Misplaced Pages

#30969

107-544: The discovery of neutrinoless double beta decay could shed light on the absolute neutrino masses and on their mass hierarchy ( Neutrino mass ). It would mean the first ever signal of the violation of total lepton number conservation. A Majorana nature of neutrinos would confirm that the neutrino is its own antiparticle . To search for neutrinoless double beta decay, there are currently a number of experiments underway, with several future experiments for increased sensitivity proposed as well. In 1939, Wendell H. Furry proposed

214-522: A , 76 G e , 82 S e , 96 Z r , 100 M o , 116 C d , 130 T e , 136 X e , 150 N d {\displaystyle \mathrm {^{48}Ca,^{76}Ge,^{82}Se,^{96}Zr,^{100}Mo,^{116}Cd,^{130}Te,^{136}Xe,^{150}Nd} } . They all have arguments for and against their use in an experiment. Factors to be included and revised are natural abundance , reasonably priced enrichment, and

321-467: A discharge tube allowed researchers to study the emission spectrum of the captured particles, and ultimately proved that alpha particles are helium nuclei. Other experiments showed beta radiation, resulting from decay and cathode rays , were high-speed electrons . Likewise, gamma radiation and X-rays were found to be high-energy electromagnetic radiation . The relationship between the types of decays also began to be examined: For example, gamma decay

428-490: A chemical bond. This effect can be used to separate isotopes by chemical means. The Szilard–Chalmers effect was discovered in 1934 by Leó Szilárd and Thomas A. Chalmers. They observed that after bombardment by neutrons, the breaking of a bond in liquid ethyl iodide allowed radioactive iodine to be removed. Radioactive primordial nuclides found in the Earth are residues from ancient supernova explosions that occurred before

535-529: A different chemical element is created. There are 28 naturally occurring chemical elements on Earth that are radioactive, consisting of 35 radionuclides (seven elements have two different radionuclides each) that date before the time of formation of the Solar System . These 35 are known as primordial radionuclides . Well-known examples are uranium and thorium , but also included are naturally occurring long-lived radioisotopes, such as potassium-40 . Each of

642-571: A dozen confirmed cases of nuclei that can only decay via double beta decay. The corresponding decay equation is: It is a weak process of second order. A simultaneous decay of two nucleons in the same nucleus is extremely unlikely. Thus, the experimentally observed lifetimes of such decay processes are in the range of 10 18 − 10 21 {\displaystyle 10^{18}-10^{21}} years. A number of isotopes have been observed already to show this two-neutrino double beta decay. This conventional double beta decay

749-551: A final section, is bound state beta decay of rhenium-187 . In this process, the beta electron-decay of the parent nuclide is not accompanied by beta electron emission, because the beta particle has been captured into the K-shell of the emitting atom. An antineutrino is emitted, as in all negative beta decays. If energy circumstances are favorable, a given radionuclide may undergo many competing types of decay, with some atoms decaying by one route, and others decaying by another. An example

856-422: A given total number of nucleons . This consequently produces a more stable (lower energy) nucleus. A hypothetical process of positron capture, analogous to electron capture, is theoretically possible in antimatter atoms, but has not been observed, as complex antimatter atoms beyond antihelium are not experimentally available. Such a decay would require antimatter atoms at least as complex as beryllium-7 , which

963-467: A ground energy state, also produce later internal conversion and gamma decay in almost 0.5% of the time. The daughter nuclide of a decay event may also be unstable (radioactive). In this case, it too will decay, producing radiation. The resulting second daughter nuclide may also be radioactive. This can lead to a sequence of several decay events called a decay chain (see this article for specific details of important natural decay chains). Eventually,

1070-439: A mean lifetime over 10  yr (table below). In a typical double beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted. The process can be thought as two simultaneous beta minus decays . In order for (double) beta decay to be possible, the final nucleus must have a larger binding energy than the original nucleus. For some nuclei, such as germanium-76 ,

1177-414: A neutrino and a gamma ray from the excited nucleus (and often also Auger electrons and characteristic X-rays , as a result of the re-ordering of electrons to fill the place of the missing captured electron). These types of decay involve the nuclear capture of electrons or emission of electrons or positrons, and thus acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for

SECTION 10

#1732863174031

1284-413: A photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays". It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening

1391-447: A radioactive nuclide with a half-life of only 5700(30) years, is constantly produced in Earth's upper atmosphere due to interactions between cosmic rays and nitrogen. Nuclides that are produced by radioactive decay are called radiogenic nuclides , whether they themselves are stable or not. There exist stable radiogenic nuclides that were formed from short-lived extinct radionuclides in

1498-403: A reduction of summed rest mass , once the released energy (the disintegration energy ) has escaped in some way. Although decay energy is sometimes defined as associated with the difference between the mass of the parent nuclide products and the mass of the decay products, this is true only of rest mass measurements, where some energy has been removed from the product system. This is true because

1605-654: A refined estimate by the same authors stated the half-life was 2.3 × 10  years. This half-life has been excluded at high confidence by other experiments, including in Ge by GERDA . As of 2017, the strongest limits on neutrinoless double beta decay have come from GERDA in Ge, CUORE in Te, and EXO-200 and KamLAND-Zen in Xe. For mass numbers with more than two beta-stable isobars, quadruple beta decay and its inverse, quadruple electron capture, have been proposed as alternatives to double beta decay in

1712-528: A stable nuclide is produced. Any decay daughters that are the result of an alpha decay will also result in helium atoms being created. Some radionuclides may have several different paths of decay. For example, 35.94(6) % of bismuth-212 decays, through alpha-emission, to thallium-208 while 64.06(6) % of bismuth-212 decays, through beta-emission, to polonium-212 . Both thallium-208 and polonium-212 are radioactive daughter products of bismuth-212, and both decay directly to stable lead-208 . According to

1819-399: A third-life, or even a (1/√2)-life, could be used in exactly the same way as half-life; but the mean life and half-life t 1/2 have been adopted as standard times associated with exponential decay. Those parameters can be related to the following time-dependent parameters: These are related as follows: where N 0 is the initial amount of active substance — substance that has

1926-432: A well understood and controlled experimental technique. The higher the Q {\displaystyle Q} -value, the better are the chances of a discovery, in principle. The phase-space factor G 0 ν {\displaystyle G^{0\nu }} , and thus the decay rate, grows with Q 5 {\displaystyle Q^{5}} . Experimentally of interest and thus measured

2033-529: Is copper-64 , which has 29 protons, and 35 neutrons, which decays with a half-life of 12.7004(13) hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay to the other particle, which has opposite isospin . This particular nuclide (though not all nuclides in this situation) is more likely to decay through beta plus decay ( 61.52(26) % ) than through electron capture ( 38.48(26) % ). The excited energy states resulting from these decays which fail to end in

2140-497: Is internal conversion , which results in an initial electron emission, and then often further characteristic X-rays and Auger electrons emissions, although the internal conversion process involves neither beta nor gamma decay. A neutrino is not emitted, and none of the electron(s) and photon(s) emitted originate in the nucleus, even though the energy to emit all of them does originate there. Internal conversion decay, like isomeric transition gamma decay and neutron emission, involves

2247-399: Is a lepton number violating process. In the simplest theoretical treatment, known as light neutrino exchange, a nucleon absorbs the neutrino emitted by another nucleon. The exchanged neutrinos are virtual particles . With only two electrons in the final state, the electrons' total kinetic energy would be approximately the binding energy difference of the initial and final nuclei, with

SECTION 20

#1732863174031

2354-430: Is a random process at the level of single atoms. According to quantum theory , it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed. However, for a significant number of identical atoms, the overall decay rate can be expressed as a decay constant or as a half-life . The half-lives of radioactive atoms have a huge range: from nearly instantaneous to far longer than

2461-1876: Is a limit of the same order as that obtained by GERDA I and II. The muon decays as μ + → e + + ν e + ν ¯ μ {\displaystyle \mu ^{+}\to e^{+}+\nu _{e}+{\overline {\nu }}_{\mu }} and μ − → e − + ν ¯ e + ν μ {\displaystyle \mu ^{-}\to e^{-}+{\overline {\nu }}_{e}+\nu _{\mu }} . Decays without neutrino emission, such as μ + → e + + γ {\displaystyle \mu ^{+}\to e^{+}+\gamma } , μ − → e − + γ {\displaystyle \mu ^{-}\to e^{-}+\gamma } , μ + → e + + e − + e + {\displaystyle \mu ^{+}\to e^{+}+e^{-}+e^{+}} and μ − → e − + e + + e − {\displaystyle \mu ^{-}\to e^{-}+e^{+}+e^{-}} are so unlikely that they are considered prohibited and their observation would be considered evidence of new physics . A number of experiments are pursuing this path such as Mu to E Gamma , Comet , and Mu2e for μ + → e + γ {\displaystyle \mu ^{+}\to e^{+}\gamma } and Mu3e for μ + → e + e − e + {\displaystyle \mu ^{+}\to e^{+}e^{-}e^{+}} . Neutrinoless tau conversion in

2568-536: Is allowed in the Standard Model of particle physics . It has thus both a theoretical and an experimental foundation. If the nature of the neutrinos is Majorana, then they can be emitted and absorbed in the same process without showing up in the corresponding final state. As Dirac particles , both the neutrinos produced by the decay of the W bosons would be emitted, and not absorbed after. Neutrinoless double beta decay can only occur if The simplest decay process

2675-423: Is also a valuable tool in estimating the absolute ages of certain materials. For geological materials, the radioisotopes and some of their decay products become trapped when a rock solidifies, and can then later be used (subject to many well-known qualifications) to estimate the date of the solidification. These include checking the results of several simultaneous processes and their products against each other, within

2782-417: Is an important factor in science and medicine. After their research on Becquerel's rays led them to the discovery of both radium and polonium, they coined the term "radioactivity" to define the emission of ionizing radiation by some heavy elements. (Later the term was generalized to all elements.) Their research on the penetrating rays in uranium and the discovery of radium launched an era of using radium for

2889-578: Is believed that, if neutrinoless double beta decay is found under certain conditions (decay rate compatible with predictions based on experimental knowledge about neutrino masses and mixing), this would indeed "likely" point at Majorana neutrinos as the main mediator (and not other sources of new physics). There are 35 nuclei that can undergo neutrinoless double beta decay (according to the aforementioned decay conditions). Nine different candidates of nuclei are being considered in experiments to confirm neutrinoless double beta-decay: 48 C

2996-399: Is known as the light neutrino exchange. It features one neutrino emitted by one nucleon and absorbed by another nucleon (see figure to the right). In the final state, the only remaining parts are the nucleus (with its changed proton number Z {\displaystyle Z} ) and two electrons: The two electrons are emitted quasi-simultaneously. The two resulting electrons are then

3103-525: Is located in New Mexico (US) and uses a time-projection chamber (TPC) for three-dimensional spatial and temporal resolution of the electron track depositions. The EXO-200 experiment yielded a lifetime limit of T β β 0 ν > 3.5 ⋅ 10 25 {\displaystyle T_{\beta \beta }^{0\nu }>3.5\cdot 10^{25}} years (90% C.L.). When translated to effective Majorana mass, this

3210-423: Is possible. These theoretical decay branches have not been observed. There are 35 naturally occurring isotopes capable of double beta decay. In practice, the decay can be observed when the single beta decay is forbidden by energy conservation. This happens for elements with an even atomic number and even neutron number , which are more stable due to spin -coupling. When single beta decay or alpha decay also occur,

3317-418: Is the lightest known isotope of normal matter to undergo decay by electron capture. Shortly after the discovery of the neutron in 1932, Enrico Fermi realized that certain rare beta-decay reactions immediately yield neutrons as an additional decay particle, so called beta-delayed neutron emission . Neutron emission usually happens from nuclei that are in an excited state, such as the excited O* produced from

Neutrinoless double beta decay - Misplaced Pages Continue

3424-422: Is the lightest observationally stable nuclide whose decay is energetically possible. If the neutrino is a Majorana particle (i.e., the antineutrino and the neutrino are actually the same particle), and at least one type of neutrino has non-zero mass (which has been established by the neutrino oscillation experiments), then it is possible for neutrinoless double beta decay to occur. Neutrinoless double beta decay

3531-430: Is the nuclear matrix element, and m ββ is the effective Majorana mass of the electron neutrino. In the context of light Majorana neutrino exchange, m ββ is given by m β β = ∑ i = 1 3 m i U e i 2 , {\displaystyle m_{\beta \beta }=\sum _{i=1}^{3}m_{i}U_{ei}^{2},} where m i are

3638-401: Is the process by which an unstable atomic nucleus loses energy by radiation . A material containing unstable nuclei is considered radioactive . Three of the most common types of decay are alpha , beta , and gamma decay . The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetic and nuclear forces . Radioactive decay

3745-469: Is the sum of the kinetic energies of the two emitted electrons. It should equal the Q {\displaystyle Q} -value of the respective nucleus for neutrinoless double beta emission. The table shows a summary of the currently best limits on the lifetime of 0νββ. From this, it can be deduced that neutrinoless double beta decay is an extremely rare process, if it occurs at all. The so-called "Heidelberg-Moscow collaboration" (HDM; 1990–2003) of

3852-574: The Big Bang theory , stable isotopes of the lightest three elements ( H , He, and traces of Li ) were produced very shortly after the emergence of the universe, in a process called Big Bang nucleosynthesis . These lightest stable nuclides (including deuterium ) survive to today, but any radioactive isotopes of the light elements produced in the Big Bang (such as tritium ) have long since decayed. Isotopes of elements heavier than boron were not produced at all in

3959-684: The U.S. National Cancer Institute (NCI), International Agency for Research on Cancer (IARC) and the Radiation Effects Research Foundation of Hiroshima ) studied definitively through meta-analysis the damage resulting from the "low doses" that have afflicted survivors of the atomic bombings of Hiroshima and Nagasaki and also in numerous accidents at nuclear plants that have occurred. These scientists reported, in JNCI Monographs: Epidemiological Studies of Low Dose Ionizing Radiation and Cancer Risk , that

4066-429: The age of the universe . The decaying nucleus is called the parent radionuclide (or parent radioisotope ), and the process produces at least one daughter nuclide . Except for gamma decay or internal conversion from a nuclear excited state , the decay is a nuclear transmutation resulting in a daughter containing a different number of protons or neutrons (or both). When the number of protons changes, an atom of

4173-1159: The isobar one atomic number higher ( arsenic-76 ) has a smaller binding energy, preventing single beta decay. However, the isobar with atomic number two higher, selenium-76 , has a larger binding energy, so double beta decay is allowed. The emission spectrum of the two electrons can be computed in a similar way to beta emission spectrum using Fermi's golden rule . The differential rate is given by d N ( T 1 , T 2 , cos ⁡ θ ) d T 1 d T 2 d cos ⁡ θ = F ( Z , T 1 ) F ( Z , T 2 ) w 1 p 1 w 2 p 2 ( Q − T 1 − T 2 ) 5 ( 1 − v 1 v 2 cos ⁡ θ ) {\displaystyle {\frac {dN(T_{1},T_{2},\cos \theta )}{dT_{1}dT_{2}d\cos \theta }}=F(Z,T_{1})F(Z,T_{2})w_{1}p_{1}w_{2}p_{2}(Q-T_{1}-T_{2})^{5}(1-v_{1}v_{2}\cos \theta )} where

4280-570: The neutrino masses and the U ei are elements of the Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix . Therefore, observing neutrinoless double beta decay, in addition to confirming the Majorana neutrino nature, can give information on the absolute neutrino mass scale and Majorana phases in the PMNS matrix, subject to interpretation through theoretical models of the nucleus, which determine

4387-513: The nucleus ' proton number Z {\displaystyle Z} by one. The nucleus' mass (i.e. binding energy ) is then lower and thus more favorable. There exist a number of elements that can decay into a nucleus of lower mass, but they cannot emit one electron only because the resulting nucleus is kinematically (that is, in terms of energy) not favorable (its energy would be higher). These nuclei can only decay by emitting two electrons (that is, via double beta decay ). There are about

Neutrinoless double beta decay - Misplaced Pages Continue

4494-446: The phase space factor, | M 0 ν | 2 {\displaystyle \left|M^{0\nu }\right|^{2}} the (squared) matrix element of this nuclear decay process (according to the Feynman diagram), and ⟨ m β β ⟩ 2 {\displaystyle \langle m_{\beta \beta }\rangle ^{2}}

4601-600: The röntgen unit, and the International X-ray and Radium Protection Committee (IXRPC) was formed. Rolf Sievert was named chairman, but a driving force was George Kaye of the British National Physical Laboratory . The committee met in 1931, 1934, and 1937. After World War II , the increased range and quantity of radioactive substances being handled as a result of military and civil nuclear programs led to large groups of occupational workers and

4708-483: The 1930s, after a number of cases of bone necrosis and death of radium treatment enthusiasts, radium-containing medicinal products had been largely removed from the market ( radioactive quackery ). Only a year after Röntgen 's discovery of X-rays, the American engineer Wolfram Fuchs (1896) gave what is probably the first protection advice, but it was not until 1925 that the first International Congress of Radiology (ICR)

4815-408: The Big Bang, and these first five elements do not have any long-lived radioisotopes. Thus, all radioactive nuclei are, therefore, relatively young with respect to the birth of the universe, having formed later in various other types of nucleosynthesis in stars (in particular, supernovae ), and also during ongoing interactions between stable isotopes and energetic particles. For example, carbon-14 ,

4922-402: The Earth's atmosphere or crust . The decay of the radionuclides in rocks of the Earth's mantle and crust contribute significantly to Earth's internal heat budget . While the underlying process of radioactive decay is subatomic, historically and in most practical cases it is encountered in bulk materials with very large numbers of atoms. This section discusses models that connect events at

5029-788: The German Max-Planck-Institut für Kernphysik and the Russian science center Kurchatov Institute in Moscow famously claimed to have found "evidence for neutrinoless double beta decay" ( Heidelberg-Moscow controversy ). Initially, in 2001 the collaboration announced a 2.2σ, or a 3.1σ (depending on the used calculation method) evidence. The decay rate was found to be around 2 ⋅ 10 25 {\displaystyle 2\cdot 10^{25}} years. This result has been topic of discussions between many scientists and authors. To this day, no other experiment has ever confirmed or approved

5136-563: The United States Nuclear Regulatory Commission permits the use of the unit curie alongside SI units, the European Union European units of measurement directives required that its use for "public health ... purposes" be phased out by 31 December 1985. The effects of ionizing radiation are often measured in units of gray for mechanical or sievert for damage to tissue. Radioactive decay results in

5243-472: The atom to move closer to the optimal ratio of protons and neutrons. As a result of this transformation, the nucleus emits two detectable beta particles , which are electrons or positrons . The literature distinguishes between two types of double beta decay: ordinary double beta decay and neutrinoless double beta decay. In ordinary double beta decay, which has been observed in several isotopes, two electrons and two electron antineutrinos are emitted from

5350-408: The atomic level to observations in aggregate. The decay rate , or activity , of a radioactive substance is characterized by the following time-independent parameters: Although these are constants, they are associated with the statistical behavior of populations of atoms. In consequence, predictions using these constants are less accurate for minuscule samples of atoms. In principle a half-life,

5457-887: The atomic number Z {\displaystyle Z} . Methods use Dirac wave functions , finite nuclear sizes and electron screening. There exist high-precision results for G 0 ν {\displaystyle G^{0\nu }} for various nuclei, ranging from about 0.23 (for 52 128 T e → 54 128 X e {\displaystyle \mathrm {^{128}_{52}Te\rightarrow _{54}^{128}Xe} } ), and 0.90 ( 32 76 G e → 34 76 S e {\displaystyle \mathrm {^{76}_{32}Ge\rightarrow _{34}^{76}Se} } ) to about 24.14 ( 60 150 N d → 62 150 S m {\displaystyle \mathrm {^{150}_{60}Nd\rightarrow _{62}^{150}Sm} } ). It

SECTION 50

#1732863174031

5564-664: The beta decay of N. The neutron emission process itself is controlled by the nuclear force and therefore is extremely fast, sometimes referred to as "nearly instantaneous". Isolated proton emission was eventually observed in some elements. It was also found that some heavy elements may undergo spontaneous fission into products that vary in composition. In a phenomenon called cluster decay , specific combinations of neutrons and protons other than alpha particles (helium nuclei) were found to be spontaneously emitted from atoms. Other types of radioactive decay were found to emit previously seen particles but via different mechanisms. An example

5671-506: The biological effects of radiation due to radioactive substances were less easy to gauge. This gave the opportunity for many physicians and corporations to market radioactive substances as patent medicines . Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie protested against this sort of treatment, warning that "radium is dangerous in untrained hands". Curie later died from aplastic anaemia , likely caused by exposure to ionizing radiation. By

5778-678: The calculation of the NME is a significant problem and it has been treated by different authors in different ways. One question is whether to treat the range of obtained values for | M 0 ν | {\displaystyle \left|M^{0\nu }\right|} as the theoretical uncertainty and whether this is then to be understood as a statistical uncertainty. Different approaches are being chosen here. The obtained values for | M 0 ν | {\displaystyle \left|M^{0\nu }\right|} often vary by factors of 2 up to about 5. Typical values lie in

5885-457: The carbon-14 in individual tree rings, for example). The Szilard–Chalmers effect is the breaking of a chemical bond as a result of a kinetic energy imparted from radioactive decay. It operates by the absorption of neutrons by an atom and subsequent emission of gamma rays, often with significant amounts of kinetic energy. This kinetic energy, by Newton's third law , pushes back on the decaying atom, which causes it to move with enough speed to break

5992-478: The case Gd) nuclides with A ≤ 260 are theoretically capable of double electron capture, where red are isotopes that have a double-electron capture rate measured and black have yet to be measured experimentally: Ar, Ca, Cr, Fe, Ni, Zn, Se, Kr , Sr, Mo, Ru, Pd, Cd, Cd, Sn, Te, Xe , Xe, Ba , Ba, Ce, Ce, Sm, Gd, Gd, Gd, Dy, Dy, Dy, Er, Er, Yb, Hf, W, Os, Pt, Hg, Rn, Rn, Ra, Th, U, Pu, Cm, Fm, and No. In particular, Ar

6099-617: The case of neutrinoless double beta decay. Therefore, there is no 'black-box theorem' and neutrinos could be Dirac particles while allowing these type of processes. In particular, if neutrinoless quadruple beta decay is found before neutrinoless double beta decay then the expectation is that neutrinos will be Dirac particles. So far, searches for triple and quadruple beta decay in Nd have remained unsuccessful. Decay rate Radioactive decay (also known as nuclear decay , radioactivity , radioactive disintegration , or nuclear disintegration )

6206-543: The cases Ca, Zr, and Rn ) nuclides with A ≤ 260 are theoretically capable of double beta decay, where red are isotopes that have a double-beta rate measured experimentally and black have yet to be measured experimentally: Ca, Ca , Zn, Ge , Se, Se , Kr, Zr, Zr , Mo, Mo , Ru, Pd, Cd, Cd , Sn, Sn, Te , Te , Xe, Xe , Ce, Nd, Nd, Nd , Sm, Gd, Er, Yb, W, Os, Pt, Hg, Po, Rn, Rn, Ra, Th, U , Pu, Cm, Cf, Cf, and Fm. The following known beta-stable (or almost beta-stable in

6313-409: The concept of a particle being its own antiparticle. Particles of this nature were subsequently named after him as Majorana particles. Neutrinoless double beta decay is one method to search for the possible Majorana nature of neutrinos. Neutrinos are conventionally produced in weak decays. Weak beta decays normally produce one electron (or positron ), emit an antineutrino (or neutrino) and increase

6420-467: The dangers involved in the careless use of X-rays were not being heeded, either by industry or by his colleagues. By this time, Rollins had proved that X-rays could kill experimental animals, could cause a pregnant guinea pig to abort, and that they could kill a foetus. He also stressed that "animals vary in susceptibility to the external action of X-light" and warned that these differences be considered when patients were treated by means of X-rays. However,

6527-409: The decay energy is transformed to thermal energy, which retains its mass. Decay energy, therefore, remains associated with a certain measure of the mass of the decay system, called invariant mass , which does not change during the decay, even though the energy of decay is distributed among decay particles. The energy of photons, the kinetic energy of emitted particles, and, later, the thermal energy of

SECTION 60

#1732863174031

6634-424: The decay energy must always carry mass with it, wherever it appears (see mass in special relativity ) according to the formula E  =  mc . The decay energy is initially released as the energy of emitted photons plus the kinetic energy of massive emitted particles (that is, particles that have rest mass). If these particles come to thermal equilibrium with their surroundings and photons are absorbed, then

6741-531: The decaying nucleus. In neutrinoless double beta decay , a hypothesized process that has never been observed, only electrons would be emitted. The idea of double beta decay was first proposed by Maria Goeppert Mayer in 1935. In 1937, Ettore Majorana demonstrated that all results of beta decay theory remain unchanged if the neutrino were its own antiparticle, now known as a Majorana particle . In 1939, Wendell H. Furry proposed that if neutrinos are Majorana particles, then double beta decay can proceed without

6848-423: The discovery of the positron in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons ( positron emission ), along with neutrinos (classical beta decay produces antineutrinos). In electron capture, some proton-rich nuclides were found to capture their own atomic electrons instead of emitting positrons, and subsequently, these nuclides emit only

6955-545: The double beta decay half-life of Te was measured by geochemical methods to be 1.4×10  years, reasonably close to the modern value. This involved detecting the concentration in minerals of the xenon produced by the decay. In 1956, after the V − A nature of weak interactions was established, it became clear that the half-life of neutrinoless double beta decay would significantly exceed that of ordinary double beta decay. Despite significant progress in experimental techniques in 1960–1970s, double beta decay

7062-735: The double beta decay rate is generally too low to observe. However, the double beta decay of U (also an alpha emitter) has been measured radiochemically. Two other nuclides in which double beta decay has been observed, Ca and Zr , can also theoretically single beta decay, but this decay is extremely suppressed and has never been observed. Similar suppression of energetically barely possible single beta decay occurs for Gd and Rn, but both these nuclides are rather short-lived alpha emitters. Fourteen isotopes have been experimentally observed undergoing two-neutrino double beta decay (β β ) or double electron capture (εε). The table below contains nuclides with

7169-428: The early Solar System. The extra presence of these stable radiogenic nuclides (such as xenon-129 from extinct iodine-129 ) against the background of primordial stable nuclides can be inferred by various means. Radioactive decay has been put to use in the technique of radioisotopic labeling , which is used to track the passage of a chemical substance through a complex system (such as a living organism ). A sample of

7276-520: The emission of any neutrinos, via the process now called neutrinoless double beta decay . It is not yet known whether the neutrino is a Majorana particle, and, relatedly, whether neutrinoless double beta decay exists in nature. As parity violation in weak interactions would not be discovered until 1956, earlier calculations showed that neutrinoless double beta decay should be much more likely to occur than ordinary double beta decay, if neutrinos were Majorana particles. The predicted half-lives were on

7383-467: The form τ → 3 μ {\displaystyle \tau \to 3\mu } has been searched for by the CMS experiment. Double beta decay In nuclear physics , double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons , or vice versa, inside an atomic nucleus . As in single beta decay , this process allows

7490-515: The formation of the Solar System . They are the fraction of radionuclides that survived from that time, through the formation of the primordial solar nebula , through planet accretion , and up to the present time. The naturally occurring short-lived radiogenic radionuclides found in today's rocks , are the daughters of those radioactive primordial nuclides. Another minor source of naturally occurring radioactive nuclides are cosmogenic nuclides , that are formed by cosmic ray bombardment of material in

7597-417: The heavy primordial radionuclides participates in one of the four decay chains . Radioactivity was discovered in 1896 by scientists Henri Becquerel and Marie Curie , while working with phosphorescent materials. These materials glow in the dark after exposure to light, and Becquerel suspected that the glow produced in cathode-ray tubes by X-rays might be associated with phosphorescence. He wrapped

7704-437: The idea of the Majorana nature of the neutrino, which was associated with beta decays. Furry stated the transition probability to even be higher for neutrino less double beta decay. It was the first idea proposed to search for the violation of lepton number conservation. It has, since then, drawn attention to it for being useful to study the nature of neutrinos (see quote). The Italian physicist Ettore Majorana first introduced

7811-665: The isobars with the greatest energy excess. These decays are energetically possible in eight nuclei, though partial half-lives compared to single or double beta decay are predicted to be very long; hence, quadruple beta decay is unlikely to be observed. The seven candidate nuclei for quadruple beta decay include Zr, Xe, and Nd capable of quadruple beta-minus decay, and Xe, Ba, Gd, and Dy capable of quadruple beta-plus decay or electron capture (though Gd and Dy are non-primordial alpha-emitters with geologically short half-lives). In theory, quadruple beta decay may be experimentally observable in three of these nuclei – Zr, Xe, and Nd – with

7918-479: The latest experimentally measured half-lives, as of December 2016, except for Xe (for which double electron capture was first observed in 2019). Where two uncertainties are specified, the first one is statistical uncertainty and the second is systematic. Searches for double beta decay in isotopes that present significantly greater experimental challenges are ongoing. One such isotope is Xe . The following known beta-stable (or almost beta-stable in

8025-418: The limit of measurement) to radioactive decay. Radioactive decay is seen in all isotopes of all elements of atomic number 83 ( bismuth ) or greater. Bismuth-209 , however, is only very slightly radioactive, with a half-life greater than the age of the universe; radioisotopes with extremely long half-lives are considered effectively stable for practical purposes. In analyzing the nature of the decay products, it

8132-406: The most promising candidate being Nd. Triple beta-minus decay is also possible for Ca, Zr, and Nd; triple beta-plus decay or electron capture is also possible for Gd and Dy. Moreover, such a decay mode could also be neutrinoless in physics beyond the standard model. Neutrinoless quadruple beta decay would violate lepton number in 4 units, as opposed to a lepton number breaking of two units in

8239-411: The names alpha , beta , and gamma, in increasing order of their ability to penetrate matter. Alpha decay is observed only in heavier elements of atomic number 52 ( tellurium ) and greater, with the exception of beryllium-8 (which decays to two alpha particles). The other two types of decay are observed in all the elements. Lead, atomic number 82, is the heaviest element to have any isotopes stable (to

8346-534: The neutrinoless process, raising the half-life lower bound to approximately 10  years. Geochemical experiments continued through the 1990s, producing positive results for several isotopes. Double beta decay is the rarest known kind of radioactive decay; as of 2019 it has been observed in only 14 isotopes (including double electron capture in Ba observed in 2001, Kr observed in 2013, and Xe observed in 2019), and all have

8453-437: The new epidemiological studies directly support excess cancer risks from low-dose ionizing radiation. In 2021, Italian researcher Sebastiano Venturi reported the first correlations between radio-caesium and pancreatic cancer with the role of caesium in biology, in pancreatitis and in diabetes of pancreatic origin. The International System of Units (SI) unit of radioactive activity is the becquerel (Bq), named in honor of

8560-612: The nuclear matrix elements, and models of the decay. The observation of neutrinoless double beta decay would require that at least one neutrino is a Majorana particle , irrespective of whether the process is engendered by neutrino exchange. Numerous experiments have searched for neutrinoless double beta decay. The best-performing experiments have a high mass of the decaying isotope and low backgrounds, with some experiments able to perform particle discrimination and electron tracking. In order to remove backgrounds from cosmic rays, most experiments are located in underground laboratories around

8667-432: The nuclear recoil accounting for the rest. Because of momentum conservation , electrons are generally emitted back-to-back. The decay rate for this process is given by Γ = G | M | 2 | m β β | 2 , {\displaystyle \Gamma =G|M|^{2}|m_{\beta \beta }|^{2},} where G is the two-body phase-space factor, M

8774-407: The only emitted particles in the final state and must carry approximately the difference of the sums of the binding energies of the two nuclei before and after the process as their kinetic energy. The heavy nuclei do not carry significant kinetic energy. In that case, the decay rate can be calculated with where G 0 ν {\displaystyle G^{0\nu }} denotes

8881-434: The order of 10 ~10  years. Efforts to observe the process in laboratory date back to at least 1948 when E.L. Fireman made the first attempt to directly measure the half-life of the Sn isotope with a Geiger counter . Radiometric experiments through about 1960 produced negative results or false positives, not confirmed by later experiments. In 1950, for the first time

8988-473: The process occurs as conversion of two protons to neutrons, emitting two electron neutrinos and absorbing two orbital electrons (double electron capture). If the mass difference between the parent and daughter atoms is more than 1.022 MeV/ c (two electron masses), another decay is accessible, capture of one orbital electron and emission of one positron . When the mass difference is more than 2.044 MeV/ c (four electron masses), emission of two positrons

9095-501: The products of alpha and beta decay . The early researchers also discovered that many other chemical elements , besides uranium, have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Pierre and Marie Curie to isolate two new elements: polonium and radium . Except for the radioactivity of radium, the chemical similarity of radium to barium made these two elements difficult to distinguish. Marie and Pierre Curie's study of radioactivity

9202-852: The proof of the Majorana nature of neutrinos and the measurement of this effective Majorana mass ⟨ m β β ⟩ {\displaystyle \langle m_{\beta \beta }\rangle } (can only be done if the decay is actually generated by the neutrino masses). The nuclear matrix element (NME) | M 0 ν | {\displaystyle \left|M^{0\nu }\right|} cannot be measured independently; it must, but also can, be calculated. The calculation itself relies on sophisticated nuclear many-body theories and there exist different methods to do this. The NME | M 0 ν | {\displaystyle \left|M^{0\nu }\right|} differs also from nucleus to nucleus (i.e. chemical element to chemical element). Today,

9309-678: The public being potentially exposed to harmful levels of ionising radiation. This was considered at the first post-war ICR convened in London in 1950, when the present International Commission on Radiological Protection (ICRP) was born. Since then the ICRP has developed the present international system of radiation protection, covering all aspects of radiation hazards. In 2020, Hauptmann and another 15 international researchers from eight nations (among them: Institutes of Biostatistics, Registry Research, Centers of Cancer Epidemiology, Radiation Epidemiology, and also

9416-601: The range of from about 0.9 to 14, depending on the decaying nucleus/element. Lastly, the phase-space factor G 0 ν {\displaystyle G^{0\nu }} must also be calculated. It depends on the total released kinetic energy ( Q = M nucleus before − M nucleus after − 2 m electron {\displaystyle Q=M_{\text{nucleus}}^{\text{before}}-M_{\text{nucleus}}^{\text{after}}-2m_{\text{electron}}} , i.e. " Q {\displaystyle Q} -value") and

9523-446: The release of energy by an excited nuclide, without the transmutation of one element into another. Rare events that involve a combination of two beta-decay-type events happening simultaneously are known (see below). Any decay process that does not violate the conservation of energy or momentum laws (and perhaps other particle conservation laws) is permitted to happen, although not all have been detected. An interesting example discussed in

9630-706: The result of the HDM group. Instead, recent results from the GERDA experiment for the lifetime limit clearly disfavor and reject the values of the HDM collaboration. Neutrinoless double beta decay has not yet been found. The Germanium Detector Array (GERDA) collaboration's result of phase I of the detector was a limit of T β β 0 ν > 2.1 ⋅ 10 25 {\displaystyle T_{\beta \beta }^{0\nu }>2.1\cdot 10^{25}} years (90% C.L.). It used germanium both as source and detector material. Liquid argon

9737-530: The same sample. In a similar fashion, and also subject to qualification, the rate of formation of carbon-14 in various eras, the date of formation of organic matter within a certain period related to the isotope's half-life may be estimated, because the carbon-14 becomes trapped when the organic matter grows and incorporates the new carbon-14 from the air. Thereafter, the amount of carbon-14 in organic matter decreases according to decay processes that may also be independently cross-checked by other means (such as checking

9844-467: The scientist Henri Becquerel . One Bq is defined as one transformation (or decay or disintegration) per second. An older unit of radioactivity is the curie , Ci, which was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)". Today, the curie is defined as 3.7 × 10 disintegrations per second, so that 1  curie (Ci) = 3.7 × 10  Bq . For radiological protection purposes, although

9951-585: The square of the effective Majorana mass. First, the effective Majorana mass can be obtained by where m i {\displaystyle m_{i}} are the Majorana neutrino masses (three neutrinos ν i {\displaystyle \nu _{i}} ) and U e i {\displaystyle U_{ei}} the elements of the neutrino mixing matrix U {\displaystyle U} (see PMNS matrix ). Contemporary experiments to find neutrinoless double beta decays (see section on experiments ) aim at both

10058-452: The subscripts refer to each electron, T is kinetic energy, w is total energy, F ( Z , T ) is the Fermi function with Z the charge of the final-state nucleus, p is momentum, v is velocity in units of c , cos ⁡ θ {\displaystyle \cos \theta } is the angle between the electrons, and Q is the Q value of the decay. For some nuclei,

10165-429: The substance is synthesized with a high concentration of unstable atoms. The presence of the substance in one or another part of the system is determined by detecting the locations of decay events. On the premise that radioactive decay is truly random (rather than merely chaotic ), it has been used in hardware random-number generators . Because the process is not thought to vary significantly in mechanism over time, it

10272-541: The surrounding matter, all contribute to the invariant mass of the system. Thus, while the sum of the rest masses of the particles is not conserved in radioactive decay, the system mass and system invariant mass (and also the system total energy) is conserved throughout any decay process. This is a restatement of the equivalent laws of conservation of energy and conservation of mass . Early researchers found that an electric or magnetic field could split radioactive emissions into three types of beams. The rays were given

10379-770: The treatment of cancer. Their exploration of radium could be seen as the first peaceful use of nuclear energy and the start of modern nuclear medicine . The dangers of ionizing radiation due to radioactivity and X-rays were not immediately recognized. The discovery of X‑rays by Wilhelm Röntgen in 1895 led to widespread experimentation by scientists, physicians, and inventors. Many people began recounting stories of burns, hair loss and worse in technical journals as early as 1896. In February of that year, Professor Daniel and Dr. Dudley of Vanderbilt University performed an experiment involving X-raying Dudley's head that resulted in his hair loss. A report by Dr. H.D. Hawks, of his suffering severe hand and chest burns in an X-ray demonstration,

10486-479: The world. Recent and proposed experiments include: While some experiments have claimed a discovery of neutrinoless double beta decay, modern searches have found no evidence for the decay. Some members of the Heidelberg-Moscow collaboration claimed a detection of neutrinoless beta decay in Ge in 2001. This claim was criticized by outside physicists as well as other members of the collaboration. In 2006,

10593-515: Was almost always found to be associated with other types of decay, and occurred at about the same time, or afterwards. Gamma decay as a separate phenomenon, with its own half-life (now termed isomeric transition ), was found in natural radioactivity to be a result of the gamma decay of excited metastable nuclear isomers , which were in turn created from other types of decay. Although alpha, beta, and gamma radiations were most commonly found, other types of emission were eventually discovered. Shortly after

10700-507: Was also produced by non-phosphorescent salts of uranium and by metallic uranium. It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light. At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Ernest Rutherford , Paul Villard , Pierre Curie , Marie Curie , and others showed that this form of radioactivity

10807-539: Was found and thus a new limit was set to T β β 0 ν > 5.3 ⋅ 10 25 {\displaystyle T_{\beta \beta }^{0\nu }>5.3\cdot 10^{25}} years (90% C.L.). The detector has stopped working and published its final results in December 2020. No neutrinoless double beta decay was observed. The Enriched Xenon Observatory-200 experiment uses xenon both as source and detector. The experiment

10914-570: Was held and considered establishing international protection standards. The effects of radiation on genes, including the effect of cancer risk, were recognized much later. In 1927, Hermann Joseph Muller published research showing genetic effects and, in 1946, was awarded the Nobel Prize in Physiology or Medicine for his findings. The second ICR was held in Stockholm in 1928 and proposed the adoption of

11021-600: Was not observed in a laboratory until the 1980s. Experiments had only been able to establish the lower bound for the half-life – about 10  years. At the same time, geochemical experiments detected the double beta decay of Se and Te . Double beta decay was first observed in a laboratory in 1987 by the group of Michael Moe at UC Irvine in Se . Since then, many experiments have observed ordinary double beta decay in other isotopes. None of those experiments have produced positive results for

11128-442: Was obvious from the direction of the electromagnetic forces applied to the radiations by external magnetic and electric fields that alpha particles carried a positive charge, beta particles carried a negative charge, and gamma rays were neutral. From the magnitude of deflection, it was clear that alpha particles were much more massive than beta particles . Passing alpha particles through a very thin glass window and trapping them in

11235-414: Was significantly more complicated. Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula. Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another. Subsequently, the radioactive displacement law of Fajans and Soddy was formulated to describe

11342-683: Was the first of many other reports in Electrical Review . Other experimenters, including Elihu Thomson and Nikola Tesla , also reported burns. Thomson deliberately exposed a finger to an X-ray tube over a period of time and suffered pain, swelling, and blistering. Other effects, including ultraviolet rays and ozone, were sometimes blamed for the damage, and many physicians still claimed that there were no effects from X-ray exposure at all. Despite this, there were some early systematic hazard investigations, and as early as 1902 William Herbert Rollins wrote almost despairingly that his warnings about

11449-421: Was used for muon vetoing and as a shielding from background radiation. The Q {\displaystyle Q} -value of Ge for 0νββ decay is 2039 keV, but no excess of events in this region was found. Phase II of the experiment started data-taking in 2015, and it used around 36 kg of germanium for the detectors. The exposure analyzed until July 2020 was 10.8 kg yr. Again, no signal

#30969