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100-425: Due to its mode of beta decay , iodine-131 causes mutation and death in cells that it penetrates, and other cells up to several millimeters away. For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation. For example, children treated with moderate dose of I for thyroid adenomas had

200-665: A bathroom connected to it to limit unintended exposure to family members. Many airports have radiation detectors to detect the smuggling of radioactive materials. Patients should be warned that if they travel by air, they may trigger radiation detectors at airports up to 95 days after their treatment with I. The I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g. I- metaiodobenzylguanidine (I-MIBG) for imaging and treating pheochromocytoma and neuroblastoma . In all of these therapeutic uses, I destroys tissue by short-range beta radiation . About 90% of its radiation damage to tissue

300-426: A capsule, due to "greater ease to the patient and the superior radiation protection for caregivers". Ablation doses are usually administered on an inpatient basis, and IAEA International Basic Safety Standards recommend that patients are not discharged until the activity falls below 1100 MBq. ICRP advice states that "comforters and carers" of patients undergoing radionuclide therapy should be treated as members of

400-403: A decontaminant specially made for radioactive iodine removal may be advised. The use of chlorine bleach solutions, or cleaners that contain chlorine bleach for cleanup, are not advised, since radioactive elemental iodine gas may be released. Airborne I-131 may cause a greater risk of second-hand exposure, spreading contamination over a wide area. Patient is advised if possible to stay in a room with

500-441: A detectable increase in thyroid cancer, but children treated with a much higher dose did not. Likewise, most studies of very-high-dose I for treatment of Graves' disease have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with I absorption at moderate doses. Thus, iodine-131 is increasingly less employed in small doses in medical use (especially in children), but increasingly

600-733: A first-order reaction is given by the following equation: [ A ] 0 / 2 = [ A ] 0 exp ⁡ ( − k t 1 / 2 ) {\displaystyle [{\ce {A}}]_{0}/2=[{\ce {A}}]_{0}\exp(-kt_{1/2})} It can be solved for k t 1 / 2 = − ln ⁡ ( [ A ] 0 / 2 [ A ] 0 ) = − ln ⁡ 1 2 = ln ⁡ 2 {\displaystyle kt_{1/2}=-\ln \left({\frac {[{\ce {A}}]_{0}/2}{[{\ce {A}}]_{0}}}\right)=-\ln {\frac {1}{2}}=\ln 2} For

700-407: A first-order reaction, the half-life of a reactant is independent of its initial concentration. Therefore, if the concentration of A at some arbitrary stage of the reaction is [A] , then it will have fallen to ⁠ 1 / 2 ⁠ [A] after a further interval of ⁠ ln ⁡ 2 k . {\displaystyle {\tfrac {\ln 2}{k}}.} ⁠ Hence,

800-471: A fundamentally new type in 1903 and termed gamma rays . Alpha, beta, and gamma are the first three letters of the Greek alphabet . 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

900-572: A half-life of about 12.7 hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay. This particular nuclide (though not all nuclides in this situation) is almost equally likely to decay through proton decay by positron emission ( 18% ) or electron capture ( 43% ) to 28 Ni , as it is through neutron decay by electron emission ( 39% ) to 30 Zn . Most naturally occurring nuclides on earth are beta stable. Nuclides that are not beta stable have half-lives ranging from under

1000-446: A human being is about 9 to 10 days, though this can be altered by behavior and other conditions. The biological half-life of caesium in human beings is between one and four months. The concept of a half-life has also been utilized for pesticides in plants , and certain authors maintain that pesticide risk and impact assessment models rely on and are sensitive to information describing dissipation from plants. In epidemiology ,

1100-421: A maximal energy of 606 keV (89% abundance, others 248–807 keV) and 364 keV gamma rays (81% abundance, others 723 keV). Beta decay also produces an antineutrino , which carries off variable amounts of the beta decay energy. The electrons, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of 0.6 to 2 mm . Iodine in food

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1200-573: A medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border. Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment Used for the first time in 1951 to localize leaks in a drinking water supply system of Munich , Germany, iodine-131 became one of the most commonly used gamma-emitting industrial radioactive tracers , with applications in isotope hydrology and leak detection. Since

1300-420: A neutrino: An example of electron capture is one of the decay modes of krypton-81 into bromine-81 : 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 2 m e c , β  decay is not energetically possible, and electron capture is the sole decay mode. If the captured electron comes from

1400-611: A positron and an electron neutrino. β decay is also known as positron emission . Beta decay conserves a quantum number known as the lepton number , or the number of electrons and their associated neutrinos (other leptons are the muon and tau particles). These particles have lepton number +1, while their antiparticles have lepton number −1. Since a proton or neutron has lepton number zero, β decay (a positron, or antielectron) must be accompanied with an electron neutrino, while β decay (an electron) must be accompanied by an electron antineutrino. An example of electron emission (β decay)

1500-553: A positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example of β  decay ( positron emission ), which they termed artificial radioactivity since 15 P is a short-lived nuclide which does not exist in nature. In recognition of their discovery, the couple were awarded the Nobel Prize in Chemistry in 1935. The theory of electron capture

1600-585: 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 19 K , which undergoes all three types of beta decay ( β , β and electron capture) with a half-life of 1.277 × 10  years . B = n q − n q ¯ 3 {\displaystyle B={\frac {n_{q}-n_{\bar {q}}}{3}}} where Beta decay just changes neutron to proton or, in

1700-462: A similar but otherwise-unexposed group. The risk can be mitigated by taking iodine supplements, raising the total amount of iodine in the body and, therefore, reducing uptake and retention in the face and chest and lowering the relative proportion of radioactive iodine. However, such supplements were not consistently distributed to the population living nearest to the Chernobyl nuclear power plant after

1800-417: A substance can be complex, due to factors including accumulation in tissues , active metabolites , and receptor interactions. While a radioactive isotope decays almost perfectly according to first order kinetics, where the rate constant is a fixed number, the elimination of a substance from a living organism usually follows more complex chemical kinetics. For example, the biological half-life of water in

1900-562: A value of +1, antileptons −1, and non-leptonic particles 0. n → p + e − + ν ¯ e L : 0 = 0 + 1 − 1 {\displaystyle {\begin{matrix}&{\text{n}}&\rightarrow &{\text{p}}&+&{\text{e}}^{-}&+&{\bar {\nu }}_{\text{e}}\\L:&0&=&0&+&1&-&1\end{matrix}}} For allowed decays,

2000-417: A virtual W boson leading to creation of an electron/antineutrino or positron/neutrino pair. For example, a neutron, composed of two down quarks and an up quark, decays to a proton composed of a down quark and two up quarks. Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In electron capture, an inner atomic electron

2100-399: Is a half-life describing any exponential-decay process. For example: The term "half-life" is almost exclusively used for decay processes that are exponential (such as radioactive decay or the other examples above), or approximately exponential (such as biological half-life discussed below). In a decay process that is not even close to exponential, the half-life will change dramatically while

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2200-417: Is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron ), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino ; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in what

2300-465: Is absorbed by the body and preferentially concentrated in the thyroid where it is needed for the functioning of that gland. When I is present in high levels in the environment from radioactive fallout , it can be absorbed through contaminated food, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid. The primary risk from exposure to I is an increased risk of radiation-induced cancer in later life. Other risks include

2400-417: Is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino. 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 does not change the number ( A ) of nucleons in the nucleus, but changes only its charge   Z . Thus the set of all nuclides with

2500-433: Is around 1  MeV , but can range from a few keV to a few tens of MeV. 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 . In the case of Re, the maximum speed of the beta particle is only 9.8% of the speed of light. The following table gives some examples: Half-life Half-life (symbol t ½ )

2600-440: Is called positron emission . Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons . The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy . The binding energies of all existing nuclides form what

2700-425: Is called the nuclear band or valley of stability . For either electron or positron emission to be energetically possible, the energy release ( see below ) or Q value must be positive. Beta decay is a consequence of the weak force , which is characterized by relatively long decay times. Nucleons are composed of up quarks and down quarks , and the weak force allows a quark to change its flavour by means of

2800-404: Is captured by a proton in the nucleus, transforming it into a neutron, and an electron neutrino is released. The two types of beta decay are known as beta minus and beta plus . In beta minus (β ) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino ; while in beta plus (β ) decay, a proton is converted to a neutron and the process creates

2900-450: Is contraindicated in breast-feeding and pregnancy Iodine-131, in higher doses than for thyrotoxicosis, is used for ablation of remnant thyroid tissue following a complete thyroidectomy to treat thyroid cancer . Typical therapeutic doses of I-131 are between 2220 and 7400 megabecquerels (MBq). Because of this high radioactivity and because the exposure of stomach tissue to beta radiation would be high near an undissolved capsule, I-131

3000-467: 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 of the recoiling nucleus can generally be neglected.) Beta particles can therefore be emitted with any kinetic energy ranging from 0 to Q . A typical Q

3100-403: Is due to the relative ease of creating I by neutron bombardment of natural tellurium in a nuclear reactor, then separating I out by various simple methods (i.e., heating to drive off the volatile iodine). By contrast, other iodine radioisotopes are usually created by far more expensive techniques, starting with cyclotron radiation of capsules of pressurized xenon gas. Iodine-131 is also one of

Iodine-131 - Misplaced Pages Continue

3200-424: Is known as the parent nuclide while the resulting element (in this case 7 N ) is known as the daughter nuclide . Another example is the decay of hydrogen-3 ( tritium ) into helium-3 with a half-life of about 12.3 years: An example of positron emission (β decay) is the decay of magnesium-23 into sodium-23 with a half-life of about 11.3 s: β decay also results in nuclear transmutation, with

3300-567: Is nearly a billion times that of I. It is discharged to the atmosphere in small quantities by some nuclear power plants. I decays with a half-life of 8.0249(6) days with beta minus and gamma emissions. This isotope of iodine has 78 neutrons in its nucleus, while the only stable nuclide, I, has 74. On decaying, I most often (89% of the time) expends its 971 keV of decay energy by transforming into stable xenon-131 in two steps, with gamma decay following rapidly after beta decay: The primary emissions of I decay are thus electrons with

3400-415: Is only one known beta-stable isobar. For even  A , there are up to three different beta-stable isobars experimentally known; for example, 50 Sn , 52 Te , and 54 Xe are all beta-stable. There are about 350 known beta-decay stable nuclides . Usually unstable nuclides are clearly either "neutron rich" or "proton rich", with the former undergoing beta decay and

3500-457: Is proportional to the square of the concentration. By integrating this rate, it can be shown that the concentration [A] of the reactant decreases following this formula: 1 [ A ] = k t + 1 [ A ] 0 {\displaystyle {\frac {1}{[{\ce {A}}]}}=kt+{\frac {1}{[{\ce {A}}]_{0}}}} We replace [A] for ⁠ 1 / 2 ⁠ [A] 0 in order to calculate

3600-400: Is sometimes administered to human patients in a small amount of liquid. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container. For administration to animals (for example, cats with hyperthyroidism), for practical reasons the isotope must be administered by injection. European guidelines recommend administration of

3700-399: Is the decay of carbon-14 into nitrogen-14 with a half-life of about 5,730 years: In this form of decay, the original element becomes a new chemical element in a process known as nuclear transmutation . This new element has an unchanged mass number A , but an atomic number Z that is increased by one. As in all nuclear decays, the decaying element (in this case 6 C )

3800-421: Is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity. In a medical context, the half-life may also describe the time that it takes for the concentration of a substance in blood plasma to reach one-half of its steady-state value (the "plasma half-life"). The relationship between the biological and plasma half-lives of

3900-401: Is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. The term is also used more generally to characterize any type of exponential (or, rarely, non-exponential ) decay. For example, the medical sciences refer to

4000-433: Is used for unsealed source radiotherapy in nuclear medicine to treat several conditions. It can also be detected by gamma cameras for diagnostic imaging , however it is rarely administered for diagnostic purposes only, imaging will normally be done following a therapeutic dose. Use of the I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid gland. Major uses of I include

4100-465: Is used only in large and maximal treatment doses, as a way of killing targeted tissues. This is known as "therapeutic use". Iodine-131 can be "seen" by nuclear medicine imaging techniques (e.g., gamma cameras ) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or "image"

Iodine-131 - Misplaced Pages Continue

4200-585: Is usually 400–600 megabecquerels (MBq). Radioactive iodine (iodine-131) alone can potentially worsen thyrotoxicosis in the first few days after treatment. One side effect of treatment is an initial period of a few days of increased hyperthyroid symptoms. This occurs because when the radioactive iodine destroys the thyroid cells, they can release thyroid hormone into the blood stream. For this reason, sometimes patients are pre-treated with thyrostatic medications such as methimazole, and/or they are given symptomatic treatment such as propranolol. Radioactive iodine treatment

4300-468: Is via beta radiation, and the rest occurs via its gamma radiation (at a longer distance from the radioisotope). It can be seen in diagnostic scans after its use as therapy, because I is also a gamma-emitter. Because of the carcinogenicity of its beta radiation in the thyroid in small doses, I-131 is rarely used primarily or solely for diagnosis (although in the past this was more common due to this isotope's relative ease of production and low expense). Instead

4400-493: The Cowan–Reines neutrino experiment . The properties of neutrinos were (with a few minor modifications) as predicted by Pauli and Fermi. In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction 2 He  +  13 Al  → 15 P  +  0 n , and observed that the product isotope 15 P emits

4500-429: The biological half-life of drugs and other chemicals in the human body. The converse of half-life (in exponential growth) is doubling time . The original term, half-life period , dating to Ernest Rutherford 's discovery of the principle in 1907, was shortened to half-life in the early 1950s. Rutherford applied the principle of a radioactive element's half-life in studies of age determination of rocks by measuring

4600-1191: The law of large numbers suggests that it is a very good approximation to say that half of the atoms remain after one half-life. Various simple exercises can demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program . An exponential decay can be described by any of the following four equivalent formulas: N ( t ) = N 0 ( 1 2 ) t t 1 / 2 N ( t ) = N 0 2 − t t 1 / 2 N ( t ) = N 0 e − t τ N ( t ) = N 0 e − λ t {\displaystyle {\begin{aligned}N(t)&=N_{0}\left({\frac {1}{2}}\right)^{\frac {t}{t_{1/2}}}\\N(t)&=N_{0}2^{-{\frac {t}{t_{1/2}}}}\\N(t)&=N_{0}e^{-{\frac {t}{\tau }}}\\N(t)&=N_{0}e^{-\lambda t}\end{aligned}}} where The three parameters t ½ , τ , and λ are directly related in

4700-514: The mass number and atomic number of the decaying nucleus, and X and X′ are the initial and final elements, respectively. Another example is when the free neutron ( 0 n ) decays by β  decay into a proton ( p ): 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

4800-417: The probability of a radioactive atom decaying within its half-life is 50%. For example, the accompanying image is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not exactly one-half of the atoms remaining, only approximately , because of the random variation in the process. Nevertheless, when there are many identical atoms decaying (right boxes),

4900-474: The proton-neutron model of the nucleus . Beta decay leaves the mass number unchanged, so the change of nuclear spin must be an integer. However, the electron spin is 1/2, hence angular momentum would not be conserved if beta decay were simply electron emission. From 1920 to 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

5000-449: The "neutrino" ('little neutral one' in Italian). In 1933, Fermi published his landmark theory for beta decay , where he applied the principles of quantum mechanics to matter particles, supposing that they can be created and annihilated, just as the light quanta in atomic transitions. Thus, according to Fermi, neutrinos are created in the beta-decay process, rather than contained in the nucleus;

5100-699: The 3070 counties in the USA. The calculations are taken from data collected regarding fallout from the nuclear weapons tests conducted at the Nevada Test Site . On 27 March 2011, the Massachusetts Department of Public Health reported that I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant. Farmers near

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5200-464: The I, and should appear mostly years after exposure, long after the I has decayed. Other studies did not find a correlation. Most I production is from neutron irradiation of a natural tellurium target in a nuclear reactor. Irradiation of natural tellurium produces almost entirely I as the only radionuclide with a half-life longer than hours, since most lighter isotopes of tellurium become heavier stable isotopes, or else stable iodine or xenon. However,

5300-400: The absorption of a W . When a W boson is emitted, it decays into a positron and an electron neutrino : 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

5400-456: The amount of radioactivity retained may be small and there is no medical proof of an actual risk from radioiodine treatment. Such a precaution would essentially eliminate direct fetal exposure to radioactivity and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine." These guidelines vary from hospital to hospital and will depend on national legislation and guidance, as well as

5500-417: The analogous formula is: 1 T 1 / 2 = 1 t 1 + 1 t 2 + 1 t 3 + ⋯ {\displaystyle {\frac {1}{T_{1/2}}}={\frac {1}{t_{1}}}+{\frac {1}{t_{2}}}+{\frac {1}{t_{3}}}+\cdots } For a proof of these formulas, see Exponential decay § Decay by two or more processes . There

5600-417: The beta decay process. This spectrum was puzzling for many years. 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 later explained by

5700-485: The beta particle is in fact an electron. 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 states that beta (i.e., β ) emission from one element produces another element one place to

5800-507: The beta spectrum has an effective upper bound in energy. Niels Bohr had suggested that the beta spectrum could be explained if conservation of energy was true only in a statistical sense, thus this principle might be violated in any given decay. However, the upper bound in beta energies determined by Ellis and Mott ruled out that notion. Now, the problem of how to account for the variability of energy in known beta decay products, as well as for conservation of momentum and angular momentum in

5900-1107: The case of positive beta decay ( electron capture ) proton to neutron so the number of individual quarks doesn't change. It is only the baryon flavor that changes, here labelled as the isospin . Up and down quarks have total isospin I = 1 2 {\textstyle I={\frac {1}{2}}} and isospin projections I z = { 1 2 up quark − 1 2 down quark {\displaystyle I_{\text{z}}={\begin{cases}{\frac {1}{2}}&{\text{up quark}}\\-{\frac {1}{2}}&{\text{down quark}}\end{cases}}} All other quarks have I = 0 . In general I z = 1 2 ( n u − n d ) {\displaystyle I_{\text{z}}={\frac {1}{2}}(n_{\text{u}}-n_{\text{d}})} L ≡ n ℓ − n ℓ ¯ {\displaystyle L\equiv n_{\ell }-n_{\bar {\ell }}} so all leptons have assigned

6000-418: The decay is happening. In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on. A biological half-life or elimination half-life

6100-403: The decay of a proton inside the nucleus to a neutron: 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

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6200-429: The decay period of radium to lead-206 . Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed. A half-life often describes the decay of discrete entities, such as radioactive atoms. In that case, it does not work to use

6300-418: The definition that states "half-life is the time required for exactly half of the entities to decay". For example, if there is just one radioactive atom, and its half-life is one second, there will not be "half of an atom" left after one second. Instead, the half-life is defined in terms of probability : "Half-life is the time required for exactly half of the entities to decay on average ". In other words,

6400-570: The disaster, though they were widely distributed to children in Poland. Within the US, the highest I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh milk from sources contaminated as the result of above-ground testing of nuclear weapons. The National Cancer Institute provides additional information on the health effects from exposure to I in fallout, as well as individualized estimates, for those born before 1971, for each of

6500-448: The dose of radiation given. Some also advise not to hug or hold children when the radiation is still high, and a one- or two- metre distance to others may be recommended. I-131 will be eliminated from the body over the next several weeks after it is given. The majority of I-131 will be eliminated from the human body in 3–5 days, through natural decay, and through excretion in sweat and urine. Smaller amounts will continue to be released over

6600-462: The following way: t 1 / 2 = ln ⁡ ( 2 ) λ = τ ln ⁡ ( 2 ) {\displaystyle t_{1/2}={\frac {\ln(2)}{\lambda }}=\tau \ln(2)} where ln(2) is the natural logarithm of 2 (approximately 0.693). In chemical kinetics , the value of the half-life depends on the reaction order : The rate of this kind of reaction does not depend on

6700-403: The half-life of a first order reaction is given as the following: t 1 / 2 = ln ⁡ 2 k {\displaystyle t_{1/2}={\frac {\ln 2}{k}}} The half-life of a first order reaction is independent of its initial concentration and depends solely on the reaction rate constant, k . In second order reactions, the rate of reaction

6800-602: The half-life of second order reactions depends on the initial concentration and rate constant . Some quantities decay by two exponential-decay processes simultaneously. In this case, the actual half-life T ½ can be related to the half-lives t 1 and t 2 that the quantity would have if each of the decay processes acted in isolation: 1 T 1 / 2 = 1 t 1 + 1 t 2 {\displaystyle {\frac {1}{T_{1/2}}}={\frac {1}{t_{1}}}+{\frac {1}{t_{2}}}} For three or more processes,

6900-533: The half-life of the reactant A 1 [ A ] 0 / 2 = k t 1 / 2 + 1 [ A ] 0 {\displaystyle {\frac {1}{[{\ce {A}}]_{0}/2}}=kt_{1/2}+{\frac {1}{[{\ce {A}}]_{0}}}} and isolate the time of the half-life ( t ½ ): t 1 / 2 = 1 [ A ] 0 k {\displaystyle t_{1/2}={\frac {1}{[{\ce {A}}]_{0}k}}} This shows that

7000-437: The heaviest naturally occurring tellurium nuclide, Te (34% of natural tellurium) absorbs a neutron to become tellurium-131, which beta decays with a half-life of 25 minutes to I. A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, with evolved I then eluted into an alkaline solution. More commonly, powdered elemental tellurium is irradiated and then I separated from it by dry distillation of

7100-503: 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. If it comes from the L-shell, the process is called L-capture, etc. 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

7200-500: The iodine, which has a far higher vapor pressure . The element is then dissolved in a mildly alkaline solution in the standard manner, to produce I as iodide and hypoiodate (which is soon reduced to iodide). I is a fission product with a yield of 2.878% from uranium-235 , and can be released in nuclear weapons tests and nuclear accidents . However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel , unlike iodine-129 whose half-life

7300-447: The isotope, other less-damaging radioisotopes of iodine such as iodine-123 (see isotopes of iodine ) are preferred in situations when only nuclear imaging is required. The isotope I is still occasionally used for purely diagnostic (i.e., imaging) work, due to its low expense compared to other iodine radioisotopes. Very small medical imaging doses of I have not shown any increase in thyroid cancer. The low-cost availability of I, in turn,

7400-434: The kinetic energy distribution, or spectrum, of beta particles measured by Lise Meitner and Otto Hahn in 1911 and by Jean Danysz in 1913 showed multiple lines on a diffuse background. These measurements offered the first hint that beta particles have a continuous spectrum. In 1914, James Chadwick used a magnetic spectrometer with one of Hans Geiger's new counters to make more accurate measurements which showed that

7500-547: The late 1940s, radioactive tracers have been used by the oil industry. Tagged at the surface, water is then tracked downhole, using the appropriated gamma detector, to determine flows and detect underground leaks. I-131 has been the most widely used tagging isotope in an aqueous solution of sodium iodide . It is used to characterize the hydraulic fracturing fluid to help determine the injection profile and location of fractures created by hydraulic fracturing . Beta decay In nuclear physics , beta decay (β-decay)

7600-510: 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 energetically favorable for the radionuclide to decay to an even-proton, even-neutron isobar either by undergoing beta-positive or beta-negative decay. An often-cited example is the single isotope 29 Cu (29 protons, 35 neutrons), which illustrates three types of beta decay in competition. Copper-64 has

7700-508: The more purely gamma-emitting radioiodine iodine-123 is used in diagnostic testing ( nuclear medicine scan of the thyroid). The longer half-lived iodine-125 is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and in brachytherapy treatment (isotope confined in small seed-like metal capsules), where the low-energy gamma radiation without a beta component makes iodine-125 useful. The other radioisotopes of iodine are never used in brachytherapy. The use of I as

7800-548: The most commonly used gamma-emitting radioactive industrial tracer . Radioactive tracer isotopes are injected with hydraulic fracturing fluid to determine the injection profile and location of fractures created by hydraulic fracturing. Much smaller incidental doses of iodine-131 than those used in medical therapeutic procedures, are supposed by some studies to be the major cause of increased thyroid cancers after accidental nuclear contamination. These studies suppose that cancers happen from residual tissue radiation damage caused by

7900-402: The mother nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron, and a neutrino and into the kinetic energy of these particles. This process is opposite to negative beta decay, in that the weak interaction converts a proton into a neutron by converting an up quark into a down quark resulting in the emission of a W or

8000-442: The net orbital angular momentum is zero, hence only spin quantum numbers are considered. 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). For forbidden decays, orbital angular momentum must also be taken into consideration. The Q value

8100-460: 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 ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, Paul Villard identified a still more penetrating type of radiation, which Rutherford identified as

8200-469: The next several weeks, as the body processes thyroid hormones created with the I-131. For this reason, it is advised to regularly clean toilets, sinks, bed sheets and clothing used by the person who received the treatment. Patients may also be advised to wear slippers or socks at all times, and avoid prolonged close contact with others. This minimizes accidental exposure by family members, especially children. Use of

8300-545: The plant dumped raw milk, while testing in the United States found 0.8 pico- curies per liter of iodine-131 in a milk sample, but the radiation levels were 5,000 times lower than the FDA's "defined intervention level". The levels were expected to drop relatively quickly A common treatment method for preventing iodine-131 exposure is by saturating the thyroid with regular, stable iodine-127 , as an iodide or iodate salt. Iodine-131

8400-609: The positively charged ( + ⁠ 2 / 3 ⁠ e ) up quark promoteby by a virtual W boson ; the W boson subsequently decays into an electron and an electron antineutrino: 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: This may be considered as

8500-430: The possibility of non-cancerous growths and thyroiditis . The risk of thyroid cancer in later life appears to diminish with increasing age at time of exposure. Most risk estimates are based on studies in which radiation exposures occurred in children or teenagers. When adults are exposed, it has been difficult for epidemiologists to detect a statistically significant difference in the rates of thyroid disease above that of

8600-531: The process, became acute. 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 beta decay (thus accounting for the known missing energy, momentum, and angular momentum), but it had simply not yet been observed. In 1931, Enrico Fermi renamed Pauli's "neutron"

8700-409: The public for dose constraint purposes and any restrictions on the patient should be designed based on this principle. Patients receiving I-131 radioiodine treatment may be warned not to have sexual intercourse for one month (or shorter, depending on dose given), and women told not to become pregnant for six months afterwards. "This is because a theoretical risk to a developing fetus exists, even though

8800-459: The reactant. Thus the concentration will decrease exponentially. [ A ] = [ A ] 0 exp ⁡ ( − k t ) {\displaystyle [{\ce {A}}]=[{\ce {A}}]_{0}\exp(-kt)} as time progresses until it reaches zero, and the half-life will be constant, independent of concentration. The time t ½ for [A] to decrease from [A] 0 to ⁠ 1 / 2 ⁠ [A] 0 in

8900-409: The resulting element having an atomic number that is decreased by one. The beta spectrum, or distribution of energy values for the beta particles, is continuous. The total energy of the decay process is divided between the electron, the antineutrino, and the recoiling nuclide. In the figure to the right, an example of an electron with 0.40 MeV energy from the beta decay of Bi is shown. In this example,

9000-417: The right in the periodic table , while alpha emission produces an element two places to the left. The study of beta decay provided the first physical evidence for the existence of the neutrino . In both alpha and gamma decay, the resulting alpha or gamma particle has a narrow energy distribution , since the particle carries the energy from the difference between the initial and final nuclear states. However,

9100-468: The same happens to electrons. The neutrino interaction with matter was so weak that detecting it proved a severe experimental challenge. Further indirect evidence of the existence of the neutrino was obtained by observing the recoil of nuclei that emitted such a particle after absorbing an electron. Neutrinos were finally detected directly in 1956 by the American physicists Clyde Cowan and Frederick Reines in

9200-460: 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 presents a local minimum of the mass excess : if such a nucleus has ( A , Z ) numbers, the neighbour nuclei ( A , Z −1) and ( A , Z +1) have higher mass excess and can beta decay into ( A , Z ) , but not vice versa. For all odd mass numbers A , there

9300-400: The spectrum was continuous. The distribution of beta particle energies was in apparent contradiction to the law of conservation of energy . If beta decay were simply electron emission as assumed at the time, then the energy of the emitted electron should have a particular, well-defined value. For beta decay, however, the observed broad distribution of energies suggested that energy is lost in

9400-575: The substrate concentration , [A] . Thus the concentration decreases linearly. [ A ] = [ A ] 0 − k t {\displaystyle [{\ce {A}}]=[{\ce {A}}]_{0}-kt} In order to find the half-life, we have to replace the concentration value for the initial concentration divided by 2: [ A ] 0 / 2 = [ A ] 0 − k t 1 / 2 {\displaystyle [{\ce {A}}]_{0}/2=[{\ce {A}}]_{0}-kt_{1/2}} and isolate

9500-412: The time: t 1 / 2 = [ A ] 0 2 k {\displaystyle t_{1/2}={\frac {[{\ce {A}}]_{0}}{2k}}} This t ½ formula indicates that the half-life for a zero order reaction depends on the initial concentration and the rate constant. In first order reactions, the rate of reaction will be proportional to the concentration of

9600-422: The total decay energy is 1.16 MeV, so the antineutrino has the remaining energy: 1.16 MeV − 0.40 MeV = 0.76 MeV . An electron at the far right of the curve would have the maximum possible kinetic energy, leaving the energy of the neutrino to be only its small rest mass. Radioactivity was discovered in 1896 by Henri Becquerel in uranium , and subsequently observed by Marie and Pierre Curie in thorium and in

9700-409: The treatment of thyrotoxicosis (hyperthyroidism) due to Graves' disease , and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is not malignant). The therapeutic use of radioiodine to treat hyperthyroidism from Graves' disease was first reported by Saul Hertz in 1941. The dose is typically administered orally (either as a liquid or capsule), in an outpatient setting, and

9800-617: The weak force. In recognition of their theoretical work, Lee and Yang were awarded the Nobel Prize for Physics in 1957. However Wu, who was female, was not awarded the Nobel prize. 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. The generic equation is: where A and Z are

9900-448: The weak force. They sketched the design for an experiment for testing conservation of parity in the laboratory. Later that year, Chien-Shiung Wu and coworkers conducted the Wu experiment showing an asymmetrical beta decay of Co at cold temperatures that proved that parity is not conserved in beta decay. This surprising result overturned long-held assumptions about parity and

10000-509: 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 V. Alvarez went on to study electron capture in Ga and other nuclides. 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

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