 parts of alcohol in the blood for every part in the breath. However, the actual ratio... | Blood alcohol content |
doc29478 | Alcohol is absorbed throughout the gastrointestinal tract, but more slowly in the stomach than in the small or large intestine. For this reason, alcohol consumed with food is absorbed more slowly, because it spends a longer time in the stomach. Furthermore, alcohol dehydrogenase is present in the stomach lining. After ... | Blood alcohol content |
doc29479 | Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. | Blood alcohol content |
doc29480 | Alcohol is metabolized mainly by the group of six enzymes collectively called alcohol dehydrogenase. These convert the ethanol into acetaldehyde (an intermediate more toxic than ethanol). The enzyme acetaldehyde dehydrogenase then converts the acetaldehyde into non-toxic acetic acid. | Blood alcohol content |
doc29481 | Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic halflife (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol a... | Blood alcohol content |
doc29482 | Such persons have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severe hangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not use alcoholic beverages have lower levels of alcohol dehydroge... | Blood alcohol content |
doc29483 | Currently, the only known substance that can increase the rate of metabolism of alcohol is fructose. The effect can vary significantly from person to person, but a 100Â g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. Fructose also increases false positives of high BAC ratio readin... | Blood alcohol content |
doc29484 | Alcohol absorption can be slowed by ingesting alcohol on a full stomach.[42] The belief that the food absorbs the alcohol is a common misconception. Alcohol absorption is slowed because the stomach sphincter closes in order to break down the food. The alcohol cannot be absorbed through the stomach, thus cannot be absor... | Blood alcohol content |
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